MUON source having internal electrodes and methods of making use thereof

Abstract

Methods and systems of producing muons for various purposes are disclosed. A system includes a target having multiple target plates spaced apart from each other and arranged such that a portion of each target plate is in a path of a beam of particles from a particle accelerator. The system further includes a voltage source configured to apply a voltage to a surface of each target plate to provide a voltage difference between adjacent plates. The system further includes an apparatus configured to apply a magnetic field to at least a region of the target.

Description

Docket No.: 367182.00102MUON SOURCE HAVING INTERNAL ELECTRODES AND METHODS OF MAKING USE THEREOFCROSS-REFERENCE TO RELATED APPLICATIONS[0001 J This application claims the priority and benefit of U.S. Provisional Application No. 63 / 650,345, filed on May 21, 2024, the entirety of which is incorporated herein by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with U.S. government support under Grant Number DE-AR0001798, awarded by the U.S. Department of Energy, Advanced Research Projects Agency for Energy (ARPA-E). The Government has certain rights in this invention.FIELD OF THE TECHNOLOGY

[0003] The technology relates to Radioactive sources (G21G4) and, in particular, to Radioactive sources other than neutron sources. (G21G4 / 04)BACKGROUND

[0004] Muons are fundamental subatomic particles which are similar to electrons, but have approximately 206 times the mass. Muons can have positive or negative charge. Muons are relatively long-lived among the short-lived subatomic particles, with a mean lifetime of 2.2 microseconds in vacuum - after which the muon typically decays into an electron (or positron, depending on its charge) plus two neutrinos.

[0005] When a muon traveling through space encounters matter, it will lose kinetic energy until it reaches thermal equilibrium. When this happens we say the muon has stopped in the material. When a negatively charged muon stops, it can readily displace atomic electrons and enter an atomic orbital to form a muonic atom. The muon can transfer to another atom, decay in orbit, or be captured into the nucleus.Docket No.: 367182.00102

[0006] When a muon is captured by a nucleus, it often transmutes the nucleus from one element to another. This transmutation may be employed, for example, for the production of isotopes with medical or industrial uses.

[0007] When a muon stops in material, it is typically first captured into a higher-energy atomic orbital, and then cascades down to successively lower-energy atomic orbitals until it reaches the ground state. This cascade process emits X-rays or gamma rays with characteristic energy levels which allow remote identification of the chemical element. When accelerated to high speeds, muons can travel through hundreds of meters of rock before stopping. The combination of these phenomena make muons useful for tomographic imaging and mapping, for example to locate and identify mineral deposits underground, inspect cargo, or to identify hidden chambers in buildings.

[0008] When a negatively charged muon stops in matter, it can catalyze nuclear fusion reactions - this effect is called muon catalyzed fusion. The muon orbits about 206 times closer to the nucleus than an electron. The muon screens the nuclear charge, allowing nuclei to come close enough to fuse at temperatures much lower than those required by thermonuclear fusion. The muon catalyzed fusion process is especially rapid in purified mixtures of deuterium and tritium, where a single muon may catalyze more than one hundred fusion reactions during its lifetime. Potential applications for muon catalyzed fusion include fusion energy production and use as a neutron source.

[0009] Muons may be beneficial as a form of radiation therapy, because, as compared with protons, they deposit a lower entrance dose in the surrounding tissue for the same Bragg peak energy deposited in the target tissue.

[0010] Muons are widely used by particle physicists to make sensitive tests of the standard model, in part in order to look for evidence of new particles, forces, and fields. Particle physicists are exploring construction of a muon collider, which would allow cleaner and higher energy collisions than are feasible by colliding other types of particles.

[0011] In summary, muons are extremely useful particles, with many potential high-value industrial, scientific, and medical uses.

[0012] Muons are produced in nature by high energy particles from outer space colliding with the upper atmosphere. These cosmic ray muons are useful for some applications (e.g. looking for minerals underground) but most applications of muons require them atDocket No.: 367182.00102higher rates and greater spatial concentration than can be practically obtained from cosmic rays.

[0013] There are several facilities worldwide which produce intense beams of muons for scientific and industrial uses. These are sometimes called “meson factories” or “muon facilities.” Examples include Fermilab in the USA, PSI in Switzerland, RIKEN-RAL in the UK, TRIUMF in Canada, and J-PARC in Japan.

