Trends in runaway electron plateau partial recombination by massive H 2 or D 2 injection in DIII-D and JET and first extrapolations to ITER and SPARC

Nuclear Fushion

article

E.M. Hollmann¹  L. Baylor²  A. Boboc³  P. Carvalho³  N.W. Eidietis⁴  J.L. Herfindal²  S. Jachmich⁵  A. Lvovskiy⁴  C. Paz-Soldan⁶  C. Reux⁷  D. Shiraki²  R. Sweeney⁸ 

[1] University of California—San Diego;Oak Ridge National Laboratory;CCFE, UKAEA, Culham Science Centre;General Atomics;ITER Organization;Department of Applied Physics, Columbia University;CEA;Massachusetts Institute of Technology

关键词: tokamak;    runaway electrons;    ITER;   

DOI  :  10.1088/1741-4326/acb4aa

来源: Institute of Physics Publishing Ltd.

【 摘 要 】

Experimental trends in thermal plasma partial recombination resulting from massive {{ext{D}}_2}injection into high-Z (Ar) containing runaway electron (RE) plateaus in DIII-D and JET are studied for the purpose of achieving sufficiently low electron density ({n_{ext{e}}} approx {10^{18}}{{ext{m}}^{ - 3}} ) to increase RE final loss MHD levels. In both DIII-D and JET, thermal electron density {n_{ext{e}}}is found to drop by ∼100imeswhen the thermal plasma partially recombines, with a minimum at a vacuum vessel-averaged {{ext{D}}_2}density in the range {10^{20}}!!-!!{10^{21}}{{ext{m}}^{ - 3}} . RE effective resistivity also drops after partial recombination, indicating expulsion of the Ar content. The {n_{ext{e}}}level after partial recombination is found to increase as RE current is increased. The amount of initial Ar in the RE plateau is not observed to have a strong effect on partial recombination. Partial recombination timescales of order 5 ms in DIII-D and 15 ms in JET are observed. These basic trends and timescales are matched with a 1D diffusion model, which is then used to extrapolate to ITER and SPARC tokamaks. Within the approximations of this model, it is predicted that ITER will be able to achieve sufficiently low {n_{ext{e}}}values on time scales faster than expected RE plateau vertical drift timescales (of order 100 ms), provided sufficient {{ext{D}}_2}or {{ext{H}}_2}is injected. In SPARC, it is predicted that achieving significant {n_{ext{e}}}recombination will be challenging, due to the very high RE current density. In both ITER and SPARC, it is predicted that achieving low {n_{ext{e}}}will be easier with Ar as a background impurity (rather than Ne).

【 授权许可】

Unknown