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5205. Laser cooling of heavy-ion beams
Classified abstracts 5198-5209 reported by Owen. The results obtained show that the material undergoes crosslinking. (Egypt) S Aziz and E M H Ibrahim, Rad Effects, 56 13/4), 1981, 213 218. ' 35 5198. Theory of the spatial distribution of defects in radiation cascades in crystals. I. The cascade of moving atoms. (USA) The kinetic Eq (2) is derived governing the flux density of moving atoms in a radiation cascade with account of scattering of moving atoms, ejection of host atoms and formation of dynamic crowdions. The solution of Eq (2) is presented as a series expansion in orthogonal polynoms. Lindhard's interaction cross-section of moving atoms with hosts is used. The zerothorder moment ofthe flux density determines the flux of moving atoms with energy e and the cascade function. The spatial distribution of moving atoms is obtained in the zeroth-order approximation. (USSR) A N Orlov and Yu V Trushin, Rad E{/~'cts. 56 (3/4), 1981, 193 198. 35 5199. Theory of the spatial distribution of defects in radiation cascades in crystals. II. The structure of the cascade region. I USA) The spatial distribution of vacancies and interstitials in radiation cascades in crystals is calculated with account of instantaneous recombination of Frenkel pairs during the formation of the cascade. Analytical expressions (15), 1181 are obtai.aed for the shape of the depleted zone. (USSR) A N Orlov and Yu V Trushin, Rad E././bcts, 56 (3/4), 1981, 199 204. 35 5200. High density cascade effects. (USA) The objective of this article is to review the effects of high density cascades in solids. Such cascades can be separated into those occurring in which 'high density" refers to either the density of atomic collision events or to the density of ionization. Both types ofcascade are discussed with reference to their effects in the bulk (i.e. damage production and inert gas detrapping) and on the surface properties (i.e. sputtering, secondary ion and electron emission). The appropriate experimental data are reviewed and discussed in relation to the various proposed spike models: i.e. displacement, thermal, plasticity and ionization spikes. (Canada) D A Thompson, Rad EJ./~,cts, 56 (3/4), 1981. 105 150.
36. P A R T I C L E BEAMS A N D S O U R C E S 36 5201. Ion beam characteristics of a gas-filled accelerator tube. (USA) A gas-filled tube used to produce a pulsed neutron flux with D(T,He*)n reaction is described. Deuterium and tritium ions generated in a reflex discharge are extracted and accelerated to 100 keV by means of an accelerator electrode onto a deutero-tritide target electrode. The electrodes are designed to focus the ion beam onto the target. Total tube currents consisting of extracted ions, unsuppressed secondary electrons, and ions generated by interactions with the background gas are typically 100 mA. Characteristics of the extracted ion beam are discussed. Accelerating voltages greater than 50 keV are required to focus the beana through the accelerator aperture for configurations that give beams with the proper energy density at the target. The perveance of the beam is defined. M a x i m u m perveance values are 2 -10 nanopervs. Tube focusing and neutron production characteristics are described. R S Berg et al, d Vac Sci Technol, 18 (3), 1981, 983 986. 36 5202. H - ion formation from a surface conversion type ion source. (USA) Volume-produced H - ions have been extracted from a multicusp ion source. In addition, a molybdenum converter is installed in the source to generate surface-produced H - ions. Without cesium, the production of H - ions by the surface process is very small compared with those generated by volume production. However, the presence of cesium can greatly enhance the surface production yield. The energy spectrum shows that the surface-generated H ions contain two distinct groups when cesium is added to the discharge. The energy of one group is essentially that of the sheath potential and appears to be produced by a desorption process, The second group of H - ions has a slightly higher energy and appears to be formed by a reflection process. Different types of converter materials have also been tested. K N Leung and K W Ehlers, d Appl Phys, 52 (6), 1981, 3905 3911. 36 5203. Magnetic effects in high current ion beams. (USA) It is known that, in intense ion beams being developed for use in neutral injection, the space charge of the ions is almost totally compensated by electrons. In the limit of total compensation, it is shown that there is a critical ion current, l~, above which transport is no longer emittance but
456
