B. R. Cheo

Perpendicular electron cyclotron resonance heating by ordinary modes

Electron heating at resonance by the ordinary mode is analyzed. The equations of motion are integrated along the resonance trajectory showing no parallel heating. Evolution of the distribution functions shows that T⊥ grows exponentially in t2 for second harmonic heating and algebraically at the fundamental.

Analysis of the harmonic gyrotron traveling wave amplifier

A single nonlinear differential equation is derived for describing the spatial evolution of the wave field in a gyrotron amplifier of the cylindrical guide geometry. This equation is then used to determine the efficiencies and the optimized interaction lengths for gyrotrons operated with TEN1 modes at the N-th cyclotron harmonic.

Parametric excitation of coupled plasma waves

A general approach to analyze the parametric decay processes of plasma waves is presented. The approach is based on the modal Hamiltonians of the decay waves and is valid for all wave types. In the limiting cases of B0=0 and of longitudinal waves, results of previous investigations are recovered. Comparisons with experiments are favorable.

Analysis of the electron cyclotron maser instability

Abstract A single nonlinear equation which describes the temporal evolution of the field amplitude of the electron cyclotron maser instability is derived self-consistently. The results deduced from this nonlinear equation are found to agree well with those of particle simulation.

Relativistic adiabatic invariants of electron motion under ECRH

Abstract Three adiabatic invariants of the electron motion under electron cyclotron resonance heating have been derived. The relativistic effect has been included in the analysis. It is shown that the relativistic effect always tends to reduce the parallel energy of the electrons during the early stage of heating.

The effect of the bouncing motion of electrons on electron cyclotron resonance heating

Cyclotron resonance heating of bouncing electrons by an obliquely incident wave field is analyzed. Continuous interaction between electrons and wave fields throughout the entire range of electron excursion has been considered in the analysis. The results show that the bouncing motion of electrons serves to alleviate the detuning effect of frequency mismatch and efficient heating can be achieved. The kinetic temperature is found to increase algebraically in t2 for the fundamental resonance and exponentially in t for the second harmonic heating. Due to the interaction between electrons and the parallel component of the wave electric field, heated electrons tend to focus to the midplane and their excursion amplitudes also become filamented in the steady state.

Fault currents in MHD Faraday generators

In a previous paper the authors derived an equivalent circuit for MHD generators with segmented electrodes and determined its parameters for a Faraday channel. This circuit was used to find the terminal currents and voltages under three typical faults: 1) short circuit at one electrode pair (Faraday catastrophe), 2) one-load rejection, and 3) short circuit between two adjacent anode segments (Hall catastrophe). Such information is important for the design of the power takeoff equipment. The parameters of the equivalent circuit were calculated by integrating the generalized Ohms law of the plasma core over proper paths in the channel in order to define terminal currents and voltages. However, one parameter, the Hall resistance R /SUB xx/ , was left unknown in the process of integration and was determined separately by making use of the simplified results of a two-dimensional analysis of fault case 1. Since the equivalent circuit is defined in terms of exact V-I characteristics at the terminals, the resulting lumped parameter circuit can reproduce the terminal performance features of the original channel with sufficient accuracy.

Turbulent heating of parametric instabilities in unmagnetized plasmas

Consideration of the effect of a uniform pump field on the particle orbits in a Vlasov plasma leads to a modified diffusion coefficient. When the particles oscillate in the pump field, the turbulent wave phase velocity seen by the particles is Doppler shifted by multiples of ω0/k (ω0 is the pump frequency). Hence, strong interactions between the particles and various components of the turbulent field will take place. It is shown that when the pump field is sufficiently strong: E0⩾(4πn0Te)1/2, bulk heating can dominate over tail heating and excitation of electrons to energy levels higher than the normal suprathermal values is possible. This field strength is within the range of laser fusion.