Studies of Impurity Assimilation During Massive Argon Gas Injection in DIII-D
Fast shutdown of discharges using massive gas injection (MGI) is a promising technique for reducing tokamak wall damage during disruptions [1]. An outstanding concern, however, is the generation of runaway electrons (RE) during the shutdown. Although RE formation observed during MGI in present-day experiments is quite small (typically <1% of the main plasma current I{sub p} in DIII-D), it is thought that even this small RE current could be amplified to significant levels in reactor-scale tokamaks such as ITER [2]. It is expected that complete collisional suppression of any potential RE amplification during the CQ can be achieved for suppression parameters {gamma}{sub crit} {triple_bond} E{sub crit}/E{sub {psi}} > 1, where E{sub crit} = [2{pi}e{sup 3}ln{Lambda}(2n{sub e} + n{sub B})]/mc{sup 2} is the critical electric field [2] and E{sub {psi}} {approx} -[({mu}{sub 0}l{sub i})/4{pi}][-({partial_derivative}I{sub p}/{partial_derivative}t)+ {alpha}{sub L}(I{sub W}/{tau}{sub W})] is the toroidal electric field resulting from the decay of the plasma current I{sub p}. n{sub e} is the free electron density, n{sub B} is the bound electron density, {alpha}{sub L} {approx} 2[ln(8R/r{sub w})-2]/l{sub i} is the ratio of external (outside conducting wall) to internal (inside conducting wall) self-inductance, I{sub w} is the wall current, and {tau}{sub w} is the wall time. The densities required to achieve {gamma}{sub crit} > 1 are typically quite large, e.g. n{sub tot} {triple_bond} n{sub e} + n{sub B}/2 {approx} 10{sup 16} cm{sup -3} for DIII-D. To have a possibility of achieving the required density in the DIII-D plasma (with volume V{sub p} {approx} 20 m{sup 3}), an MGI system using argon must be able to deliver of order 10{sup 22} argon atoms to the plasma within the shutdown timescale of about 10 ms.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 940868
- Report Number(s):
- UCRL-JRNL-232261; TRN: US0807230
- Journal Information:
- Proceedings of the 34th EPS Conference on Plasma Physics, vol. 31F, na, July 2, 2007, P1.128, Vol. 31F
- Country of Publication:
- United States
- Language:
- English
Similar Records
DIII-D Studies of Massive Gas Injection Fast Shutdowns for Disruption Mitigation
Relative merits of size, field, and current on ignited tokamak performance: A comparison of ''CITs'' and ''Super-JETs''