K. X. Yu

Measurement of 2/1 intrinsic error field of Joint TEXT tokamak

The amplitude and spatial phase of the intrinsic error field of Joint TEXT (J-TEXT) tokamak were measured by scanning the spatial phase of an externally exerted resonant magnetic perturbation and fitting the mode locking thresholds. For a typical plasma with current of 180 kA, the amplitude of the 2∕1 component of the error field at the plasma edge is measured to be 0.31 G, which is about 1.8 × 10(-5) relative to the base toroidal field. The measured spatial phase is about 317° in the specified coordinate system (r, θ, ϕ) of J-TEXT tokamak. An analytical model based on the dynamics of rotating island is developed to verify the measured phase.

Measurement of toroidal vessel eddy current during plasma disruption on J-TEXT

In this paper, we have employed a thin, printed circuit board eddy current array in order to determine the radial distribution of the azimuthal component of the eddy current density at the surface of a steel plate. The eddy current in the steel plate can be calculated by analytical methods under the simplifying assumptions that the steel plate is infinitely large and the exciting current is of uniform distribution. The measurement on the steel plate shows that this method has high spatial resolution. Then, we extended this methodology to a toroidal geometry with the objective of determining the poloidal distribution of the toroidal component of the eddy current density associated with plasma disruption in a fusion reactor called J-TEXT. The preliminary measured result is consistent with the analysis and calculation results on the J-TEXT vacuum vessel.

High-voltage power supply for ECRH system on J-TEXT Tokamak

A 100kV/60A high-voltage power supply (HVPS) has been established to energize the electron cyclotron resonance heating (ECRH) system for J-TEXT tokamak. With the pulse step modulation (PSM) technology, the HVPS has many advantages, especially the low stored energy and short protective time in case of short-circuit fault. This paper gives a description and key design features for the isolated transformers, switch power supplies (SPS) modules, measurement equipments and controller. In this HVPS, 4 dry-type transformers with 36 secondary-windings drive the 144 series SPS modules and isolate the high voltage between the rectifiers and the 6.3kV AC bus. A controller based on the PXI technology, which conforms to the ITER CODAC standard, has been developed to operate the series switches in each SPS module. The error signals from all the modules are monitored by the controller and the fast protection responses any over current fault in less than 5 μs. Moreover, to acquire better dynamic response and stability, a control strategy improved from the conventional PWM phase-shift modulation method has been proposed. The experimental results are also presented and show that the power supply system performing good.

Reconstruction Progress of the COMPASS-D ECRH System on J-TEXT

To make the J-TEXT tokamak more flexible for physics experiments, an electron cyclotron resonance heating (ECRH) system is being developed. The main parts of the J-TEXT ECRH system are donated by the Culham Science Center from the former COMPASS-D, including six 60 GHz/200 kW/5 s (0.5 s) gyrotrons, six magnets, and auxiliary power supplies for the gyrotrons, transmission parts, and so on. For the ECRH system, the output mode of the gyrotron from the former Varian Associates, Inc. is TE02 mode and converted to TE01 mode for low loss transmission. The TE01-TE11-HE11 mode converter is used at the end of the transmission lines for efficient coupling. Then, the high-power wave is injected to the desired area of the plasma by a rotatable quasi-optical launcher. A 100 kV/60 A power supply based on a pulse step modulation technology has been developed to feed all the gyrotrons. The control system based on the compact reconfigurable I/O-9068 platform of National Instruments for monitoring, timing, and protection is being designed. Other units, such as the cooling loops, the launcher, and a spared auxiliary power supply, are on the way. We hope that four subsystems can be finally used on J-TEXT.

Dummy Load Prototype Design for ITER Coil Power Supply System

This paper mainly introduces the design of the dummy load prototype, whose functions are to verify the capability of the International Thermonuclear Experimental Reactor magnetic power supply systems to operate at their rated power levels without energizing the superconducting coils. The rated inductance is 6.73 mH and the extreme pulse operation mode is 68 kA/15 s ON and 900 s OFF. Therefore, in order to meet the special requirements of the large inductance and the large pulse test current, a structure of dry-type air-core water-cooling prototype with epoxy resin casting technique is presented. The finite-element simulation analysis is introduced in detail, focusing on the thermal performance and dynamic stability, especially under the extreme pulse operation condition. In addition, the electromagnetic environment around the dummy load is also analyzed to provide the input for the instrumentations selection and the delimitation of personal safe area. Finally, seismic analysis is introduced to verify the antiseismic property of the dummy load.

