Tokamak Electron Cyclotron Resonance Heating Research Articles

The behaviour of the argon transport with electron cyclotron resonance heating in J-TEXT

The transport of impurities is very important for burning plasma; in particular, the accumulation of highly charged impurities will lead to the deterioration of plasma performance and trigger disruption by radiation losses. In order to study impurity transport in Joint Texas EXperimental Tokamak electron cyclotron resonance heating (ECRH) plasmas, argon has been injected at the discharge flattop in an amount approximately 1% that of fuelling hydrogen gas to ensure no significant effect on the discharge. Experimental results show that precursor oscillations with a sawtooth appearance are beneficial for argon ion transport to the wall. The argon behaviour has been modulated by ECRH, with the power deposited inside/outside the sawtooth inverse radius. The ECRH power deposited outside the sawtooth inverse radius can induce larger precursor oscillations in the end of sawtooth and promote the argon transport. The ECRH power deposited inside the sawtooth inverse radius can induce oscillations in the mid-phase of the sawtooth and decrease the core toroidal rotation velocity, which can enhance argon transport. The results of the analysis that these oscillations can lead to an outward convection velocity, which means that the argon ions are transported to the wall. In addition, the oscillations in the mid-phase of the sawtooth can strongly enhance the argon transport.

Design and application of a new control system for tokamak ECRH power supply

ABSTRACTThe biggest challenge of designing and building tokamak electron cyclotron resonance heating (ECRH) pulse step modulation (PSM) power supply is satisfying its required output voltage rising time to be less than 100 µs while suppressing the voltage overshoot to be no more than 1%. To fulfill the two requirements, a new control strategy with startup time in microsecond range is proposed in this paper, and a new control system to realize the control strategy is introduced. The control system was built and tested on 60 kV/50 A ECRH power supply. The experimental results indicate that the control system can restrain the overshoot effectively, increase response speed, and obviously improve the dynamic characteristics of the PSM power supply system. Thus, the proposed control system helps the PSM power supply to meet the design specifications.

Electron Heat Transport in an HL-1M Tokamak ECRH Plasma

Electron temperature profiles, the normalized temperature gradientlength and the electron heat diffusivity calculated by the heat pulsetransfer method in a plasma confinement region, are investigatedduring electron cyclotron resonance heating (ECRH) in an HL-1M tokamak.The electron temperature profiles remain almost constant. Thenormalized temperature gradient length is in the range of 7–13.Electron heat diffusivity in the ECRH plasmas is larger than that inthe ohmically heated plasmas. Electron heat diffusivity during off-axis(ρ<0.3) ECRH discharge is similar to that during on-axis ECRHdischarge.

Fokker-planck study of tokamak electron cyclotron resonance heating

A Fokker-Planck study is carried out for tokamak electron cyclotron resonance heating by writing the quasi-linear diffusion operator into a form adaptive to the collision operator and considering the wave absorption characteristics of both the O-mode and the X-mode in different magnetic surfaces. Though the Fokker-Planck code is non-relativistic in nature, however, if the relativistic resonance condition for the nearly perpendicularly propagating waves is treated suitably, we can obtain correct results. The energy loss mechanism through anomalous transport is also modelled using a suitable loss term. In the heating phase, the electron distribution deviates from the Maxwellian distribution substantially, which leads to non-linear absorption characteristics. The wave damping rate is non-linear and changes with time. The electron pressure is usually anisotropic under different conditions: pe⊥/pe∥>2 for differentD0 and τe.

The Design of an Elliptical Reflector in the Gaussian-like Antenna Used in HT-7 ECRH System

The structure of the antenna which will be used in HT-7 tokamak electron cyclotron resonance heating (ECRH) experiment and the design of its key component (the elliptical reflector) were introduced. A quasi-Gaussian TE11 wave sent from the TE01-TE11 mode converter was reflected by two mirrors from the waveguide aperture to the plasma center area. One of the two mirrors is a plane mirror and the other is an elliptical mirror. In this process, the wave beam will be converged by the two reflecting mirrors and the emissive direction of the wave is also controlled by them. As requested physically for ECRH experiment, the arrangement of the two mirrors can ensure the wave to be launched from the low-field side of the tour.

An inexpensive instrument to detect radio-frequency leakage from transmission lines at millimeter wavelengths for personnel safety

Arrays of thermopile detectors arranged on flat panels were used to measure stray radiation from high-power transmission lines at 140 GHz in the FTU tokamak electron cyclotron resonance heating experiment. These instruments are insensitive to polarization and to the direction of propagation within ±40° off normal incidence. They have a time constant of 120 ms, therefore amplification and synchronous detection are required for the measurement of short radiation pulses. No special measurement techniques are required with long pulses or cw radiation. The typical sensitivity is 2 mV cm2/mW in long pulse operation and 47 μV cm2/mW for 1 ms pulses. The detectors are sensitive to light and adequate filtering should be added to suppress it if necessary. These characteristics are adequate for the measurement of human exposure levels to electromagnetic radiation in the millimeter wave range.

Poloidal electric field due to electron-cyclotron resonance heating in tokamaks

The poloidal electric field generated by electron-cyclotron resonance heating is investigated for a tokamak plasma in the collisionless regime. This poloidal electric field is calculated by solving an adjoint equation to the linearized Fokker-Planck equation with a quasi-linear diffusion term. It is found from this calculation that the magnitude and the sign of the poloidal electric field depend strongly on the values of the inverse aspect ratio, the poloidal angle of the absorption point, the parallel velocity of resonant electrons normalized by the thermal velocity, and the strength of the relativistic correction to the resonance condition.