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Role of inert gases in first wall phenomena in fusion devices

Description: The first wall surfaces of fusion devices will be exposed to bombardment by inert gaseous projectiles such as helium. The flux, energy and angular distribution of the helium radiation will depend not only on the type of device but also on its design parameters. For near term tokamak devices, the first wall surface phenomena caused by helium bombardment that appear to be quite important are physical sputtering and radiation blistering. Examples of these processes for a number of first wall candidate materials are discussed. While the physical sputtering phenomen is well understood, the mechanism of blister formation is still not fully understood. The various models proposed for radiation blistering of metal during helium bombardment is critically reviewed in the light of most recent experimental results.
Date: January 1, 1979
Creator: Das, S.K.
Partner: UNT Libraries Government Documents Department

Reduction of surface erosion caused by helium blistering in sintered beryllium and sintered aluminum powder

Description: Studies have been conducted to find materials with microstructures which minimize the formation of blisters. A promising class of materials appears to be sintered metal powder with small average grain sizes and low atomic number Z. Studies of the surface erosion of sintered aluminum powder (SAP 895) and of aluminum held at 400$sup 0$C due to blistering by 100 keV helium ions have been conducted and the results are compared to those obtained earlier for room temperature irradiation. A significant reduction of the erosion rate in SAP 895 in comparison to annealed aluminum and SAP 930 is observed. In addition results on the blistering of sintered beryllium powder (type I) irradiated at room temperature and 600$sup 0$C by 100 keV helium ions are given. These results will be compared with those reported recently for vacuum cast beryllium foil and a foil of sintered beryllium powder (type II) which was fabricated differently, than type I. For room temperature irradiation only a few blisters could be observed in sintered beryllium powder type I and type II and they are smaller in size and in number than in vacuum cast beryllium. For irradiation at 600$sup 0$C large scale exfoliation of blisters was observed for vacuum cast beryllium but much less exfoliation was seen for sintered beryllium powder, type I, and type II. The results show a reduction in erosion rate cast beryllium, for both room temperature and 600$sup 0$C.
Date: January 1, 1976
Creator: Das, S.K. & Kaminsky, M.
Partner: UNT Libraries Government Documents Department

Surface erosion of fusion reactor components due to radiation blistering and neutron sputtering

Description: Radiation blistering and neutron sputtering can lead to the surface erosion of fusion reactor components exposed to plasma radiations. Recent studies of methods to reduce the surface erosion caused by these processes are discussed. (auth)
Date: January 1, 1975
Creator: Das, S.K. & Kaminsky, M.
Partner: UNT Libraries Government Documents Department

Reduction of surface erosion caused by helium blistering: comparison between vacuum-cast and sintered-beryllium

Description: The blister formation and the erosion associated with blistering in a vacuum cast beryllium foil and in a foil of sintered beryllium powder have been investigated for irradiation at room temperature and at 600$sup 0$C with 100 keV $sup 4$He$sup +$ ions for total doses of 0.5 to 1.0 C cm$sup -2$. For room temperature irradiation the blisters in sintered beryllium powder are smaller in size than in vacuum cast beryllium. For irradiation at 600$sup 0$C large scale exfoliation of blisters was observed for vacuum cast beryllium but only small amount of exfoliation was seen for sintered beryllium powder. The results show a reduction in erosion rate in sintered beryllium as compared to the erosion rate in vacuum cast beryllium. For room temperature irradiation no erosion rate could be determined for the sintered beryllium foil since no blister exfoliation was observed. For 600$sup 0$C irradiation the erosion rate for sintered beryllium foil is more than an order of magnitude smaller than for vacuum cast beryllium. (auth)
Date: January 1, 1975
Creator: Das, S.K. & Kaminsky, M.
Partner: UNT Libraries Government Documents Department

Particle emission from polycrystalline and monocrystalline niobium under 14.1 MeV neutron impact

