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Ion-accelaration mechanisms in vacuum diodes
Classified
abstracts
4540-4547
J111+‘11 where
J and 4 are the elemental impingement rates and thermal sticking probabilities, respectively. At any value of r investigated, a value of V, could be found such that for negative substrate biases greater than this value, the films were single phase. No preferential resputtering was observed for V, up to 250 V in films in which JsbQsb = J,,,$,,,. Thus, the range of r and T$ values over which single-phase stoichiometric films could be deposited from the vapour phase was extended by low energy ion bombardment of the growing film.
A H Eltoukhy
et al, J Vuc Sci Technol,
16 (2),
500 eV e- impacting on SS (304) samples (- 1000 cm* surface area) prepared by : (i) a degrease treatment; (ii) an acid cleaning (l/3 HF, l/3 HNO,, l/3 H,Ol, (iii) concentrated HF. Three separate samples were analysed for the first two treatments allowing the sample-tosample variation to be determined (10’&20:/; yield variations). The unit yield energy E0 (electron energy for which the total secondary electron emission is 1.0) has also been measured for each of the above treatments.
D Edwards,
J Vat Sci Technol,
16 (2), 1979, 758-760.
1979, 321-323 4544. Synchrotron-radiation-induced storage ring vacuum system. (USA)
32.
EVACUATION
AND
SEALING
32 4540.
Ion-acceleration mechanisms in vacuum diodes. (USA) A study of proton acceleration in a Lute diode has been carried out. Measurements of beam-neutralization times, electron and ion energy distributions, and induced radioactivity have been made. These measurements show that the effective potential-well depth at the beam head is less than the electron-accelerating voltage. Also, the relative activity of Mylar and copper foils indicates that ion energy increases with mass for Z = 1 particles. Both of these observations are consistent with ion acceleration resulting from a moving potential well. R J Adler and J A Nation, J Appl Phys, 50 (7), 1979, 5025-5027.
33.
NUCLEONICS
4541. Ultra-high vacuum compatibility materials: K-rami& and ATJ graphite.
of two possible
fusion
33 reactor
(USA) Outgassing characteristics of K-rami (manufactured by Kaman Nuclear) and ATJ graphite were evaluated under various treatments. For K-ramic,O total outgassing rates of 2 x 10m9 torr I s-’ cm-’ unbaked and 7 x IO-” torr Is-’ cme2 baked were measured. Mass spectroscopic measurements showed H, and CO to be the dominant residual gases. For ATJ, graphite the treatment consisted of repeated heatings in CCICI,O to 1250 K as well as repeated exposures to atmosphere. Residual gas analysis measured the time dependence of desorbed quantities of H2, H,O, CO,, CO and CH,. During the initial heating, the maximum species atom to lattice atom ratios were obtained yielding values of 2.6 >: IO-” for Hz, 3.4 x 10e5 for HZO, 1.6 x 10ms for CO,, 7.6 Y 10e6 for CO, and 5.2 x 10e6 for CHa. The total outgassed material from the graphite sample decreased by a factor of 10” after successive heatings.
R Moore,
J Vat Sci Technol,
16 (2), 1979, 748-751. 33
4542. Observations of changes in residual with discharge cleaning in PLT. (USA)
gas and surface
composition
Hydrogen discharge cleaning of the PLT vacuum vessel has been studied by mass spectroscopy of desorbed gases and surface analysis of exposed samples. Several modes of vessel conditioning have been studied to date: (I) a high-power discharge cleaning (PDC) mode, with a peak power density lo the vessel wall P, -0.6 W cm-* and a peak electron temperature T, - 100 eV: (2) low-power (Taylor-type) discharge cleaning (TDC) with P, -0.05 W cm-’ and T, < 5 eV. The predominant residual gases produced during PDC are CH, v IO-’ torr), whereas TDC pro(l-5 x 10e6 torr) and CO (I-IO duced primarily Hz0 (l-2 x 10e6 torr) and CH, (I-IO :.’ IO-’ torr). The transient behaviour of the residual gases is not simply related to pumping time constants, and provides evidence for the role of surface chemical reactions and diffusion on the formation of these gases. In situ surface analysis of hydrocarbon-covered stainless steel has shown significant decreases in carbon coverage occurring after 103lo4 pulses of either cleaning mode. Observed changes in oxygen coverage are more difficult to interpret because of the presence of the passivation oxide layer on the stainless-steel substrates.
