Techniques for confinement in improved magnetic fusion devices.

Abstract

Techniques are disclosed for initiating and maintaining a transport barrier within a magnetically confined plasma of a plasma fusion device. In a toroidal magnetic configuration, a characteristic region of a magnetic field can be established by generating an electric current within the plasma or by other means. The location of the characteristic region can be controlled to be appropriately close to an inner wall of the plasma fusion device to allow a quantity of particles to be injected into the plasma at or within the characteristic region. The quantity of particles can increase the density of the plasma and create a density gradient within the characteristic region, resulting in the formation of a transport barrier at or within the characteristic region.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of and priority to U.S. Provisional Application No. 63 / 326,659, filed April 1, 2022, which is incorporated by reference herein in its entirety.

[0002] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with Government support under Grant No. DE-FG02-04ER54742 awarded by the Department of Energy. The Government has certain rights in the invention.

[0003] This disclosure relates to magnetic confinement of plasmas, and in particular, techniques are described for enhancing confinement of plasmas in devices used for fusion processes. [Background technology]

[0004] Nuclear fusion continues to be a focus of research into scalable energy sources. As the world's demand for clean, renewable energy increases, so does the desirability of nuclear fusion as that energy source. However, to date, fusion technology has not achieved a reaction sustained enough to produce more energy than is needed to operate the reactor.

[0005] In nuclear fusion, two nuclei (e.g., deuterium or tritium) combine to form one nucleus (e.g., helium) and generate significant energy. To accomplish this reaction, a plasma or ionized gas must be confined and heated to several million °C. Confinement is typically achieved using a strong magnetic field inside the reactor, so that magnetic confinement keeps the reacting plasma away from the reactor structures (e.g., the walls of the chamber). The most successful reactor designs include toroidal vessels, such as tokamas, in which the plasma is generated inside a vacuum chamber and confined by a toroidal shaped magnetic field.

[0006] Inside a tokamak-type or similar toroidal fusion reactor, plasma confinement is achieved by establishing a stable magnetic field inside the reactor using several external magnetic field coils and by generating electric currents inside the plasma. Because the plasma is ionized, its constituent particles become electrically charged and tend to tightly orbit around the magnetic field lines in relatively small orbits. In essence, the plasma attaches to the magnetic field lines, but can easily move along them. The magnetic field generated in the reactor has both a toroidal component (in the direction of the "ring" of the torus) and a poloidal component (in the direction "around" the torus), resulting in a helical magnetic field through the interior of the reactor. This magnetic field configuration therefore includes regions of nested toroidal magnetic surfaces that contain magnetic field lines that are closed and do not touch the inner surface of the reactor vessel. The plasma can then be suspended in the closed magnetic region for long periods of time without touching the reactor surface. However, some processes allow the plasma to be transported out of the confinement region across the magnetic field lines, resulting in a loss of energy and particles from the region where fusion occurs. Therefore, improving plasma confinement by limiting the transport of energy and particles across the confining field is a goal of modern research. Summary of the Invention [Problem to be solved by the invention]

[0007] One aspect of confined plasmas is the presence of "transport barriers" of steep gradients in plasma density, temperature, and / or pressure. Transport barriers indicate a weakening of one or more processes that result in instabilities of the confined plasma and transport of energy and particles from the confinement region, including turbulent plasma flow. Depending on the magnetic field configuration, such weakening can be caused by velocity shear, magnetic shear, or similar mechanisms. Velocity shear has long been thought to be the primary mechanism for suppressing turbulent transport processes in confined plasmas. However, low-velocity shear-driven fusion operating regimes are possible and likely crucial for further progress. Therefore, methods to control the formation (e.g., location, duration, extent) of transport barriers are desired. [Means for solving the problem]

[0008] Embodiments of the present disclosure relate to improving the confinement of plasma in fusion devices. The plasma can be confined by a magnetic field, which can be created and manipulated by applying currents both outside the plasma (e.g., external coils) or inside the plasma (e.g., current in the plasma itself). A characteristic region of the confining magnetic field with specific properties can be created. By injecting particles into the plasma at or within the characteristic region of the magnetic field, a transport barrier can be initiated that can reduce the transport of plasma particles and energy out of the confining region of the magnetic field, thereby improving the confinement of the plasma. This transport barrier can be maintained by subsequent injection of additional particles.

[0009] One embodiment relates to a method that can include generating, in a plasma confinement device, a characteristic region of a magnetic field that confines a plasma, and injecting a quantity of particles into the plasma at or within the characteristic region.

[0010] In various examples, the characteristic region may be defined by a region of negative magnetic shear, low magnetic shear, large Shafranov shift, a particular shape of the magnetic surface of the magnetic field that confines the plasma with which the magnetic perturbation is resonating, or any combination of these defining features. In some examples, the characteristic region may be created by generating a current in the plasma that is parallel to the magnetic field in the characteristic region. According to certain examples, injecting a quantity of particles at or inside the characteristic region can create a transport barrier. The transport barrier may be characterized by a large pressure gradient in the plasma. The resonant magnetic perturbation induces transport of particles and heat, and inducing them in the characteristic region can help to control the pressure gradient there. In some embodiments, this can be useful to increase the width of the transport barrier and to avoid magnetohydrodynamic instabilities. The transport barrier may be created at about 70% of the minor radius of the plasma confinement device. In some examples, the transport barrier may be created at about 80% of the minor radius or about 90% of the minor radius of the plasma confinement device. In some examples, the quantity of particles can include fusion fuel particles including deuterium and / or tritium, hi some examples, the quantity of particles can include impurity particles including carbon, silicon, a noble gas, or an element with an atomic number Z less than 21.

[0011] Another embodiment is directed to a second method that may include generating a characteristic region of a magnetic field that confines a plasma, injecting a first amount of particles into the plasma at or within the characteristic region, and injecting a second amount of particles into the plasma at or within the characteristic region. The first amount of particles may be injected for a first period of time at a first time and the second amount of particles may be injected for a second period of time at a second time.

[0012] In various examples, the characteristic region may be defined by a region of negative magnetic shear, low magnetic shear, large Shafranov shift, a particular shape of the magnetic surface of the magnetic field that confines the plasma at which the magnetic perturbation is resonating, or any combination of these defining features. In some examples, the first amount of particles may include at least a portion of impurity particles. In some examples, the second amount of particles may include impurity particles, fusion fuel particles, and / or a mixture of impurity particles and fusion fuel particles. According to certain examples, both the first amount of particles and the second amount of particles may be injected at a time-averaged rate. The time-averaged particle injection rate of the second amount of particles may be lower than the time-averaged injection rate of the first amount of particles. In some examples, the first amount of particles may include a first proportion of fusion fuel particles and the second amount of particles may include a second proportion of fusion fuel particles, the second proportion being greater than the first proportion.

[0013] Yet another embodiment relates to a system that can include a plasma confinement device, a particle injector, and a controller. The controller can have one or more processors and one or more memories storing computer-executable instructions that, when executed by the one or more processors, cause the system to adjust a current in a plasma confined by a magnetic field within the plasma confinement device to generate a characteristic region of the magnetic field, and to inject a quantity of particles into the plasma at or within the characteristic region using the particle injector, thereby forming a transport barrier at or within the characteristic region.

