Stability of tokamak plasmas with internal transport barriers against high n ideal magnetohydrodynamic ballooning mode

A ballooning mode equation for tokamak plasma, with the toroidicity and the Shafranov shift effects included, is derived for a shift circular flux tokamak configuration. Using this equation, the stability of the plasma configuration with an internal transport barrier （ITB） against the high n （the toroidal mode number） ideal magnetohydrodynamic （MHD） ballooning mode is analysed. It is shown that both the toroidicity and the Shaftanov shift effects are stabilizing. In the ITB region, these effects give rise to a low shear stable channel between the first and the second stability regions. Out of the ITB region towards the plasma edge, the stabilizing effect of the Shaftanov shift causes the unstable zone to be significantly narrowed.     

Tokamak resistive magnetohydrodynamic ballooning instability in the negative shear regime

Improved confinement of tokamak plasma with central negative shear is checked against the resistive ballooning mode. In the negative shear regime, the plasma is always unstable for purely growing resistive ballooning mode. For a simplest tokamak equilibrium model, the s--α model, characteristics of this kind of instability are fully clarified by numerically solving the high n resistive magnetohydrodynamic ballooning eigen-equation. Dependences of the growth rate on the resistivity, the absolute shear value, the pressure gradient are scanned in detail. It is found that the growth rate is a monotonically increasing function of α while it is not sensitive to the changes of the shear s, the initial phase \ta₀ and the resistivity parameter \va_R.     

Stability of Tokamak Equilibrium with Internal Transport Barrier against High-n MHD Ballooning Mode

A new eigen-mode equation for the tokamak high-n （the toroidal mode number） ideal magnetohydrodynamic （MHD） ballooning mode in tokamak plasmas is derived to include the toroidal effects that are significant for stability of configurations with internal transport barriers （ITBs）, Fot tokamak equilibria of shift circular flux surfaces, these toroidal effects basically are the finite inverse aspect ratio and the Shafranov shift. The former yields the averaged favorable curvature stabilization while the latter further strengthens this effect, leading to a low shear stable channel connecting the first and second stability regions, and to the shrinkage of unstable region in the （8,α） diagram. The dependence of the critical shear, below which the plasma is stable, on these effects is given. These results are important for understanding the ITB physics to some regards.     

The Poloidal Rotation Caused by LH Waves in Tokamak Plasma Edge

Understanding the improved confinement still remain one of the major goals of the tokamak fusion program, and most important research schemes in tokamak relate to plasma confinement with auxiliary heating and current drive. When auxiliary power exceeds a threshold value, L-H transition will take place. Theoreties and experiments show that this transition is concerned with the sheared plasma poloidal rotation in the edge. Whenan external electromagnetic wave is injected into plasma by antenna,     

Refined Study of ECR Wave Propagation and Absorption in the Weakly Relativistic Plasma

The ECR wave heating is now a routine method for plasma heating and profile control in fusion devices and also in plasma applications. Theoretical study of ECR wave propagation and absorption began very early in 1950‘s. Basic theoretical work had accomplished in 1970～1980. For toroidal devices like the tokamak, the fundamental O-mode and X-mode with nearly perpendicular propagation were used very often. For pure O-mode and X-mode with kx=O,     

The first results of divertor discharge and supersonic molecular beam injection on the HL-2A tokamak

HL-2A tokamak is the first tokamak with divertors in China. The plasma boundary and the position of the striking point on the target plates of the HL-2A closed divertor were simulated by the current filament code and they were in agreement with the diagnostic results in the divertor. Supersonic molecular beam injection (SMBI) system was first installed and tested on the HL-2A tokamak in 2004. In the present experiment low pressure SMBI fuelling on the HL-2A closed divertor was carried out. The experimental results indicate that the divertor was operated in the `linear regime' and during the period of SMB pulse injection into the HL-2A plasma the power density convected at the target plate surfaces was 0.4 times of that before or after the beam injection. It is a useful fuelling method for decreasing the heat load on the neutralizer plates of the divertor.     

