DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 183: Improved Gas Jet Disruption Mitigation by I-coil-Enhanced Impurity Transport | ||
| Name: | Dave Humphreys ( |
Affiliation: | General Atomics |
| Research Area: | Disruptions | Presentation time: | Requested | Co-Author(s): | T. Evans, E. Hollman, T. Jernigan, J. Wesley |
| Description: | Explore possible improvements to disruption mitigation effects by massive gas injection using the I-coil to impose high Chirikov parameter fields on pre-disruption and plasmas and during injection. | ||
| Experimental Approach/Plan: | Move standard disruption target plasmas into close proximity of I-coil and gas jet (R+1) to increase penetration of I-coil field (high Chirikov parameter). Establish baseline jet injection pre-emptive disruption mitigation without I-coil field. Then test several different scenarios, including cases with I-coil at full current/field before firing gas jet, and ramping field as jet fires; high vs low frequency time-varying I-coil field; and using either Ar or D+Ar. | ||
| Background: | Recent experiments with impurity injection to mitigate disruption effects have shown severe limits to both impurity neutrals and ions producing electron assimilation fractions below 10% of the Rosenbluth density. While massive impurity injection appears to effectively mitigate many damaging disruption effects including divertor heat loads and halo current forces, mitigation of runaway electrons via thermal (free+bound) electron collisions will require much increased transport in order to place the necessary particle density deep in the core where runaways are expected to be born. RMP experiments have suggested that I-coil fields with high Chirikov parameter can enhance particle transport at the edge, helping to reduce the energy in the pedestal and suppress ELMs. Using the same principle in a pre-emptively mitigated disruption may serve to improve impurity particle transport in the same way. Varying the I-coil current slowly or rapidly may serve to further stochastize the edge field and further enhance particle transport. Even if the transport only serves to increase the impurity density to within the rho~0.90 surface, the ensuing global MHD events may transport a larger number of ions into the core than when the ion population is confined to the SOL or outside. | ||
| Resource Requirements: | Massive gas jet hardware (MEDUSA valve), Ar, D+Ar gases | ||
| Diagnostic Requirements: | Usual disruption diagnostics: 5 kHz magnetics, DISRAD, Thomson, new IR camera strongly desirable, fast cameras (LLNL and UCSD) | ||
| Analysis Requirements: | KPRAD, other impurity/radiation codes; | ||
| Other Requirements: | -- | ||
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