[en] This report discusses the: Pisces Program; Pisces Facilities; Pisces Experiments: Materials and Surface Physics; Pisces Experiments: Edge Plasma Physics; and, Theoretical Analysis: Edge Plasma Behavior

[en] This program investigates and characterizes the behavior of materials under plasma bombordment, in divertor regions. The PISCES facility is used to study divertor and plasma edge management concepts (in particular gas target divertors), as well as edge plasma turbulence and transport. The plasma source consists of a hot LaB₆ cathode with an annular, water-cooled anode and attached drift tube. This cross sectional area of the plasma can be adjusted between 3 and 10 cm. A fast scanning diagnostic probe system was used for mapping plasma density profiles during biased limiter and divertor simulation experiments. Some experimental data are given on: (1) materials and surface physics, (2) edge plasma physics, and (3) a theoretical analysis of edge plasma modelling

[en] This paper briefly describes the following topics: an overview of graphite wall pumping effects; wall pumping experiments in PISCES-A; and non-saturable walls in toroidal devices. 11 figs., 2 tabs

[en] It is well known in the fusion engineering community that the plasma confinement performance in magnetic fusion devices is strongly affected by edge-plasma interactions with surface components. These plasma-material interactions (PMI) include fuel particle recycling and impurity generation both during normal and off-normal operation. To understand and then to control PMI effects, considerable effort has been made, particularly over the last decade in US, supported by Department of Energy, Division of Development and Technology. Also, because plasma-facing components are generally expected to receive significant amount of heat due to plasma bombardment and run-away electrons, materials must tolerate high-heat fluxes (HHF). The HHF-component research has been conducted in parallel with PMI research. One strong motivation for these research activities is that DT-burning experiments are currently planned in the Tokamak Test Fusion Reactor (TFTR) in early 1990s. Several different but mutually complementary approaches have been taken in the PMI+HHF research. The first approach is to conduct PMI experiments using toroidal fusion devices such as TFTR. The second one is to simulate elemental processes involved in PMI using ion beams and electron beams, etc. The last one but not least is to use non-tokamak plasma facilities. Along with these laboratory activities, new materials have been developed and evaluated from the PMI+HHF point of view. In this paper, several major PMI+HHF research facilities in US and their activities are briefly reviewed. 21 refs., 10 figs., 2 tabs

[en] This report discusses the following topics: PISCES-A facility; PISCES-B facility; PISCES-C facility; fast scanning probes; spectroscopic diagnostics; PISCES laboratory data acquisition system; SEM ampersand EDX facilities; vacuum outgassing facility; evaluation of bulk-boronized graphites; chemical sputtering of C-C composites; D-retention in redeposited carbon; TEXTOR-exposed graphite; oxygen plasma reactions with graphite; gaseous divertor simulation; experimental; proof of RF-limiter; H-mode transition by DC-biasing; edge-plasma physics experiments in the CCT-tokamak; and He-spectroscopy for edge-plasma diagnosis

[en] A simple method is proposed to describe the hydrogen reemission behavior from a reactive metal film in which the implanted hydrogen concentration may exceed the dilute solution range under some conditions. In this method, the conventional thermodynamic information for the metal system, namely, the phase diagram and the P-C-T (Pressure-Concentration-Temperature) relation, is used extensively to determine the reemitted hydrogen flux. As a specific case, this method has been applied to the hydrogen reemission from a titanium film

[en] This publication comprises papers from the PISCES and ALT-II Programs at UCLA which were presented at the International Plasma Surface Interactions Meeting held in Juelich, FRG, on May 2-6, 1988. A list of publications from the PISCES and ALT-II contained in this report are: Deuterium pumping and erosion behavior of selected graphite materials under high flux plasma bombardment in PISCES; Erosion and redeposition behavior of selected NET-candidate materials under high-flux hydrogen, deuterium plasma bombardment in PISCES; Presheath profiles in simulated tokamak edge plasmas; Boundary asymmetries and plasma flow to the ALT-II toroidal belt pump limiter; ALT-II toroidal belt pump limiter performance in TEXTOR; and An in-situ spectroscopic erosion yield measurement with applications to sputtering and surface morphology alterations