Neutral Beam Injection Experiments in the HL-1M Tokamak

Neutral beam injection (NBI) experiments have been carried out with two operation modes of a bucket ion source in the HL-1M tokamak. During the first mode, more than 30% rise in ion temperature above the Ohmic level is routinely achleved after NBI power about 0.5 MW is injected. Ion temperature only increases 20-30% for the second operation mode, which is often limited by current termination. The heating effects of the NBI have been analysed experimentally and theoretically. The performance of the NBI system is well described.     

The Power Supply System for HL-2A Tokamak

The HL-2A is the first divertor tokamak in China. Its construction is based on the main components of ASDEX from IPP and an entirely new power supply system is required to power its magnetic field coils and the plasma heating system. The most important electric parameters of HL-2A are toroidal field of 2. 8kA with a flat topT, plasma current of 450 of 5 s.     

Finite Larmor radius magnetohydrodynamic analysis of the ballooning modes in tokamaks

In this paper,the effect of finite Larmor radius (FLR) on high n ballooning modes is studied on the basis of FLR magnetohydrodynamic (FLR-MHD) theory.A linear FLR ballooning mode equation is derived in an ’s α’ type equilibrium of circular-flux-surfaces,which is reduced to the ideal ballooning mode equation when the FLR effect is neglected.The present model reproduces some basic features of FLR effects on ballooning mode obtained previously by kinetic ballooning mode theories.That is,the FLR introduces a real frequency into ballooning mode and has a stabilising effect on ballooning modes (e.g.,in the case of high magnetic shear s ≥ 0.8).In particular,some new properties of FLR effects on ballooning mode are discovered in the present research.Here it is found that in a high magnetic shear region (s ≥ 0.8) the critical pressure gradient (α c,FLR) of ballooning mode is larger than the ideal one (α c,IMHD) and becomes larger and larger with the increase of FLR parameter b 0.However,in a low magnetic shear region,the FLR ballooning mode is more unstable than the ideal one,and the α c,FLR is much lower than the α c,IMHD.Moreover,the present results indicate that there exist some new weaker instabilities near the second stability boundary (obtained from ideal MHD theory),which means that the second stable region becomes narrow.     

Simulation on effect of poloidal power spectrum on lower hybrid wave propagation

The coupling of lower hybrid wave to the plasma is a crucial issue for efficient current drive in tokamaks. This paper establishes a new coupling model which assumes the antenna to be a curved face and the plasma to be a cylinder. Power spectrum considering the coupling between wave-guides in both poloidal and toroidal direction is simply estimated and discussed. The effect of the poloidal wave vector on wave propagation, power deposition and driven current is also investigated with the help of lower hybrid current drive code. Results show that the poloidal wave vector affects the ray tracing, and also has effect on power deposition and driven current. The effect of the poloidal wave vector on power deposition and driven current profile depends on plasma parameters. Preliminary studies suggest that it seems possible to control the current profile by adjusting the poloidal phase difference between the waveguide in poloidal direction.     

Role of Advance Refuelling and Heating on Edge Reynolds Stress—Induces Poloidal Flow in HL—1M

The radial profile of electrostatic Reynolds stress,plasma poloidal rotations,radial and poloidsal electric fields have been measured in the plasma boundary region of the HL-1M tokamak using a multiarray of Mach/Langmuir probes.In the experiments of ohmic discharge,lower hybrid current drive,supersoniuc molecular beam injection (SMBI)and multi-shot pellet injection,the correlation between the Reynolds stress and poloidal flow in the edge plasma is presented.The adial profile changes of the Reynolds stress and poloidal flow velocity Vpol with lower hybrid wave injection power and SMBI injection are obtained.The results indicate that the sheared poloidal flow can be generated in tokamak plasma due to the radially varying Reynolds stress.     

Design of Anode HVPS of ECRH on HL-2A Tokamak

The ECRH is an effective way of plasma heating on tokamak. The gyrotrons with two high voltage power supplies （ HVPS ） are used in ECRH experiment on the HL-2A tokamak. This type of gyrotron is benefit to improve the output efficiency and HVPS design. So the anode HVPS with higher output power, reliable characteristic and controlling easily are necessary for the work of gyrotron normally.     

Wave field structure and power coupling features of blue-core helicon plasma driven by various antenna geometries and frequencies

This paper deals with wave propagation and power coupling in blue-core helicon plasma driven by various antennas and frequencies. It is found that compared to non-blue-core mode, for blue-core mode, the wave can propagate in the core region, and it decays sharply outside the core. The power absorption is lower and steeper in radius for blue-core mode.Regarding the effects of antenna geometry for blue-core mode, it shows that half helix antenna yields the strongest wave field and power absorption...     