[0014] Muons are produced in the meson factories through a process based on hadron collisions. Protons, neutrons, and pions are all examples of hadrons. When hadrons collide with each other at center-of-mass energies greater than about 200 MeV, they can produce pions. Pions are another type of short-lived subatomic particle. Pions can be positively-charged, negatively-charged, or neutral. Charged pions have a lifetime in vacuum of about 26 ns, after which they decay into a muon and a neutrino with nearly 100% probability.

[0015] At the PSI muon facility, a cyclotron is used to accelerate protons to 590 MeV kinetic energy. These protons are guided by magnetic lenses through an evacuated beamline, and directed toward a disc made of graphite, which is about 1 cm thick. This disc is called the production target. When the protons from the beam collide with the protons and neutrons making up the disc, pions may be created. Some of these pions stop in the disc and are absorbed, while others exit the disc and enter the surrounding vacuum space. The pions leave the target in all directions. A fraction of the pions enter the output beam lines and are focused by a series of magnetic lenses. While traveling in the beamlines, the pions naturally decay into muons over time. The muons are then available to experimenters at several target stations. The experimenter can control the current in the various magnets in the beamline in order to set the momentum of the muons delivered to the target station, as well as other characteristics of the beam such as the momentum width, spot size, and focus distance. The muon production target is heated by ionization energy loss by the protons in the beam. To keep the disc-shaped target from overheating, it is partially immersed in a tank of water, and spun by a motor about its central axis.

[0016] Two factors which limit the range of applications for which muons may be usefully employed are their energy cost and their economic cost. A useful metric for the energy cost to produce a muon is the wall-plug energy cost per muon. This is the totalDocket No.: 367182.00102electrical power consumed by the facility from the electrical power grid, divided by the rate at which it produces muons and delivers them to the targets. Typically this includes power consumption by the particle accelerator, the beamline magnets, cooling systems, and control systems. A useful metric of the economic cost of a muon is the amortized capital cost plus operating cost of the facility, divided by the rate at which it can produce usable muons.

[0017] To allow application of muons in a wider range of industrial, scientific, and medical applications, it would be advantageous and useful to have a muon source with reduced energy cost per muon, reduced economic cost per muon, or both, compared with the present state-of-the-art.

[0018] In addition, several highly compelling applications for muons only become technically or economically feasible if the energy cost or economic cost of muons can be brought below a particular threshold. For example, production of electricity for the commercial power grid via muon catalyzed fusion is only feasible if the energy cost of a muon is low enough that the overall plant can produce net energy. Production of medical isotopes via nuclear muon capture only becomes economically feasible if the market value of the isotopes produced is higher than the economic cost to produce the needed muons.SUMMARY

[0019] Aspects of the present disclosure relate to a muon source having internal electrodes, and methods for making use thereof, that may be used for various purposes. The electrodes allow the muon source to produce and deliver many more muons for the same input energy, greatly reducing both the energy cost and economic cost of muon production. This reduced cost may enable many new industrial, scientific, and medical applications for muons, such as generation of electrical power via muon catalyzed fusion, production of medical isotopes via nuclear muon capture, muon therapy, and tomographic imaging.

[0020] In an embodiment, a system includes a target having multiple target plates spaced apart from each other and arranged such that a portion of each target plate is in a path of a beam of particles from a particle accelerator. The system further includes a voltage source configured to apply a voltage to a surface of each target plate to provide a voltageDocket No.: 367182.00102difference between adjacent plates. The system further includes an apparatus configured to apply a magnetic field to at least a region of the target

[0021] Implementations of the disclosure may include one or more of the following optional features. In some examples, the target is configured to, when the beam of particles is steered onto one or more plates of the target, cause the one or more plates of the target to produce one or more charged pions. At least one of the target plates may include a flexible plate and a drive mechanism may be configured to drive the flexible plate so that a different portion of the flexible plate is in the path of the beam of particles. At least one of the target plates may include a liquid. At least one of the target plates may be configured to move through a cooling system. The system may include a fusion reaction chamber adjacent to the target, the fusion reaction chamber containing fusion fuel. The fusion fuel may include deuterium and / or tritium. The fusion reaction chamber may include a lithium breeding blanket. The system may further include a cooling system for the lithium breeding blanket. The target plates may include lithium deuteride.

