Method for plasma start-up in a spherical tokamak

Abstract

The application relates to the technical field of magnetic confinement fusion, in particular to a plasma starting method of a spherical tokamak. Wherein, current is passed through the toroidal field coil and the equilibrium field coil of the spherical tokamak device to perform first current ramping until the current requirement of the first current platform is met, and the first plasma current is driven by microwaves; current is passed through the ohmic field coil of the spherical tokamak device to perform second current ramping until the current requirement of plasma starting is met; the coil current of the toroidal field coil and the equilibrium field coil is ramped until the current requirement of the second current platform is met, and is used for restraining and balancing the plasma current, and the application optimizes the ohmic discharge environment. To some extent, the problems of the installation precision of the spherical tokamak magnet coil and the stray field influence caused by the vacuum wall eddy current can be relieved, the harsh discharge condition is improved correspondingly, and the toroidal field and the equilibrium field are twice matched.

Description

Technical Field

[0001] This invention relates to the field of magnetic confinement fusion technology, and in particular to a plasma start-up method for a spherical tokamak. Background Technology

[0002] Nuclear fusion energy is safe, clean, and abundant. Magnetic confinement fusion based on tokamak devices is currently the most promising approach to the peaceful use of nuclear fusion energy. In 1986, Dr. Yuan-Kai Peng of Oak Ridge National Laboratory in Tennessee, USA, first proposed the concept of a spherical tokamak with a low torus ratio. The torus ratio refers to the ratio of the large radius to the small radius of the device. A low torus ratio makes the entire plasma spherical, allowing for more efficient utilization of magnetic energy and superior magnetohydrodynamic stability. Future fusion reactors based on spherical tokamas can significantly reduce size and cost. Simultaneously, the compact spherical tokamak can greatly reduce the construction and operating costs of the device. Currently, the United States, the United Kingdom, Russia, Japan, India, Brazil, and other countries are competing to build more than 20 spherical tokamas. This type of device is well-suited for operation in universities, giving students the opportunity to gain a comprehensive understanding of the device's characteristics and physical processes. It also plays a crucial role in fusion research and talent training.

[0003] Plasma current start-up is the most fundamental process in a tokamak device, primarily depending on the initial plasma state formed during plasma breakdown. There are two types of plasma start-up: induced current start-up and non-induced current start-up. Induced current start-up uses an ohmic transformer to initiate the plasma current and perform ohmic heating. Non-induced heating methods, generally called auxiliary heating, can be used for current-driven processes and mainly include neutral particle beam injection and radio frequency electromagnetic wave injection. If an ohmic transformer is not used at all, this non-traditional ohmic transformer current start-up method is called non-induced current start-up, such as electron cyclotron current start-up and coaxial helical injection.

[0004] In plasma discharge experiments, the toroidal field is first activated, and its current waveform exhibits a wave packet shape. Then, when the current in the toroidal field coil reaches or approaches its peak, the ohmic field coil is engaged to achieve gas breakdown and plasma formation. The equilibrium field needs to provide a force that balances the thermal pressure of the plasma to confine it. Existing ohmic plasma initiation conditions are quite demanding: the toroidal electric field E... T ≥0.30 V / m, circumferential electric field E T • Circumferential magnetic field B T / Stray Field B V≥1000 (V / m). The capability of the ohmic field, the accuracy of coil installation, and the stray field caused by the eddy currents in the vacuum wall are all important factors affecting plasma discharge. Due to the compact structure of the spherical tokamak device and the small area of ​​the central column, the transformer volt-seconds provided by the existing ohmic heating field are limited, which makes it impossible to start the spherical tokamak. Summary of the Invention

[0005] This invention aims to at least improve one of the technical problems existing in the prior art. To this end, this invention proposes a plasma start-up method for a spherical tokamak.

[0006] A plasma start-up method for a spherical tokamak according to a first aspect of the present invention, comprising:

[0007] Current is passed through the circumferential field coil and the balanced field coil of the spherical tokamak device to perform the first current ramp-up until the current requirement of the first current platform is met. The first plasma current is generated in the cavity of the tokamak device. The first plasma current is driven by microwave to construct the plasma pre-start-up environment.