[0014] In some examples, the plasma confinement device may be a tokamak device, a stellarator, or a toroidal pinch device. In some examples, the particle injector may be configured to inject the amount of particles as a high velocity pellet, including a portion of a cryogenically frozen pellet, or as a magnetically confined plasma, including a compact toroid. In some examples, the amount of particles may be a first amount of particles injected at a first time and a first duration. The one or more memories of the controller may store additional instructions that, when executed, cause the system to further inject a second amount of particles using the particle injector at a second time for a second duration, the second amount of particles maintaining the transport barrier for the second duration. According to certain examples, the first amount of particles may include impurity particles, and the second amount of particles may include fusion fuel particles or a mixture of fusion fuel particles and impurity particles. In some examples, the first amount of particles may include a first proportion of fusion fuel particles, and the second amount of particles may include a second proportion of fusion fuel particles, the second proportion being greater than the first proportion. In some examples, the time-averaged particle infusion rate of the second quantity of particles can be lower than the time-averaged infusion rate of the first quantity of particles. [Brief description of the drawings]

[0015] [Figure 1A] 1 is a schematic diagram of a cross section of an exemplary plasma confinement system, in accordance with some embodiments. [Figure 1B] 1 is a schematic diagram of a cross section of an exemplary plasma confinement system, in accordance with some embodiments.

[0016] [Diagram 2] FIG. 1 illustrates a cross-sectional view of a confined plasma having a characteristic region for forming a transport barrier according to at least one embodiment.

[0017] [Diagram 3] FIG. 1 is a simplified diagram of a toroidal magnetic configuration having characteristic regions for forming a transport barrier, according to at least one embodiment.

[0018] [Figure 4] 1 is a simplified diagram of a plasma confinement system for generating a transport barrier in a characteristic region of a confining magnetic field, according to at least one embodiment.

[0019] [Diagram 5] 1 is a plot illustrating an exemplary mode of operation of a plasma confinement device.

[0020] [Figure 6] 11 is another plot illustrating an example temperature gradient in a confined plasma illustrating the generated transport barriers, according to at least one embodiment.

[0021] [Figure 7] FIG. 1 is a simplified diagram of an example method for generating a characteristic region in a magnetic field that confines a plasma, according to at least one embodiment.

[0022] [Figure 8] FIG. 13 is another simplified diagram of an exemplary method for initiating a transport barrier with a first amount of particles and maintaining the transport barrier with a second amount of particles according to at least one embodiment.

[0023] [Figure 9] FIG. 1 is a simplified diagram of an example method for generating a transport barrier in a characteristic region of a magnetically confined plasma according to at least one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The techniques described herein relate to systems and methods for controlling the creation of transport barriers (TBs) inside a magnetically confined plasma. In particular, the techniques involve manipulating the magnetic configuration of the confinement to establish a region of a magnetic field with a particular property (e.g., negative magnetic shear or reduced magnetic shear) and then injecting a quantity of particles (e.g., fusion fuel particles) at or inside the property region to form the transport barrier. The increase in density from the injected particles can result in the formation of a transport barrier (e.g., a steep radial gradient in the plasma's temperature, density, and / or pressure). The transport barrier can form at or near the property region. By controlling where the property region forms, the position of the resulting transport barrier can also be controlled, thereby allowing the TB to form in a favorable location for confining the plasma.

[0025] Current plasma confinement devices used for fusion applications typically operate in one of several confinement modes that result in the formation of TBs at various locations. As a specific example (see FIG. 5), tokamaks (and stellarators) can operate in high confinement mode (H-mode, e.g., H-mode 504 in FIG. 5) that results in inner TBs (ITBs, e.g., ITB 508, TBs located away from the inner wall of the device) as well as edge TBs (e.g., edge TB 510). H-mode can be distinguished from low confinement mode (L-mode, e.g., L-mode 506), which exists before the confined plasma is strongly heated. The transition from L-mode to H-mode is generally believed to result from the suppression of turbulence in the plasma. The ITBs in H-mode can define an inner "core" region of the plasma (e.g., core region 502) where sufficient temperature and density are achieved to promote the fusion process. The edge TBs in H-mode are typically close to the inner wall of the reactor, where the magnetic field lines are open and particle flux is unconfined and may impinge on the wall and other structures.

[0026] As mentioned above, the formation of TBs can occur when certain plasma instabilities (e.g., turbulent plasma processes) are weakened or suppressed. These instabilities can be characterized by one or more modes of the system, including ion temperature gradient (ITG) modes, electron temperature gradient, trapped electron mode (TEM) modes, and / or coupling between one or more modes. In general, plasma instabilities are due to the "drift" of particles across the magnetic field lines. Several drifts are characteristic in plasmas and are related to both the geometry of the magnetic field (e.g., gradient, curvature, etc.) and the kinetics of the charged particles (ions and electrons). Drift can be:

number

number

number

number

[0027] However, velocity shear scales poorly to larger geometries, resulting in poor suppression of turbulent processes, and therefore is unlikely to be sufficient to provide adequate confinement to the plasma in larger reactors.

[0028] Suppression of turbulent transport processes can also occur in the presence of magnetic shear. For a toroidal magnetic configuration (such as those in a tokamak), the magnetic shear of the magnetic field can be defined as the radial gradient of the "rotational transformation" ι, which is a measure of the number of poloidal transitions the magnetic field lines make for each toroidal transition of the line (essentially, the number of helical twists the field lines make as they move around the torus). Mathematically, the magnetic shear is given by

number

number

[0029] Suppression of turbulent transport processes can also occur in the presence of a large Shafranov shift. The Shafranov shift is the outward radial displacement of the center of the magnetic flux plane with minor radius r, caused by the plasma pressure or hoop forces. For the purposes of this disclosure, the Shafranov shift is defined as the parameter

number

number

number

number

[0030] Electric currents inside the confined plasma can be induced with an external coil (e.g., the central solenoid of a tokamak) by supplying a variable current. For example, a central solenoid can be used to induce a toroidal current in the plasma by applying a linear ramp current to the solenoid. By configuring the geometry of the external coil and the supplied current, electric currents inside the confined plasma can be generated at specific locations with orientations that are primarily aligned with the magnetic field at those locations. The induced currents can then generate the appropriate magnetic shear to create a characteristic region suitable for initiating and sustaining an ITB.

[0031] TBs can be initiated in several ways. As discussed above for the case of H-mode confined plasmas, TBs can form when a critical heating threshold is exceeded in the core plasma. The initial plasma can be generated using radio frequency discharges, microwave discharges, neutral beam heating, etc. Once ionized and confined, the plasma can be heated by ohmic heating (from induced currents), adiabatically by compressing the confining magnetic field, by neutral beam injection, and / or by combinations of these and similar mechanisms.

