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6204. Multichannel heterodyne radiometer with computer control for electron cyclotron emission measurements of a tokomak plasma
Classified abstracts 6201-6212 4 in. wafers. No decomposition of the sealing fluid could be observed. Any fluid remaining when exchanging the filter elements can practically be recovered by centrifuging. P Bachmann. .I Vat Sci Technol. A3.1985. 5099511. 35 6201. Glow discharge cleaning of stainless steel accelerator beam tubes Glow discharae cleaning has been emnloved successfullv in the CERN ISR to eliminate b;am induced pressure bumps and had been adopted as a final surface treatment for the beam vacuum system of CBA. A glow discharge cleaning facility for beam tubes up to 5.5 m in length has been constructed and is in operation. To ensure efficient and thorough cleaning of the long tubes, a residual gas analyzer was used to monitor the exhaust during cleaning. Quantitative studies of the glow discharge process were performed on several tubes by using Ar or Ar/O, mixture (0.1-10 Pa) and by varying the discharge density (<30 nA cm-‘). The results of the studies, such as the desorption yields of H,O, CO, and CO, with respect to the accumulated dosage, the depletion of 0, in Ar/O, mixture, will be reported here. The effect of venting to air and CO,, as well as plasma deposition of carbon will also be discussed. H C Hseuh et al, J Vat Sci Technol, A3, 1985, 518-522.
IV. Plasma technology 40. GASEOUS
DISCHARGES
AND PLASMA
DEVICES
40 6202. Status of TFTR with ohmic beating and neutral beam injection The main body of the paper addresses the current status of the Tokamak fusion test reactor (TFTR) as of December 1984, with emphasis on the vacuum and surface physics aspects of its operation. A brief review is given of the first paper on the vacuum aspects of controlled fusion research to be presented to a Symposium of the American Vacuum Society. This was given at the Fifth Symposium in October 1958 by the author of this paper. A comparison is made of the devices of that time with TFTR. The vacuum vessel diameter has gone from 2 in. to 7 ft, the plasma durations from 2 ms to many seconds, and the energy confinement time has increased by a factor of 1000 to 0.4 s. TFTR olasmas have reached densities of 4 x lOi cm-s with electron and- ion temperatures of 3 keV. Very preliminary results, with the injection of only 2 MW of 5c-70 keV neutral hydrogen into deuterium plasma, show the expected ion heating and increase in neutron flux. These experiments also show roughly a 30% reduction in the energy confinement time from that of plasmas with only Ohmic heating, as has been noted in other tokamaks. Attention is called to the continuing importance of impurity control in fusion devices. D J Grove, J Vat Sci Technol, A3,1985, 1145-l 150. 40 6203. Lanthanum hexaboride tapered filament in a plasma source A directly heated lanthanum hexaboride tapered filament has been tested in a plasma generator. A uniform temperature distribution at 1820 K has been achieved. The heating and cooling power calculated from measured quantities are balanced. A maximum arc current of 80 A was obtained, limited only by the power supply and plasma generator. The corresponding hydrogen ion current density was 0.6 A cm-’ when the arc voltage was 80 V and the filament heater current was about 5 A. The filament wad capable of emitting 100 A of current at an operating temperature of 1900 K. The estimated lifetime for this filament is 900 h. P A Pincosy and K N Leung, Rev Sci Znstrum, 56, 1985, 6555658. 40 6204. Multichannel beterodyne radiometer with computer control for electron cyclotron emission measurements of a tokomak plasma A multichannel heterodyne radiometer in the frequency range 5G-75 GHz which has been used to measure the second-harmonic cyclotron emission of the Thor Tokomak plasma is described. Real-time frequency switching, analog output averaging, autocalibration, data-acquisition, and graphical display are all functions performed under control of an Apple II personal computer. Typical experimental results are presented to illustrate the measuring capabilities of the instrument. G Cima et al, Rev Sci Znstrum, 56, 1985, 187&1872. 40 6205. Experimental study of the current penetration in a dense Z pinch We study the oscillations superimposed on an intense discharge feeding a dense Z pinch. The periods, measured in different conditions, allow the measurement of the plasma inductance. We show that the variation of this inductance is related to the current penetration in the plasma, the
anomalous current distribution, and the superconductive behavior dense turbulent plasma. M Skowronek and P Romeas, J appl Phys, 57,1985,2519-2523.
