DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 14: Develop near-balanced NBI for use in intrinsic rotation scaling experiments. | ||
| Name: | John Degrassie ( |
Affiliation: | General Atomics |
| Research Area: | Rotation Physics (2009) | Presentation time: | Requested | Co-Author(s): | J.Rice, W. Solomon, J. Ferron |
| Description: | We want to develop an understanding of how to use near-balanced NBI to raise BetaN and still accurately measure the intrinsic rotation. For relevance, the discharges will be dominated by ELMing H-modes, or if we can achieve RMP ELM-suppression with near-balanced NBI, this would be extremely valuable for a target discharge. Scans will be taken with varying degrees of near-balanced NBI added to ECH. We will go from ECH only to NBI only. We want the greatest range in BetaN attainable. Density scans will be needed because it is anticipated that the local torque density in near-balanced NBI will depend upon the NBI deposition profile. Scans in q95 should also be taken. It may facilitate the experiment to use Ferron's feedback of NBI torque on W/Ip, which we did not get to try in 2007. | ||
| Experimental Approach/Plan: | The majority of discharges will be H-modes. ELMing H-modes are desirable for more steady state conditions. If we can get RMP ELM stabilization in near-balanced conditions, this would provide an excellent target. The goal will be to show that we can follow Rice's scaling with a mixture of ECH and near-balanced NBI, going from essentially all ECH to much higher power NBI + ECH. We anticipate that detailed analysis will show that these intrinsic rotation values will be obtained with near zero NBI torque density inside of rho of about 0.8. Density scans will be very important since the torque density profile will depend somewhat on the NBI deposition profile. It is also important to do different Ip scans, that is, get more than one data path in the expected increase in intrinsic toroidal velocity with W. This experiment will be facilitated by using John Ferron's new capability to feed back torque on W, put into the pcs but not tried in 2007. | ||
| Background: | John Rice's scaling shows that intrinsic toroidal velocity increases with W/Ip, the plasma stored energy over the magnitude of the plasma current. The increase is in the co-Ip direction. This scaling has been found apply in many tokamaks, as described in Rice's 2006 IAEA paper. In DIII-D ECH H-modes, and Ohmic H-modes, we find this scaling near the outer ¾ region of the minor radius with the intrinsic velocity in the center apparently affected by something to do with ECH. This scaling can be recast as velocity increasing with BetaN, for a fixed machine size and fixed B. To date the points in the multi machine database barely exceed BetaN ~ 1 because they are from Ohmic discharges or RF-heated L- and H-mode discharges. We need NBI power to increase BetaN in order to have any confidence in an extrapolation toward ITER. But the large torques in the co- and counter-Ip NBI make this balance a sensitive one.
We have clear evidence of intrinisic rotation in the midst of near-balanced NBI, but moving to confidence that we can accurately measure the intrinsic rotation in such a case takes more work. For example, we need to develop a methodology wherein we can look at a case (with all the analysis codes) and say that we are seeing the remnant intrinsic rotation in the midst of 10 MW of near-balanced beam power, plus ECH, that has brought BetaN up to ~ 3! | ||
| Resource Requirements: | NBI: ideally all 7, minimally 21R/L, 30L, 33L/R
ECH: more is better, minimally 2 gyrotrons, enough to get H-mode in LSN in the good direction. | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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