Description: A brief review of recent results on particle emission from cold-rolled and annealed niobium with coarse surface finishes, and from monocrystalline niobium surfaces under 14.1-MeV neutron impact is given. For the cold-rolled and annealed samples two types of deposits were discovered on collector surfaces facing the irradiated targets. One type appeared as a fractional atom layer covering the surface, the other in the form of chunks. No chunk emission was observed for the monocrystalline niobium surface. The chunk deposits on the collectors facing the cold-rolled samples are not uniformly distributed over the collector area but are clustered along certain streaks or appear in patches. Furthermore, the number of chunks per unit collector area and the average chunk size were larger for the rough, cold-rolled samples than for the annealed samples. These observations suggest that the release of stresses (e.g. stresses caused by cold-rolling) in the surface regions by the energy deposited by primary recoils, and surface roughness affect the chunk emission significantly. Previously reported crude estimates of sputtering yields were improved on the basis of information which has become available from additional neutron irradiation runs. (auth)
Date: January 1, 1975
Creator: Kaminsky, M. & Das, S.K.
Partner: UNT Libraries Government Documents Department

Sputtering of vanadium and niobium under 14.1 MeV neutron impact

Description: The recent studies of particle emission from cold-rolled and annealed niobium under 14.1-MeV neutron impact were extended to a heavily etched, polycrystalline niobium surface and to cold worked vanadium surfaces with different degrees of microstructure. The type and amount of material released and deposited on collector surfaces facing the irradiated targets were determined by three analytical techniques. Two types of deposits were found for certain types of surfaces--one in the form of chunks; the other as a fractional atom layer covering the surface. The chunks vary significantly in size. The small number of chunks observed suggests that the ejection of chunks is a relatively rare event in comparison to the total number of primary knock-on events produced by 14-MeV neutrons in near surface regions. Estimates of the total sputtering yield based on the chunk deposits and on the fractional atom layer deposit will be given. (auth)
Date: January 1, 1976
Creator: Kaminsky, M. & Das, S.K.
Partner: UNT Libraries Government Documents Department

Radiation blistering in metals and alloys

Description: Radiation blistering in solids has been identified as a process leading to damage and erosion of irradiated surfaces. Some of the major parameters governing the blistering process in metals and some metallic alloys are the type of projectile and its energy, total dose, dose rate, target temperature, channeling condition of the projectile, orientation of the irradiated surface plane, and target material and its microstructure. Experimental results and models proposed for blister formation and rupture are reviewed. The blistering phenomenon is important as an erosion process in applications such as fusion reactor technology (plasma-wall interactions) and accelerator technology (erosion of components and targets). A description of methods for the reduction of surface erosion caused by blistering is included.
Date: August 25, 1975
Creator: Das, S. K. & Kaminsky, M.
Partner: UNT Libraries Government Documents Department

Radiation blistering: recent developments. [/sup 4/He/sup +/]

Description: Different metals have been proposed for radiation blistering of metals. For example, for the formation of blisters on helium bombarded metal surfaces such models are based on the coalescence of gas bubbles and the build-up of excess gas pressure in the implant region, causing large enough stresses for the occurrence of plastic deformation of the surface regions; or the percolation of helium in the lattice; or the build-up of large, lateral stresses in the implant layer causing buckling. These models are critically reviewed in the light of recent experimental results. A discussion of blistering effects at high doses is included.
Date: January 1, 1978
Creator: Kaminsky, M. & Das, S.K.
Partner: UNT Libraries Government Documents Department

