Studies of Impurity Assimilation During Massive Argon Gas Injection in DIII-D

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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 ... continued below

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6 p. (0.4 MB)

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Hollmann, E; Jernigan, T; Parks, P; Baylor, L; Boedo, J; Combs, S et al. June 27, 2007.

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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.

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6 p. (0.4 MB)

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PDF-file: 6 pages; size: 0.4 Mbytes

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  • Journal Name: Proceedings of the 34th EPS Conference on Plasma Physics, vol. 31F, na, July 2, 2007, P1.128; Journal Volume: 31F

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  • Report No.: UCRL-JRNL-232261
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 940868
  • Archival Resource Key: ark:/67531/metadc902323

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  • June 27, 2007

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  • Sept. 27, 2016, 1:39 a.m.

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  • April 17, 2017, 12:21 p.m.

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Hollmann, E; Jernigan, T; Parks, P; Baylor, L; Boedo, J; Combs, S et al. Studies of Impurity Assimilation During Massive Argon Gas Injection in DIII-D, article, June 27, 2007; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc902323/: accessed September 26, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.