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MAST ST developments towards high- , steady-state tokamak operation

Explore the progress in high-β, steady-state operation of the MAST tokamak, discussing upgrades, results, and future goals presented at the Culham-Ioffe Symposium. Key focus on enhancing plasma performance and control systems.

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MAST ST developments towards high- , steady-state tokamak operation

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  1. IEA ‘04, WS59: High-, Steady-State Tokamak Operation Culham-Ioffe Symposium, 30.11.04 MAST ST developments towards high-, steady-state tokamak operation Anthony Field for the MAST team

  2. Overview ST Power Plant Culham-Ioffe Symposium, 30.11.04 • Introduction • MAST • Overview • Results • Component test facility (CTF) • Overview • Current drive • Proposed MAST Upgrades • Overview • NBI systems for current profile control • Summary

  3. Introduction Culham-Ioffe Symposium, 30.11.04 EU ST programme: Based at UKAEA Culham and focussed on the MAST Spherical Tokamak MAST Spherical Tokamak • Goals of MAST: • Advance tokamak physics for ITER • Explore the long-term potential of the ST • On-going design studies at Culham: • ST Power Plant (STPP) • Component Test Facility (CTF) • Proposed upgrades to MAST facility: • Test physics basis of CTF • Adaptable heating, Paux ~ 10 MW • Pumped divertor • PF system enhancements

  4. MAST Parameters Culham-Ioffe Symposium, 30.11.04 Plasma cross-section and current comparable to ASDEX-U and DIII-D Adaptable fuelling systems - inboard & outboard gas puffing plus multi-pellet injector Digital plasma control implemented June 2003 (PCS supplied by GA)

  5. MAST 2004 Upgrades Pre-2004 2004 Culham-Ioffe Symposium, 30.11.04 New centre column New divertor • Towards longer pulses: • Longer centre column (more Vs) • New divertor to handle power • New error field correction system • Relocated P2 with reversing switch

  6. ne 30% lower MAST: Error field correction Locked mode 0.0 0.1 0.2 0.3 0.4 time (s) Culham-Ioffe Symposium, 30.11.04 Error field correction coils installed outside vessel Locked modes avoided at low density

  7. MAST: Ideal no-wall -limit approached unstable stable KINX calculations: b) a) Menard calculation: - q*/q0=3 - q*/q0=1.5 Culham-Ioffe Symposium, 30.11.04 • N > 5, (N > 5li) achieved by avoiding NTMs • Ideal no-wall beta limit approached - no obvious MHD limit to performance • Main limit due to initial NBI system capabilities PNBI = 2.8 MW fBS ~ 40 - 50% Wfast ~ 15 - 20% Matthew Hole, Richard Buttery et al

  8. MAST: Confinement Scaling at high  and  IPB(y,2): IPB(y,2)-(PBXM, …)+MAST: Culham-Ioffe Symposium, 30.11.04 • MAST data points expand the range of e by a factor 2.2 and bT by 2.5 • Replaces data from devices with non-conventional cross-sections • Supports existing IPB(y,2) scaling, strengthens e dependence Interplay of e and b dependencies: Assuming confinement independent of b gives negativee dependence Matthew Hole, Richard Buttery et al

  9. MAST ‘hybrid-like’, sawtooth-free H-mode discharge Current densities Magnetic shear and q • Hollow current profile produced with NBI heating during current ramp • Weak magnetic shear s improves confinement of core plasma A R Field, R J Akers et al

  10. MAST: Transport in sawtooth-free H-mode plasma  Kinetic profiles Transport Analysis • Sawtooth-free, hybrid-like plasmas have improved core transport • Ion transport close to neo-classical over much of plasma radius A R Field, R J Akers et al

  11. MAST: High Rotation Enhances Confinement Culham-Ioffe Symposium, 30.11.04 CTF MAST • Toroidal rotation increases with applied torque from NBI (M 1.2) • Confinement increases with Tand is highest with counter injection • Approaches that required for CTF (HH ~ 1.3) or STPP (1.6) R J Akers et al