H F Dylla
et al, J Vuc Sci Technol,
4543. Ion and electron steel (304). (USA)
desorption
16 (2). 1979.752-757. of neutral
The vacuum performance of both electron (as well as certain types of fusion reactors) to the desorption of neutral molecules wall by -keV charged particles. In this of Hz, CO, CO* and CH, are reported
molecules
from
33 stainless
and proton storage rings is expected to be sensitive from the vacuum chamber study the desorption yields from 1000 eV Ar+ and
heating
effects
in
the
33 PEP
The advent of large high-energy storage rings has facilitated the need for more detailed analysis of synchrotron radiation interactions and related thermal effects. In the PEP storage ring, a maximum of 5 MW of synchrotron radiation with a critical energy of 44 keV will interact with 2200 m of vacuum hardware. A Monte Carlo based computer code, EGS, was employed to follow electromagnetic reactions of the synchrotron radiation through various computerized models of the vacuum system. The computer simulated structures with hundreds of discrete rkgions and varying materials. Results showed that typically 70”/, of the svnchrotron power was absorbed in incident surfaces and 204/, was scattered outside the vacuum vessel. The remaining power was deposited in varied vacuum components. Sensitive PEP ring components, particularly distributed ion pumps, were subsequently designed to minimize power absorption and to maximize cooling effects. Other thermal calculations were employed to design for minimal wall temperatures in areas of direct synchrotron radiation incidence.
T W Martin,
J Yuc Sci Techttol.
16 (2), 1979, 761-762. 33
4545.
Residual
gas analysis
in the ISX-A
tokamak.
(USA) A computer-controlled mass analyser was utilized to observe the residual gases in the ISX-A tokamak. This residual gas analysis (RCA) system enabled time resolved measurements of preselected m/e peak heights to be made during and after tokamak discharges. Routine mass scans were also made and displayed in the form of semilogarithmic plots of partial pressure (torr) vs m/e. Wall conditioning of the stainless steel torus consisted of hydrogen discharge cleaning and titanium gettering. which ultimately produced gauge pressures on the order of IO-’ and 10e9 torr, respectively. The dominant plasma impurities, carbon and oxygen, were observed by the RCA as light hydrocarbons and water vapour. Entrapment of deuterium by the walls was investigated by monitoring the residual Dz content after the working gas was changed lo Hz. The effective nuclear charge (Z.,,) was found to be proportional lo the residual contaminants measured by the RGA immediately following a discharge.
J E Simpkins
et al, J Vat Sci Techtrol,
4546.
impurity
16 (2). 1979, 763-765. 33
Surface
studies
in the ISX-A
tokamak.
(USA)
The Impurity Study Experiment (ISX-A) was a tokamak designed to study impurity sources, plasma wall interactions, impurity behaviour within the plasma, and related phenomena. An Auger electron spectrometer, attached to the tokamak by means of a uhv sample transfer system. has been the primary tool used for surface studies of the first wall. Stainless steel samples positioned at the wall edge were used to follow the progressive ‘clean-up’ of the torus wall. Cleaning consisted of low energy hydrogen discharge plasmas, and later titanium gettering. The principal contaminants initially were carbon, oxygen and sulphur. As cleaning proceeded, the surface oxide layers were reduced to substoichiometric levels, and the carbon deposits appeared to be converted to metallic carbides. The sulphur was largely removed. A decrease in the effective nuclear charge of the plasma could be correlated with these surface changes. Discharge cleaning reduced Zcrr from -4 to 1.6 over a period of several months while titanium gettering produced values approaching 1.0.
