- Email: [email protected]
Ultrahigh-vacuum manipulator for LEED studies
Classified
abstracts
949-961
32 949. Plasma density measurements by electron-plasma wave pulses in a Q-machine. (GB) An accurate determination of plasma densities in a Q-machine can be given by observations of electron-plasma wave pulses. A universal chart to evaluate the plasma density from the propagation speed of wave pulses is provided. It is shown that the radial density distribution should be taken into account in this diagnostic method. Comparison between this method and Langmuir probe methods is presented. It is concluded that speed measurements of electron plasma wave pulses offer a rapid reliable method for determining the density of a low-density plasma (106-lo9 cme3). (Austria) H Sugai and E Mark, J Phys D: Appl Phys, 7 (16) 1974. 2198-2204. 32 950. The self-focusing of electromagnetic beams in a strongly ionized magnetoplasma. (GB) This paper presents an investigation of the self-focusing of Gaussian electro-magnetic beams propagating in a strongly ionized plasma along a static magnetic field. The nonlinearity in the dielectric tensor of the plasma arises because of the heating and consequent redistribution of electrons along the wavefront. At low values of magnetic field the main source of electron energy dissipation is thermal conduction; for large magnetic fields the carrier mean free path becomes comparable to or greater than the Larmor radius of the electrons, and the collisional loss of energy becomes dominant. This investigation revels that the length of self-focusing of the beam in the extraordinary as well as ordinary mode of propagation is reduced by the application of the magnetic field, for low values of the magnetic field (w, <’ w). For higher values of the magnetic field the selffocusing of the extraordinary mode is further enhanced while that of the ordinary mode is reduced. (India) M S Sodha et al, JPhys D: Appl Phys. 7 (l6), 1974, 2188-2197. 32 951. Quasilinear theory of the loss of isotropy in a plasma with suprathermal particles. (Canada) A magnetoplasma with isotropic distribution of particle velocities is unstable against the electron cyclotron modes, excited by the presence of a population of suprathermal electrons. The nonlinear interaction of these waves with resonant suprathermal electrons, whose initial velocity distribution was isotropic, causes diffusion in the velocity space. The distribution of suprathermal electrons becomes anisotropic This may under certain conditions lead to new instabilities driven by the anisotropy in the velocity space. The temporal evolution of the ‘plateau’ and the characteristic relaxation time of the quasilinear interaction has been analysed. E Marquis and J Teichmann, Can J Phys, 52 (20). 1974, 20 14-202 I. 32 952. Disorientation of Na(3ZP,,z) atoms, induced in collisions with noble gases. (Canada) The cross sections for disorientation of 3*PI11 sodium atoms, induced in collisions with noble gas atoms, have been determined by following the depolarization of Na-D, resonance fluorescence in relation to noble gas pressure. Sodium vapour at low density, mixed with a noble gas in a fluorescence cell, was irradiated with circularly polarized D, resonance radiation and the resulting D, resonance fluorescence, observed in an approximately backward direction, was analysed with respect to circular polarization. The variation of the degree of polarization with gas pressure was interpreted on the basis of a ‘.I randomization’ model for the collisions, and yielded the following disorientation cross sections which are appropriately corrected for effects due to nuclear spin. Na-He: 28.1 + 4.0 A*: Na-Ne: 27.8 5 4.0 A’; Na-Ar: 57.b _I 8.0 A’; Na-Kr: 78.0 f IO A’: Na-Xe: 87.0 i 13 A’. B Niewitecka et al, Can J Phys, 52 (20), 1974, 1956-1960. 32 953. Experimental study of an aluminium oxide plasma vessel. (France) The problem of impurities is a crucial one in the experiments of plasma physics and thermonuclear fusion for the energy balance equations. A large amount of impurities is released by the wall of the vacuum vessel. In the Tokamak type experiments the wall of the vacuum vessel is generally made of stainless steel. In the experiment PETULA built in Grenoble half part of the vacuum vessel will be made of aluminium oxide so as to make it possible to introduce high frequency power in the plasma. In this paper we report studies on outgassing of aluminium oxide in ultra high vacuum (10e9 torr) and 292
facing a dense plasma. The mass spectrum and the partial pressures of the different impurities are measured with a mass analyser. R Frank, Vi&, 29 (I 70). 1974, 314-000 (in Frencl7). 32 954. Computation of the most probable nuclear energy loss of slow ions in thin absorbers. (Germany) A computation method of N. Bohr for the approximative determination of most probable losses of nuclear energy by the transmission ot heavy particles through absorbers, is developed for the application with total energy losses IE: nearly equal the primary energy &,_ The conditions to apply the method also to light ions in heav! absorbers are proved. G Thieme, VGkuum-Tech. 23 (7). 1974, 193.-197 (in Ger7~7ur7).