R&D on dummy load prototype for ITER coil power supply system

This paper mainly introduces the research and development (R&D) of the dummy load prototype, whose functions are to verify the capability of the ITER magnetic power supply systems to operate at their rated power levels without energizing the superconducting coils. The rated inductance is 6.73 mH and the extreme pulse operation mode is 68 kA/15 s on and 900 s off. Therefore, in order to meet the special requirements of the large inductance and the thermal and dynamic stability, a new structure of dry-type air-core watercooling prototype with epoxy resin casting technique is presented, which has a higher energy density in comparison with the traditional structures. The finite-element simulation analysis is introduced in detail, focusing on the thermal performance of coil and water-cooling system during the whole operation and the dynamic stability, especially under the extreme pulse operation condition. In addition, the electromagnetic environment (EME) around the dummy load is also analyzed under normal and pulse operation, which is the input for the instrumentations selection and the delimitation of personal safe area.

Development of super-synchronization speed control assembly for joint-texas experimental tokamak doubly-fed motor

The main power of joint-texas experimental tokamak (J-TEXT) power supply is a 100MVA pulse generator unit, which is consisted of a 1417kW motor, a 75T flywheel and a 100MVA pulse generator. The generator unit was designed in USA, with a grid of 12kV/60Hz, but in China the grid is 10kV/50Hz. Due to the difference of grid frequency, the rotational speed can only reach 5/6 of the rated value, and the stored energy can only reach 70% of the rated value. To raise the speed from 598rpm to rated speed 713rpm, a new super-synchronization speed control assembly was developed. Under the MT coordinate system, a novel doubly-fed control strategy is designed to control the speed and rotor current of the motor. The converter regulate the rotor current by space vector pulse width modulation (SVPWM) control technology. The software system of double-fed control system is integrated into J-TEXT Control, Data Access and Communication (CODAC) system. The speed control system was fabricated, and put into operation, which can be successfully used to power the J-TEXT.

Reconstruction of the COMPSS-D ECRH Systems on the J-TEXT tokamak

As a flexible and controllable auxiliary heating method, electron cyclotron resonance heating and current drive has been widely used in various plasma confinement devices and also will be used on J-TEXT. The main parts of the J-TEXT electron cyclotron systems under development are donated by the Culham Science Center, including six 60 GHz/200 kW/5 s (0.5 s) gyrotrons, six magnets and auxiliary power supplies for the gyrtrons, transmission parts, etc. For these systems, the output mode of the gyrotron is TE02 mode and converted to TE01 mode for low loss transmission. Then the HE11 mode for efficient coupling is obtained at the end of the transmission lines by a TE01 - TE11 - HE11 mode conversion sequence. A 100kV/60A pulse step modulation power supply has been developed to feed all the six gyrotrons. The control system based on the Compact Reconfigurable I/O - 9068 platform of National Instruments for monitoring, timing and protection is being designed. Other units such as the cooling loops, a new quasi-optical launcher and a spared auxiliary power supply are on the way. It is hoped that four to six EC subsystems can be finally used on the J-TEXT tokamak, and the first one is scheduled to be completed at the end of 2015.

Research of the soft start circuit for the high voltage power supply based on PSM technology

The power supply based on pulse step modulation (PSM) technology has been widely used as the high voltage power supply for additional heating systems, such as RF H&CD and NBI in tokamaks. The topology contains numbers of converters and multi-secondary transformers. For the magnetic inrush of the transformer and the charge current of the converters connecting with the secondary windings of transformer, the power up of the power supply system is quite complex. PSM power supply starts up by two steps: the soft start of transformer and the pre-charge of the converters. Resistor branches series with the transformer and each converter are used to limit the inrush current. A lot of resister branches and parallel contactors in the converter modules are required, as a result the dissipation and electromagnetic interference (EMI) are serious. In this paper, the soft start circuit is simplified to only one step for decreasing the dissipation and EMI. The pre-charge circuits of the converters which are connected to the secondary at first are diverted to the primary winding of transformer can also limit the magnetic inrush current. Since the multi-secondary transformer powers up as the same time as converters, the capacitors in all converters will limit the ramp up rate of the transformer voltage, and the magnetic inrush current can be ignored. To analyze the characters of the precharge branches, all converters can be equaled as parallel during the soft start process. The equivalent circuit, a series RLC circuit, is proposed in this paper. A 1.2kV power supply, contains 12 converters, with soft-start has been built up in laboratory. Simulation and experiment results are shown to verify the theoretical analysis. A new soft start circuit of 100kV high voltage power supply system was designed.