Electron Cyclotron Heating Experiments in Tokamaks and Stellarators

This paper reviews the application of high-frequency microwave radiation to plasma heating near the electron cyclotron frequency in tokamaks and stellarators. Successful plasma heating by microwave power has been demonstrated in numerous experiments. Predicted future technological developments and current theoretical understanding suggest that a vigorous program in plasma heating will continue to yield promising results.     

A Numerical Study on Current Drive by Electron Cyclotron Waves in a Toroidal Plasma Device

A survey of the main features of ECR current driving in toroidal plasmas is presented. Numerical calculations are performed in order to obtain the spatial profiles of the ECT energy deposition and of the correlated current density as a function of temperature and of the direction of the wave vector with respect to the toroidal magnetic field. The results indicate a very strong dependence of the ECR absorption profiles and of the driven current densites on the direction of launching of the wave.     

Finite Temperature and Wall Effects on the Absorption of Electron Cyclotron Waves in an EBT Plasma

The absorption of electron cyclotron waves propagating along an externally applied magnetic field in a uniform plasma surrounded by a cylindrical metallic cavity wall is studied. In the model, the cavity wall, the vacuum-plasma interface, and the effects of finite electron temperature are considered, and the dispersion relation for the wave propagation is derived. The results are then applied to the ELMO Bumpy Torus (EBT-I) plasma, and the propagation characteristics are computed. The wave absorption in the ordinary mode is found to be a result of the wall effects, which cannot be predicted with the infinite plasma theory. The loaded quality factor QL is also estimated from the model to be about 14, which is in good agreement with the experimentally observed value.     

Parametric Instability of Surface Waves on the Second Harmonic of Electron Cyclotron Frequency in a Plasma Layer

The parametric instability of surface waves on the second harmonic of electron cyclotron frequency (SWCF) in a plasma filled dielectric wave guide is examined in a kinetic approximation. The studied surface waves are extraordinary polarized modes and propagate across the external steady magnetic field. The amplitude of the electrical pump wave is assumed to be small. Simple expressions for increments of the parametric instability of the SWCF are calculated. The otained results can be used in controlled fusion researches in order to avoid undesirable regimes of plasma periphery heating in that fusion devices which use the resonance electron cyclotron heating method.     

Evolution of Ring Current Protons Induced by Electromagnetic Ion Cyclotron Waves

We investigate the evolution of the phase space density （PSD） of ring current protons induced by electromagnetic ion cyclotron （EMIC） waves at the location L=3.5, calculate the diffusion coefficients in pitch angle and momentum, and solve the standard two-dimensional Fokker-Planck diffusion equation. The pitch angle diffusion coefficient is found to be larger than the momentum diffusion coefficient by a factor of about 103 or above at lower pitch angles. We show that EMIC waves can produce efficient pitch angle scattering of energetic （- 100 keV） protons, yielding a rapid decrement in PSD, typically by a factor of - 10 within a few hours, consistent with observational data. This result further supports previous findings that wave-particle interaction is responsible for the rapid ring current decay.     

高频ECR离子源的最新进展

As they are first optimized for their ion losses,ECRISs are always under a fundamental compromise: having high losses and strong confinement at the same time.To help ECR ion source developers in the design or improvement of existing machines,general comments are presented in a review article being soon published. In this 160 pages contribution,fundamental aspects of ECRISs are presented,with a discussion of electron temperature and confinement and ion confinement.Then,as microwaves play a key role in these machines, a chapter presents major guidelines for microwave launching and coupling to ECR plasma.Moreover,once ECR plasma is created,understanding this plasma is important in ion sourcery;and a section is dedicated to plasma diagnostics with an emphasis on the determination of electron and ion density and temperature by vacuum ultraviolet(VUV)spectroscopy.Another chapter deals with the role of magnetic confinement and presents updated scaling laws.Next chapter presents different types of ECRISs designed according to the main parameters previously described.Finally,some industrial applications of ECRISs and ECR plasmas in general are presented like ion implantation and photon lithography.Some hints taken from this review article are presented in the following article.     

Electron Cyclotron Absorption of Microwaves with Small Propagation Angle in Dense Plasmas

We derive an approximate dispersion equation for slow waves with frequency near electron cyclotron frequency, propagating quasi-longitudinally in plasmas. This equation is studied both numerically and within the framework of perturbation theory. The obtained cyclotron-absorption coefficients do not have singularities in the limiting case of strictly longitudinal propagation and ensure correct transition to well-known expressions for the case of large propagation angles. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 8, pp. 641–647, August 2005.     

Ray Tracing near the Electron Cyclotron Frequency with Application to EBT

The general problem of ray tracing in the electron cyclotron range of frequencies is addressed with the view of applying geometrical optics techniques to microwave heating in ELMO Bumpy Torus (EBT). It is shown that the usual formulation of geometrical optics breaks down at cyclotron resonance due to the large anti-Hermitian part of the dispersion tensor. A consistent eikonal expansion is presented which is valid near cyclotron resonance for cases in which the waves are weakly damped. The geometrical optics code, RAYS, which was developed for the EBT study is described. Ray tracing in plane-stratified plasma geometries is discussed and examples given of the various types of ray paths which occur in plasmas stratified perpendicular to the magnetic field and stratified along magnetic field lines. The application of ray tracing techniques to EBT is discussed and typical results are presented of rays traced in a bumpy cyclinder magnetic-field configuration with plasma parameters characteristic of EBT-I.     