[0032] Another method for initiating TB, and a principle of this disclosure, is to inject particles into the confined plasma. Particles (e.g., pellets of fusion fuel, pellets of impurity atoms) can be injected into the confined plasma to increase the local density gradient. Due to the conservation constraints of the plasma system, such injection into the confined plasma can initiate sustainable TB. TBs can be formed at locations where the magnetic configuration of the confining magnetic field has certain characteristics (e.g., negative magnetic shear, large positive magnetic shear, reduced magnetic shear, large Shafranov shift, etc.).

[0033] Due to dynamic processes inside the confined plasma, injecting particles (e.g., pellets) deep into the core region may not be feasible. For example, a pellet fired from outside the confinement region at a speed of 1 km / s may only penetrate 20 cm into the confinement region before ionization and collapse. Thus, creating a characteristic region of magnetic field too close to the center of the confinement region prevents deposition of injected particles in that region. Similarly, the ITBs associated with typical operating modes of fusion reactors form very far from the exterior of the confined plasma, allowing particle injection to sustain the mode after formation. Furthermore, edge TBs in the H-mode operating regime create significant instabilities near the edges of the confinement region, where the edge TBs repeatedly weaken and allow plasma particles and energy to escape into the open field regions of the reactor, depositing substantial energy on the vessel walls and equipment. The techniques of the present disclosure solve many of these problems by enabling the creation of a characteristic magnetic region close enough to the exterior of the confined plasma region to allow injected particles to initiate and sustain TBs.

[0034] The basis of the techniques disclosed herein is the recognition of fundamental physical constraints on the dynamics of plasma processes occurring in reactors. Typically, the presence of large gradients such as TBs is a source of substantial free energy in the system, thereby driving various instabilities that reduce or eliminate the gradients. However, as discussed above, TBs can form in magnetically confined plasmas when turbulent processes are suppressed. The main constraint that allows the suppression of turbulent processes is that the turbulent transport is ambipolar, so that the net charge flux due to turbulence in the plasma is zero (i.e., the turbulent processes do not generate a flux of ions disproportionate to the flux of electrons). Since steep density gradients tend to drive ionic charge fluxes much more than electronic charge fluxes, flux constraints can prevent strong instabilities from arising because transport from such instabilities cannot satisfy the conditions for ambipolar transport. If the necessary conditions for ambipolar transport are not met, instabilities cannot occur. If the ambipolar constraints cannot be met, the free energy at the steep density and temperature gradients is not available for instabilities. This suppresses turbulence. Combining this observation with the creation of specific regions of confining magnetic geometry allows the injected particles to generate sustainable gradients of both temperature and density in specific regions, forming TBs with properties beneficial for large-scale fusion reactions.

[0035] The present technique offers many advantages over current methods known in the state of the art. By controlling the generation of the characteristic region of the magnetic geometry, the characteristic region can be formed at an appropriate location to allow injection of particles into that region. This location allows the generation of the TB further away from the center of the confinement region, creating a larger and more stable core plasma region where the fusion reaction can occur, resulting in improved fusion power and better confinement for larger reactors. The characteristic region can also be formed at an appropriate distance from the inner wall of the reactor vessel, thereby allowing the formation of the TB further away from the edge region, limiting or eliminating the presence of edge localized modes and other modes that interact strongly with the reactor vessel physical equipment (e.g., walls, diverters, limiters, probes, etc.). Because the resulting TB is further away from the center of the confinement region, additional particles can be injected into the region beyond the TB to maintain the TB (e.g., maintain the density gradient) without degrading or destroying the TB.

[0036] Turning now to the drawings, FIG. 1A is a schematic diagram of a cross section of an exemplary plasma confinement system 100, according to at least one embodiment. The plasma confinement system 100 can include a plasma confinement device 101. The plasma confinement device 101 can be a toroidal device having axial symmetry about a central axis 112. As shown in FIG. 1A, the plasma confinement device 101 can have a D-shaped cross section, similar to many tokamak designs. Other cross-sectional profiles are possible, including circular, elliptical, etc. Additionally, other configurations of the toroidal confinement device are contemplated, including stellarators, spheroids, toroidal pinch devices (e.g., reversed field pinch), etc.

[0037] The plasma confinement device 101 may have a wall 110 that provides a physical boundary to an interior of the device. The interior volume may be a vacuum chamber suitable for supporting the ionized gas or plasma required for fusion. The plasma confinement device 101 may have a major radius 114 defined from a central axis 112 to a center of the interior of the torus. Similarly, the interior may have a minor radius 116 defined from the center of the interior to an inner surface of the wall 110.

[0038] A suitable magnetic field can be generated in the volume to suspend and confine the plasma inside the plasma confinement device 101. The magnetic field can be generated by one or more external coils (not shown in FIG. 1A ), including a central solenoid, one or more toroidal field coils, one or more poloidal field coils, and / or one or more additional coils, to generate a magnetic field inside the plasma confinement device 101. In some embodiments, one or more of the external coils can be configured to inductively couple with the suspended plasma to drive a current inside the plasma. The plasma current can then generate a corresponding magnetic field inside the plasma confinement device 101. For example, a central solenoid can be used to generate a variable external field that couples with the toroidally confined plasma and generates a toroidal current in the plasma. The toroidal current can then generate a poloidal magnetic field inside the plasma confinement device. This poloidal magnetic field can then be the poloidal component of the resulting magnetic field that suspends and confines the plasma. Further details regarding the magnetic geometry of the toroidal confinement device are presented below with respect to Figures 2 and 3. In yet other embodiments, the external coil can generate a resonant magnetic perturbation, i.e., a magnetic perturbation that resonates with the plasma.

[0039] For a plasma confinement device 101 having a toroidal configuration, the internally generated magnetic field may be divided into two regions corresponding to the nature of the magnetic flux. The two regions may be separated by a separatrix 104, which defines a boundary between a region of closed magnetic flux (e.g., closed magnetic field lines) surrounded by the separatrix 104 and a region of open magnetic flux (e.g., open magnetic field lines) outside the separatrix 104. Further details of the geometry of the internal magnetic field are presented below in connection with FIG. 2.

[0040] Inside the closed magnetic field region defined by the separatrix 104 may be the core plasma region 102 where temperature and pressure can reach values ​​high enough to initiate a fusion reaction. The closed magnetic field lines form a surface called the magnetic surface. Heating of the core plasma region 102 may be achieved using ohmic heating (e.g., induced current flow in the plasma), RF discharge, microwave discharge, adiabatic compression (e.g., compressing the confining magnetic field), neutral beam injection, and other similar methods. Because particles and energy may diffuse across the magnetic field lines via transport processes (e.g., turbulent transport), maintaining strong confinement by limiting transport processes may be necessary to maintain the plasma at a temperature high enough to sustain a fusion reaction for an extended period of time.