magnetic self-field dominated. A Monte Carlo model of beam neutralization in the presence of the self-field is presented and applied to the example of the JET injectors. Results show a foreshortening of the injector focus, a rise in beamlet emittance, and an increase in the angular divergence (of order 0.1 J in high current neutral injectors. It is shown that, because of stochastic neutralization effects, there is a fundamental limit to the ability to focus an injector uniquely. IGB) G A Cottrell, Rer Sci lnstrum, 52 (8), 1981, 1174 1181. 36 5204. Molecular beam facility for studying mass spectrometer performance. (USA) An apparatus is described which produces neutral gas beams in the velocity range from thermal to 6 km/s. This facility makes possible studies simulating the motion of instruments through tenuous atmospheres. The use of the apparatus in studying the response of an open-source mass spectrometer sirnilar to those carried on high-speed spacecraft, such as earth satellites or planetary probes for investigating ambient atmospheric composition, is examined. Experiments performed included ones of response of an open source mass spectrometer when: (a) the instrument was in a normal mode of operation: (b) the instrument's ion source potentials were adjusted so as to reject gas particles which struck instrument surfaces; Ic) the gas beam was restricted so that selected portions of the ion source were struck: and {d) the gas beam struck the ion source at angles other than normal incidence. John O Ballenthin and Alfred O Nier, Re~" Sci Instrmn, 52 (7). 1981. 1016 1024. 36 5205. laser cooling of heavy-ion beams. (USA) We present a new technique for cooling heavy-ion beams. Tile discrete absorption spectrum of the ions and the transverse Doppler shift distinguish the transverse direction of velocity and cool the ions by photon absorption. We evaluate the total energy and time requirements for a particular example relevant to heavy-ion fusion. Paul J ChannelL J App/Phys, 52 16). 1981, 3791 3793. 36 5206. Ion beam extraction from a plasma with aberration reduction by method of mutual exclusion. (USA) Using an algorithm for solution of the Poisson-Vlasov equations for ions extracted from a plasma, an electrode shape is considered which has high optimum perveance and low beam divergence. J H Wheahon et al, J Appl Phys, 52 (6), 1981, 3787 3790. 36 5207. Faraday cup analysis of ion beams produced by a dense plasma focus. (USA) The design and performance of a Faraday cup which is used in a time-offlight technique to measure the energy spectrum of ions accelerated away from the anode of a plasma focus are described. The cup is located in a differentially pumped ( < 20 ,,) chamber which is separated from the main plasma focus chamber by a 0.0457-cm diam hole positioned 16 cm above the anode. This arrangement allows a bias voltage of - 400 V to be applied to the cup to stop comoving electrons and permits the observation of deuteron energies down to - 25 keV. G Gerdin el al, J App/ Pfiys, 52 15), 1981, 3269 3275. 36 5208. Influence of spherical and chromatic aberrations on the half-radius of an electron beam. (USA) Root mean square deviation and half-radius (containing a half of the beam current I of an axially symmetric beam from a point source, as a function of the beam crossover plane position, were solved analytically. Current density distributions and values of the half-radius of a beam generated from a source with a Gaussian current density distribution were numerically calculated. The spherochromatic aberration with electron energy dispersion (Maxwell and rectangular energy distributions) and without it (focusing deviation) were taken into account. The quadratic Igeometric) way of aberration mixing has been confirmed, with the mixed quantities defined. (Poland W Slowko, J I'ac Sci Teclmol, 19 131. 1981. 733 738. 36 5209. Mass transport in liquid gallium ion beam sources. (GB) The mass loss of the anode ofa positive-Ga-ion source is determined from microbalance measurements, when the source is operated in a steady state. The anode consists of a short W point electrode covered by a film of liquid Ga, kept at 6 9 kV with respect to an earthed cathode. From spectrograms of the light emitted by this ion source it is known that neutral Ga atoms are produced during operation, besides fast positive ions. The rate
36. P A R T I C L E BEAMS A N D S O U R C E S 36 5201. Ion beam characteristics of a gas-filled accelerator tube. (USA) A gas-filled tube used to produce a pulsed neutron flux with D(T,He*)n reaction is described. Deuterium and tritium ions generated in a reflex discharge are extracted and accelerated to 100 keV by means of an accelerator electrode onto a deutero-tritide target electrode. The electrodes are designed to focus the ion beam onto the target. Total tube currents consisting of extracted ions, unsuppressed secondary electrons, and ions generated by interactions with the background gas are typically 100 mA. Characteristics of the extracted ion beam are discussed. Accelerating voltages greater than 50 keV are required to focus the beana through the accelerator aperture for configurations that give beams with the proper energy density at the target. The perveance of the beam is defined. M a x i m u m perveance values are 2 -10 nanopervs. Tube focusing and neutron production characteristics are described. R S Berg et al, d Vac Sci Technol, 18 (3), 1981, 983 986. 