[en] Full text: It is widely recognized that particle balance in magnetic fusion devices is a critical issue, affecting the overall machine performance, fuel economy and even environmental safety. This is particularly true with future steady-state fusion devices. For short-pulsed experiments in currently operating devices, core plasma density control is often done with the help of wall pumping effects. By nature, however, wall pumping is saturable. Cryo-pumps are often employed to obtain a large pumping speed. Unfortunately, cryo-pumping has also a finite capacity, leading to the necessity of developing new concepts of non-saturable wall. To provide a technical guidance on the new concept development for plasma-facing components (PFCs), in the present work zero-dimensional particle balance modeling has been performed under conditions, relevant to those employed in LHD and also ITER, assuming 4 reservoirs; (1) core plasma; (2) Scrape-Off-Layer (SOL); (3) gas phase; and (4) wall. The particle confinement times are defined respectively for the core plasma and SOL regions. Along with ordinary vacuum pumping, wall pumping due to co-deposition and inward diffusion can be assumed in this model, as shown in the case study shown below. Effects of wall pumping on the overall particle balance will be discussed in detail. The modeling result from a case study on the density decay observed in LHD in the second campaign, when PFCs were made of stainless steel, is shown. Copyright (2002) Australian National University- Research School of Physical Sciences and Engineering

[en] The first in-depth investigation of surface modification of materials by continuous, high-flux argon plasma bombardment under simultaneous erosion and redeposition conditions have been carried out for copper and 304 stainless steel using the PISCES facility. The plasma bombardment conditions are: incident ion flux range from 10¹⁷ to 10¹⁹ ions sec^-1cm^-2, total ion fluence is controlled between 10¹⁹ and 10²² ions cm^-2, electron temperature range from 5 to 15 eV, and plasma density range from 10¹¹ to 10¹³cm^-3. The incident ion energy is 100 eV. The sample temperature is between 300 and 700K. Under redeposition dominated conditions, the material erosion rate due to the plasma bombardment is significantly smaller (by a factor up to 10) than that can be expected from the classical ion beam sputtering yield data. It is found that surface morphologies of redeposited materials strongly depend on the plasma bombardment condition. The effect of impurities on surface morphology is elucidated in detail. First-order modelings are implemented to interpret the reduced erosion rate and the surface evolution. Also, fusion related surface properties of redeposited materials such as hydrogen reemission and plasma driven permeation have been characterized

[en] The modification of surfaces during exposure to plasma bombardment is a critical issue in the development of limiter and wall materials for fusion confinement experiments. Controlled studies of the erosion and redeposition of materials during high flux and fluence plasma exposure are now possible in the PISCES facility. PISCES is a continuously operating plasma device which has achieved hydrogen plasma densities of over 10¹³ cm^-3 and electron temperatures of 5 to 24 eV over large areas. Ion fluxes of 10¹⁷ to 10¹⁹ cm^-2 sec^-1 and fluences of up to 10²³ cm^-2 have been used to bombard biased samples inserted into the plasma. The plasma parameters can be selected to produce simple sputtering, or redeposition by the ionization and recycling of the sputtered target materials. Collaborative studies on the performance of Cu and Cu-Li alloys (with ANL), stainless steel (with SNLL), and graphite (with IPP at Garching, and SNLL) have been undertaken. Surface topography modification is always observed after a sufficient fluence is achieved. The net erosion rate is significantly lower during redeposition than one would expect from classical sputtering yields. The transport and deposition of different materials by the plasma to the samples during redeposition conditions results in greatly modified surface composition and morphology. Chemical sputtering of graphite during low energy, high flux (>10¹⁸ cm^-2 sec^-1) plasma bombardment is observed. Chemically formed hydrocarbons are relatively easily redeposited compared to sputtered carbon. The performance of these materials, the surface morphology evolution, and the characteristics of the redeposited materials are discussed