[0041] To improve confinement of the plasma in the core plasma region 102, a transport barrier (TB) may be created by the plasma confinement system 100. The particle injector 106 may be configured to inject a quantity of particles into the confined plasma at or within a characteristic region 108. The characteristic region 108 may be a region of the magnetic field that confines the plasma having a suitable geometry or other characteristic parameters to establish a TB. In some embodiments, the characteristic region 108 may be a region of low or negative magnetic shear in the magnetic field. In other embodiments, the characteristic region 108 may be a region of strong Shafranov shift. In other embodiments, the characteristic region may be a region having a particular shape of the magnetic surface of the magnetic field that promotes the formation of a transport barrier. In still other embodiments, the characteristic region may be a location where magnetic perturbations resonate. Although shown as a rectangle in FIG. 1A, the characteristic region 108 may be radially defined to form a radial layer that is approximately aligned with the magnetic flux surface of the confined magnetic field. In some embodiments, the characteristic region 108 may be localized on the outer periphery of the core plasma region 102 (eg, further from the central axis 112 ).

[0042] 1B illustrates another example of the plasma confinement system 100. The characteristic region 108 may be localized on the inner periphery (e.g., closer to the central axis 112) of the plasma confinement device 101. Similarly, the particle injector 106 may be on the inner periphery of the plasma confinement device.

[0043] Establishing the characteristic region 108 can include generating an electric current within the confined plasma. The electric current can be parallel to the magnetic field at the location where the electric current is generated, thereby generating a magnetic shear region (e.g., negative magnetic shear, reduced magnetic shear, etc.) in the characteristic region 108. In some embodiments, the electric current that generates the characteristic region 108 may not pass through the characteristic region (e.g., the generated current density in the characteristic region is small). The electric current can be generated by one or more external coils that can change the shape of the magnetic surface. In other embodiments, the characteristic region can have a strong Shafranov shift.

[0044] Once the characteristic region 108 is established, the particle injector 106 can be used to inject a quantity of particles into the characteristic region or inside the characteristic region. By "inside" the characteristic region 108, we mean deeper inside the core plasma 102, closer to the center of the core plasma where the minor radius 116 is smaller. The quantity of particles can increase the density of the characteristic region and / or inside the characteristic region, forming a density gradient inside the characteristic region 108. As mentioned above, the density gradient can form a TB via physical constraints inside the confined plasma system. In some embodiments, the particle injector 106 can be configured to inject a second quantity of particles into the characteristic region 108 after the TB is established. This second quantity of particles can maintain the transport barrier for a longer period of time than the self-organization process of the confined plasma can typically allow. In various embodiments, the particle injector 106 may be configured to inject a quantity of particles as pellets (e.g., cryogenically frozen pellets), particle beams, small magnetically confined plasmas (e.g., small spheromak guns), gas puffs, or other similar delivery methods. The particles used to initiate a TB may be different from the particles used to sustain a TB. For example, the particles used to initiate a TB may include a percentage of "impurity" particles, while the particles used to sustain a TB may be fully fused fuel particles or only a smaller percentage of impurity particles. Impurity particles with higher atomic numbers (higher Z) may increase the density gradient and result in stronger constraints on diffusion inside the confined plasma and therefore may be more effective at initiating a TB.

[0045] In the case of a nuclear fusion reactor, the fusion fuel is primarily deuterium and / or tritium, which may be the major component of the confined plasma. In some cases, such as in the case of the fusion device ITER, there is a test phase of operation in which the plasma consists primarily of helium or protons. These are not strictly fusion fuels. However, they are intended to play the role of fusion fuel for the purposes of testing plasma dynamics. Thus, as used in this disclosure, helium and protons play the same role as fusion fuel for the proposal to test plasma behavior, and the formation of TBs can also be considered as fusion fuel, since it is an important aspect of plasma behavior that can be tested in this phase of operation. The impurity particles can be ions of any other species other than fusion fuel, or ions that play the role of fusion fuel, including but not limited to lithium, neon, carbon, nitrogen, silicon, and other elements with atomic numbers Z=3 or Z>3. The amount of particles injected by the particle injector 106 can include fusion fuel particles, impurity particles, or any combination of fusion fuel particles and impurity particles. In some embodiments, the composition of the particles in the quantity can be changed over time depending on the type of particles desired at or within the characteristic region to maintain the TB and aid in the fusion process being contained.

[0046] 2 is a cross-sectional view of a confined plasma in a plasma confinement device 200 having a characteristic region 208 for forming a transport barrier, according to at least one embodiment. The plasma confinement device 200 may be an example of the plasma confinement device 101 of FIG. 1A. The plasma confinement device 200 may have an inner wall 204 that defines an interior volume of the device in which a confining magnetic field may be established.

[0047] As mentioned above, the magnetic field can be characterized by a separatrix 202 (an example of the separatrix 104 in FIG. 1A). The open magnetic field lines (e.g., dashed lines in FIG. 2) can terminate at a surface of the plasma confinement device 200, including the inner wall 204, diverter, limiter, or other device. The closed magnetic field lines inside the separatrix can form a toroidally nested surface of constant magnetic flux, called a magnetic surface. The magnetic surface (e.g., solid lines inside the separatrix 202) has magnetic field lines that are typically "twisted" in the poloidal direction as they pass in a toroidal direction along the interior of the plasma confinement device. Because the plasma particles are ionized, the particles tend to bind ("stick") to the closed magnetic field lines in small gyroscopic orbits, such that the particles can move relatively freely along the magnetic field lines, but can move relatively slowly across the magnetic field lines.

[0048] A characteristic region 208 of the magnetic field can be generated at a location inside the plasma confinement device 200. The characteristic region 208 can be an example of the characteristic region 108 described above with reference to FIG. 1A. Like the characteristic region 108, the characteristic region 208 can have a radial orientation and shape such that the characteristic region 208 is approximately aligned with a surface of magnetic flux in the closed magnetic field region. In some embodiments, the characteristic region 208 can be a region of low magnetic shear, reduced magnetic shear, or negative magnetic shear. Generating the characteristic region 208 can include generating a current in the plasma parallel to the magnetic field at or near the characteristic region 208. In some other embodiments, the characteristic region can have a large Shafranov shift. In still other embodiments, the characteristic region can be a region having a particular shape of the magnetic surface of the magnetic field that promotes the formation of a transport barrier. In still other embodiments, the characteristic region 108 can be a location where a magnetic perturbation is resonant.

[0049] The characteristic region 208 can be generated at a distance 206 from the separatrix 202 of the plasma confinement device 200. In some embodiments, the distance 206 can be 10% of the radial distance from the center of the toroidal cross section of the plasma confinement device 200 (e.g., the minor radius 116 in FIG. 1A). Thus, the characteristic region 208 can be formed close to the separatrix 202, but not close enough that the resulting transport barrier would result in instabilities (e.g., edge localized modes) near the edge of the plasma confinement region. The distance value of 10% from the separatrix 202 is presented as an example. Other locations for the characteristic region 208 are contemplated and present suitable locations for forming a transport barrier according to the present disclosure.

[0050] 3 is a simplified diagram of a toroidal magnetic configuration 300 having a characteristic region 308 for forming a transport barrier, according to at least one embodiment. The characteristic region 308 may be an example of the characteristic region 208 of FIG. 2 or the characteristic region 108 of FIG. 1A.