[0022] The system may include a current monitor configured to detect electrical charge accumulating on one or more of the target plates. In some examples, the voltage difference between adjacent plates, the applied magnetic field, and a thickness of the plates are configured to cause the target to, when the beam of particles is steered onto the target, produce charged pions. The apparatus may include one or more permanent magnets. The apparatus may be configured to apply a substantially uniform magnetic field to the at least the region of the target. In some examples, target plates are substantially parallel to each other and the apparatus is configured to apply the magnetic field so as to be substantially perpendicular to an electric field produced by the voltage difference between the substantially parallel target plates. In some examples, the voltage difference between adjacent plates varies between sets of adjacent plates.

[0023] In an embodiment, a method is disclosed. The method includes providing a muon production system including target plates spaced apart from each other and arranged such that a portion of each target plate is in a path of a beam of particles from a particle accelerator. The method further includes steering the beam of particles onto one or more plates of the target, causing the one or more plates of the target to produce one or more charged pions and allowing the one or more charged pions to decay into muons.Docket No.: 367182.00102

[0024] Implementations of the disclosure may include one or more of the following optional features. In some examples, steering the beam of particles comprising dynamically scanning a size or a position of the beam of particles onto the one or more plates. Steering the beam of particles may include steering a beam of tritonsBRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other aspects, advantages and novel features of the invention will become more apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings which are incorporated into this document and form a part of the disclosure, wherein:

[0026] Fig. 1 depicts the use of the muon source in an electrical power plant, including the accelerator, primary beamline, active pion production target, secondary beamline, fusion cell, turbine plant, and generator.

[0027] Fig. 2 depicts the basic structure of the pion production target with embedded electrodes.

[0028] Fig. 3 depicts the pion production target with embedded electrodes in schematic form. The structure of the target, together with notional particle paths to aid understanding of the operational principle are shown.

[0029] Fig 4. depicts a simulation result for the muon source with embedded electrodes of the type shown in Fig 1. Particle paths simulated using GEANT4 software are shown.

[0030] Figs. 5A-5D depict a fluid target muon source, in which the pion production occurs at least in part in the flowing fluid contained within ducts, and the target may be contained within a vacuum chamber.

[0031] Figs. 6A-6B depicts a muon source with a flexible solid target that is spooled through the beam area.

[0032] Figs. 7A and 7B depict a rotating plate for a pion and muon production source.

[0033] Fig. 8 shows a flowchart of a method for producing muons.DETAILED DESCRIPTIONDocket No.: 367182.00102

[0034] This document describes system, apparatus, device, and / or method embodiments, and / or combinations and sub-combinations of any of the above, for the production of muons. While preferred embodiments of the invention are disclosed in the attached materials, many other implementations will occur to one of ordinary skill in the art and are all within the scope of the invention. Each of the various embodiments described may be combined with other described embodiments in order to provide multiple features. Furthermore, while the attached materials describe a number of separate embodiments of the apparatus and method of the present invention, what has been described is merely illustrative of the application of the principles of the present invention. Other arrangements, methods, modifications, and substitutions by one of ordinary skill in the art are therefore also considered to be within the scope of the present invention.

[0035] In some embodiments, as used in the specification and including the appended claims, the singular forms “a,” “an,” and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” or “approximately” one particular value and / or to “about” or “approximately” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It is also understood that all spatial references, such as, for example, horizontal, vertical, top, upper, lower, bottom, left and right, are for illustrative purposes only and can be varied within the scope of the disclosure. For example, the references “upper” and “lower” are relative and used only in the context to the other and are not necessarily “superior” and “inferior.” Generally, similar spatial references of different aspects or components indicate similar spatial orientation and / or positioning, i.e., that each “first end” is situated on or directed towards the same end of the device.

[0036] Some embodiments will now be described with reference to the figures. Like elements in the various figures may be referenced with like numbers for consistency. In the following description, numerous details are set forth to provide an understanding of various embodiments and / or features.Docket No.: 367182.00102

[0037] It is to be appreciated that the Detailed Description section, and not any other section, is intended to be used to interpret the claims. Other sections can set forth one or more but not all exemplary embodiments as contemplated by the inventor(s), and thus, are not intended to limit this disclosure or the appended claims in any way.

