DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 327: Understanding the role of wall sources and sinks during RMP H-modes | ||
| Name: | Todd E. Evans ( |
Affiliation: | General Atomics |
| Research Area: | ELM Control & Pedestal Physics | Presentation time: | Not requested | Co-Author(s): | tbd |
| Description: | The goal of this experiment is to understand the relative importance of wall sources and sinks in determining the rate of density decay and the saturated density level during RMP ELM control experiments. Can the density decay rate and final density in the ELM suppressed state be altered with plasma shape changes, the lenght of the glow between plasma discharges or the delay between the L-H transition and the I-coil pulse. | ||
| Experimental Approach/Plan: | Establish long reproducible ELM suppressed RMP H-modes with the largest possible I-coil current starting at approximately the same time as the first ELM following the L-H transition with 7 minute glow between plasmas. Reproduce this case at lease 4 times or until the rate of density decay remains constant from shot to shot. Delay the start of the I-coil pulse by 1 s and compare the denstiy decay rate and saturated density level with the previous shots. Repeat this sequence several times adding a 1 s delay in the I-coil pulse at each step. Reduce the length of the glow to 3 minutes and repeat that last few steps of the previous case. Repeat with no glow. If time premits repeat the 7 minute glow sequence with dRsep increased to approximately zero and the upper x-point positioned for maximum pumping with the upper cyropumps. | ||
| Background: | Previous RMP H-mode experiments have shown significant differences in the amount of density pump out that appears to be related to changes in wall conditions (i.e., the relative contributions of neutral sources and sinks dur to the walls). In some cases the saturated density during the ELM suppressed phase is of order 50-60% of that before the I-coil pulse and in other cases it is of orser 5-10% of the pre-I-coil density. An analysis of the cryopump data indicated that these differences are not due to changes in the pumping throughput. It is important to understand the wall are involved in the density pump out effect because the wall conditions in ITER will be very different than those in DIII-D and the RMP may not result in a large density pump out in that case. There is also evidence that the level of the saturated density is not a critical parameter for ELM suppression suggexting that the physics of RMP EM suppression may not be uniquely related to changes in the pedestal pressure gradient. | ||
| Resource Requirements: | 7 kA I-coil and stable wall conditions (i.e., ths experiment should not be scheduled following any days that will have an adverse effect on the condition of the walls). | ||
| Diagnostic Requirements: | ELM and pedestal diagnostics | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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