(EX/9-3) Dust Studies in DIII-D and TEXTOR

D.L. Rudakov1), A. Litnovsky2), W.P. West3), J.H. Yu1), J.A. Boedo1), B.D. Bray3), S. Brezinsek2), N.H. Brooks3), M.E. Fenstermacher4), M. Groth4), E.M. Hollmann1), A. Huber2), A.W. Hyatt3), S.I. Krasheninnikov1), C.J. Lasnier4), R.A. Moyer1), A.Yu. Pigarov1), V. Philipps2), A. Pospieszczyk2), R.D. Smirnov1), J.P. Sharpe5), W.M. Solomon6), J.G. Watkins7), C.P.C. Wong3)
1) University of California-San Diego, La Jolla, United States of America
2) Institut für Energieforschung-Plasmaphysik, Forschungszentrum Jülich, Association EURATOM-FZJ, 52425 Germany
3) General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
4) Lawrence Livermore National Laboratory, Livermore, California 94551, USA
5) Idaho National Engineering and Environmental Laboratory, Fusion Safety Program, Idaho Falls, Idaho 83415, USA
6) Princeton Plasma Physics Laboratory, Princeton, New Jersey, USA
7) Sandia National Laboratories, Albuquerque, New Mexico 87185, USA

Abstract.  Studies of naturally occurring and artificially introduced carbon dust are conducted in DIII-D and TEXTOR. Dust production and accumulation impose safety and operational concerns for ITER by contributing to tritium inventory rise and leading to radiological and explosion hazards. In DIII-D, dust does not present operational concerns except immediately after entry vents. In the first 2 - 3 plasma discharges after an entry vent cameras detect thousands of dust particles per discharge. After a few days of operations (∼70 discharges) dust levels are reduced to a few observed events per discharge. Energetic plasma disruptions produce significant amounts of dust. However, dust production by disruptions alone is insufficient to account for the estimated in-vessel dust inventory in DIII-D. Submicron sized dust is routinely observed using Mie scattering from a Nd:Yag laser. The source is strongly correlated with the presence of Type I ELMs. Migration of pre-characterized carbon dust is studied in DIII-D and TEXTOR by injecting micron-size dust in plasma discharges. In DIII-D, a sample holder filled with ∼30 mg of dust is introduced in the lower divertor and exposed to high-power lower single-null ELMing H-mode discharges with strike points swept across the divertor floor. After a brief exposure (∼0.1 s) at the outer strike point, part of the dust is injected into the plasma, raising the core carbon density by a factor of 2 - 3 and resulting in a twofold increase of the radiated power. Individual dust particles are observed moving at velocities of 10 - 100 m/s, predominantly in the toroidal direction, consistent with the drag force from the deuteron flow and in agreement with modelling by the 3D DustT code. In TEXTOR, instrumented dust holders with 1 - 45 mg of dust are exposed in the scrape-off layer 0 - 2 cm radially outside of the last closed flux surface in neutral beam heated discharges (NBI power of 1.4 MW). Dust is launched either in the beginning of the discharge or at the initiation of NBI. Preliminary analysis of the video sequences show the launch of dust perpendicular to the toroidal magnetic field presumably because of E×B drift.

This work supported by the US Department of Energy under DE-FG02-04ER54758, DE-FC02-04ER54698, DE-AC52-07NA27344, and DE-AC04-94AL85000.

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