[0038] Fig 1 depicts a system 100 including an electrical power plant utilizing a muon source and a muon catalyzed fusion cell to produce electricity. A particle accelerator 101 is used to produce a beam of primary particles 103. For example, the primary particles 103 may be tritons with energy of 1 GeV / nucleon. The accelerator 101 may be a LINAC, synchrotron, or any other type of particle accelerator producing a primary beam 103 of sufficient energy. The primary particles 103 pass through a primary beamline 102, and impact internal components of the active pion and muon source 104, which is shown in more detail in subsequent figures.

[0039] The resulting pions and muons from the source 104 travel down a secondary beamline 114. Pions have a mean lifetime of approximately 26 ns, after which they decay with near 100% probability into muons. One function of the beamline is to allow the pions time to decay into muons. Muons have a mean lifetime of approximately 2.2 us, almost 100 times as long.

[0040] The secondary beamline 114 may include optical elements designed to guide and focus beams of charged particles, such as solenoid magnets, magnetic quadrupole lenses, Einzel lenses, and the like to guide the pions and muons along the secondary beamline 114. Devices to reduce the emittance of the beam (for example, ionization cooling arrays, analyzing magnets and wedge-shaped beam degraders, or similar devices known in the art of particle beam manipulation) may be used in the secondary beamline 114 to tune the secondary beam for the desired characteristics.

[0041] At the end of the secondary beamline 114, the pions and muons pass through a beam window that defines the interface between the secondary beamline and the muon-catalyzed fusion cell 106. The pions and muons then enter the fusion cell 106. The muon catalyzed fusion cell 106 includes fusion fuel, typically in the form of a flowing stream and including hydrogen isotopes (and / or ions of hydrogen isotopes). The fusion fuel may, for example, be a pressurized mixture of deuterium and tritium gas. The muons cause nuclear fusion reactions in the gas. In deuterium-tritium fusion, the fusion produces alphaDocket No.: 367182.00102particles and neutrons. The alpha particles have a short range and predominantly heat the deuterium-gas. The majority of the neutrons pass into a surrounding (optional) breeding blanket, which is used to absorb the energy from the neutrons and to produce tritium. The breeding blanket may include lithium or other substance which readily produces further fusion fuel. In some examples, the interior walls of the fusion cell 106 are lined with breeding blankets.

[0042] Heat is produced in the pion and muon production target 104, the fusion cell 106, and the breeding blanket. Heat from some or all of these sources may be collected by a fluid flowing through pipes 111, 112, 113, and used by a heat engine or other power generation system 107 to produce mechanical work 110. The heat engine may use the Rankine cycle, Brayton cycle, Stirling cycle, or any other thermodynamic cycle useful for converting heat to work. The heat engine block 107 is understood to contain any circulating pumps, cooling towers, control systems, and other similar needed components.

[0043] Some or all of this mechanical work may be used to turn an electrical generator 108 to produce electrical power 109. Some or all of this power may be used to provide electrical power to the accelerator 101.

[0044] The pion and muon source may provide or supply electrical power from its port 117, depending on the operating mode. With appropriate power controllers, power coming from or going to each component may be combined on a common bus and interconnected to the electrical power grid.

[0045] In variations of this embodiment, the fusion cell 106 may be replaced, or supplemented, by other devices requiring a beam of pions, muons, or neutrons for operation. This may include, for example, a transmutation target for production of useful isotopes, an object to be imaged using muon or neutron tomography, or a target and particle detector for a scientific experiment.

[0046] Figure 2 depicts components of the example pion / muon source 104 of Fig. 1. The example source includes one or more plates 301 in the path of the primary beam 103. Voltage sources 309 may provide electric fields between adjacent plates 301. Magnets (e.g., electromagnets or permanent magnets), which are not shown, may provide a magnetic field 302 within the example pion / muon source 104. As shown in Fig. 2, theDocket No.: 367182.00102direction of the magnetic field 302 is out of the drawing page, i.e., perpendicular to the electric fields between the plates 301, and the magnetic field 302 is substantially uniform across the device. Other relative arrangements of the electric and magnetic fields 302 are also possible.

