Studies of the Structure of C Pellet Ablation Clouds in W7-AS

Journal Article · Fri Apr 15 04:00:00 EDT 2005 · Plasma Physics Reports

DOI:https://doi.org/10.1134/1.1904144· OSTI ID:20717512

Bakhareva, O A; Sergeev, V Yu; Kuteev, B V; Skokov, V G; Timokhin, V M ^[1]; Burhenn, R ^[2]

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1. State Polytechnical University, Politekhnicheskaya ul. 29, St. Petersburg, 195251 (Russian Federation)
2. Max Planck Institut fuer Plasmaphysik, Sub-Institute Greifswald, EURATOM Association, Wendelsteinstrasse 1, 17491 Greifswald (Germany)

The structure of the ablation clouds surrounding carbon pellets injected into the ECR-heated Wendelstein 7-AS plasma has been studied. Snapshot and integrated photographs obtained in the spectral ranges containing the CII (720 {+-} 5 nm and 723 {+-} 1 nm) and CIII (770 {+-} 5 nm) spectral lines were analyzed over a wide range of the bulk plasma parameters. It is found that the cloud luminosity profile along the magnetic field is exponential with either one or two characteristic decay lengths of about a few millimeters and a few centimeters. The smaller length corresponds to the zone closer to the pellet. There is good agreement between the characteristic decay lengths deduced from snapshot and integrated photographs. The characteristic decay lengths were obtained along the entire pellet trajectory and were found to change weakly in the central region and to grow at the plasma periphery (generally, in inverse proportion to the plasma electron density). In the central region, the characteristic decay lengths are about a few millimeters and 1 cm. They depend weakly on the bulk plasma temperature and decrease with increasing bulk plasma density. These lengths agree fairly well with estimates of the ionization length of carbon ions into the C{sup 2+}, C{sup 3+}, and C{sup 4+} charge states, respectively, assuming that ionization is provided by the hot electrons of the bulk plasma and that the cloud expands with the ion-acoustic velocity at a temperature of {approx}1 eV. The results obtained prove that the cloud structure in the vicinity of the pellet is mainly determined by the bulk plasma electrons.

• OSTI ID: 20717512
• Journal Information: Plasma Physics Reports, Journal Name: Plasma Physics Reports Journal Issue: 4 Vol. 31; ISSN PPHREM; ISSN 1063-780X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ABLATION
CARBON IONS
CHARGE STATES
ELECTRON DENSITY
ELECTRON TEMPERATURE
ELECTRONS
EV RANGE
ION TEMPERATURE
IONIZATION
LENGTH
MAGNETIC FIELDS
PLASMA
PLASMA CONFINEMENT
PLASMA DENSITY
PLASMA DIAGNOSTICS
RF SYSTEMS
WENDELSTEIN-7 STELLARATOR