36 5202. H - ion formation from a surface conversion type ion source. (USA) Volume-produced H - ions have been extracted from a multicusp ion source. In addition, a molybdenum converter is installed in the source to generate surface-produced H - ions. Without cesium, the production of H - ions by the surface process is very small compared with those generated by volume production. However, the presence of cesium can greatly enhance the surface production yield. The energy spectrum shows that the surface-generated H ions contain two distinct groups when cesium is added to the discharge. The energy of one group is essentially that of the sheath potential and appears to be produced by a desorption process, The second group of H - ions has a slightly higher energy and appears to be formed by a reflection process. Different types of converter materials have also been tested. K N Leung and K W Ehlers, d Appl Phys, 52 (6), 1981, 3905 3911. 36 5203. Magnetic effects in high current ion beams. (USA) It is known that, in intense ion beams being developed for use in neutral injection, the space charge of the ions is almost totally compensated by electrons. In the limit of total compensation, it is shown that there is a critical ion current, l~, above which transport is no longer emittance but
456
magnetic self-field dominated. A Monte Carlo model of beam neutralization in the presence of the self-field is presented and applied to the example of the JET injectors. Results show a foreshortening of the injector focus, a rise in beamlet emittance, and an increase in the angular divergence (of order 0.1 J in high current neutral injectors. It is shown that, because of stochastic neutralization effects, there is a fundamental limit to the ability to focus an injector uniquely. IGB) G A Cottrell, Rer Sci lnstrum, 52 (8), 1981, 1174 1181. 36 5204. Molecular beam facility for studying mass spectrometer performance. (USA) An apparatus is described which produces neutral gas beams in the velocity range from thermal to 6 km/s. This facility makes possible studies simulating the motion of instruments through tenuous atmospheres. The use of the apparatus in studying the response of an open-source mass spectrometer sirnilar to those carried on high-speed spacecraft, such as earth satellites or planetary probes for investigating ambient atmospheric composition, is examined. Experiments performed included ones of response of an open source mass spectrometer when: (a) the instrument was in a normal mode of operation: (b) the instrument's ion source potentials were adjusted so as to reject gas particles which struck instrument surfaces; Ic) the gas beam was restricted so that selected portions of the ion source were struck: and {d) the gas beam struck the ion source at angles other than normal incidence. John O Ballenthin and Alfred O Nier, Re~" Sci Instrmn, 52 (7). 1981. 1016 1024. 36 5205. laser cooling of heavy-ion beams. (USA) We present a new technique for cooling heavy-ion beams. Tile discrete absorption spectrum of the ions and the transverse Doppler shift distinguish the transverse direction of velocity and cool the ions by photon absorption. We evaluate the total energy and time requirements for a particular example relevant to heavy-ion fusion. Paul J ChannelL J App/Phys, 52 16). 1981, 3791 3793. 36 5206. Ion beam extraction from a plasma with aberration reduction by method of mutual exclusion. (USA) Using an algorithm for solution of the Poisson-Vlasov equations for ions extracted from a plasma, an electrode shape is considered which has high optimum perveance and low beam divergence. J H Wheahon et al, J Appl Phys, 52 (6), 1981, 3787 3790. 36 5207. Faraday cup analysis of ion beams produced by a dense plasma focus. (USA) The design and performance of a Faraday cup which is used in a time-offlight technique to measure the energy spectrum of ions accelerated away from the anode of a plasma focus are described. The cup is located in a differentially pumped ( < 20 ,,) chamber which is separated from the main plasma focus chamber by a 0.0457-cm diam hole positioned 16 cm above the anode. This arrangement allows a bias voltage of - 400 V to be applied to the cup to stop comoving electrons and permits the observation of deuteron energies down to - 25 keV. G Gerdin el al, J App/ Pfiys, 52 15), 1981, 3269 3275. 36 5208. Influence of spherical and chromatic aberrations on the half-radius of an electron beam. (USA) Root mean square deviation and half-radius (containing a half of the beam current I of an axially symmetric beam from a point source, as a function of the beam crossover plane position, were solved analytically. Current density distributions and values of the half-radius of a beam generated from a source with a Gaussian current density distribution were numerically calculated. The spherochromatic aberration with electron energy dispersion (Maxwell and rectangular energy distributions) and without it (focusing deviation) were taken into account. The quadratic Igeometric) way of aberration mixing has been confirmed, with the mixed quantities defined. (Poland W Slowko, J I'ac Sci Teclmol, 19 131. 1981. 733 738. 36 5209. Mass transport in liquid gallium ion beam sources. (GB) The mass loss of the anode ofa positive-Ga-ion source is determined from microbalance measurements, when the source is operated in a steady state. The anode consists of a short W point electrode covered by a film of liquid Ga, kept at 6 9 kV with respect to an earthed cathode. From spectrograms of the light emitted by this ion source it is known that neutral Ga atoms are produced during operation, besides fast positive ions. The rate