Plasma Impurities resulting from the limiters and walls of tokamaks are a recognized problem for fusion reactors. This paper reports recent measurements of Impurity fluxes and differential changes at a surface probe near the plasma edge of Alcator-A. High purity aluminum samples were prepared and Auger analyzed in an interlocking UHV chamber using a retractable probe. Rutherford backscattertng is used to determine the quantities of implanted species. Time resolved measurements are made by rotating a disc-shaped sample behind an aperature during discharges. Estimates are made for C, N, O, Fe and Mo fluxes at the plasma edge.

Stage I recovery is investigated for Fe, Zr and Cu irradiated at 17.5 K with 10,14 and 16 MeV protons. Several sub-stages are measured and analyzed. In relation to published electron and neutron irradiation data, the present results show that 16 MeV protons approximate the damage induced in metals due to fusion reactor spectra. The present results also indicate that the damage state created by protons in metals is similar to an intermediate state between those due to electron and fast-neutron irradiations.

Energy spectra and charge fractions for hydrogen and helium backscattered from silicon targets are reported. The primary energy of the incident particle varies from 5 to 15 keV. The backscattered energy distributions are measured down to 500 eV and the results are compared to a Monte-Carlo computer simulation. Good agreement is found between the theoretical model and the experimental data. Charge fractions are measured by differentiating between scattered ions and neutrals. For hydrogen, neutralization occurs primarily at the surface for the backscattered particles and no depth effects are found. Helium shows a large peak in the ion yield for surface scattering with a much reduced ion yield for particles scattered from within the solid.

Iron, zirconium and copper samples were irradiated at 17.5 K by 10 to 16 MeV protons. The resistivity change was measured as a function of the bombarding dose. Values of the resistivity damage rate are determined from the experimental data and are compared with the corresponding estimates obtained from a modified Kinchin-Pease model and from a vacancy-recombination model. Good agreement is found between the latter model and the experimental results. The data are also compared with other proton irradiation and d-Be neutron experiments.

Iron and copper samples have been irradiated at 17K with 10–16 MeV protons to investigate the damage produced and, where possible, draw conclusions in relation to the use of such bombardments to simulate the damage resulting from the fusion neutron spectrum. The damage-dose behaviour and isochronal anneals appear to support the model of stimulated Frenkel-pair recombination in the vicinity of high energy density cascades.

X-ray photoelectron spectroscopy (XPS or ESCA) has been extensively used in recent years to investigate the chemical composition of various surfaces. In our laboratory XPS has been used primarily to monitor elemental atomic ratios and binding energy shifts produced by surface modifications of glassy carbon samples. A major method of modification has been by radio frequency plasma treatments to improve surface electrochemical properties. To maintain surface integrity for XPS analysis by avoiding exposure of the treated sample surface to oxygen, water vapor or other contaminants in the ambient laboratory air, a versatile sample treatment and transfer system has been built and attached to the analysis chamber of a Physical Electronics Industries Model 548 Electron Spectrometer. The resulting system has proven to be more suited to meet our needs than any previously reported or commercially available system. The system consists of two sample transfer side-arms, each with a magnetically coupled transfer rod compatible with our custom sample carriers. The sample isolation side-arm is used exclusively to enter samples into the analyzer chamber without contamination. The general purpose side-arm has two appendage ports which support a radio frequency plasma chamber, a sample introduction lock and a combination chemical treatment/electrochemical cell chamber. Each of the appendage ports and the two transfer housings can be isolated using UHV gate valves. The sample transfer and transport mechanisms and the system performance are discussed. Examples of the effects of exposure of RF plasma treated glassy carbon surfaces to air and water vapor are use to demonstrate the capabilities of the sample handling system.

Using a time-of-flight technique, we have measured the energy distributions of hydrogen and helium backscattered from well characterized silicon targets. Silicon single crystal samples were first oxidized to selected depths and then analyzed using Auger depth profiling and MeV He channeling. The energy spectra have been measured and are compared to a computer simulation theory. For the cases considered the oxide layer reduced the reflection coefficient by a maximum of approximately 25% for He and less than half of this amount for H.

An analysis system using the time-of-flight technique has been developed to measure the energy spectra of light (H, He, N) ions and neutrals backscattered from solid surfaces. The system employs a 30–150 ns pulsed 5–20 keV ion beam to measure backscattered energy spectra down to approximately 500 eV. Sensitivity and energy resolution are studied by measuring backscattered spectra for silicon targets covered with thin silver films. Using He incident ions, the sensitivity is found to be better than 120 of a monolayer for silver on silicon. The sensitivity is limited by the system time resolution, fast sputtered particles from the target, and neutrals from the ion source. Energy resolution is approximately 5% for the experimental configuration. Charge fraction data for H, He, and N are discussed briefly.

Total scattering cross sections, the related recoil energy distributions, and damage energies are evaluated for 14 MeV neutrons and 10–20 MeV protons on Fe, Ni, Cu, Zr, Nb, and Au. The validity and limitations of using protons to simulate high energy neutron bombardment are discussed.

The design of a low temperature cryostat suitable for accelerator based radiation damage studies is presented. The system employs a commercial two-stage closed cycle helium gas cryorefrigerator and a mechanical heat switch to permit sample irradiations at 13–15 K and rapid temperatures cycling up to 300 K for post irradiation isochronal anneal studies. Al-In and Al-Ag switch contacts are evaluated for the cryostat.

Total reflection coefficients ( R ), backscattered energy fractions (γ), and backscattered energy spectra are evaluated using a binary collision Monte Carlo technique for a variety of light ions (H, D, T, He) in the energy range 0.25–8 keV, incident on amorphous targets (C, Fe, Nb). The scattering is also evaluated for H on Nb for a range of incident angles and two electronic stopping values. The average scattered energy per reflected particle and the backscattered energy spectra are found to vary in a universal manner as a function of the reflection coefficient between the Rutherford high energy limit and a low energy multiple collision limit. Single crystal effects are also briefly discussed using a diffusional dechanneling model.

Damage distributions in n-Si bombarded at 45 K with 10–40 keV H+ ions have been measured using the channeling technique. A comparison of the measured distributions with those determined using Monte Carlo calculation techniques indicates that (a) the electronic stopping cross-section is ∼ 60% higher than the standard Lindhard value over the energy range of 10–40 keV and, (b) calculated deposited energy distribution better approximates the measured displaced atom distribution if recoil energies < 50 eV are not included in the calculation. Annealing studies showed significant recovery occurring below 120 K compatible with vacancy migration.

Scattered energy distributions are calculated for light ions incident on Nb and Mo surfaces of interest for controlled nulcear fusion reactors. The scattered energy is found to vary as a function of the reflection coefficient between a multiple-collision limit at low energies and a single-collision Rutherford scattering limit at high energies. High-energy peaking of the scattered particle distributions is also found for low incident energies.

The design and the thin film characteristics of a refractory metal thin film evaporator-target chamber for keV ion backscattering studies are reported. High temperature evaporation is accomplished using a 3 kW electron beam at a background pressure of 10−9−10−10 torr. Vanadium films (300–1800 Å) are analysed using a variety of standard characterization techniques. The films are found to be relatively flat with a consistently reproducible polycrystalline B.C.C. microstructure.