[0047] Figure 3 depicts a pion and muon source, which is designed to efficiently produce pions and muons and guide them to exit in a particular direction.

[0048] When pions are produced through hadronic interactions, their typical range in solid or liquid materials before stopping or absorption may be only a few millimeters. Prior art pion and muon sources must be thin in at least one dimension, either parallel or perpendicular to the beam direction, to allow a large number of the pions produced by interactions to be able to exit and be utilized before stopping inside the device.

[0049] This pion source described here makes use of internal electric and magnetic fields 308 to guide the pions through internal vacuum channels toward one output face of the device. This allows the source to be constructed with dimensions which are large compared with the pion range in materials, both parallel to and perpendicular to the beam axis. This greatly increases the number of pion producing interactions, both with the primary beam and with its hadronic secondaries, which may themselves be above the threshold for pion production. As a result, it greatly increases the energy efficiency of pion production as compared to prior art devices, which is advantageous.

[0050] Figure 3 illustrates one embodiment of the improved pion and muon source and shows particle paths of example particles in order to illustrate the operational principle. A primary particle beam 103 enters the source from the left. Without limitation, the beam may be composed of tritons at an average energy of 1 GeV / nucleon, protons, neutrons, deuterons, sodium ions, or any other type of particle.

[0051] The source may be used to produce positively or negatively charged muons, depending on the application. It may be advantageous to use primary particle beams containing particles containing neurons, if production of negatively charged pions or muons is desired, because collisions involving neutrons favor the production of negatively charged pions. On the other hand, it may be advantageous to use a proton beam if production of positively charged pions and muons is desired.Docket No.: 367182.00102

[0052] The primary beam impacts a series of plates 301 and (optionally) one or more beam degraders 302. The plates are located inside a vacuum chamber. In one example, the entire muon / pion source 104 consists essentially of one vacuum chamber. In other examples, the source includes several vacuum chambers or vacuum spaces with some degree of isolation from each other. In one example, each space between adjacent plates 301 is a separate vacuum chamber.

[0053] In one embodiment, the plates are made of a conductive material. In this case, a set of voltage sources 309 is used to impose a uniform electric field between each set of plates, in the manner of a stack of parallel-plate capacitors. In some examples, the plates 301 include a lithium hydride, such as lithium deuteride.

[0054] In another embodiment, the plates 301 are a laminated stack of electrically conductive, insulating, and conductive layers, similar in some respects to a circuit board substrate. The plates may be made, for example, of insulating boron nitride, laminated with a sheet of conductive beryllium metal foil on each face. A voltage source 309 is used to impose a voltage between each adjacent pair of conductive surfaces in the vacuum, forming an approximately uniform electric field in the set of vacuum spaces between each set of plates, and an oppositely directed approximately uniform electric field in the set of insulating layers inside each plate 301. This embodiment may be advantageous because it reduces the voltage difference from one end of the stack to the other and allows the use of a smaller number of voltage sources 309.

[0055] When the primary beam impacts the plates 301, and optionally the beam degraders 302, a number of physics processes may occur, some leading to the creation of pions. When the primary beam passes through the target materials, it slows down through ionization energy loss. If the particle is an ion, after traveling only a short distance through the target materials, it may tend to quickly break up into individual protons and neutrons. In the figure, a particle from the primary beam 103 is shown as a triton, and breaks up at location 303, into a proton 305, a neutron 304, and another neutron 311. At location 310, neutron 311 experiences a hadronic interaction with a plate 301 to generate a negatively charged pion 105. The pion’s trajectory is curved due to the action of the magnetic field 308. The pion slows down due to ionization energy loss as it passes through the plate materials. The electric field provides energy to the pion as itDocket No.: 367182.00102moves through the device, which reduces the probability that the pion will lose enough energy to stop inside the target and increases the probability that it will leave the target. The combined action of the crossed electric and magnetic field in the vacuum spaces between the plates, together with periodic energy loss as the pion passes through a plate, act to direct the pions out of the target in a direction which is approximately perpendicular to both field directions. Additionally, it acts to reduce the momentum spread of the pions as they emerge from the device.[00561 The magnetic field 308 also acts to suppress the formation of electron avalanches inside the vacuum spaces of the target. Essentially, this is because it causes electrons to move in spiraling paths with overall motion perpendicular to, rather than parallel to the electric field.