Particle release from niobium under 14-MeV neutron impact

Description: The particle release from cold-rolled and annealed polycrystalline niobium surfuces under 14-MeV neutron impact to a total dose of 4.6 x 10/sup 15/ neutrons/cm/sup 2/ was investigated in two separate runs at ambient temperature and under ultrahigh and high-vacuum conditions, respectively. The type and amount of material released and deposited on a substrate surface were determined independently by four analytic techniques. Surprisingly. there were two types of deposits---one in the form of large chunks. the other a more even layer covering the surface. For the cold-rolled niobium sample with a surface finish of 5 mu m the estimated particle release value is S = 0.25 plus or minus 0.10 niobium atoms per incident 14-MeV neutron. A model for the chunk emission is suggested. (auth)
Date: January 1, 1973
Creator: Kaminsky, M. & Das, S.K.
Partner: UNT Libraries Government Documents Department

Erosion of stainless steel first wall by helium blistering

Description: The blister formation and the erosion rates associated with helium blistering in annealed 304 stainless steel were investigated for helium projectiles with energies ranging from 100 keV to 1.5 MeV and for irradiation temperatures ranging from room temperature to 550 deg C. The total dose was varied from 0.l C/cm/sup 2/ to 1.0 C/cm/sup 2/. The results show that the blister size increases with increasing projectile energy. The degree of blistering, and the erosion rates associated with blister rupture and exfoliation are found to be strongly temperature dependent. Maximum erosion rates were observed at irradiation temperature of around ~450 deg C. The erosion rates decreased at higher temperature ~550 deg C. The degree of blistering is found to increase with increasing dose. (auth)
Date: January 1, 1973
Creator: Das, S.K. & Kaminsky, M.
Partner: UNT Libraries Government Documents Department

Surface damage of 316 stainless steel irradiated with /sup 4/He/sup +/ to high doses

Description: Surface blistering of niobium by implantation with helium ions in the 9 to 15 keV range was investigated. The apparent disappearance of blisters at sufficiently high doses was believed to be an equilibrium effect. To determine whether high temperature annealing causes the equilibrium condition, stainless steel-316 samples were irradiated at a constant 450/sup 0/C. Results are presented. (GHT)
Date: January 1, 1978
Creator: Kaminsky, M. & Das, S.K.
Partner: UNT Libraries Government Documents Department

Surface erosion phenomena in connection with CTR applications

Description: The interaction of plasma radiations with the exposed surfaces of components of plasma devices and future controlled thermonuclear fusion reactors (CTR) can cause a variety of surface effects. In turn, such surface effects can cause (a) the release of plasma contaminants, and (b) the damage and erosion of the irradiated surfaces. The contamination of the plasma can have serious effects on plasma stability and on plasma temperature, and the surface erosion can seriously limit the lifetime of the irradiated components. At present, knowledge of surface erosion rates for the plasma parameters and materials envisioned in CTR applications is only fragmentary. To what extent the erosion rates will be affected by synergistic effects due to the simultaneous bombardment of surfaces by high fluxes of energetic particles of various types and by photons is almost completely unknown. A summary of some of the major surface erosion phenomena which have been identified as being important for CTR applications by using single irradiation sources (e.g., accelerators) will be given. A discussion of some potential solutions to reduce surface erosion will be included. The main features of a recently completed two component irradiation facility at ANL for CTR related surface studies will be described.
Date: January 1, 1976
Creator: Kaminsky, M. & Das, S. K.
Partner: UNT Libraries Government Documents Department

Effect of He$sup +$ and D$sup +$ ion beam flux on blister formation in niobium and vanadium

Description: From international conference applications of ion beams to metals; Albuquerque, New Mexico, USA (2 Oct 1973). The effect of incident ion beam flux on the blister formation in annealed polycrystalline niobium and vanadium has been investigated for 0.5-MeV He/sup +/ and 0.25-MeV D/sup +/ projectiles. For the He/sup +/ ions the flux was varied from 1 x 10/sup 13/ ions/(cm/sup 2/-sec) to 1 x 10/sup 15/ ions/(cm/sup 2/-sec), the targets were held at 900 deg C, and the total dose was varied from 0.1 to 1.0 C/cm/sup 2/. For the D/sup +/ ion irradiation ihe flux was varied from 1 x 10/sup 14/ to 1 x 10/sup 15/ ions/ (cm/ sup 2/-sec), the niobium targets were held at 700 deg C, and the total dose was 2.0 C/cm/sup 2/. For both the helium implanted vanadium and riobium the blister density shows a stronger flux dependence than the average blister diameter. For deuteron implanted niobium the blister size increased as the flux was increased from 1 x 10/sup 14/ to 1 x 10/sup 15/ ions/(cm/sup 2/-sec). (auth)
Date: January 1, 1973
Creator: Das, S.K. & Kaminsky, M.
Partner: UNT Libraries Government Documents Department