  12. MAST: Particle transport Culham-Ioffe Symposium, 30.11.04 • Density peaks and temperature flattens with counter injection • Particle balance dominated by NBI fuelling and Ware pinch (Deffn ~ 0) • Small additional (<10%) pinch due to NBI torque: ctr-in/co-out • Ware pinch absent in steady-state (CTF) - Beam fuelling peak density R J Akers et al

  13. MAST: Electron ITB formed with counter-NBI  Culham-Ioffe Symposium, 30.11.04 • Highest rotation achieved with counter-NBI, M 1.2 • ExB flow shear far exceeds ITG growth rate with low magnetic shear • Strong electron ITB indicates suppression of electron transport A R Field, R J Akers et al

  14. MAST: Pedestal width scalings Averaged values HFS local values  - JT-60  - DIII-D + - C-MOD  - MAST Culham-Ioffe Symposium, 30.11.04 • MAST data supports using local, rather than flux-surface averaged • values of B in HFS pedestal width scalings, e.g. with banana width • Subject of on-going NSTX/MAST/DIII-D joint identity experiment • (aim to determine aspect ratio scaling at fixed pedestal r* and n*) A R Field, R J Akers et al

  15. MAST: NBI Upgrade 2005 Culham-Ioffe Symposium, 30.11.04 • Two JET-type PINIs (2.5 MW, 75 keV) for high-power, • long-pulse operation (5 MW, 5 s) • Actively cooled calorimeters • Residual ion dumps with hyper-vapotrons • Operation SW: April ‘05 (M5), SS: late ‘05 JET-type PINI for MAST Calorimeter Residual Ion Dumps

  16. 1.0 GW STPP Physics Parameters Culham-Ioffe Symposium, 30.11.04 Culham STPP Howard Wilson, Garry Voss et al

  17. STPP Parameter Determinants High Bootstrap Low internal inductance High Elongation Culham-Ioffe Symposium, 30.11.04 • Neutron wall loading (3.5 MW m-2) determines the size: R = 3.4 m • Cost of electricity limits toroidal field, Irod ~Ip • MHD limits N = 8.2 • High elongation required for ~ 90% • pressure-driven current; • vertical instability •   = 3.2 (fs = 3.0) • Required fusion power (~ 3GW)  Irod = 30.2 MA (Ip = 31 MA) • Non-inductive current drive requires low density ~1.11020 m-3 • (~60% Greenwald) • Confinement, E = 1.6 IPB98(y,2) or 1.4 IPB98(y,1) fBS ~ Nh()Irod/Ip Howard Wilson et al

  18. STPP Stability Culham-Ioffe Symposium, 30.11.04 • Ballooning modes: 2nd stable solution exists with 90% pressure driven current • High central safety factor • Uniform magnetic shear across the plasma  Hollow current profile • BUT in an ST q() can remain monotonic • Close fitting wall and high q(0) ensures n=1, 2 and 3 kink mode stable • NTMs: Stabilising Glasser term very strong, high q(0) avoids low order modes Howard Wilson et al

  19. Component Test Facility (CTF) Parameters Culham-Ioffe Symposium, 30.11.04 • CTF is confinement, rather than stability limited as the STPP • Requires 60% external current drive (fBS ~ 40% at modest N ~ 3.5) • Off-axis CD required to maintain hollow current profile for qa ~ 5.2, q0 ~ 1.5) Howard Wilson et al

  20. CTF: Non-Inductive Current Drive On and off-axis NBCD On-axis ECCD • BANDIT-3D Calculations: • 2nd harmonic, O-mode • 160GHz, 20MW 150 keV 40MW 200 keV 10MW Culham-Ioffe Symposium, 30.11.04 R J Akers, M O’Brien et al

  21. CTF: -particle confinement z [m] R [m] Culham-Ioffe Symposium, 30.11.04 • -particles well confined: • Full-orbit calculations required • Orbits large near axis • ‘Pinched’ on outboard side • < 1% losses Howard Wilson et al

