1 / 15

Current rampdown at JET experimental results and modelling tasks

Explore current ramp-down at JET experimental results and modeling tasks for ITER, focusing on safe termination of burn, flux consumption, vertical instabilities prevention, and more.

bice
Download Presentation

Current rampdown at JET experimental results and modelling tasks

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. Current rampdown at JETexperimental results and modelling tasks I Nunes G Saibene G Sips

  2. Preparing ramp-down for ITER • Rampdown phase in ITER must: • Terminate the burn including H-L transition • Avoid flux consumption (mainly from the CS coils) • Avoid vertical instabilities • Remain in X-point as long as possible until limiter plasmas are ok (few MA) • Maintain particle and power handling • Avoid disruptions (large heat loads, hence damage to PFCs) • Experiments at JET • Current ramp-down rate • Heating • Plasma shape I Nunes - ISM: ITER ramp-down simulation at JET

  3. Varying Ip ramp-rate Vary current ramp rate from 0.07MA/s to 0.5MA/s (~300s to ~80s in ITER) I Nunes - ISM: ITER ramp-down simulation at JET

  4. Ramp-down summary • Slowest ramps (0.07 and 0.14MA/s) • Transition type I ELMy H-mode/L-mode • bp and li approx. constant before transition • Small variation of bpand li after transition • Faster ramp (0.28 and 0.5MA/s) • transition from type I/III ELMy H-mode before the end of additional heating • Increase of li and bp before the end of additional heating due to transition to a lower confinement regime • Larger variation of li and bp 0.1s after heating switch-off *Times relative to heating switch-off **Times relative to 0.1s I Nunes - ISM: ITER ramp-down simulation at JET

  5. li evolution during the ramp-down phase • Evolution of li during the ramp-down phase (with heating) for all 4 cases as function of dIp/dt • Evolution is within the projected ITER VS capability • Typically ITER should be in H-mode up to ~0.5IpFT and after in L-mode/ohmic I Nunes - ISM: ITER ramp-down simulation at JET

  6. What if H-mode is lost during flat top? • H-L transition at the end of the current flat top… • dIp/dt=0.14MA/s • WDIA = 4.6MJ • DW(0.1s) = 3.655MJ • DW(1.8s) = 1.386MJ • Note: Elongation decreases and minor radius increases during ramp-down #72207 NBI+ICRH Ip bp H98y Ha WDIA li q95 a k I Nunes - ISM: ITER ramp-down simulation at JET

  7. Marginal H-mode during ramp-down #72244 • dIp/dt=0.14MA/s • Note: Very close to L-H threshold  large single ELMS  could cause large disruptions NBI+ICRH Ip bp H98y Ha WDIA li q95 a k I Nunes - ISM: ITER ramp-down simulation at JET

  8. Can we avoid sudden W drop? #74405 • H-L transition during ramp-down with slow turn-off of additional heating (simulation of soft stop at JET or decay of Pa) • dIp/dt=0.5MA/s • Large variation of plasma size before end of heating • Note: TOG increased by 10cm NBI+ICRH Ip bp H98y Ha WDIA li q95 a k I Nunes - ISM: ITER ramp-down simulation at JET

  9. Decreasing k • Possible to strongly decrease k (small k more stable plasma) • Slowest increase of plasma inductance for faster and larger reduction of k although not lower enough in ohmic plasmas ohmic I Nunes - ISM: ITER ramp-down simulation at JET

  10. Ohmic ramp-down using k reduction • Same reduction of elongation with slower Ip rate • Good control of li and almost constant flux In JET it is possible to control li and flux if H-mode is lost during ramp down (in X-point) without using flux I Nunes - ISM: ITER ramp-down simulation at JET

  11. H-mode ramp-down using k reduction #72463 • Type I/type III/dithering ELMs • dIp/dt=0.5MA/s • Plasma shrinking TOG=60cm • Avoid fast transition of WDIA and li • TOG increased by 70 cm NBI+ICRH Ip bp H98y Ha WDIA li q95 a k I Nunes - ISM: ITER ramp-down simulation at JET

  12. Summary • Safe landing: H-mode + moderate current ramp (JET examples 0.07MA/s and 0.14MA/s) • H-L transition during ramp-down: moderate dIp/dt shows better control of li and flux consumption doesn’t seem to be an issue in these examples Future work: • How to extrapolate to ITER requires more work and simulations  accurate contribution to total flux from resistive, external and inductive flux • Transport modelling (ITER profiles, H-L transition, etc.) (V Parail and I Voitsekhovitch)… I Nunes - ISM: ITER ramp-down simulation at JET

  13. Modelling work • Select which ramp-down cases we would like to have: • H-mode • Ohmic • Different ramp-down rates • Different heating levels • What is important to model? To match the entire ramp-down (1 or 2 cases)? Or concentrate on the typical behaviour such as • li excursion • Stored energy excursion • Effect of elongation/minor radius (ohmic) • Combination of the above • How to model the H-L transitions? • Which JET pulses? The underlined cases? I Nunes - ISM: ITER ramp-down simulation at JET

  14. What if H-mode is lost during flat top? • H-L transition at the end of the current flat top… • dIp/dt=0.14MA/s • WDIA = 4.6MJ • DW(0.1s) = 3.655MJ • DW(1.8s) = 1.386MJ • Note: Elongation decreases and minor radius increases during ramp-down #72207 NBI+ICRH Ip bp H98y Ha WDIA li q95 a k I Nunes - ISM: ITER ramp-down simulation at JET

  15. Ohmic ramp-down using k reduction • Same reduction of elongation with slower Ip rate • Good control of li and almost constant flux The red case!! I Nunes - ISM: ITER ramp-down simulation at JET

More Related