[0051] 3, the magnetic confinement region 302 includes a poloidal magnetic field 304 aligned along a torus with a toroidal magnetic field 306. The resulting total magnetic field therefore includes helical magnetic field lines that are poloidally twisted in the direction of the poloidal magnetic field 304 while following the toroidal magnetic field 306. The poloidal magnetic field 304 can be generated by induced currents in the plasma parallel to the toroidal magnetic field 306.

[0052] To generate the characteristic region 308, a current 310 can be generated in the magnetic confinement region 302. The current 310 can be parallel or substantially parallel to the magnetic field of the characteristic region 308. The current 310 can generate another component (e.g., an additional poloidal magnetic field) that contributes to the magnetic field in the characteristic region. For example, the current 310 can generate an additional poloidal magnetic field such that the gradient of the rotational transformation becomes larger and the resulting magnetic shear in the characteristic region becomes negative.

[0053] 4 is a simplified diagram of a plasma confinement system 400 for generating a transport barrier in a characteristic region 408 of a confining magnetic field, according to at least one embodiment. The plasma confinement system 400 may be an example of the plasma confinement system 100 described above with respect to FIG. 1A. The plasma confinement system 400 may include a plasma confinement device 404, depicted here in cross-sectional view. The plasma confinement system 400 may also include a particle injector 406 and a controller 410. The particle injector 406 may be an example of the particle injector 106 of FIG. 1A.

[0054] Similar to FIG. 2, the magnetically confined plasma of the plasma confinement device 404 can be suspended in a region of closed magnetic flux defined by the separatrix 402 to form a confinement region, which in turn can include a core plasma region (e.g., core plasma region 102 of FIG. 1A). A characteristic region 408 of the confinement magnetic field can be generated at a suitable location inside the confinement region. The characteristic region 408 can be created close enough to a particle injector to generate a density gradient sufficient to allow a quantity of particles to be deposited at or inside the characteristic region 408 and to aid in the formation of a transport barrier (TB). This deposition can be achieved by ionizing a substantial quantity of neutral particles from the injector at or inside the characteristic region. Again, the "inner" characteristic region can refer to a region close to the core of the plasma, having a minor radius shorter than the characteristic region 408.

[0055] The controller 410 may be any suitable controller or control system configured to operate the particle injector 406. The controller 410 may include one or more processors and one or more memories configured to store computer-executable instructions that can cause the particle injector 406 to inject a large amount of particles into a confinement region (e.g., at or inside the characteristic region 408) of the confined plasma of the plasma confinement device 404. The controller 410 may be configured to perform any suitable number of operations to carry out the techniques of the present disclosure. In some embodiments, the controller 410 may be configured to receive one or more signals from one or more other components (e.g., sensors, probes, detectors, power supplies, etc.) of the plasma confinement system 400. The controller 410 may be configured to use the received signals to modify one or more operations under its control. For example, the controller 410 may receive a signal corresponding to a measured gradient (e.g., temperature gradient) at a location (e.g., characteristic region 408). The signal may indicate that the formed TB is weakening and additional particles should be injected to maintain the TB. Based on the signal, the controller 410 can respond by injecting additional amounts of particles to maintain TB. Other parameters (e.g., type of particles injected, time period between injections, etc.) can be similarly modified based on the received signal.

[0056] In some embodiments, the controller 410 may also be configured to output control signals to one or more other components of the plasma confinement system 400. For example, the controller 410 may send signals to control the current used to establish a characteristic region (e.g., characteristic region 408).

[0057] FIG. 5 is a plot 500 illustrating an exemplary operating mode of a plasma confinement device. The plot shows an arbitrary plasma pressure versus normalized radius r / a, where r is the radial coordinate from the center of the toroidal cross section of the plasma confinement device, and a is the minor radius (e.g., minor radius 116 in FIG. 1A). As previously mentioned, the tokamak can operate in a high confinement mode (H-mode) 504, which results in an internal transport barrier (ITB) 508 as well as an edge TB 510. The H-mode can be distinguished from a low confinement mode 506 (L-mode), which exists before the confined plasma is strongly heated. The transition from L-mode to H-mode is generally believed to result from the suppression of turbulence in the plasma. The ITB of the H-mode can define an inner "core" region 502 of the plasma where sufficient temperature and density are achieved to support the fusion process. The edge TB 510 of the H-mode is typically close to the inner wall of the reactor, where the magnetic field lines are open and particle flux is not confined and may impinge on the wall and other structures.

[0058] As shown in FIG. 5, the ITB 508 can reside in an interior region relatively far from the walls of the plasma confinement device (

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[0059] 6 is another plot 600 illustrating an exemplary temperature gradient in a confined plasma showing a generated transport barrier 608, according to at least one embodiment. Plot 600 shows ion temperature 602 (arbitrary units) versus normalized radius. Typical values ​​of ion temperature and electron temperature in the current confinement region are about 17 keV and 7 keV, respectively. Higher values, especially of ion temperature, can be achieved in devices with improved confinement according to embodiments of the present disclosure.

[0060] The gradient of ion temperature 602 may occur in a region corresponding to a transport barrier 608. The transport barrier 608 may occur in a characteristic region of a magnetic field that confines the plasma, which may be similar to the characteristic regions described herein. The transport barrier 608 may be located at a distance 606 from an inner wall of the plasma confinement device. The distance 606 may be such that the gradient is formed in the appropriate location that is maintained by the injection of particles.

[0061] FIG. 7 is a simplified diagram of an exemplary method 700 for generating a characteristic region in a magnetic field that confines a plasma, according to at least one embodiment. The method 700 can be performed by one or more components of a plasma confinement system (e.g., the plasma confinement system 100 of FIG. 1A, the plasma confinement system 400 of FIG. 4). The method 700 is illustrated as a logical flow diagram, each operation of which represents a sequence of operations that can be implemented in hardware, computer instructions, or a combination thereof. In the context of computer instructions, the operations represent computer-executable instructions stored on one or more computer-readable storage media that, when executed by one or more processors, perform the recited operations. For example, the controller 410 of FIG. 4, or a similar computing system within the plasma confinement system. In general, computer-executable instructions include routines, programs, objects, components, data structures, etc. that perform a particular function or implement a particular data type. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described operations can be omitted or combined in any order and / or in parallel to perform a process.

[0062] Part or all of method 700 (or any other process described herein, or variations and / or combinations thereof, e.g., method 800 of FIG. 8, method 900 of FIG. 9) may be performed under the control of one or more computer systems (e.g., controller 410 of FIG. 4) configured with executable instructions, may be implemented by hardware or a combination thereof as code (e.g., executable instructions, one or more computer programs, or one or more applications) that collectively execute on one or more processors. The code may be stored in a computer-readable storage medium (e.g., one or more memories of a computer system), for example, in the form of a computer program including a plurality of instructions executable by one or more processors. The computer-readable storage medium may be non-transitory.

