Title: Helium experiments on Alcator C-Mod in support of ITER early operations

Abstract

Helium majority experiments on Alcator C-Mod were performed to compare with deuterium discharges, and inform ITER early operations. ELMy H-modes were produced with a special plasma shape at B_T = 5.3 T, I _P = 0.9 MA, at q₉₅ ~ 3.8. The He fraction ranged over, n _He,L/n_L = 0.2–0.4, with n _D,L/n _L = 0.15–0.26, compared to D plasmas with n _D,L/n _L = 0.85–0.97. The power to enter the H-mode in He was found to be greater than ~2 times that for D discharges, in the low density region <1.4 × 10²⁰/m³. However, it appears to follow the D threshold for higher densities. The stored energies in the He discharges were about 80% of those in D, and about 40% higher net power was required to sustain them compared to D. Global particle confinement times for tungsten of $$\tau _{{\rm W}}^{{\rm *}}$$ /τ _E ~ 4 were obtained with ELMy H-modes in He, however accumulation occurred when the ELMs were irregular and infrequent. The electron temperatures and densities in the pedestal were similar between D and He discharges, and the ΔT _e/T _e and Δn _e/n _e values were similar or larger in He than D. The higher net power required to access the H-mode, and sustain it in flattop, for He discharges in C-Mod, imply some limitations for He operation in ITER.

Authors:

Kessel, C. E.  ^[1];

• Search DOE PAGES for author "Kessel, C. E."
• Search DOE PAGES for ORCID "0000-0002-2072-1134"

Wolfe, S. M. ^[2]; Reinke, M. L. ^[3]; Hughes, J. W.  ^[2];

• Search DOE PAGES for author "Hughes, J. W."
• Search DOE PAGES for ORCID "0000-0003-4802-4944"

Lin, Y. ^[2]; Wukitch, S. J. ^[2]; Baek, S. G. ^[2]; Bonoli, P. T. ^[2]; Chilenski, M. ^[2]; Diallo, A. ^[1]

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+ Show Author Affiliations

1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Publication Date:

Tue Mar 13 00:00:00 EDT 2018

Research Org.:

Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

Sponsoring Org.:

USDOE

Contributing Org.:

the Alcator C-Mod Team

OSTI Identifier:

1432049

Grant/Contract Number:  

AC02-09CH11466; FC02-99ER54512

Resource Type:

Accepted Manuscript

Journal Name:

Nuclear Fusion

Additional Journal Information:

Journal Volume: 58; Journal Issue: 5; Journal ID: ISSN 0029-5515

Publisher:

IOP Science

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; tokamak; helium discharge; ITER; ELMy H-mode