Radiation blistering of structural materials for fusion devices and reactors

Description: From surface effects in controlled thermonuclear fusion devices and reactors meeting; Argonne. Illinois, USA (10 Jan Radiation blistering can be an important erosion process when the structural components of controlled thermonuclear fusion devices or reactors are exposed to the impact of energetic particles leaving the plasma region. A brief review of some of the important parameters governing the radiation blistering process is given. Erosion rates associated with helium blistering in V, Nb, and Type 304 stainless steel are reported for different irradiation temperatures and different projectile energies. (auth)
Date: January 1, 1974
Creator: Das, S.K. & Kaminsky, M.
Partner: UNT Libraries Government Documents Department

Blistering phenomena I: metals and alloys

Description: A summary of the major parameters affecting the blistering process is given. Brief discussions of the blistering mechanisms are included. The following topics are described: (1) projectile-target system, (2) projectile energy, (3) critical dose for blister formation, (4) effect of total dose, (5) dose rate, (6) target temperature, (7) crystallographic orientation of the irradiated surface, (8) models for blister formation, and (9) surface erosion of fusion reactor components by blistering. (MOW)
Date: January 1, 1976
Creator: Kaminsky, M. & Das, S. K.
Partner: UNT Libraries Government Documents Department

Deuterium and helium-ion irradiation effects on TiB/sub 2/ coatings

Description: The surface damage and erosion of chemically vapor deposited TiB/sub 2/ coatings and commercial grade Ti, caused by 40-, 60- and 120-keV D/sup +/ and /sup 4/He/sup +/ irradiation, has been studied for the as deposited coatings and for the coating surfaces that were mechanically polished prior to irradiation. SEM analysis of polished TiB/sub 2/ samples irradiated with D/sup +/ and /sup 4/He/sup +/ to a dose of 3.1 x 10/sup 18/ ions/cm/sup 2/ reveal significant surface damage due to blistering and flaking whereas for identical irradiation conditions, the as deposited TiB/sub 2/ coatings show very little damage. For similar irradiation conditions the Ti metal samples showed blistering for the /sup 4/He/sup +/ irradiation case but no significant surface damage for the D/sup +/ case. Estimates of the irosion yields due to blister exfoliation in polished TiB/sub 2/ samples show an increase with increasing projectile energy for the total dose studied.
Date: January 1, 1979
Creator: Das, S.K. & Kaminsky, M.
Partner: UNT Libraries Government Documents Department

Methods to reduce surface erosion caused by radiation blistering

Description: One method described for reducing the surface erosion due to helium blistering in fusion reactor components is to maintain the surfaces at a high enough temperature so that some of the implanted helium is released without forming large bubbles. Cold working is another method discussed along with grain size and dispersion of second phase. The use of a graphite cloth and protective coating is also mentioned. (MOW)
Date: January 1, 1976
Creator: Kaminsky, M. & Das, S. K.
Partner: UNT Libraries Government Documents Department

Sputtering and surface damage of TFTR protective plate materials (Mo, TZM, graphite) by energetic D/sup +/ ion irradiation. Final report for Princeton Plasma Physics Laboratory