[0063] The method 700 can begin at block 702, where a characteristic region can be generated in a magnetic field that confines the plasma. The magnetic field can be generated inside a plasma confinement device (e.g., plasma confinement device 101 of FIG. 1A). The characteristic region can be characterized by negative magnetic shear, reduced magnetic shear, a large Shafranov shift, a particular flux profile, or other similar properties of the magnetic field, or a combination of these properties. The characteristic region can be generated by generating an electric current in the plasma confined by the magnetic field. The electric current can be parallel or substantially parallel to the magnetic field at the location of the characteristic region. The electric current can be generated by one or more external coils that can be inductively coupled with the plasma, or by radio waves that are generated outside the plasma and absorbed in the characteristic region, or by a neutral particle beam, or by other means known in the art.

[0064] At block 704, a quantity of particles may be injected at or within the characteristic region generated at block 702. The particles may be injected by one or more particle injectors (e.g., particle injector 106 of FIG. 1A). The particles may include fusion fuel particles (e.g., deuterium, tritium), impurity particles (e.g., neon, other noble gases, carbon, silicon, etc.), or a combination of fuel particles and impurity particles. The quantity of particles may be in the form of pellets (e.g., cryogenic pellets) and may include two or more pellets. In some embodiments, the quantity of particles may include particles confined in a compact toroid (e.g., a compact magnetically confined plasma) that may be injected into a confined plasma of a plasma confinement device.

[0065] In some embodiments, a transport barrier (TB) may be created when a certain amount of particles are injected. The TB may be created at the location of the characteristic region. The combination of the increased density gradient due to the injected particles and the magnetic geometry (e.g., magnetic shear, Shafranov shift, etc.) in the characteristic region may sufficiently suppress the turbulent transport process to allow the formation of the TB. The TB may be characterized by a large and stable gradient of the parameters of the plasma, including pressure, temperature, and density. The TB may be created at a location of about 90% of the minor radius distance (e.g., minor radius 116 in FIG. 1A) of the toroidal cross section of the plasma confinement device. In other words, the TB may be formed at about 90% of the distance from the center of the confined plasma to the inner wall of the plasma confinement device. In other embodiments, the TB may be formed at a different location suitable for injecting particles to initiate and sustain the TB. For example, the TB may be formed at about 70% of the minor radius distance or about 80% of the minor radius distance.

[0066] As noted above, TB can be characterized by a large and stable gradient in plasma pressure. For example, a pressure gradient above a threshold value.

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[0067] It should be appreciated that the specific steps illustrated in Figure 7 result in a particular method of generating a characteristic region of a magnetic field that confines a plasma, in accordance with an embodiment of the present invention. The individual steps illustrated in Figure 7 may include multiple sub-steps that may be performed in various orders as appropriate for the individual step. Additionally, additional steps may be added or removed depending on the particular application. Those skilled in the art will recognize numerous variations, modifications, and alternatives.

[0068] 8 is another simplified diagram of an exemplary method 800 for initiating a transport barrier with a first amount of particles and maintaining the transport barrier with a second amount of particles, according to at least one embodiment. Similar to method 700 of FIG. 7, method 800 can be performed by one or more components of a plasma confinement system (e.g., plasma confinement system 100 of FIG. 1A, plasma confinement system 400 of FIG. 4).

[0069] The method 800 may begin at block 802 where a characteristic region of a magnetic field is generated to confine a plasma. The operations of block 802 may be similar to the operations of block 702 of FIG.

[0070] In block 804, a first amount of particles may be injected into the plasma and deposited in the plasma at or inside the characteristic region. The particles may be injected by a particle injector (e.g., particle injector 106 of FIG. 1A), which may include a pellet injector, a neutral beam injector, a spheromak gun or other small toroidal plasma injector, or a similar device. The first amount of particles may be impurity particles that initiate the formation of a transport barrier (TB) at or inside the characteristic region. The first amount of particles injected may include all or a portion of the impurity particles, since impurity particles (e.g., particles with a high Z number) may be better at initiating TB. The first amount of particles may be injected at a first time and for a first period of time. The first amount of particles may be injected over a first period of time (e.g., injecting some pellets at one location and injecting pellets at different toroidal locations along the confinement region). Injecting the particles over a first period of time may define a time-averaged injection rate of the first amount of particles. In some embodiments, the time-averaged infusion rate may be based on an average of a time period different from the first period.

[0071] At block 806, a second amount of particles may be injected into the plasma and deposited in the plasma at or inside the characteristic region. Similar to block 804, the second amount of particles may be injected by a particle injector. The second amount of particles may include fusion fuel particles (e.g., deuterium, tritium). The injection of the second amount of particles may occur after the formation of the TB (e.g., the TB formed by the injection of the first amount of particles). The second amount of particles may be larger, smaller, or the same as the first amount of particles depending on the desired density to be enhanced in the characteristic region. For example, the first amount of particles may be a relatively large amount of impurity particles (e.g., large pellets) to initiate the TB, and the second amount of particles may be a relatively small amount of fusion fuel to maintain the TB. The second amount of particles may be injected over a second period of time, which may define a time-averaged injection rate of the second amount of particles. In some embodiments, the second period of time may be longer than the first period of time. For example, the injection of the second amount of fusion fuel particles to maintain TB may occur over a much longer period of time than the injection of the first amount of particles to initiate TB, and the time-averaged rate of injection of particles to effect the second injection may be significantly less than the time-averaged rate of injection of particles to effect the first injection.

[0072] In some embodiments, both the first quantity of particles and the second quantity of particles can include impurity particles, fused fuel particles, or any suitable combination of particles. For example, the first quantity of particles can include impurity particles, and the second quantity of particles can include a mixture of impurity particles and fused fuel particles. The first quantity of particles can be the same type of particles as the second quantity of particles. In some embodiments, the first quantity of particles can include a first proportion of fused fuel particles (e.g., a portion of the total amount of the first quantity of particles), and the second quantity of particles can include a second proportion of fused fuel particles. The second proportion can be greater than the first proportion.

[0073] In some embodiments, the amount of particles may be injected by more than one particle injector, e.g., in the case of a toroidal confinement device, particle injection may be performed at multiple locations around the torus of the device to form TB along the toroidal direction of the confined plasma.

[0074] It should be appreciated that the specific steps illustrated in FIG. 8 result in a particular method of injecting two quantities of particles into a characteristic region of a magnetic field that confines a plasma, according to an embodiment of the present invention. Other sequences of steps may be performed according to alternative embodiments. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. Additionally, individual steps illustrated in FIG. 8 may include multiple sub-steps that may be performed in various orders as appropriate for the individual step. Additionally, additional steps may be added or removed depending on the particular application. Those skilled in the art will recognize numerous variations, modifications, and alternatives.

[0075] 9 is a simplified diagram of an example method 900 for generating a transport barrier in a characteristic region of a magnetically confined plasma, according to at least one embodiment. Method 900 can be performed by one or more components of a plasma confinement system (e.g., plasma confinement system 100 of FIG. 1A, plasma confinement system 400 of FIG. 4). The plasma confinement system can include a plasma confinement device (e.g., a tokamak), a particle injector (or particle injectors), and a controller including one or more processors and one or more memories capable of storing and executing instructions for performing method 900.

[0076] The method 900 may begin at block 902 with adjusting a current in a plasma to generate a characteristic region of a magnetic field. The plasma may be confined by a magnetic field inside a plasma confinement device. The current may be adjusted by one or more control signals from a controller. Adjusting the current may generate a current parallel or substantially parallel to the magnetic field in the characteristic region.

