Title: 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

Abstract

Experimental trends in thermal plasma partial recombination resulting from massive $${{\text{D}}_2}$$ 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 ($${n_{\text{e}}} \approx {10^{18}}{{\text{m}}^{ - 3}}$$) to increase RE final loss MHD levels. In both DIII-D and JET, thermal electron density $${n_{\text{e}}}$$ is found to drop by ~100$$ \times $$ when the thermal plasma partially recombines, with a minimum at a vacuum vessel-averaged $${{\text{D}}_2}$$ density in the range $${10^{20}}\!\!-\!\!{10^{21}}{{\text{m}}^{ - 3}}$$. RE effective resistivity also drops after partial recombination, indicating expulsion of the Ar content. The $${n_{\text{e}}}$$ 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 $${n_{\text{e}}}$$ values on time scales faster than expected RE plateau vertical drift timescales (of order 100 ms), provided sufficient $${{\text{D}}_2}$$ or $${{\text{H}}_2}$$ is injected. In SPARC, it is predicted that achieving significant $${n_{\text{e}}}$$ recombination will be challenging, due to the very high RE current density. In both ITER and SPARC, it is predicted that achieving low $${n_{\text{e}}}$$ will be easier with Ar as a background impurity (rather than Ne).

Authors:

Hollmann, E. M.; Baylor, L.; Boboc, A.; Carvalho, P.; Eidietis, N. W. ;

• Search DOE PAGES for author "Eidietis, N. W."
• Search DOE PAGES for ORCID "0000-0003-0167-5053"

Herfindal, J. L. ;

• Search DOE PAGES for author "Herfindal, J. L."
• Search DOE PAGES for ORCID "0000-0003-2846-597X"

Jachmich, S.; Lvovskiy, A. ;

• Search DOE PAGES for author "Lvovskiy, A."
• Search DOE PAGES for ORCID "0000-0002-3649-1169"

Paz-Soldan, C. ;

• Search DOE PAGES for author "Paz-Soldan, C."
• Search DOE PAGES for ORCID "0000-0001-5069-4934"

Reux, C. ;

• Search DOE PAGES for author "Reux, C."
• Search DOE PAGES for ORCID "0000-0002-5327-4326"

Shiraki, D.; Sweeney, R.

• Search DOE PAGES for author "Sweeney, R."
• Search DOE PAGES for ORCID "0000-0003-3408-1497"

Publication Date:

Thu Feb 02 00:00:00 EST 2023

Research Org.:

General Atomics, San Diego, CA (United States); University of California-San Diego, La Jolla, CA (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES)

OSTI Identifier:

1922864

Alternate Identifier(s):

OSTI ID: 1909948; OSTI ID: 1960104; OSTI ID: 1998189; OSTI ID: 2320365

Grant/Contract Number:  

AC05-00OR22725; FG02-07ER54917; FC02-04ER54698; AC52-07NA27344; FG02-04ER54744; SC0020296; SC0020299; SC0022270; AC05-06OR23100

Resource Type:

Published Article

Journal Name:

Nuclear Fusion

Additional Journal Information:

Journal Name: Nuclear Fusion Journal Volume: 63 Journal Issue: 3; Journal ID: ISSN 0029-5515

Publisher:

IOP Publishing

Country of Publication:

IAEA

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; tokamak; runaway electrons; ITER