33. GENERAL
PHYSICS
AND
ELECTRONICS
33 955. Vacuum oneratine thermoluminescence snectrometers. CUSA) Two instruments are- described suited for-recording thermolhminescent glow spectra respectively below and above room temperature. Their most remarkable property is the fact that the samples are kept under vacuum. Thermal insulation, thus. is good enough to allon samples to be placed only 15 mm from the light detector, even if they are heated up to 500°C or cooled down to liquid N, temperature. Consequently, the light collection efficiency turns out to be ver) high. These instruments are equipped with both analogue and digital recorders, thus obtaining an accurate gathering of data. (Italy) F Aramu et al, Rea Scient Instrum, 45 (1 I), 1974, 1414-1416. 33 956. Beam control in a Martin-type electron gun. (GB) A simple model for the gun structure, together with the resultant improvements in gun operation, are given. (Venezuela) G Riitzer and J France, J Phys E: Scient Instrum, 7 (I 2). 1974, 880882. 33 957. Ultrahigh-vacuum manipulator for LEED studies. (USA) A simple manipulator is described which allows rotation of a target crystal about two mutually perpendicular axes in addition to the normal up-down, tilt and translational motions. M R O’Neill and F B Dunning, Rea Sri Instrum, 45 (I 2). 1974, I6 I I 1612. 33 958. Error analysis and adjustment of the LEED goniometer. (USA) The error analysis and the adjustment procedure which are necessary for the setting and determination of angular coordinates of the electron beams in the LEED goniometer are described. This analysis is most useful for experiments made at constant energy, so that residual inhomogeneous magnetic fields do not introduce significant errors. (France) D Aberdam et al, Rer Sci Insrrum, 45 (I 2), 1974, 1573-l 579. 33 959. A LEED goniometer. (USA) An hemispherical display type low energy electron diffraction apparatus, having complete freedom of incident and diffracted beams directions with high angular precision, high resolution, and high sensitivity. is described. (France) L De Bersuder, Rel%Sci Instrum, 45 (I 2). 1974, 1569-l 572. 33 960. Seeded supersonic alkali atom beams. (USA) A seeded supersonic beam source for alkali atoms is described which provides velocities up to -5 km/s. Potassium or rubidium vapoul at -0.02 to 0.2 torr is mixed with a diluent gas of Hz. He, or Ar at -800 torr and expanded through a pinhole nozzle. The beam properties are found to compare well with the simple theory of isentropic expansions. Typically, the alkali flux is _ 10’h atoms sr-’ s- I and the velocity spread is 5 8 % (FWHM). R A Larsen et al, Ret Sri Instrurn. 45 (I 2), 1974. I5 I I I5 16. 33 961. Ultra-high vacuum, high pressure and temperature infraredultraviolet-visible spectrophotometer cell. (USA) An ir-uv-visible spectrophotometer cell for examining gas-solid interactions at elevated temperatures up to 600 ‘C and high pressures or ultrahigh vacuum has been designed and fabricated. The cell is employed for characterization of reactive catalyst species and reaction intermediates which exist only at conditions above ambient. The pressure maxima are limited by the window material which in turn
abstracts
949-961
32 949. Plasma density measurements by electron-plasma wave pulses in a Q-machine. (GB) An accurate determination of plasma densities in a Q-machine can be given by observations of electron-plasma wave pulses. A universal chart to evaluate the plasma density from the propagation speed of wave pulses is provided. It is shown that the radial density distribution should be taken into account in this diagnostic method. Comparison between this method and Langmuir probe methods is presented. It is concluded that speed measurements of electron plasma wave pulses offer a rapid reliable method for determining the density of a low-density plasma (106-lo9 cme3). (Austria) H Sugai and E Mark, J Phys D: Appl Phys, 7 (16) 1974. 2198-2204. 