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M9: Stability & Pedestal Experiments

M9: Stability & Pedestal Experiments. Ian Chapman & Samuli Saarelma on behalf of all contributors to MAST stability team. M9 headlines. ELM control with 3D magnetic perturbations Evolution and stability of the edge pedestal Role of ion-scale turbulence in core transport

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M9: Stability & Pedestal Experiments

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  1. M9: Stability & PedestalExperiments Ian Chapman & Samuli Saarelma on behalf of all contributors to MAST stability team

  2. M9 headlines • ELM control with 3D magnetic perturbations • Evolution and stability of the edge pedestal • Role of ion-scale turbulence in core transport • Development of integrated scenarios for the MAST upgrade • Development and benchmarking of edge modelling tools in benefit of the divertor upgrade • Fast-ion transport to guide profile and heating optimisations

  3. Proposals Process • Proposals considered: • 38 through proposal webpage • 2 transferred to Integrated Plasma Scenarios Area • 3 transferred from Transport and Confinement Area • 1 raised during Stability meetings • = 40 proposals requesting 643 shots • Amalgamation and prioritisation led to: • 13 experiments requiring 273 shots

  4. Main Experiments

  5. Parasitic Experiments

  6. Back-up Experiments

  7. Headline Coverage • Headline 1 (RMP ELM control) • 8 experiments, 1 parasitic, 178 shots • 8 by CCFE PiC • Headline 2 (Pedestal evolution) • 3 experiments, 2 parasitic, 48 shots • 2 led by non-CCFE PiC, 1 by CCFE PiC • Non-headlines • 2 experiments, 2 parasitic, 47 shots • 1 led by non-CCFE PiC, 1 by CCFE PiC

  8. ITPA Contributions • Contributing to the following ITPA experiments: • PEP 6: Pedestal structure and ELM stability in DN • PEP 19: Basic mechanisms of edge transport with resonant magnetic perturbations in toroidal plasma confinement devices • PEP 23: Quantification of the requirements for ELM suppression and mitigation by magnetic perturbations • PEP 32: Access to and exit from H-mode with ELM mitigation at low input power above PLH • MDC 1: Disruption mitigation by massive gas jets • MDC 15: Disruption database development • PEP 29: Vertical jolts/kicks for ELM triggering and control

  9. M9-MHD-001: RMPs in 400kA SND • Aim • Investigate RMPs in n=3,4,6 on a sawtooth-free discharge • Is a LSND n=3 case best route to ELM suppression if we can avoid rotation braking (perhaps by lower Ip) • Strategy • Repeat shot 28168 (a LSND 400 kA shot) • Apply RMPs in n=3 n=4 and n=6 configurations and optimise ELM mitigation/ suppression • Increase density until ne/NGW > 0.53 and attempt to suppress type I ELMs

  10. M9-MHD-002: Rotating RMPs • Aim • Investigate rotating RMPs in time and effect on the strike point splitting and coil penetration • Strategy • Develop a LSN shot in which ELM mitigation can be performed using n=3 perturbations • Assess impact of rotating strike point on L-mode heat flux • Rotate phase of the perturbation during the shot & monitor strike points for rotation of splitting patterns • Then in inter-ELM and ELMing discharges • Monitor strike point splitting and effectiveness of ELM mitigation (via pump out, ELM frequency changes etc) • Specific requirements • New IR view, as required by splitting experiments

  11. M9-MHD-003: RMPs on L-H & 1st ELM • Aim • Determine impact of RMPs on L-H transition • n=3,4,6; q95 scan (match ITER Ip ramp); vary ne; IELM • Determine impact of ELM coils on dithery I-mode phase • Mitigate 1st ELM (determine ∆W on with various RMPs) • Demonstrate ELM mitigation close to Pthr w n=4 and n=6 • Strategy • Find L-H threshold in plasma with no RMP • Find threshold (delayed or at same time) with RMPs • Change q95 & density and repeat power scans • Specific requirements • ECELESTE and RP for edge Er and turbulence data • Visible and IR Cameras set up for lobe and strike point measurements respectively; Burst TS at L-H time

  12. M9-MHD-004: RMPs at low/high collisionality • Aim • Obtain ELM suppression at low/high collisionality (seen in DIII-D for ν*e <0.3 or ν*e >2.0 and AUG for ne/nGW >0.53) • Strategy • Take LSND (eg 27205) and reduce pedestal collisionality by reducing the density and heating early • (See for example 14643 which has ne,ped = 1.9x1019m-3 and Te,ped = 380eV giving ν*e = 0.03) • For high n/nGW drop Ip and increase the density

