1 / 4

XP-826: Investigation of “X-point limiter” plasmas M. Bell, R. Maingi, K-C. Lee

XP-826: Investigation of “X-point limiter” plasmas M. Bell, R. Maingi, K-C. Lee. Define LCFS by a limiter contact close to and just inside the X-point An alternative to conventional poloidal divertor H-mode has been obtained reliably without an X-point on the boundary

selena
Download Presentation

XP-826: Investigation of “X-point limiter” plasmas M. Bell, R. Maingi, K-C. Lee

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. XP-826: Investigation of “X-point limiter” plasmas M. Bell, R. Maingi, K-C. Lee • Define LCFS by a limiter contact close to and just inside the X-point • An alternative to conventional poloidal divertor • H-mode has been obtained reliably without an X-point on the boundary • Flux expansion near X-point and tangential contact spread heat load • XP-826 tried to make an X-point limiter on lower outer divertor plate • SOL contact at location of Liquid Lithium Divertor plates • Approach • Start with 0.9MA, 65kA TF LSN plasma with 2-source NBI • Set PF2L/Ip = 4kA/MA, PF2U/Ip = 2.5kA/MA; PF1AL/Ip, PF1AU/Ip to zero • Adjust vertical position down and, depending on the variation in li, adjust PF2L/Ip to bring the X-point close to lower outer divertor plate • Attempt feedback control of the X-point location with rtEFIT • Repeat shots to condition contact point then assess H-mode access • Experiment could also provide X-point height scan (proposed by K-C. Lee)

  2. Ip 0.9MA; ITF -65kA; PNBI 4.0MW XP≠826 -1.4 Center column XP=826 ZX-point (m) -1.6 Inner divertor Outer divertor 0.2 0.4 0.6 0.8 RX-point (m) Discharges Produced with X-Point Close to Outboard Divertor Plate • ~4 hours total runtime on 3 days (4/25, 5/2, 6/16) • Essentially as “filler” on latter 2 days • 12 productive shots plus initial baseline shot 128756, 0.3s

  3. Stability Appeared to be Reduced • Higher TF needed to maintain q95 > 7 • H-mode transition occurred while plasma limited on inner wall • Confinement appears similar to pre-lithium shots in standard LSN shape • Reduced lower triangularity 0.3–0.4 expected to reduce N limit • Not able to assess conditioning effect with small number of shots • Shots after lithium experiments collapsed at even lower N

  4. Experiment was Limited Success • X-point limiter configuration was achieved transiently • Provides a proof-of-principle for experiments with LLD • Appears to be compatible with H-mode • Need to optimize control strategy to improve reproducibility • Using dRsep control may not be best method • X-point control has not been used routinely on NSTX • Increasing cross-sectional area (taller, fatter plasma) would relax need for high TF (65kA) and modest Ip (0.9MA) to maintain q95 above practical limit • Too few shots were run to assess possible effects of conditioning a new contact area on the PFCs

More Related