Study of Ultrashort-Pulse Microwave-Plasma Interaction and its Application to Plasma Diagnostics

点击翻译按钮获取中文摘要

1) During the period of this research project, an ultrashort-pulse reflectometer (USPR) has heen fabricated.i) Input source utilizes a 8 V,65 psec full-width half-maximum (FWHM) pulse which is stretched into a chirped pulse by a dispersive waveguide. The resultant waveform is amplified (23 dB,6-18 GHz) and irradiated via X-band horn into a plasma. ii) The received waveform is amplified (40 dB,6-18 GHz), and then filtered/detected via an 8 channel receiver system, comprising frequency channels spanning 8-15 GHz at 1.0 GHz intervals. The detector output i s sampled and stored using a fast digitizer (10 GS/sec, 750 MHz bandwidth). A constant fraction discriminator and time-to-amplitude converter (TAC) enables time-of flight measurements with a high repetition (>200 kHz) and high resolution (25 psec) measurements.2) The USPR system for electron density profile and density fluctuation measurements has heen applied to the GAMMA 10 tandem mirror. The observed values of the time-of-flight are … More in agreement with those calculated using the Abel-inverted profile from interferometry data. The oscillation of the cut-off layr is observed from the time-of-flight measurement using TAC.The frequency spectrum of the oscillation agrees with that of the microwave scattering signal.3) Ultrafast FM reflectometers (8-26 GHz) have been applied to GAMMA 10. The density profiles are reconstructed using several analysis methods. It is found that the profile reconstruction improves for sweeping faster than 20-30 mus. The results shows that the demands on the sweep rate becomes low when the data analysis method is improved.4) Diagnostic simulator models performing computer experiments on USPR diagnostics is presented. The models decribe 2-dimensional cold magnetized plasma, and the full Maxwell equations are solved numerically to describe propagation, reflection, and scattering of microwaves. The effects of waveguide for incident waves and wall boundary of vacuum vessel are included. The appropriate parameters of the USPR (frequency pulse width, etc.) is clarified in order to apply any magnetic confinement systems.5) Interaction of charged particles with dispersive electrostatic pulses is numerically investigated. It is found that the dispersive pulses can essentially trap and/or accelerate electrons as other type of pulses and sinusoidal waves. This trapping can play a significant role in Langmuir turbulence generated by relatively low-density electron beams.6) Fully monolithic detector with integration of antenna, mixer and amplifier is fabricated, and applied to the plasma daignostics for the first time. Less