L C Emerson
et al, J Vuc Sci Technol,
16 (2). 1979, 766-768. 33
4547. A convenient method for the measurement from an intense neutral beam. (USA)
of species composition
We present a method to infer the approximate species mixture neutral beam sources which accelerate positive hydrogen ions. idealized neutral beam is specified by the accelerating voltage, neutralizer thickness (molecules of hydrogen per cm*), and
of An the the 349
abstracts
4540-4547
J111+‘11 where
J and 4 are the elemental impingement rates and thermal sticking probabilities, respectively. At any value of r investigated, a value of V, could be found such that for negative substrate biases greater than this value, the films were single phase. No preferential resputtering was observed for V, up to 250 V in films in which JsbQsb = J,,,$,,,. Thus, the range of r and T$ values over which single-phase stoichiometric films could be deposited from the vapour phase was extended by low energy ion bombardment of the growing film.
A H Eltoukhy
et al, J Vuc Sci Technol,
16 (2),
500 eV e- impacting on SS (304) samples (- 1000 cm* surface area) prepared by : (i) a degrease treatment; (ii) an acid cleaning (l/3 HF, l/3 HNO,, l/3 H,Ol, (iii) concentrated HF. Three separate samples were analysed for the first two treatments allowing the sample-tosample variation to be determined (10’&20:/; yield variations). The unit yield energy E0 (electron energy for which the total secondary electron emission is 1.0) has also been measured for each of the above treatments.
D Edwards,
J Vat Sci Technol,
16 (2), 1979, 758-760.
1979, 321-323 4544. Synchrotron-radiation-induced storage ring vacuum system. (USA)
32.
EVACUATION
AND
SEALING
32 4540.
Ion-acceleration mechanisms in vacuum diodes. (USA) A study of proton acceleration in a Lute diode has been carried out. Measurements of beam-neutralization times, electron and ion energy distributions, and induced radioactivity have been made. These measurements show that the effective potential-well depth at the beam head is less than the electron-accelerating voltage. Also, the relative activity of Mylar and copper foils indicates that ion energy increases with mass for Z = 1 particles. Both of these observations are consistent with ion acceleration resulting from a moving potential well. R J Adler and J A Nation, J Appl Phys, 50 (7), 1979, 5025-5027.
33.
NUCLEONICS
4541. Ultra-high vacuum compatibility materials: K-rami& and ATJ graphite.
of two possible
fusion
33 reactor
(USA) Outgassing characteristics of K-rami (manufactured by Kaman Nuclear) and ATJ graphite were evaluated under various treatments. For K-ramic,O total outgassing rates of 2 x 10m9 torr I s-’ cm-’ unbaked and 7 x IO-” torr Is-’ cme2 baked were measured. Mass spectroscopic measurements showed H, and CO to be the dominant residual gases. For ATJ, graphite the treatment consisted of repeated heatings in CCICI,O to 1250 K as well as repeated exposures to atmosphere. Residual gas analysis measured the time dependence of desorbed quantities of H2, H,O, CO,, CO and CH,. During the initial heating, the maximum species atom to lattice atom ratios were obtained yielding values of 2.6 >: IO-” for Hz, 3.4 x 10e5 for HZO, 1.6 x 10ms for CO,, 7.6 Y 10e6 for CO, and 5.2 x 10e6 for CHa. The total outgassed material from the graphite sample decreased by a factor of 10” after successive heatings.
R Moore,
J Vat Sci Technol,
16 (2), 1979, 748-751. 33
4542. Observations of changes in residual with discharge cleaning in PLT. (USA)
gas and surface
composition
Hydrogen discharge cleaning of the PLT vacuum vessel has been studied by mass spectroscopy of desorbed gases and surface analysis of exposed samples. Several modes of vessel conditioning have been studied to date: (I) a high-power discharge cleaning (PDC) mode, with a peak power density lo the vessel wall P, -0.6 W cm-* and a peak electron temperature T, - 100 eV: (2) low-power (Taylor-type) discharge cleaning (TDC) with P, -0.05 W cm-’ and T, < 5 eV. The predominant residual gases produced during PDC are CH, v IO-’ torr), whereas TDC pro(l-5 x 10e6 torr) and CO (I-IO duced primarily Hz0 (l-2 x 10e6 torr) and CH, (I-IO :.’ IO-’ torr). The transient behaviour of the residual gases is not simply related to pumping time constants, and provides evidence for the role of surface chemical reactions and diffusion on the formation of these gases. In situ surface analysis of hydrocarbon-covered stainless steel has shown significant decreases in carbon coverage occurring after 103lo4 pulses of either cleaning mode. Observed changes in oxygen coverage are more difficult to interpret because of the presence of the passivation oxide layer on the stainless-steel substrates.
