S. Aihara

Generation of energetic electrons by electron cyclotron heating in a magnetic mirror field

Electron cyclotron heating that generates hot-electron plasma in a magnetic mirror trap by microwaves is studied experimentally. The evolution of the energy distribution functions for the high-energy electrons is observed in steps of milliseconds during 200 ms of the heating period from the initial stage at the microwave power input until the stationary final state. According to the proposed statistical model for the cyclotron heating, heating rates are estimated to be 10 MeV/s typically, in the three characteristic cases of mirror field configuration with heating microwave power as a parameter. Some problems associated with stochastic cyclotron heating are discussed in the light of the experiments.

Propagation of Ion Waves in a Radio Frequency Electric Field

The wavelength of an ion wave decreases in an rf electric field. This phenomenon is explained by the additional pressure which is produced by the spatial modulation of the rf field by the ion wave.

QUENCHING OF ION OSCILLATIONS AT THE SHEATH-PLASMA RESONANCE.

Abstract Ion oscillations are damped by an external r.f. electric field when the condition of sheath-plasma resonance is reached.

HOT-ELECTRON CONFINEMENT IN MAGNETIC CUSP GEOMETRIES.

A hot electron plasma is established by ECR (6.4 GHz) in a simple cusped magnetic field. The plasma thus generated consists of hot electrons, cold electrons and helium ions. The hot-electron temperature is determined from X-ray spectra to be about 30 keV and the density of the hot electrons is of the order of 1010 cm−3, which is about 10% of the cold-electron density. The effect of the cusp field is particularly noticeable in the electron-density distribution, which has a void at the centre. Plasma decay times (10 – 60 ms) are observed to increase with the field current. There are several collision processes which cause the loss of hot electrons. The authors derive a simple equation which determines the confinement time of hot-electron plasma and study the confinement of hot electrons by ECR-wrapping. With a wrapping microwave power of 150 W, the decay time is observed to increase to more than three times that without the wrapping power.

Harmonics of ion oscillations in a neutralized ion beam plasma

Abstract Harmonics of ion plasma oscillations are observed in a helium plasma produced by a back diffusion source.

Heating of ions by modulated microwaves

Abstract Ion heating is studied by modulating a microwave power at low frequencies in a hot electron plasma generated by microwave discharge in a mirror machine. The modulation is observed to be effective for heating ions.

Analysis of Hot‐Electron Confinement by Electron Cyclotron Plugging

Plugging and confinement of hot‐electron plasma by microwaves making use of the electron cyclotron resonance is studied. Experimentally, the plugging is observed to make a plasma decay time several times longer than that without the plugging microwave power, and the mechanism is analyzed theoretically.

9.4 Hot Electron Confinement in a Cusped Magnetic Field by ECRH Wrapping

The confinement of a hot electron plasma in a cusped magnetic field is studied. The hot electron plasma whose temperature is about 30 keV is produced in the electron cyclotron resonance region within the cusped magnetic field by a 20‐msec pulse of 6.4 GHz having a power up to 5 kW. During the afterglow plasma, a weak 6.4 GHz microwave power is supplemented. Up to 150 W of supplemented power, the decay time increases linearly up to about 30 msec, about three times that without the supplement. With further increase of the power, the decay time decreases. The increase in the plasma containment time is explained to be due to the force 〈 F 〉 = −(e2/4m) ∇ [E2/ω2−Ωe2].