(IT/P1-2) Benchmarking of Lower Hybrid Current Drive Codes with Application to ITER-Relevant Regimes

P.T. Bonoli1), R.W. Harvey2), C. Kessel3), F. Imbeaux4), T. Oikawa5), M. Schneider4), E. Barbato6), J. Decker4), G. Giruzzi4), C.B. Forest7), S. Ide5), Y. Peysson4), A.E. Schmidt1), A.C.C. Sips8), A.P. Smirnov2), A. Tuccillo6), J.C. Wright1)
1) Plasma Science and Fusion Center, MIT, Cambridge, MA 02139, USA.
2) CompX, Del Mar, CA 92014, USA.
3) Princeton Plasma Physics Laboratory, Princeton, NJ 08543, USA.
4) Association EURATOM-CEA, CEA, Cadarache, FRANCE.
5) Naka Fusion Research Establishment, JAERI, Ibaraki-ken, JAPAN.
6) Associazione EURATOM-ENEA, Frascati (Roma), ITALY.
7) University of Wisconsin, Madison, WI 53706, USA.
8) Max Planck Institut für Plasmaphysik, Garching, GERMANY.

Abstract.  Lower hybrid (LH) waves have the attractive property of damping strongly via electron Landau resonance on relatively fast tail electrons. Consequently these waves are well-suited to driving current in the plasma periphery where the electron temperature is lower, making lower hybrid current drive (LHCD) a promising technique for off-axis current profile control in reactor grade plasmas. In addition, the RF source frequency can be chosen high enough to minimize the parasitic interaction of LH waves with fusion-generated alpha particles. The relatively high phase speed also minimizes deleterious effects due to particle trapping which can become important in the periphery. Given these physics considerations, we have undertaken a detailed benchmarking exercise in which we compared the predictions of several advanced simulation models for LHCD using a test case based on a proposed steady state operating mode (Scenario #4) for the ITER-FEAT device [ITER Technical Basis Document (IAEA, Vienna, 2001) Doc. No. GAO FDR 1 00-07-13 R1.0, Section 4.3.3]. The most advanced models that we have used combine a 3D Fokker Planck calculation with a toroidal ray tracing package. The modules iterate to compute a self-consistent nonthermal electron distribution function. Preliminary estimates for ITER-FEAT [ITER Technical Basis Document (IAEA, Vienna, 2001) Doc. No. GAO FDR 1 00-07-13 R1.0, Section 4.3.3] indicate that 2.0 MA of LH current can be generated at r/a = 0.60-0.65, using 30 MW of LHRF power. The advanced Fokker Planck - ray tracing code predictions have also been compared with simulation models that combine a response function treatment of the Fokker Planck equation with a 1D parallel velocity damping estimate, where the collision operator has been corrected for 2D velocity space effects due to pitch angle scattering. We shall also present recent calculations of the LH wave-alpha particle interaction using a Monte Carlo orbit following code, and discuss their implications in terms of the choice of LH source frequency. These results strongly promote the scientific case for the use of LHCD on ITER, in that sophisticated and benchmarked tools are now

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