Generation of Electron Beams in the Range of Forevacuum Pressures

This paper presents the results of a study on the generation of electron beams at gas pressures ranging from 0.01 to 0.1 Torr. The fact that this range of pressures is attainable with mechanical pumps only has provoked interest in this problem. To generate an electron beam, use is made of a plasma source based on a hollow-cathode discharge in combination with a plane-parallel acceleration gap. In the given range of pressures, the peculiarities of emission and acceleration of electrons are related to the high probability of ionization of the gas in the acceleration gap and to the formation of an ion flow propagating toward the electron beam. This causes a decrease in discharge operating voltage and also an increase in plasma density in the emission region. Two types of breakdown are observed in the acceleration gap: an interelectrode breakdown and a breakdown in the plasma–electrode system. The designed electron source allows one to obtain beams of cylindrical cross section with currents of up to 1 A and energies of up to 10 keV.     

Resonances,Absorption and Linear Excitation of Cyclotron Harmonic Waves in a Discharge Plasma

Standing cyclotron harmonic waves below the second harmonic are observed using the noise radiation of a mercury discharge tube at 1465 MHz. From the positions of the Buchsbaum-Hasegawa resonances the density profile and the electron temperature are derived, these parameters agree quite well with the behaviour of the collision-free, magnetized plasma column. A onedimensional model applicable to our waveguide geometry is developed taking into account linear excitation of cyclotron harmonic waves by a quasistationary external field in a bounded plasma. Absorption and excitation are controlled by the scale length L₁ at the hybrid point and a coupling length l_c, introduced by Eq. (20); the electron gyration radius r_c, scale length L₁, coupling length l_c, and slab thickness 2a obeying the relation r_c?l_c?L₁?2a. The main absorption is caused by enhanced collisional damping at the upper hybrid region and only a small fraction being dissipated in the wave mode, though its field strength is large compared with that at the plasma boundary (E_W/E(a) ≈ 6). An estimation of the mean field strength within the coupling region shows, that such a low power as 1 mW/cm² absorbed in the hybrid region may produce fieldstrength exceeding the typical threshold values for non-linear excitation mechanism.     

Renormalization of the Cyclotron Frequency in a Screened Two-Dimensional Electron System with Strong Retardation

JETP Letters - Resonant microwave absorption by two-dimensional electron systems based on GaAs/AlGaAs heterostructures with a metallic back gate is investigated. The regime where the velocity of a...     

托卡马克等离子体不同平衡位形下的电子回旋波电流驱动

在给定的等离子体总电流和中心电流密度条件下,数值求解平衡方程,求出不同拉长比和三角形变因子的托卡马克等离子体温度、密度、磁场分布,然后通过求解波迹方程和Fokker-Planck方程,分别计算这些位形下的电子回旋波波迹和电流驱动.结果表明：电子回旋波X模从顶部发射时,随着拉长比的增大,波迹会向弱场侧偏移.电子回旋波X模从弱场侧发射时,电子回旋波在等离子体中传播沉积的功率份额随着拉长比的增大而增加,驱动电流位置随着三角形变因子的增大向等离子体中心移动.驱动电流位置随环向和极向发射角的减小向中心移动,对应的电流密度峰值也变大.     

On the Choice of Electron Cyclotron Heating Frequency for T-15MD Tokamak

Physics of Atomic Nuclei - Electron cyclotron heating is one of the methods of additional plasma heating and noninductive current drive in the T-15MD tokamak. One to eight gyrotrons with a total...     

Spatial Investigations of Point-Radiated Fields above the Electron Cyclotron Frequency in an Inhomogeneous Magnetized Plasma

Spatial behaviors of mode-converted electron Bernstein waves at the upper hybrid layer in an inhomogeneous magnetized plasma are investigated experimentally and theoretically when the radiated source is located outside the upper hybrid layer. The theoretical spatial field patterns in two dimensions which include the mode-converted cyclotron harmonic wave radiated from a point source are found to be in near accord with the experimental results.     

Stability of the Electron Cyclotron Resonance

We consider the magnetic AC Stark effect for the quantum dynamics of a single particle in the plane under the influence of an oscillating homogeneous electric and a constant perpendicular magnetic field. We prove that the electron cyclotron resonance is insensitive to impurity potentials.     

Instability Entanglement in the Electron Cyclotron Maser

Investigation of absolute instability (AI) and convective instability (CI) of the electron cyclotron maser has independently led to the birth of gyrotron oscillators and amplifiers. Here, it is demonstrated that these instabilities can form a cooperative relationship owing to the nonlinear behavior of the stimulated electron beam. The CI can be induced in a zero-drive system with the assistance of AI, and the ohmic losses of all the excited waves inside the system are greatly reduced, which is called “instability entanglement” here. According to the theoretical and experimental study of a 167/330 GHz gyrotron, when instability entanglement occurs, the ohmic dissipation decreases to one-ninth of the AI-only condition, and the output power is enhanced by 20%. This discovery is promising for surpassing the ceiling of output power and frequency of gyrodevices placed by ohmic losses.     

Bounce-averaged Pitch-angle Diffusion by Electromagnetic Ion Cyclotron Waves in Multi-ion Plasmas

We present a study on the gyroresonant interaction particles in multi-ion （H^＋, He^＋, and O^＋） plasmas between electromagnetic ion cyclotron waves and ring current We provide a first evaluation of the bounce-averaged pitch angle diffusion coefficient 〈Dαα〉 for three typical energies of 50, 100 and 150keV at L ≈ 3.5, the heart of the symmetrical ring current. We show that in the H^＋-band and He^＋-band, 〈Dαα〉 can approach - 10^-4 s^-1 for ion H^＋, and - 5 × 10^-5 s^-1 /or ion He^＋; meanwhile, in the O^＋-band, 〈Dαα〉 can reach - 10^-5 s^-1 for ions He^＋ and O^＋. The results above show that the EMIC wave can efficiently produce precipitation loss of energetic （- 100 keV） ions （H^＋, He^＋ and even O^＋）, and such a wave tends to be a serious candidate responsible for the ring current decay.