of a
40 6206. Modulational instability of ionixation waves The modulation instability evolving from a continuously amplitudemodulated perturbation is observed in the ionization waves excited in the He positive column of a glow discharge. The degree of modulation increases with wave propagation, and an isolated pulse-like wave evolves. The so-called envelope soliton propagates toward the anode, retaining its own waveform. The measured growth rate of the modulational instability agrees well with that of the calculated one. The growth rate becomes maximum at a certain modulation frequency, as is predicted by a coupled mode theory. Kayazuki Ohe and Masashi Hashimoto, J appl Phys, 57, 1985, 822-829. 40 6207. Pulsed electrical discharges in helium gas The electron drift velocity, IF, and the longitudinal diffusion coefficient as a ratio of the electron mobility D,/p, have been measured in helium gas over the electron swarm energy range 20Td < E/N< lOOTd, using the photon flux technique. The uncertainty observed in these data is significantly larger than that previously noted in the work in the molecular gases hydrogen and nitrogen. Furthermore, the nature of the uncertainty in the experimental results leads to the postulate that W and D,/p are spatially dependent. A Monte Carlo simulation of the travelling electron swarm in helium supports this contention. B W Amies et al, J Phys D: Appl Phys, 18, 1985, 2023-2028. 40 6208. Superdense high-temperature exploded-wire plasma observations in a high-current vacuum diode Experiments are described in which a high-current electron accelerator is used to generate, by AI wire explosion, super-high-density (N,= 5 x 10” cmm3), high-temperature (T,=400 eV) plasmas. The X-ray emission characteristics of the plasma are analysed. A Ya Faenov et al, .I Whys D: Appl Phys, 18, 1985, 1347-1351. 40 6209. A high-current hollow cathode as a source of intense line radiation in the VUV The VUV line emission of a high-current dc hollow cathode was investigated in the wavelength region 10 nm to 100 nm. Spectra of quadruply ionised atoms could be observed. The radiance in the Al IV lines at 13 nm and 16 nm and in the He II Lyman-series was determined by a comparison with the spectral concentration of radiant intensity of the synchrotron radiation emitted by the electron storage ring BESSY. We found the radiance of the lines to be reproducible within &25%. K Danzmann et al, J Phys D: Appl Phys, 18, 1985, 1299-1305. 40 6210. Monte Carlo and Boltzmann calculations of the density gradient expanded energy distribution functions of electron swarms in gases We have developed an arbitrary-collision sampling technique for Monte Carlo calculations of the diffusion term in the density gradient expanded energy distribution functions. The technique is shown to provide for an alternative and accurate Monte Carlo calculation of the diffusion coefficients. Comparisons of the diffusion distribution function for the cases of electron swarm transport in the ramp model gas and CH, show excellent agreement with the results obtained by the Boltzmann method of Pitchford and Phelps. However, there remains a discrepancy for the case of N,. B M Penetrante et al, J Phys D: Appl Phys, 18, 1985, 1087-l 100. 40 6211. The space distribution of the electron beam in a glow discharge electron gun and its correlation with the cathode geometry Results of experimental research on the space distribution of the energetic electron beam generated in a glow discharge electron gun are presented. A computational method to determine the cathode geometry as a function of the electron distribution on a target is given. M Bgl&ceanu et al, J Phys D: Appl Phys, 18, 1985, 835-841. 40 6212. Non-equilibrium In low pressure rare gas discharges Low current, low pressure steady electrical discharges in pure helium, neon and argon have been investigated using the photon flux technique. Such discharges have been found to form layers of luminosity throughout the inter-electrode space which indicate a spatial variation of the electron transport parameters. The layers can be quenched by adding a few per cent of nitrogen to the rare gas. J Fletcher, J Phys D: Appl Phys, 18, 1985, 221-227. 737
IV. Plasma technology 40. GASEOUS
DISCHARGES
AND PLASMA
DEVICES
40 6202. Status of TFTR with ohmic beating and neutral beam injection The main body of the paper addresses the current status of the Tokamak fusion test reactor (TFTR) as of December 1984, with emphasis on the vacuum and surface physics aspects of its operation. A brief review is given of the first paper on the vacuum aspects of controlled fusion research to be presented to a Symposium of the American Vacuum Society. This was given at the Fifth Symposium in October 1958 by the author of this paper. A comparison is made of the devices of that time with TFTR. The vacuum vessel diameter has gone from 2 in. to 7 ft, the plasma durations from 2 ms to many seconds, and the energy confinement time has increased by a factor of 1000 to 0.4 s. TFTR olasmas have reached densities of 4 x lOi cm-s with electron and- ion temperatures of 3 keV. Very preliminary results, with the injection of only 2 MW of 5c-70 keV neutral hydrogen into deuterium plasma, show the expected ion heating and increase in neutron flux. These experiments also show roughly a 30% reduction in the energy confinement time from that of plasmas with only Ohmic heating, as has been noted in other tokamaks. Attention is called to the continuing importance of impurity control in fusion devices. D J Grove, J Vat Sci Technol, A3,1985, 1145-l 150. 40 6203. Lanthanum hexaboride tapered filament in a plasma source A directly heated lanthanum hexaboride tapered filament has been tested in a plasma generator. A uniform temperature distribution at 1820 K has been achieved. The heating and cooling power calculated from measured quantities are balanced. A maximum arc current of 80 A was obtained, limited only by the power supply and plasma generator. The corresponding hydrogen ion current density was 0.6 A cm-’ when the arc voltage was 80 V and the filament heater current was about 5 A. The filament wad capable of emitting 100 A of current at an operating temperature of 1900 K. The estimated lifetime for this filament is 900 h. P A Pincosy and K N Leung, Rev Sci Znstrum, 56, 1985, 6555658. 40 6204. Multichannel beterodyne radiometer with computer control for electron cyclotron emission measurements of a tokomak plasma A multichannel heterodyne radiometer in the frequency range 5G-75 GHz which has been used to measure the second-harmonic cyclotron emission of the Thor Tokomak plasma is described. Real-time frequency switching, analog output averaging, autocalibration, data-acquisition, and graphical display are all functions performed under control of an Apple II personal computer. Typical experimental results are presented to illustrate the measuring capabilities of the instrument. G Cima et al, Rev Sci Znstrum, 56, 1985, 187&1872. 40 6205. Experimental study of the current penetration in a dense Z pinch We study the oscillations superimposed on an intense discharge feeding a dense Z pinch. The periods, measured in different conditions, allow the measurement of the plasma inductance. We show that the variation of this inductance is related to the current penetration in the plasma, the
anomalous current distribution, and the superconductive behavior dense turbulent plasma. M Skowronek and P Romeas, J appl Phys, 57,1985,2519-2523.