Three Dimensional Identification of Zonal Flows in the HL-2A Tokamak

1 Introduction Zonal flows （ZF） have been studied in some fusion devices. For example, geodesic acoustic mode （GAM） is observed with the frequency of fGAM - 15 kHz, poloidal mode number （m〈3） and radial wave number （ krρi -0.2） using beam emission spectroscopy at plasma edge in the D Ⅲ- D tokamak.     

Density Fluctuation Measurements Using FIR Interferometer on HL-2A Tokamak

Density fluctuations were first measured in the core region of HL-2A tokamak plasma using a newly developed multi-channel FIR interferometer system. In divertor ohmic discharges, we measured the radial density fluctuation levels of 5%, which increase to 10-20% during the appearance of MHD activity. Most of the power density in the density fluctuation spectrum is directly associated with m = 2 tearing modes. The fluctuation levels reduce to 1/3 and plasma confinement is improved during off-axis electron-cyclotron-resonance heating （ECRH）.     

Analytic Study of Propagation and Absorption of Nearly Perpendicular Injected Electron Cyclotron Ordinary Wave

Electron cyclotron resonance heating (ECRH), such as the fundamental heating and the second harmonic heating, is a basic and powerful method to heat the plasma in tokamak and stellarator devices. Theoretical studies of this heating has been done in rather early literatures, however, the understanding of some important problems is still uncertain. These include: the coupling of the O-mode and the E-mode and the role of this coupling in wave damping, the O-mode damping mechanism,     

SECRAL等离子体中EUV光功率的产生

The high power EUV source is one of key issues in the development of EUV lithography which is considered to be the most promising technology among the next generation lithography.However neither DPP nor LPP seems to meet the requirements of the commercial high-volume product.Insufficiency of DPP and LPP motivate the investigation of other means to produce the EUV radiation required in lithography.ECR plasma seems to be one of the alternatives.In order to investigate the feasibility of ECR plasma as a EUV light source,the EUV power emitted by SECRAL was measured.A EUV power of 1.03W in 4~ sr solid angle was obtained when 2000W 18GHz rf power was launched,and the corresponding CE was 0.5%.Considering that SECRAL is designed to produce very high charge state ions,this very preliminary result is inspiring. Room-temperature ECR plasma and Sn plasma are both in the planned schedule.     

Simulation of radio-frequency atmospheric pressure glow discharge in γ mode

The existence of two diffe1：ent discharge modes has been verified in an rf （radio-frequency） atmospheric pressure glow discharge （APGD） by Shi [J. Appl. Phys. 97, 023306 （2005）]. In the first mode, referred to as a mode, the discharge current density is relatively low and the bulk plasma electrons acquire the energy due to the sheath expansion. In the second mode, termed γ mode, the discharge current density is relatively high, the secondary electrons emitted by cathodc under ion bombardment in the cathode sheath region play an important role in sustaining the discharge. In this paper, a one-dimensional self-consistent fluid model for rf APGDs is used to simulate the discharge mechanisms in the mode in helium discharge between two parallel metallic planar electrodes. The results show that as the applied voltage increases, the discharge current becomes greater and the plasma density correspondingly increases, consequentially the discharge transits from the a mode into the γ mode. The high collisionality of the APGD plasma results in significant drop of discharge potential across the sheath region, and the electron Joule heating and the electron collisional energy loss reach their maxima in the region. The validity of the simulation is checked with the available experimental and numerical data.     

Magneto-Hydrodynamic High-n Ballooning Mode Instability of an Analytic Axi-Symmetric Toroidal Equilibrium with Arbitrary Aspect Ratio

An exact ballooning mode eigen-equation is derived to study stability of axi-symmetric toroidal plasma with arbitrary aspect ratio, including the tokamak, the finite aspect ratio and the spherical torus plasmas. For comparison with the widely used （ s-α） model, an analytic exact equilibrium configuration with circular magnetic surfaces is analysed in detail. It is indicated that the （s - α） model needs to be improved for more realistic configurations.