[0077] Once the characteristic region is created, particles may be injected into the plasma at the characteristic region, according to block 904. Injection of the particles into the characteristic region may form a transport barrier in the characteristic region. The operations of block 904 may be similar to those described above for blocks 704 and 804 of Figures 7 and 8, respectively.

[0078] It should be appreciated that the specific steps illustrated in Figure 9 result in a particular method of generating a transport barrier in a characteristic region of a magnetic field that confines a plasma, in accordance with an embodiment of the present invention. The individual steps illustrated in Figure 9 may include multiple sub-steps that may be performed in various orders as appropriate for the individual step. Furthermore, additional steps may be added or removed depending on the particular application. Those skilled in the art will recognize numerous variations, modifications, and alternatives.

[0079] A computing device, such as a system plasma confinement system (e.g., plasma confinement system 100) for generating a characteristic region in a magnetic field and injecting a quantity of particles into the characteristic region, can be incorporated as part of the aforementioned system. The computing device can be useful for performing aspects of the aforementioned method. For example, the computing device can be useful for controlling particle injection rate, injection time, injection duration, for selecting particles (e.g., fusion fuel pellets, impurity pellets), for controlling the current of the plasma that generates the characteristic region, for receiving signals corresponding to measurements of parameters of the plasma (e.g., temperature, pressure, etc.), and the like. An exemplary computing device comprises hardware elements that can be electrically coupled (or otherwise in communication) via a bus. The hardware elements can include one or more processors, including but not limited to one or more general-purpose processors and / or one or more special-purpose processors (e.g., digital signal processing chips, graphics acceleration processors, video decoders, etc.), one or more input devices that can include, but are not limited to, a mouse, a touch screen, a keyboard, a remote control, voice input, etc., one or more output devices that can include, but are not limited to, a display device, a printer, a speaker, a servo, a linear actuator, a rotary actuator, etc.

[0080] A computing device may further include (and / or be in communication with) one or more non-transitory storage devices, which may include, but are not limited to, local and / or network accessible storage, and / or may include, but are not limited to, disk drives, drive arrays, optical storage devices, solid-state storage drives, such as solid-state drives ("SSDs"), random access memory ("RAM"), and / or read-only memory ("ROM"), which may be programmable, flash-updateable, etc. Such storage devices may be configured to implement any suitable data store, including, but not limited to, various file systems, database structures, and the like.

[0081] The computing device may also include a communications subsystem that may include, but is not limited to, a modem, a network card (wireless or wired), an infrared communication device, a wireless communication device, and / or a chipset (e.g., a Bluetooth device, a Bluetooth Low Energy or BLE device, an 802.11 device, an 802.15.4 device, a WiFi device, a WiMax device, a cellular communication device, etc.), a G.hn device, etc. The communications subsystem may enable data to be exchanged with a network, other computer systems, and / or any other device described herein. In many embodiments, the computing device further comprises a working memory that may include a RAM or ROM device, as described above.

[0082] A computing device may also include software elements as disposed within the working memory, including an operating system, device drivers, executable libraries, and / or other code, such as one or more application programs, which may include computer programs provided by various embodiments and / or may be designed to perform methods and / or configure systems provided by other embodiments as described herein. By way of example only, one or more procedures described with respect to the methods described above may be implemented as code and / or instructions executable by a computer (and / or a processor therein). In aspects, such code and / or instructions may then be used to configure and / or adapt a computer (or other device) to perform one or more operations in accordance with the described methods.

[0083] A set of these instructions and / or code may be stored on a non-transitory computer-readable storage medium, such as the non-transitory storage devices described above. In some cases, the storage medium may be incorporated within a computer system, such as the computing device described above. In other embodiments, the storage medium may be separate from the computer system (e.g., a removable medium such as a compact disc, or a cloud- or network-based storage system) and / or may be provided in an installation package, where the storage medium may be used to program, configure, and / or adapt a computer with the stored instructions / code. These instructions may take the form of executable code, executable by a computing device or a component thereof, and / or may take the form of source and / or installable code that takes the form of executable code upon compilation and / or installation on a computing device (e.g., using any of a variety of commonly available compilers, installation programs, compression / decompression utilities, etc.).

[0084] It will be apparent to those skilled in the art that substantial variations may be made according to particular requirements. For example, customized hardware may be used and / or particular elements may be implemented in hardware, software (including portable software such as applets), or both. Furthermore, connection to other computing devices, such as network I / O devices, may be employed.

[0085] As mentioned above, in one aspect, some embodiments may use a computing device to perform methods according to various embodiments. According to one set of embodiments, some or all of the steps of such methods are performed by a computing device in response to a processor executing one or more sequences of one or more instructions (which may be embedded in other code, such as an operating system and / or application program) contained in a working memory (e.g., one or more memories). Such instructions may be read into the working memory from another computer-readable medium, such as one or more non-transitory storage devices. By way of example only, execution of a sequence of instructions contained in the working memory may cause the processor to perform one or more steps of the methods described herein.

[0086] As used herein, the terms "machine-readable medium," "computer-readable storage medium," and "computer-readable media" refer to any medium that participates in providing data that causes a machine to operate in a specific manner. These media may be non-transitory. In an embodiment implemented using a computing device, various computer-readable media may participate in providing instructions / code to a processor for execution and / or may be used to store and / or carry such instructions / code. In many implementations, computer-readable media are physical and / or tangible storage media. Such media may take the form of non-volatile media or volatile media. Non-volatile media include, for example, optical and / or magnetic disks, such as non-transitory storage devices. Volatile media include, but are not limited to, dynamic memory, such as working memory.

[0087] Common forms of physical and / or tangible computer readable media include, for example, a floppy disk, a flexible disk, a hard disk, a magnetic tape or any other magnetic medium, a CD-ROM, any other optical medium, any other physical medium having a pattern of marks, a RAM, a PROM, an EPROM, a Flash EPROM, any other memory chip or cartridge, or any other medium from which a computer can read instructions and / or code. Network-based and cloud-based storage systems can also be useful forms of computer readable media.

[0088] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to a processor for execution. By way of example only, the instructions may initially be carried on a magnetic and / or optical disk of a remote computer. The remote computer may load the instructions into its dynamic memory and transmit the instructions as signals over a transmission medium which are received and / or executed by the computing device.

[0089] The communications subsystem (and / or its components) typically receives signals, and a bus can then carry the signals (and / or the data, instructions, etc. carried by the signals) to a working memory, from which a processor retrieves and executes the instructions. The instructions received by the working memory may optionally be stored in a non-transitory storage device either before or after execution by the processor.

[0090] It should be further understood that the components of a computing device may be distributed. For example, some processing may be performed in one location using a first processor, and other processing may be performed by another processor remote from the first processor. Optionally, the systems described herein may include multiple independent processors that may exchange instructions or issue commands or provide data to each other. Other components of a computing device may be distributed as well. Thus, a computing device may be interpreted as a distributed computing system that performs processing at multiple locations. In some cases, a computing device may be interpreted as a single computing device, such as separate laptops, desktop computers, etc., depending on the context.

