High Frequency Plasma Generators for Ion Thrusters

The results of a one year program to experimentally adapt two new types of high frequency plasma generators to Argon ion thrusters and to analytically study a third high frequency source concept are presented. Conventional 30 cm two grid ion extraction was utilized or proposed for all three sources. The two plasma generating methods selected for experimental study were a radio frequency induction (RFI) source, operating at about 1 MHz, and an electron cyclotron heated (ECH) plasma source operating at about 5 GHz. Both sources utilize multi-linecusp permanent magnet configurations for plasma confinement. The plasma characteristics, plasma loading of the rf antenna, and the rf frequency dependence of source efficiency and antenna circuit efficiency are described for the RFI Multi-cusp source. In a series of tests of this source at Lewis Research Center, minimum discharge losses of 220+/-10 eV/ion were obtained with propellant utilization of .45 at a beam current of 3 amperes. Possible improvement modifications are discussed

An analytic solution of the Boltzmann equation in the presence of self-generated magnetic fields in astrophysical plasmas

Through relating a self-generated magnetic field to the regular motion of free electrons that is responsible for the magnetic field generation in astrophysical plasmas, we solve the Boltzmann kinetic equation in the presence of the self-generated magnetic fields to obtain a steady-state, collisional invariant analytic solution of the equation.Comment: 4 pages, no figure, in REVTeX, accepted for publication in Phys. lett.

RF Driven Multicusp H- Ion Source

An rf driven multicusp source capable of generating 1-ms H{sup -} beam pulses with a repetition rate as high as 150 Hz has been developed. This source can be operated with a filament or other types of starter. There is almost no lifetime limitation and a clean plasma can be maintained for a long period of operation. It is demonstrated that rf power as high as 25 kW could be coupled inductively to the plasma via a glass-coated copper-coil antenna. The extracted H{sup -} current density achieved is about 200 mA/cm{sup 2}

Microwave scaling of laser plasma interactions. Final report

The limitations of previous target plasmas and the requirements for improved target plasmas are discussed. Two distinctly different approaches were pursued successfully. The first approach represents a relatively minor modification of the discharge techniques previously used in the QUIPS facility. Utilizing a combination of the pulsed rf plasma production techniques developed under the previous year's contract with a new pulsed magnetic field technique, we have produced a target plasma possessing all of the desirable properties of previous target plasmas, with an order of magnitude higher fractional ionization and improved boundary conditions. The second target plasma production technique is based on plasma production by intense, short pulse laser irradiation of a solid target. The resulting blowoff plasma expands into vacuum and, after a suitable delay time, is irradiated by a pulsed mirowave beam. The blowoff plasma properties and preliminary results of microwave interaction experiments are described

Photocurrent spectroscopy measurements of Si-Ge alloys and superlattices

We used photocurrent spectroscopy at 300 K, 77 K and 4.2 K to investigate the optical absorption processes of (001) Si-Ge strained layer superlattices and alloys with an average composition of 50%Si-50%Ge. We observed an evolution toward higher energies of the threshold in the photocurrent spectra as the period of the superlattices decreases, with the spectrum of the shortest period superlattices (2:2) approaching that of the alloy. The energy dependence of absorption in these Si-Gr heterostructures is quite distinct from that measured in elemental silicon

Optimization of an RF driven H sup minus ion source

A radio-frequency driven multicusp source has recently been developed to generate volume-produced H{sup {minus}} ion beams with extracted current density higher than 200 mA/cm{sup 2}. We have improved the output power of the rf generator and the insulation coating of the antenna coil. We have also optimized the antenna positions and geometry and the filter magnetic field for high power pulsed operation. A total H{sup {minus}} current of 30 mA can be obtained with a 5.4-mm-diam extraction aperture and with an rf input power of 50 kW. 4 refs., 5 figs