[0057] The pions have a mean lifetime of approximately 26 ns, after which they decay with near 100% probability into muons. For some pions, this occurs inside vacuum spaces between the plates, but for others, it occurs outside. The source may be used to provide pions directly or may be connected to a secondary beamline 114 to allow pions to decay to muons before reaching a target.

[0058] Pions tend to be produced in forward-biased direction, relative to the beam.Therefore, to add energy to negatively charged pions, the voltages on the plates may be set such that it accelerates negatively-charged particles in the direction of propagation of the beam. Similarly, to add energy to positively charged poisons, the voltages on the plates may be set in the reverse direction.

[0059] In simulations of the production and guidance of negatively charged pions, we have found that electrical power tends to flow out of the plates into the voltage sources. In part, this is because the primary beam is slowed down by the imposed electric field as it passes through the vacuum gaps, inducing the flow of electrical current, and causing a net power flow out of the device. This power may be converted to a useful voltage using a switching converter and used to assist in powering the accelerator, or to do other useful work.

[0060] In order to minimize the overall energy per muon, it may be advantageous to divide the target plates into segments and apply different voltages, possibly in different directions, at each place in the target. It also may be advantageous for the plates to beDocket No.: 367182.00102curved (for example, to be conical, parabolic, or another shape) rather than being flat. It may be advantageous for the plates to have a variable thickness over their extent, to have a variable vacuum gap between them, or both.

[0061] It may be advantageous to use materials in the construction for the target which reduce the amount, lifetime, or both of induced radioactivity in the target. To this end, hydrogen, helium, lithium hydride, lithium deuteride, beryllium, beryllium boride, boron carbide, graphite, and graphite consisting of purified carbon-12 can be used. For increased production of negative pions, it is advantageous to use target materials with enhanced neutron content.

[0062] To spread out the structural damage caused by the beam over a wider area, it may be advantageous to defocus the primary beam as it reaches the target, to actively scan it over an area with beam elements, or to translate or rotate the target.

[0063] It may be advantageous to surround the source with energy absorbing shielding material, to absorb energy from high energy particles emitted by the source, such as neutrons and gamma rays. These energy absorbers may be useful both for personnel and equipment safety, to contain radiation inside the system, and to collect the energy in these particles and convert it to heat for the purpose of energy recovery. These energy absorbers may be composed, for example, of tungsten or lead for stopping or gamma rays, and or borated polyethylene for the stopping of neutrons. The energy absorbers may include ducts to allow liquids or gasses to flow through for cooling and for recovery of heat for useful purposes.

[0064] Optionally, it may be advantageous to add neutron multiplying materials such as beryllium to the plates, as well as materials which undergo exothermic nuclear reactions, such as lithium-6, uranium, or thorium, in order to increase the amount of heat energy produced in the source.

[0065] Fig 4. depicts the results of a simulation of a target having the design shown in Fig 1. The simulation was done using CERN GEANT4, using the QGSP-BIC physics list The simulation of the motion of the particles in the applied electric and magnetic fields, and the interactions of the particles with the target. In the simulation, 500 simulated tritons are shot into-the-page in particle beam 103 toward a target composed of plates 301 and beam degraders 307. In this simulation, the target plates were square, 10 m on eachDocket No.: 367182.00102side. The plates were made of lithium-7 deuteride and were 9 mm thick. The plates were separated from each other by 135 mm thick layers of vacuum. The number of plates was 300. The triton beam was centered on the plate in one direction, and 1.5 m from the edge of the plate in the other direction. Cylindrical beam degraders 307 made of lithium-7 deuteride were used between each pair of plates, each 20 mm in diameter, centered on the beam axis. The electric field intensity in the vacuum spaces between the plates was 80 MV / m. The magnetic flux density was 0.4 T.[00661 The trajectories of particles above the energy threshold for pion production 401 are shown in the figure, as well as pions and muons produced 105. In the simulation, the net energy expended per negative pion exiting the target was 3.3 GeV. Note also that most of the pions and muons emerge from the top face of the device. This is significantly improved versus prior art negative pion production targets, which tend to use 5 - 10 GeV of energy per pion and produce pions over a broad solid angle.