[0008] Based on the completed plasma pre-start environment, current is passed through the ohmic field coil of the spherical tokamak device to provide the required volt-seconds to meet the plasma start-up requirements;

[0009] The current in the circumferential field coil and the balancing field coil is increased until the current requirement of the second-stage current plateau is met, which is used to confine and balance the plasma current, thus completing the plasma start-up process of the spherical tokamak.

[0010] According to the plasma start-up method of the spherical tokamak according to embodiments of the present invention, a relatively low plasma current is driven by the combined action of microwaves, a toroidal field coil, and a balancing field coil. Secondly, activating the ohmic field coil can achieve a higher plasma current. This is because activating the ohmic field in the presence of a low plasma current optimizes the ohmic discharge environment. To a certain extent, this alleviates problems such as the installation accuracy of the spherical tokamak magnet coil and the stray field effects caused by vacuum wall eddy currents. Finally, the coil currents of both the toroidal and balancing field coils need to reach a secondary current plateau to achieve constraint and balance. The power supply systems of the toroidal and balancing field coils will no longer employ a single-step power supply method, but will instead achieve a step-up at the moment the ohmic field coil is activated to meet different plasma current magnitudes and their discharge conditions. Different current magnitudes need to be activated at different discharge moments for the toroidal and balancing field coils. After the frequencies of the toroidal field coil and the microwave resonate, the toroidal field coil needs to be raised to the discharge level required for normal ohmic start-up. The low plasma current is balanced by the balancing field current provided by a constant current source, while the high plasma current is balanced by the balancing field current provided by a capacitor bank. Therefore, the harsh discharge conditions are improved accordingly, and the circumferential field and the equilibrium field are matched a second time.

[0011] In one possible implementation of the first aspect, the microwave is generated by a high-power gyrotron with a rated power of 15 kW and a microwave frequency of 2.45 GHz. For the first harmonic, the resonant absorption of the 2.45 GHz microwave occurs at a position with a circumferential magnetic field strength of 0.0875 T. The circumferential field first-order current plateau of about 4 kA can form a region of 0.0875 T inside the vacuum chamber.

[0012] In one possible implementation of the first aspect, the current of the first-stage current platform is 4 kA, which is expected to reduce the waste of ohmic field flux during the breakdown stage, thereby achieving better start-up effect under the same ohmic field flux change and saving volt-seconds.

[0013] In one possible implementation of the first aspect, the circumferential field coil current of the secondary current platform is 15 kA and the balancing field coil current is 3 kA, used to confine and balance the plasma current.

[0014] In one possible implementation of the first aspect, a current in the hundreds of amperes is passed through the balancing field coil when the microwave drives the first plasma current to balance the low plasma current.

[0015] In one possible implementation of the first aspect, the current in the balancing field coil is provided by a constant current source of the spherical tokamak during the first current ramp-up.

[0016] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a plasma start-up method for a spherical tokamak according to an embodiment of the present invention;

[0019] Figure 2 This is a waveform diagram of the circumferential field coil current of a spherical tokamak according to an embodiment of the present invention;

[0020] Figure 3 This is a waveform diagram of the balanced field coil current of a spherical tokamak according to an embodiment of the present invention;

[0021] Figure 4 This is a graph showing the starting current results of microwave-driven plasma;

[0022] Figure 5 This is a diagram showing the starting current results of the plasma starting method for a spherical tokamak according to an embodiment of the present invention. Detailed Implementation

[0023] The embodiments of the present invention are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0024] It should be noted that when a component is said to be "fixed to" another component, it can be directly attached to the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] The terms "first," "second," "third," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects and not to describe a particular order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, it may include a series of steps or units, or optionally, steps or units not listed, or other steps or units inherent to these processes, methods, products, or devices.

