Kim, Y.-M. (Corresponding author)

1999
Forschungszentrum, Zentralbibliothek Jülich

Report No.: Juel-3670

Abstract: The recently in TEXTOR-94 discovered Radiative Improved mode (RI-mode) plasmas, at which a radiating plasma boundary is produced by a controlled seeding of impurities such as neon or argon, are showing an improved energy- and particle-confinement. Despite the importance of the characteristics of retention and recycling of the impurities seeded, there are only a few direct investigations concerning this. For a better understanding of the Rl-mode, the characteristics of retention and recycling of neon, argon and xenon in and on graphite were investigated in ion beam experiments and in Rl-mode plasma ofTEXTOR-94. The retention and reemission processes of neon and argon in graphite (EK98) were investigated in an ion beam apparatus with ion energies between 2 and 10 keY. In the early phase of irradiation the majority of incident ions are retained. After saturation, the reemission reaches unity. The desorption processes of both neon and argon are first order ones. Argon, in comparison with neon, has a broader desorption spectra with a higher maximum temperature (850 K, Eb = 2.06 eV, for argon and 780 K, Eb = 2.35 eV for neon). The retention at saturation is almost independent of ion energy. The saturation concentration of neon (Ne/C = 0.15 for 10 keY Ne+ up to Ne/C =0.55 for 2 keY Ne+) is larger than that of argon (Ar/C =0.06 for 10 keY Ar+ up to Ar/C =0.18 for 3 keY Ar+). Ion induced release of neon was simulated by irradiating the neon saturated graphite with deuterium ion. In this trial no ion induced release was observed. However, for a better simulation of this effect under TEXTOR plasma conditions, lower ion energies of neon and deuterium and larger fluence of deuterium are needed. With increasing sample temperature less neon and argon are retained in graphite during the irradiation with ion beams and above 1200 K no retention is observed. No diffusion of neon and argon was measured at room temperature. For argon additional experiments were carried out, in which no diffusion of argon up to 800 K was observed.

Keyword(s): plasma impurity ; plasma wall interaction

1. Plasmaphysik (IEF-4)