[0091] Although examples and features of the disclosed principles are described herein, modifications, adaptations, and other implementations are possible without departing from the spirit and scope of the disclosed embodiments. Also, the words "comprising," "having," "containing," and "including," as well as other similar forms, are intended to be equivalent in meaning and open-ended in that the item or items following any one of these words are not meant to be an exhaustive listing of such item or items, but are not meant to be limited to only the item or items listed. It should also be noted that, as used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0092] It is also understood that the examples and embodiments described herein are for illustrative purposes only, and that various modifications or changes in light thereof will be suggested to those skilled in the art and are to be included within the spirit and scope of this application and the scope of the appended claims.

Claims

1. 1. A method comprising: generating in a plasma confinement device a characteristic region of a magnetic field that confines the plasma; and injecting a quantity of particles into the plasma at or inside the characteristic region, thereby creating a transport barrier at or inside the characteristic region; The method includes:

2. The method of claim 1 , wherein the characteristic region is defined by a region of negative magnetic shear of the magnetic field that confines the plasma.

3. The method of claim 1 , wherein the characteristic region is defined by a region of low magnetic shear of the magnetic field that confines the plasma.

4. The method of claim 1 , wherein the characteristic region is defined by a large Shafranov shift.

5. The method of claim 1 , wherein the characteristic region is defined by a particular shape of a magnetic surface of the magnetic field that confines the plasma.

6. The method of claim 1 , wherein the characteristic region is defined by a resonant magnetic perturbation of the magnetic field that confines the plasma.

7. 2. The method of claim 1, wherein the characteristic region is defined by a combination of magnetic shear, Shafranov shift, the shape of the magnetic surfaces of the magnetic field confining the plasma, and resonant magnetic perturbations of the magnetic field.

8. The method of claim 1 , wherein generating the characteristic region comprises generating an electric current in the plasma, the electric current being parallel to the magnetic field in the characteristic region.

9. The method of claim 1 , wherein the transport barrier is characterized by a pressure gradient dp / dr in the plasma that exceeds a threshold value.

10. 10. The method of claim 9, wherein the threshold is 5 x p / a, where p is the pressure of the plasma and a is the minor radius of the plasma confinement device.

11. The method of claim 1 , wherein the transport barrier is generated at about 70% of a minor radius of the plasma confinement device.

12. The method of claim 1 , wherein the transport barrier is generated at about 80% of a minor radius of the plasma confinement device.

13. The method of claim 1 , wherein the transport barrier is generated at about 90% of a minor radius of the plasma confinement device.

14. The method of claim 1 , wherein the quantity of particles comprises fused fuel particles.

15. 15. The method of claim 14, wherein the fusion fuel particles comprise deuterium or tritium.

16. The method of claim 1 , wherein the quantity of particles comprises impurity particles.

17. 17. The method of claim 16, wherein the impurity particles comprise at least one of the following species: carbon, silicon, a noble gas, or a species of an element with an atomic number Z less than 21.

18. 1. A method comprising: generating a characteristic region of a magnetic field that confines the plasma; injecting a first amount of particles into the plasma at or inside the characteristic region at a first time for a first period of time, thereby generating a transport barrier at or inside the characteristic region; injecting a second amount of particles into the characteristic region or into the plasma inside the characteristic region at a second time and for a second duration; A method comprising:

19. The method of claim 18 , wherein the characteristic region is defined by a region of negative magnetic shear of the magnetic field that confines the plasma.

20. The method of claim 18 , wherein the characteristic region is defined by a region of reduced magnetic shear of the magnetic field that confines the plasma.

21. The method of claim 18 , wherein the characteristic region is defined by a large Shafranov shift.

22. The method of claim 18 , wherein the characteristic region is defined by a particular shape of a magnetic surface of the magnetic field that confines the plasma.

23. The method of claim 18 , wherein the characteristic region is defined by a resonant magnetic perturbation of the magnetic field confining the plasma.

24. 20. The method of claim 18, wherein the characteristic region is defined by a combination of magnetic shear, Shafranov shift, a shape of the magnetic surface of the magnetic field confining the plasma, and a resonant magnetic perturbation of the magnetic field.

25. The method of claim 18 , wherein the first quantity of particles comprises at least a portion of impurity particles.

26. 26. The method of claim 25, wherein the second quantity of particles comprises impurity particles.

27. 26. The method of claim 25, wherein the second quantity of particles comprises fused fuel particles.

28. 26. The method of claim 25, wherein the second quantity of particles comprises a mixture of impurity particles and fused fuel particles.

29. 26. The method of claim 25, wherein a time-averaged particle infusion rate of the second quantity of particles is lower than a time-averaged infusion rate of the first quantity of particles.

30. 20. The method of claim 18, wherein the first quantity of particles comprises a first proportion of fused fuel particles and the second quantity of particles comprises a second proportion of fused fuel particles, the second proportion being greater than the first proportion.

31. The method of claim 18 , wherein the second period of time is greater than the first period of time.

32. 1. A system comprising: Plasma confinement device, A particle injector, and A controller, one or more processors; When executed by the one or more processors, the system includes at least adjusting a current of a plasma confined by a magnetic field within the plasma confinement device to generate a characteristic region of the magnetic field; and and one or more memories storing computer-executable instructions for causing the particle injector to inject a quantity of particles into the plasma at or inside the characteristic region, thereby forming a transport barrier at or inside the characteristic region.

33. 33. The system of claim 32, wherein the plasma confinement device is one of a tokamak device, a stellarator, or a toroidal pinch device.

34. 33. The system of claim 32, wherein the particle injector is configured to inject the quantity of particles as a high velocity pellet.

35. 34. The system of claim 33, wherein the quantity of particles comprises a portion of a cryogenically frozen pellet.

36. 33. The system of claim 32, wherein the particle injector is configured to inject the quantity of particles as a magnetically confined plasma.

37. 37. The system of claim 36, wherein the magnetically confined plasma comprises a compact toroid.

38. 33. The system of claim 32, wherein the quantity of particles is a first quantity of particles, the first quantity of particles being injected for a first period of time at a first time, and the one or more memories store additional computer-executable instructions that, when executed by the one or more processors, cause the system to further inject, using the particle injector, a second quantity of particles for a second period of time at a second time, the second quantity of particles maintaining the transport barrier for the second period of time.

39. 40. The system of claim 38, wherein the first quantity of particles comprises impurity particles and the second quantity of particles comprises fusion fuel particles.

40. 40. The system of claim 38, wherein the first quantity of particles comprises impurity particles and the second quantity of particles comprises a mixture of fusion fuel particles and impurity particles.

41. 39. The system of claim 38, wherein the first quantity of particles comprises a first proportion of fused fuel particles and the second quantity of particles comprises a second proportion of fused fuel particles, the second proportion being greater than the first proportion.

42. 40. The system of claim 38, wherein the time-averaged infusion rate of the second quantity of particles is less than the time-averaged infusion rate of the first quantity of particles.

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