[0067] Figs. 5A-5D depicts another embodiment, in which a pion and muon source which uses a liquid target flowing through ducts. The beam of particles 103 enters a vacuum chamber through flange 501 and reaches a series of ducts 502, which serve a similar function to plates 301, but allow the main mass of the pion production target to be made from a fluid. Heat can be efficiently removed from the system through circulation of the fluid. For example, the fluid may include lithium hydride or lithium deuteride, and the ducts 502 may include beryllium metal, boron nitride, graphite, or another suitable material for containing the fluid and for being suitably transparent to the primary beam. Fluid flows into the inlet port 508, through ducts 502, through inter-duct connectors 514, and finally out the outlet port 509. The whole assembly of ducts is contained within the vacuum chamber. If the ducts are made from a conductive material, such as a metal, electrically insulating spacer plates 512, 506 and may be placed on their surfaces.Electrode plates 513 and 505 are driven by a power control circuit to produce an electric field between each set of plates. When pions are produced through interaction of the beam 103 and the materials comprising the system, this electric field 503 supplies energy to accelerate the pions.Docket No.: 367182.00102

[0068] Beam degraders 307 may be placed in order to cause the beam to break up after traversing a smaller length of the target. It may be advantageous to cool these beam degraders by flowing liquid through them or combining them with the ducts 502.

[0069] A magnetic field 308 is applied in a direction approximately perpendicular to the electric field. The magnetic field may be supplied by an armature 511 and permanent magnets 504 and 510, as shown in Fig. 5B, or may be provided by a superconducting or non-superconducting (e g., copper) current-carrying coil, or by any other means to produce a magnetic field. For example, the embodiment of Fig. 5C includes superconducting electromagnets. The magnetic field 308 acts to suppress the formation of electron avalanches. The approximately crossed electric 503 and magnetic fields 308 in the vacuum spaced between the electrodes tends to guide the pions produced 105 in a direction which is mutually to perpendicular to both - in this case, in the direction facing into the page. The pions exit the source 104 through vacuum flange or window 515. The fluid may pass through a heat exchanger, heat engine, or other similar components to remove the heat before being recirculated into the target. A pump may be used to cause the flow of the fluid. If the fluid solidifies at ambient temperature, the pipes may be equipped with heaters to melt the fluid upon system startup. An electronic controller, e.g., interfacing with temperature sensors, may be used to control the pump, accelerator beam intensity, and other system components to keep the fluid temperature within an acceptable operating window.

[0070] It may be advantageous to place a chemical or isotopic purification system in line with the flowing liquid, to remove contaminants which may build up during operation before returning the fluid to the target.

[0071] A hole 507 may be placed through one or more of the ducts 502, or plates 301, to allow the beam to penetrate a greater distance into the target. This may be advantageous so that the pions generated by initial collisions between the beam, after the beam has traveled only a short distance through the target materials, may still be directed upwards by the action of the fields.

[0072] In some examples, such as the embodiment of Fig. 5B, a vacuum is maintained in individual slices between the ducts, rather than the whole duct assembly being placed into an overall vacuum chamber. This may be advantageous to reduce fabrication cost or toDocket No.: 367182.00102make the system more compact. Individual vacuum seals 601, optionally with gaskets or O-rings 602, are used to seal a vacuum space between each set of ducts. All vacuum spaces may join together at the exit flange 603. Vacuum feedthroughs, not shown, are used to pump down the vacuum space, monitor the vacuum pressure, and pass wiring in and out of the vacuum space.[0073 J Figs. 6A-6B depict a flexible plate for a pion and muon production source. The flexible plate may be, for example, a flexible ribbon consisting of three layers of metal with intervening insulation layers. In this embodiment, the plate is wrapped around a source spool on one side. A motor pulls the plate through the beam area, wrapping it around a take-up spool on the other side. Sliding seals allow the plate to pass into the vacuum chamber. The plate may be cooled as it passes from the vacuum chamber to the spool by flowing a cold fluid past it. This arrangement may be advantageous because it allows continuous replacement of plate materials which may be structurally weakened by ionizing radiation inside the source area. In another embodiment, the flexible plate includes an array of wires, e.g., moving on spools through the target area.