32 950. The self-focusing of electromagnetic beams in a strongly ionized magnetoplasma. (GB) This paper presents an investigation of the self-focusing of Gaussian electro-magnetic beams propagating in a strongly ionized plasma along a static magnetic field. The nonlinearity in the dielectric tensor of the plasma arises because of the heating and consequent redistribution of electrons along the wavefront. At low values of magnetic field the main source of electron energy dissipation is thermal conduction; for large magnetic fields the carrier mean free path becomes comparable to or greater than the Larmor radius of the electrons, and the collisional loss of energy becomes dominant. This investigation revels that the length of self-focusing of the beam in the extraordinary as well as ordinary mode of propagation is reduced by the application of the magnetic field, for low values of the magnetic field (w, <’ w). For higher values of the magnetic field the selffocusing of the extraordinary mode is further enhanced while that of the ordinary mode is reduced. (India) M S Sodha et al, JPhys D: Appl Phys. 7 (l6), 1974, 2188-2197. 32 951. Quasilinear theory of the loss of isotropy in a plasma with suprathermal particles. (Canada) A magnetoplasma with isotropic distribution of particle velocities is unstable against the electron cyclotron modes, excited by the presence of a population of suprathermal electrons. The nonlinear interaction of these waves with resonant suprathermal electrons, whose initial velocity distribution was isotropic, causes diffusion in the velocity space. The distribution of suprathermal electrons becomes anisotropic This may under certain conditions lead to new instabilities driven by the anisotropy in the velocity space. The temporal evolution of the ‘plateau’ and the characteristic relaxation time of the quasilinear interaction has been analysed. E Marquis and J Teichmann, Can J Phys, 52 (20). 1974, 20 14-202 I. 32 952. Disorientation of Na(3ZP,,z) atoms, induced in collisions with noble gases. (Canada) The cross sections for disorientation of 3*PI11 sodium atoms, induced in collisions with noble gas atoms, have been determined by following the depolarization of Na-D, resonance fluorescence in relation to noble gas pressure. Sodium vapour at low density, mixed with a noble gas in a fluorescence cell, was irradiated with circularly polarized D, resonance radiation and the resulting D, resonance fluorescence, observed in an approximately backward direction, was analysed with respect to circular polarization. The variation of the degree of polarization with gas pressure was interpreted on the basis of a ‘.I randomization’ model for the collisions, and yielded the following disorientation cross sections which are appropriately corrected for effects due to nuclear spin. Na-He: 28.1 + 4.0 A*: Na-Ne: 27.8 5 4.0 A’; Na-Ar: 57.b _I 8.0 A’; Na-Kr: 78.0 f IO A’: Na-Xe: 87.0 i 13 A’. B Niewitecka et al, Can J Phys, 52 (20), 1974, 1956-1960. 32 953. Experimental study of an aluminium oxide plasma vessel. (France) The problem of impurities is a crucial one in the experiments of plasma physics and thermonuclear fusion for the energy balance equations. A large amount of impurities is released by the wall of the vacuum vessel. In the Tokamak type experiments the wall of the vacuum vessel is generally made of stainless steel. In the experiment PETULA built in Grenoble half part of the vacuum vessel will be made of aluminium oxide so as to make it possible to introduce high frequency power in the plasma. In this paper we report studies on outgassing of aluminium oxide in ultra high vacuum (10e9 torr) and 292
facing a dense plasma. The mass spectrum and the partial pressures of the different impurities are measured with a mass analyser. R Frank, Vi&, 29 (I 70). 1974, 314-000 (in Frencl7). 32 954. Computation of the most probable nuclear energy loss of slow ions in thin absorbers. (Germany) A computation method of N. Bohr for the approximative determination of most probable losses of nuclear energy by the transmission ot heavy particles through absorbers, is developed for the application with total energy losses IE: nearly equal the primary energy &,_ The conditions to apply the method also to light ions in heav! absorbers are proved. G Thieme, VGkuum-Tech. 23 (7). 1974, 193.-197 (in Ger7~7ur7).