  22. MAST: Dimensionless Energy Confinement Scaling Culham-Ioffe Symposium, 30.11.04 • MAST N and * close to CTF values • Understanding * dependence • important *, MAST/*, CTF ~ 90 • MAST data alone gives M. Valovic et al

  23. Physics Goals of future MAST Upgrades Culham-Ioffe Symposium, 30.11.04 • Establish high-, steady state physics basis for CTF (STPP): • Control of current, flow and pressure profiles for optimised • long-pulse performance • Effective fuelling, exhaust and density control for • steady-state operation • Confinement scaling over extended parameter range, • e.g. lower* • Start-up without solenoid

  24. Key Elements of Proposed MAST Upgrades Culham-Ioffe Symposium, 30.11.04 • Heating upgrade (10 MW, long pulse): • 3-4  JET PINIs for 7.5-10 MW, 5 s • Off-axis NBCD capability • EBW CD, ~ 20 GHz, ~ 2 MW • New centre stack (higher Bt and Vs) • Pre-chilled, cyanate ester resin • Pumped divertor (density control): • Closed configuration • 2  100,000 L/s cryo-pumps • Modified poloidal field coils • Vertical stability at high elongation • Strike point control • Improved diagnostics, e.g. turbulence, q(r) Proposed Divertor Upgrade Baffle Additional PF coils Cryo-pump

  25. MAST Upgrades: Proposed NBI Systems • Investigating bold options for NBI current profile control • Flexible system 3-4 PINIs, 7.5-10 MW (1 counter- and 2 or 3 co-current) • Off-axis NBDC optimised with 2 off-axis co- and 2 on-axis co/counter PINIs Double box: 2 co-PINIs on- and off-axis On-axis, counter-PINI Jackable on/off-axis co-PINI

  26. MAST Upgrades: NBI current profile control NBI current density 400 12 Configuration: off on on # co co ctr 1 1 2 - 2 2 1 - 3 1 1 1 42 - 1 300 10 8 [A/m2] 200 6 100 4 2 0 0 0.0 0.0 0.0 0.2 0.2 0.2 0.4 0.4 0.4 0.6 0.6 0.6 0.8 0.8 0.8 1.0 1.0 1.0 r/a • TRANSP current profile simulations with 3 PINI operation Safety factor q(r) r/a D L Keeling

  27. MAST Upgrades: NBCD Calculations • Optimal 4-PINI configuration gives 1.05 MA NI-CD with q0 > 1.5 Configuration: # off on ctr INI [MA] 1 2 2 - 1.2 2 1 2 1 0.8 3 2 1 1 1.05 41 3 - 1.0 Ip = 1.2 MA, Bt = 0.64 T q0 = 1.7,  = 2.5,  = 1.43 Ti,e (0) = 3 keV <Ti,e> = 1.35 keV Beam driven current [A] Time [s] D L Keeling

  28. MAST Upgrades: Beam-target neutron flux On-axis PINI Off-axis PINI Current P5 geometry - for upgrade, coils will be moved towards mid-plane 70 keV, RT = -0.8 m, dZ = -0.1 m 70 keV, RT =-0.8 m, dZ = -0.6 m • Compact, intense neutron source (line-integral flux same as JET, JT-60U) • Beam-target neutron distribution sensitive diagnostic of fast-ions • Investigating possibilities for diagnostics, e.g. Stilbene detectors R J Akers

  29. Summary and Conclusions • MAST data contributes towards understanding of shape and • aspect ratio dependence of high-b tokamak performance, e.g. • Confinement and pedestal width scalings • Transport barrier formation • Role of plasma rotation • Current and proposed upgrades to MAST facility will allow • investigation of key issues for future tokamak devices, e.g. • NBI current profile and shear flow control • Scaling of confinement and transport • Density control and power handling • ST offers potential for a future steady-state burning plasma device, • e.g. CTF or STPP

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