Description: Studies have been conducted in accordance with a service request from the Plasma Physics Laboratory (PPPL) of Princeton University to determine the total sputtering yields and the surface damage of molybdenum (a candidate material for the neutral beam injector protective plate for Princeton's Fusion Test Reactor (TFTR)) caused by the impact of D/sup +/ ions at 120-keV, 60-keV and 40-keV at fluxes and total doses agreed upon between PPPL and ANL. The irradiations have been conducted in a specified pulsed mode as well as in a dc mode. The material TZM (a molybdenum alloy) was included in some tests of surface damage, but not for the full complement of doses planned for molybdenum. According to a request by PPPL the target temperature was not to be controlled (targets were allowed to reach a temperature determined by the beam power deposition and the conductive and radiative heat losses), but the target temperature was to be monitored. The irradiations were conducted at pressures ranging from 4 x 10/sup -9/ torr to 2 x 10/sup -8/ torr.
Date: March 1, 1978
Creator: Kaminsky, M.; Das, S.K. & Dusza, P.
Partner: UNT Libraries Government Documents Department

Helium blistering of ceramic coatings on Hastelloy X and Nb--1% Zr

Description: The surface damage of insulating ceramic coatings on Hastelloy X and Nb-- 1 percent Zr held at room temperature and at 300$sup 0$C was studied for both 100 keV and 250 keV helium ion irradiation for a dose range from 3.7 x 10$sup 18$ to 1 x 10$sup 19$ ions cm$sup -2$. Blisters were observed after room temperature irradiation with both 100 keV and 250 keV helium ions. However, for irradiation at 300$sup 0$C no blisters could be observed. The sharp rise in the helium permeation with temperature, observed by others for some glasses and ceramics, is thought to be responsible for this behavior. These results suggest that for the energy range studied helium blistering has a negligible surface erosion effect on such coatings if they are operated at temperatures above 300$sup 0$C. (auth)
Date: January 1, 1975
Creator: Kaminsky, M.; Das, S.K. & Ekern, R.
Partner: UNT Libraries Government Documents Department

Helium trapping in aluminum and sintered aluminum powders

Description: The surface erosion of annealed aluminum and of sintered aluminum powder (SAP) due to blistering from implantation of 100-keV $sup 4$He$sup +$ ions at room temperature has been investigated. A substantial reduction in the blistering erosion rate in SAP was observed from that in pure annealed aluminum. In order to determine whether the observed reduction in blistering is due to enhanced helium trapping or due to helium released, the implanted helium profiles in annealed aluminum and in SAP have been studied by Rutherford backscattering. The results show that more helium is trapped in SAP than in aluminum for identical irradiation conditions. The observed reduction in erosion from helium blistering in SAP is more likely due to the dispersion of trapped helium at the large Al-Al$sub 2$O$sub 3$ interfaces and at the large grain boundaries in SAP than to helium release. (auth)
Date: January 1, 1975
Creator: Das, S.K.; Kaminsky, M. & Rossing, T.
Partner: UNT Libraries Government Documents Department

Irradiation of graphite cloth at various temperatures with deutrons and helium ions

Description: Graphite cloth samples were irradiated with 100 keV deuterons and $sup 4$He$sup +$ ions at room temperature and at elevated temperatures. Scanning electron microscopy was used to examine the surfaces of irradiated and unirradiated graphite fibers. Irradiation at room temperature with $sup 4$He$sup +$ to a total dose of 3.1 x 10$sup 18$ ions cm$sup -2$ produces considerable flaking of individual fibers, which is not observed on unirradiated fibers. Identical irradiations at 400$sup 0$ and 800$sup 0$ with $sup 4$He$sup +$ did not produce any detectable flaking or other surface damage. The elevated temperatures apparently prevent an accumulation of helium in localized areas which in turn could cause flaking in near surface regions. Results obtained for deuteron bombardment of graphite cloth at room temperature and at 600$sup 0$C are also discussed. (auth)
Date: January 1, 1975
Creator: Ekern, R.; Das, S.K. & Kaminsky, M.
Partner: UNT Libraries Government Documents Department