of a
40 6206. Modulational instability of ionixation waves The modulation instability evolving from a continuously amplitudemodulated perturbation is observed in the ionization waves excited in the He positive column of a glow discharge. The degree of modulation increases with wave propagation, and an isolated pulse-like wave evolves. The so-called envelope soliton propagates toward the anode, retaining its own waveform. The measured growth rate of the modulational instability agrees well with that of the calculated one. The growth rate becomes maximum at a certain modulation frequency, as is predicted by a coupled mode theory. Kayazuki Ohe and Masashi Hashimoto, J appl Phys, 57, 1985, 822-829. 40 6207. Pulsed electrical discharges in helium gas The electron drift velocity, IF, and the longitudinal diffusion coefficient as a ratio of the electron mobility D,/p, have been measured in helium gas over the electron swarm energy range 20Td < E/N< lOOTd, using the photon flux technique. The uncertainty observed in these data is significantly larger than that previously noted in the work in the molecular gases hydrogen and nitrogen. Furthermore, the nature of the uncertainty in the experimental results leads to the postulate that W and D,/p are spatially dependent. A Monte Carlo simulation of the travelling electron swarm in helium supports this contention. B W Amies et al, J Phys D: Appl Phys, 18, 1985, 2023-2028. 40 6208. Superdense high-temperature exploded-wire plasma observations in a high-current vacuum diode Experiments are described in which a high-current electron accelerator is used to generate, by AI wire explosion, super-high-density (N,= 5 x 10” cmm3), high-temperature (T,=400 eV) plasmas. The X-ray emission characteristics of the plasma are analysed. A Ya Faenov et al, .I Whys D: Appl Phys, 18, 1985, 1347-1351. 40 6209. A high-current hollow cathode as a source of intense line radiation in the VUV The VUV line emission of a high-current dc hollow cathode was investigated in the wavelength region 10 nm to 100 nm. Spectra of quadruply ionised atoms could be observed. The radiance in the Al IV lines at 13 nm and 16 nm and in the He II Lyman-series was determined by a comparison with the spectral concentration of radiant intensity of the synchrotron radiation emitted by the electron storage ring BESSY. We found the radiance of the lines to be reproducible within &25%. K Danzmann et al, J Phys D: Appl Phys, 18, 1985, 1299-1305. 40 6210. Monte Carlo and Boltzmann calculations of the density gradient expanded energy distribution functions of electron swarms in gases We have developed an arbitrary-collision sampling technique for Monte Carlo calculations of the diffusion term in the density gradient expanded energy distribution functions. The technique is shown to provide for an alternative and accurate Monte Carlo calculation of the diffusion coefficients. Comparisons of the diffusion distribution function for the cases of electron swarm transport in the ramp model gas and CH, show excellent agreement with the results obtained by the Boltzmann method of Pitchford and Phelps. However, there remains a discrepancy for the case of N,. B M Penetrante et al, J Phys D: Appl Phys, 18, 1985, 1087-l 100. 40 6211. The space distribution of the electron beam in a glow discharge electron gun and its correlation with the cathode geometry Results of experimental research on the space distribution of the energetic electron beam generated in a glow discharge electron gun are presented. A computational method to determine the cathode geometry as a function of the electron distribution on a target is given. M Bgl&ceanu et al, J Phys D: Appl Phys, 18, 1985, 835-841. 40 6212. Non-equilibrium In low pressure rare gas discharges Low current, low pressure steady electrical discharges in pure helium, neon and argon have been investigated using the photon flux technique. Such discharges have been found to form layers of luminosity throughout the inter-electrode space which indicate a spatial variation of the electron transport parameters. The layers can be quenched by adding a few per cent of nitrogen to the rare gas. J Fletcher, J Phys D: Appl Phys, 18, 1985, 221-227. 737