[0074] Figs. 7A and 7B depict a rotating plate for a pion and muon production source. The rotating plate is rotated by a motor about an axis. A cooling system cools the plate. The cooling system may include, for example, a tank of liquid through which the plate rotates through. This may be advantageous to allow material damage from the primary beam to be distributed over a larger area.

[0075] Fig. 8 shows a flowchart 800 of a method for producing muons. At step 802, the method includes providing a muon-production system 100, such as the system 100 described above. At step 804, the method includes steering a particle beam 103 onto a target (such as a plate 301 or equivalent) of the muon-production system 100. The beam may be any of the beams described above. Furthermore, this step may also include focusing the beam 103 and / or adjusting other parameters of the beam 103, such as energy, emittance, and the like. As the beam 103 interacts with the target, the interaction may produce pions. At step 806, the method includes allowing the pions to decay into muons.

[0076] It should be understood that various aspects disclosed herein may be combined in different combinations than the combinations specifically presented in the description andDocket No.: 367182.00102accompanying drawings. For example, features, functionality, and components from one embodiment may be combined with another embodiment and vice versa unless the context clearly indicates otherwise. Similarly, features, functionality, and components may be omitted unless the context clearly indicates otherwise. It should also be understood that, depending on the example, certain acts or events of any of the processes or methods described herein may be performed in a different sequence, may be added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the techniques).

[0077] The breadth and scope of this disclosure should not be limited by any of the above-described example embodiments but should be defined only in accordance with the following claims and their equivalents.

Claims

Docket No.: 367182.00102CLAIMS1. A system for producing muons, the system comprising:a target comprising a plurality of target plates spaced apart from each other and arranged such that a portion of each target plate is in a path of a beam of particles from a particle accelerator;a voltage source configured to apply a voltage to a surface of each plate of the plurality of target plates to provide a voltage difference between adjacent plates; and an apparatus configured to apply a magnetic field to at least a region of the target.

2. The system of claim 1, wherein the target is configured to, when the beam of particles is steered onto one or more plates of the target, cause the one or more plates of the target to produce one or more charged pions.

3. The system of claim 1, wherein:at least one of the plurality of target plates comprises a flexible plate; and a drive mechanism configured to drive the flexible plate so that a different portion of the flexible plate is in the path of the beam of particles.

4. The system of claim 1, wherein at least one of the plurality of target plates comprises a liquid.

5. The system of claim 1, wherein at least one of the plurality of target plates is configured to move through a cooling system.

6. The system of claim 1, further comprising a fusion reaction chamber adjacent to the target, the fusion reaction chamber containing fusion fuel.

7. The system of claim 6, wherein the fusion fuel comprises deuterium and / or tritium.Docket No.: 367182.001028. The system of claim 6, wherein the fusion reaction chamber includes a lithium breeding blanket.

9. The system of claim 8, further comprising a cooling system for the lithium breeding blanket.

10. The system of claim 1, wherein the plurality of target plates comprise lithium deuteride.

11. The system of claim 1, further comprising a current monitor configured to detect electrical charge accumulating on one or more of the plurality of target plates.

12. The system of claim 1, wherein the voltage difference between adjacent plates, the applied magnetic field, and a thickness of the plates are configured to cause the target to, when the beam of particles is steered onto the target, produce charged pions.

13. The system of claim 1, wherein the apparatus comprises one or more permanent magnets.

14. The system of claim 1, wherein the apparatus is configured to apply a substantially uniform magnetic field to the at least the region of the target.

15. The system of claim 1, wherein the plurality of target plates are substantially parallel to each other and the apparatus is configured to apply the magnetic field so as to be substantially perpendicular to an electric field produced by the voltage difference between the substantially parallel target plates.

16. The system of claim 1, wherein the voltage difference between adjacent plates varies between sets of adjacent plates.

17. A method of producing muons comprising:Docket No.: 367182.00102providing the system of claim 1;steering the beam of particles onto one or more plates of the target, causing the one or more plates of the target to produce one or more charged pions; andallowing the one or more charged pions to decay into muons.

18. The method of claim 17, wherein steering the beam of particles comprising dynamically scanning a size or a position of the beam of particles onto the one or more plates.

19. The method of claim 17, wherein steering the beam of particles comprises steering a beam of tritons.

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