H F Dylla
et al, J Vuc Sci Technol,
4543. Ion and electron steel (304). (USA)
desorption
16 (2). 1979.752-757. of neutral
The vacuum performance of both electron (as well as certain types of fusion reactors) to the desorption of neutral molecules wall by -keV charged particles. In this of Hz, CO, CO* and CH, are reported
molecules
from
33 stainless
and proton storage rings is expected to be sensitive from the vacuum chamber study the desorption yields from 1000 eV Ar+ and
heating
effects
in
the
33 PEP
The advent of large high-energy storage rings has facilitated the need for more detailed analysis of synchrotron radiation interactions and related thermal effects. In the PEP storage ring, a maximum of 5 MW of synchrotron radiation with a critical energy of 44 keV will interact with 2200 m of vacuum hardware. A Monte Carlo based computer code, EGS, was employed to follow electromagnetic reactions of the synchrotron radiation through various computerized models of the vacuum system. The computer simulated structures with hundreds of discrete rkgions and varying materials. Results showed that typically 70”/, of the svnchrotron power was absorbed in incident surfaces and 204/, was scattered outside the vacuum vessel. The remaining power was deposited in varied vacuum components. Sensitive PEP ring components, particularly distributed ion pumps, were subsequently designed to minimize power absorption and to maximize cooling effects. Other thermal calculations were employed to design for minimal wall temperatures in areas of direct synchrotron radiation incidence.
T W Martin,
J Yuc Sci Techttol.
16 (2), 1979, 761-762. 33
4545.
Residual
gas analysis
in the ISX-A
tokamak.
(USA) A computer-controlled mass analyser was utilized to observe the residual gases in the ISX-A tokamak. This residual gas analysis (RCA) system enabled time resolved measurements of preselected m/e peak heights to be made during and after tokamak discharges. Routine mass scans were also made and displayed in the form of semilogarithmic plots of partial pressure (torr) vs m/e. Wall conditioning of the stainless steel torus consisted of hydrogen discharge cleaning and titanium gettering. which ultimately produced gauge pressures on the order of IO-’ and 10e9 torr, respectively. The dominant plasma impurities, carbon and oxygen, were observed by the RCA as light hydrocarbons and water vapour. Entrapment of deuterium by the walls was investigated by monitoring the residual Dz content after the working gas was changed lo Hz. The effective nuclear charge (Z.,,) was found to be proportional lo the residual contaminants measured by the RGA immediately following a discharge.
J E Simpkins
et al, J Vat Sci Techtrol,
4546.
impurity
16 (2). 1979, 763-765. 33
Surface
studies
in the ISX-A
tokamak.
(USA)
The Impurity Study Experiment (ISX-A) was a tokamak designed to study impurity sources, plasma wall interactions, impurity behaviour within the plasma, and related phenomena. An Auger electron spectrometer, attached to the tokamak by means of a uhv sample transfer system. has been the primary tool used for surface studies of the first wall. Stainless steel samples positioned at the wall edge were used to follow the progressive ‘clean-up’ of the torus wall. Cleaning consisted of low energy hydrogen discharge plasmas, and later titanium gettering. The principal contaminants initially were carbon, oxygen and sulphur. As cleaning proceeded, the surface oxide layers were reduced to substoichiometric levels, and the carbon deposits appeared to be converted to metallic carbides. The sulphur was largely removed. A decrease in the effective nuclear charge of the plasma could be correlated with these surface changes. Discharge cleaning reduced Zcrr from -4 to 1.6 over a period of several months while titanium gettering produced values approaching 1.0.
L C Emerson
et al, J Vuc Sci Technol,
16 (2). 1979, 766-768. 33
4547. A convenient method for the measurement from an intense neutral beam. (USA)
of species composition
We present a method to infer the approximate species mixture neutral beam sources which accelerate positive hydrogen ions. idealized neutral beam is specified by the accelerating voltage, neutralizer thickness (molecules of hydrogen per cm*), and
of An the the 349