[0027] The accompanying drawings show only the portions relevant to this application, not all of them. Before discussing exemplary embodiments in more detail, it should be noted that some exemplary embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe operations (or steps) as sequential processes, many of these operations may be performed in parallel, concurrently, or simultaneously. Furthermore, the order of the operations may be rearranged. The process may be terminated when its operation is completed, but may also have additional steps not included in the drawings. The process may correspond to a method, function, procedure, subroutine, subprogram, etc.

[0028] The terms “component,” “module,” “system,” “unit,” etc., used in this specification are used to refer to computer-related entities, hardware, firmware, combinations of hardware and software, software, or software in execution. For example, a unit can be, but is not limited to, a process running on a processor, a processor, an object, an executable file, a thread of execution, a program, and / or distributed between two or more computers. Furthermore, these units can be executed from various computer-readable media on which various data structures are stored. Units can communicate, for example, via local and / or remote processes based on signals having one or more data packets (e.g., data from a second unit interacting with another unit between a local system, a distributed system, and / or a network; for example, the Internet interacting with other systems via signals).

[0029] Example 1

[0030] A plasma start-up method for a spherical tokamak according to a first aspect of the present invention, comprising:

[0031] Current is passed through the circumferential field coil and the balanced field coil of the spherical tokamak device to perform the first current ramp-up until the current requirement of the first current platform is met. The first plasma current is generated in the cavity of the tokamak device. The first plasma current is driven by microwave to construct the plasma pre-start-up environment.

[0032] Based on the completed plasma pre-start environment, current is passed through the ohmic field coil of the spherical tokamak device to provide the required volt-seconds to meet the plasma start-up requirements;

[0033] The current in the circumferential field coil and the balancing field coil is increased until the current requirement of the second-stage current plateau is met, which is used to confine and balance the plasma current, thus completing the plasma start-up process of the spherical tokamak.

[0034] According to the plasma start-up method of the spherical tokamak according to embodiments of the present invention, a relatively low plasma current is driven by the combined action of microwaves, a toroidal field coil, and a balancing field coil. Secondly, activating the ohmic field coil can achieve a higher plasma current. This is because activating the ohmic field in the presence of a low plasma current optimizes the ohmic discharge environment. This can alleviate problems such as the installation accuracy of the spherical tokamak magnet coil and the stray field effects caused by vacuum wall eddy currents to a certain extent. Finally, the coil currents of both the toroidal and balancing field coils need to reach a secondary current plateau to achieve constraint and balance. The power supply systems of the toroidal and balancing field coils will no longer use a single-step power supply method, but will instead achieve a step-up at the moment the ohmic field coil is activated to meet different plasma current magnitudes and their discharge conditions. Different current magnitudes need to be activated at different discharge moments for the toroidal and balancing field coils. After the frequencies of the toroidal field coil and the microwave resonate, the toroidal field coil needs to be raised to the discharge level required for normal ohmic start-up. The low plasma current is balanced by the balancing field current provided by a constant current source, and the high plasma current is balanced by the balancing field current provided by a capacitor bank. Therefore, the harsh discharge conditions are improved accordingly, and the circumferential field and the equilibrium field are matched a second time.

[0035] It should be noted that the microwaves mentioned are microwaves generated by a high-power gyrotron. The rated power of the high-power gyrotron is 15 kW, and the microwave frequency is 2.45 GHz. For the first harmonic, the resonant absorption of the 2.45 GHz microwave occurs at a position with a circumferential magnetic field strength of 0.0875 T. The first-order current plateau of the circumferential field is about 4 kA, which can form a region of 0.0875 T inside the vacuum chamber.

[0036] It should be noted that the current of the first-stage current platform is 4 kA, which is expected to reduce the waste of ohmic field flux during the breakdown stage, thereby achieving better start-up effect under the same ohmic field flux change and saving volt-seconds.

[0037] It should be noted that the current in the circumferential field coil of the secondary current platform is 15 kA, and the current in the equilibrium field coil is 3 kA, which are used to confine and balance the plasma current.

[0038] It should be noted that when the microwave drives the first plasma current, a current in the hundreds of amperes is passed through the balancing field coil to balance the low plasma current.