33. GENERAL
PHYSICS
AND
ELECTRONICS
33 955. Vacuum oneratine thermoluminescence snectrometers. CUSA) Two instruments are- described suited for-recording thermolhminescent glow spectra respectively below and above room temperature. Their most remarkable property is the fact that the samples are kept under vacuum. Thermal insulation, thus. is good enough to allon samples to be placed only 15 mm from the light detector, even if they are heated up to 500°C or cooled down to liquid N, temperature. Consequently, the light collection efficiency turns out to be ver) high. These instruments are equipped with both analogue and digital recorders, thus obtaining an accurate gathering of data. (Italy) F Aramu et al, Rea Scient Instrum, 45 (1 I), 1974, 1414-1416. 33 956. Beam control in a Martin-type electron gun. (GB) A simple model for the gun structure, together with the resultant improvements in gun operation, are given. (Venezuela) G Riitzer and J France, J Phys E: Scient Instrum, 7 (I 2). 1974, 880882. 33 957. Ultrahigh-vacuum manipulator for LEED studies. (USA) A simple manipulator is described which allows rotation of a target crystal about two mutually perpendicular axes in addition to the normal up-down, tilt and translational motions. M R O’Neill and F B Dunning, Rea Sri Instrum, 45 (I 2). 1974, I6 I I 1612. 33 958. Error analysis and adjustment of the LEED goniometer. (USA) The error analysis and the adjustment procedure which are necessary for the setting and determination of angular coordinates of the electron beams in the LEED goniometer are described. This analysis is most useful for experiments made at constant energy, so that residual inhomogeneous magnetic fields do not introduce significant errors. (France) D Aberdam et al, Rer Sci Insrrum, 45 (I 2), 1974, 1573-l 579. 33 959. A LEED goniometer. (USA) An hemispherical display type low energy electron diffraction apparatus, having complete freedom of incident and diffracted beams directions with high angular precision, high resolution, and high sensitivity. is described. (France) L De Bersuder, Rel%Sci Instrum, 45 (I 2). 1974, 1569-l 572. 33 960. Seeded supersonic alkali atom beams. (USA) A seeded supersonic beam source for alkali atoms is described which provides velocities up to -5 km/s. Potassium or rubidium vapoul at -0.02 to 0.2 torr is mixed with a diluent gas of Hz. He, or Ar at -800 torr and expanded through a pinhole nozzle. The beam properties are found to compare well with the simple theory of isentropic expansions. Typically, the alkali flux is _ 10’h atoms sr-’ s- I and the velocity spread is 5 8 % (FWHM). R A Larsen et al, Ret Sri Instrurn. 45 (I 2), 1974. I5 I I I5 16. 33 961. Ultra-high vacuum, high pressure and temperature infraredultraviolet-visible spectrophotometer cell. (USA) An ir-uv-visible spectrophotometer cell for examining gas-solid interactions at elevated temperatures up to 600 ‘C and high pressures or ultrahigh vacuum has been designed and fabricated. The cell is employed for characterization of reactive catalyst species and reaction intermediates which exist only at conditions above ambient. The pressure maxima are limited by the window material which in turn