  13. M9-MHD-005: Edge current with SAMI • Aim • Use the Synthetic Aperture Microwave Imaging radiometer to measure the edge current density • Measurement of the BXO mode conversion asymmetry above and below the midplane • Strategy • Scan Te,ped as much as is reasonable, to obtain a variety of good H mode shots with different edge collisionalities • Modulate loop volts • BT scan between shots • Move SAMI to a midplane window and observe DND H modes with ELM free periods lasting 10ms or more • Specific requirements • Thomson scattering in burst mode to get measurements around at least one ELM crash in each shot

  14. M9-MHD-006: Global β and pedestal • Aim • Assess global beta evolution influence on achievable pedestal and global confinement • Obtain high quality equilibria during sharp L-H transition and in the fast post-ELM pedestal recovery. • Use these equilibria to perform gyrokinetic analysis • Strategy • Run DND with DI start-up (highest Te,ped in M8), but upshifted to keep in L-mode • Shift down to get L-H and do so at different times/power to vary β • Compare to ELITE modelling (which shows higher beta gives higher critical pressure gradient) • Trigger the TS in the burst mode at the transition time • Specific requirements • TS in burst mode, BES at the edge

  15. M9-MHD-007: RMP Midplane displacement 4 ne (1019m-3) 2 0 600 Te (eV) 400 200 0 1.35 1.45 1.55 Radius (m) • Aim • Measure and model the 3d corrugation with n=3,4,6 RMPs • Strategy • Temporarily disable the position controller when RMPs are turned on by feed-forward programming of coil currents based on a coils off shot. • Do for two phases of both n=3 and n=4 in DND plasmas, • Perform a systematic current scan, • Specific requirements • Move fast cameras; position control off Thomson Scattering

  16. M9-MHD-008: RMP alignment scan • Determine IELM threshold in even and 90L configurations and ensure that it is lower than 1 kA • Perform pitch angle scan • Modify q95 and repeat scan • Compare to vacuum and plasma response modelling • Aim • Utilise unique pitch alignment capability to show resonance effect • Strategy • Use 600 kA shot developed in IPS and perform a pitch angle alignment scan to determine resonance condition

  17. M9-MHD-009: Lobe formation time n=6 RMP • Aim • Use quickly ramping RMPs to see if there is a delay between RMP application lobe length increase • Strategy • Apply n=3, n=4 and n=6 RMPs in LSND • Ramp RMP current as quickly as possible from zero to maximum, hold constant for ~40ms, then ramp down • Do in the L-mode and one during the H-mode phase • Specific requirements • HeII (or maybe CIII) filtered camera on the lower divertor

  18. M9-MHD-010: Effect of fuelling on ELM control • Aim • To investigate if ELM mitigation/suppression is dependent on the refuelling/recycling location • Strategy • Use the HFS top bottom puff in the scenario 6 discharge (600kA) and the HFS midplane puff in the scenario 4 discharge (750kA) to investigate the effects on ELM mitigation • Repeat both with LFS fuelling

  19. M9-MHD-011: Pedestal with Ip scan • Aim • Observe how the pressure gradient varies with Ip • Strategy • CDN Ip scan (5 - 10 discharges) (600-1000kA) • LSN Ip scan (5 - 10 discharges) (400-700kA)

  20. M9-MHD-012: NTM physics and control • Strategy • Demonstrate the robustness of brief H-L-H transitions as a means of controlling 2,1 TMs • Test how quickly a detected TM can be removed • Perform earlier vertical shifts (also useful for isolating different contribution to NTM stability at small island width) • Measure NTM onset with increased/reduced n=1 • Aim • Demonstrate NTM control for MAST-U and increase understanding of TM stability in STs

  21. M9-MHD-013: Disruption mitigation • Aim • Study the effect of disruption mitigation on heat loads and halo currents at high stored energy • Investigate the efficiency of HFS mitigation using the cHFS and combined LFS mitigation • Strategy • Perform a series of mitigations at a range of stored plasma energies, including H mode • Specific requirements • Disruption mitigation valve; Halo current detectors; IR thermography for heat load measurements

  22. M9-MHD-014: Reconnection studies • Aim • Previously TS shows rapid electron heating due to magnetic reconnection. Now measure pitch angle and ion temperature during reconnection • Strategy • Use NBI from start for MSE measurements • M/C scan, ie increase P3 from 200kA to max and change P6 bias to move reconnection point up-down • Measure Ti with CXRS and pitch angle with MSE • Scan TF to vary BT effect • Specific requirements • Needs P3 start-up with >250kA to get large-bore plasma to merge so MSE can see merging point • Burst TS, Bullet cam with high res, Xsa, Xsm for Ti

  23. What has been omitted?

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