[0039] It should be noted that during the first current ramp-up, the current in the balancing field coil is provided by the constant current source of the spherical tokamak.

[0040] The following is an example of plasma startup for a spherical tokamak. First, a microwave-driven plasma current is used under a relatively low circumferential field, and then an ohmic field is immediately introduced to obtain a relatively high plasma current.

[0041] See Figure 2 The figure shows the current waveform of the toroidal field coil in a spherical tokamak. The current waveform is no longer a simple wave packet, but exhibits a secondary rise. The first current plateau is used to drive the low plasma current with microwaves (2.45 GHz). Resonant absorption occurs when the frequency of the incident wave matches the cyclotron frequency of the charged particles, and the wave energy is transferred to the charged particles. Based on the relationship between the microwave frequency (f) and the toroidal magnetic field (BT) in f = enBT / 2πme, and the parameters of the toroidal field coil in the spherical tokamak, the size of the first-stage current plateau is determined (for the first harmonic, the resonant absorption of the 2.45 GHz microwave occurs at a toroidal magnetic field strength of 0.0875 T). Figure 1 The first-stage current plateau of the circumferential field is approximately 4kA. Based on this, introducing the ohmic field coil is expected to reduce the waste of ohmic field flux during the breakdown phase, thereby achieving better startup performance with the same ohmic field flux variation and saving volt-seconds. The second ramp-up involves rapidly raising the magnetic field to the normal ohmic discharge level and immediately introducing the ohmic field to achieve the purpose of starting a high plasma current.

[0042] See Figure 3 The diagram shows the current waveform of the balancing field coil in a spherical tokamak, powered by a combination of a constant current source and a capacitor. First, when the microwave-driven plasma current is applied, a current in the hundreds of amperes (100A primary current provided by the constant current source, adjustable according to plasma equilibrium) is supplied to the balancing field coil to balance the low plasma current. Second, an ohmic field is introduced in the presence of low plasma current, saving volt-seconds and enabling the initiation of higher plasma currents even with limited ohmic field capability. Simultaneously, coil installation accuracy and stray field issues caused by vacuum wall eddy currents are further improved, optimizing the plasma discharge environment. Finally, the balancing field coil achieves a secondary ramp-up from 100A to balance plasma currents with higher parameters.

[0043] Based on the above embodiments, see Figure 4 and Figure 5 As shown, the plasma start-up method for the spherical tokamak of the present invention can obtain an ideal plasma current, and the start-up effect of the present invention is better than that of the traditional microwave start-up method.

[0044] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

[0045] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0046] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0047] Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The reference to "embodiment" herein means that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily indicate the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0048] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A plasma initiation method for a spherical tokamak, characterized in that, include: Current is passed through the circumferential field coil and the equilibrium field coil of the spherical tokamak device to perform the first current ramp-up until the current requirement of the first current platform is met. During the first current ramp-up, the current of the equilibrium field coil is provided by the constant current source of the spherical tokamak. The current of the first current platform is 4kA. The first plasma current is generated in the cavity of the tokamak device. The first plasma current is driven by a microwave with a frequency of 2.45GHz to construct the plasma pre-start-up environment. Based on the completed plasma pre-start environment, current is passed through the ohmic field coil of the spherical tokamak device to provide the required volt-seconds to meet the plasma start-up requirements; The coil current of the circumferential field coil and the balancing field coil is increased until the current requirement of the secondary current platform is met. The circumferential field coil current of the secondary current platform is 15 kA and the balancing field coil current is 3 kA, which are used to confine and balance the plasma current to complete the plasma start-up process of the spherical tokamak.

2. The plasma start-up method for a spherical tokamak according to claim 1, characterized in that, The microwaves mentioned are microwaves generated by a high-power gyrotron.

3. The plasma start-up method for a spherical tokamak according to claim 1, characterized in that, When the microwave drives the first plasma current, a current of hundreds of amperes is passed through the equilibrium field coil.

4. The plasma start-up method for a spherical tokamak according to claim 2, characterized in that, The rated power of the high-power gyrotron is 15 kW.

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