IEA 04 WS 59 High SteadyState Tokamak Operation

IEA ‘ 04, WS 59: 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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05

Overview • • • 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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 ST Power Plant

Introduction Culham-Ioffe Symposium, 30. 11. 04 EU ST programme: Based at UKAEA Culham and focussed on the 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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 MAST Spherical Tokamak

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) Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05

MAST 2004 Upgrades Culham-Ioffe Symposium, 30. 11. 04 Pre-2004 New centre column Towards longer pulses: • • Longer centre column (more Vs) New divertor to handle power New error field correction system Relocated P 2 with reversing switch Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 2004 New divertor

MAST: Error field correction Culham-Ioffe Symposium, 30. 11. 04 Error field correction coils installed outside vessel Locked modes avoided at low density ne 30% lower Locked mode 0. 0 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 0. 1 0. 2 time (s) 0. 3 0. 4

MAST: Ideal no-wall -limit approached Culham-Ioffe Symposium, 30. 11. 04 • • • N > 5, ( N > 5 li) achieved by avoiding NTMs Ideal no-wall beta limit approached - no obvious MHD limit to performance Main limit due to initial NBI system capabilities a) b) Menard calculation: PNBI = 2. 8 MW - q*/q 0=3 - q /q =1. 5 * 0 f. BS ~ 40 - 50% Wfast ~ 15 - 20% KINX calculations: unstable Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 Matthew Hole, Richard Buttery et al

MAST: Confinement Scaling at high and Culham-Ioffe Symposium, 30. 11. 04 • • • MAST data points expand the range of e by a factor 2. 2 and T by 2. 5 Replaces data from devices with non-conventional cross-sections Supports existing IPB(y, 2) scaling, strengthens e dependence IPB(y, 2): IPB(y, 2)-(PBXM, …)+MAST: Interplay of e and dependencies: Assuming confinement independent of gives negative e dependence Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 Matthew Hole, Richard Buttery et al

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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 A R Field, R J Akers et al

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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 A R Field, R J Akers et al

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 T and is highest with counter injection Approaches that required for CTF (HH ~ 1. 3) or STPP (1. 6) Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 R J Akers et al

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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 R J Akers et al

MAST: Electron ITB formed with counter-NBI Culham-Ioffe Symposium, 30. 11. 04 • • • Highest rotation achieved with counter-NBI, M 1. 2 Ex. B flow shear far exceeds ITG growth rate with low magnetic shear Strong electron ITB indicates suppression of electron transport Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 A R Field, R J Akers et al

MAST: Pedestal width scalings 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 * and *) Averaged values HFS local values - JT-60 - DIII-D + - C-MOD - MAST Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 A R Field, R J Akers et al

MAST: NBI Upgrade 2005 Culham-Ioffe Symposium, 30. 11. 04 • • Two JET-type PINIs (2. 5 MW, 75 ke. V) for high-power, long-pulse operation (5 MW, 5 s) Actively cooled calorimeters Residual ion dumps with hyper-vapotrons Operation SW: April ‘ 05 (M 5), SS: late ‘ 05 JET-type PINI for MAST Calorimeter Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 Residual Ion Dumps

1. 0 GW STPP Physics Parameters Culham-Ioffe Symposium, 30. 11. 04 Culham STPP Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 Howard Wilson, Garry Voss et al

STPP Parameter Determinants 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 Bootstrap High elongation required for ~ 90% pressure-driven current; High vertical instability Elongation = 3. 2 (fs = 3. 0) Required fusion power (~ 3 GW) 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 IPB 98(y, 2) or 1. 4 IPB 98(y, 1) Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 Howard Wilson et al f. BS ~ Nh( )Irod/Ip Low internal inductance

STPP Stability Culham-Ioffe Symposium, 30. 11. 04 • • Ballooning modes: 2 nd 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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 Howard Wilson et al

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 (f. BS ~ 40% at modest N ~ 3. 5) Off-axis CD required to maintain hollow current profile for qa ~ 5. 2, q 0 ~ 1. 5) Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 Howard Wilson et al

CTF: Non-Inductive Current Drive Culham-Ioffe Symposium, 30. 11. 04 On and off-axis NBCD On-axis ECCD BANDIT-3 D Calculations: 150 ke. V 200 ke. V 40 MW 10 MW Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 • • 2 nd harmonic, O-mode 160 GHz, 20 MW R J Akers, M O’Brien et al

z [m] CTF: -particle confinement Culham-Ioffe Symposium, 30. 11. 04 -particles well confined: • • Full-orbit calculations required Orbits large near axis ‘Pinched’ on outboard side < 1% losses R [m] Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 Howard Wilson et al

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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 M. Valovic et al

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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05

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 Proposed Divertor Upgrade 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) Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 Additional PF coils Baffle Cryo-pump

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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05

MAST Upgrades: NBI current profile control • TRANSP current profile simulations with 3 PINI operation Safety factor NBI current density 400 12 q(r) Configuration: [A/m 2] 8 6 # co co ctr 200 100 4 2 0 0. 0 off on on 300 10 1 1 2 - 2 2 1 - 3 1 1 1 4 2 - 1 0 0. 2 0. 4 0. 6 0. 8 1. 0 0. 0 r/a Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 0. 2 0. 4 0. 6 r/a D L Keeling 0. 8 1. 0

MAST Upgrades: NBCD Calculations • Optimal 4 -PINI configuration gives 1. 05 MA NI-CD with q 0 > 1. 5 Beam driven current [A] Configuration: # off on ctr INI [MA] 1 2 2 - 1. 2 2 1 0. 8 3 2 1 1 1. 05 4 1 3 - 1. 0 Ip = 1. 2 MA, Bt = 0. 64 T q 0 = 1. 7, = 2. 5, = 1. 43 Ti, e (0) = 3 ke. V <Ti, e> = 1. 35 ke. V Time [s] Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 D L Keeling

MAST Upgrades: Beam-target neutron flux On-axis PINI Off-axis PINI Current P 5 geometry - for upgrade, coils will be moved towards mid-plane 70 ke. V, RT = -0. 8 m, d. Z = -0. 1 m • • • 70 ke. V, RT =-0. 8 m, d. Z = -0. 6 m Compact, intense neutron source (line-integral flux same as JET, JT-60 U) Beam-target neutron distribution sensitive diagnostic of fast-ions Investigating possibilities for diagnostics, e. g. Stilbene detectors Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05 R J Akers

Summary and Conclusions • • • MAST data contributes towards understanding of shape and aspect ratio dependence of high- 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 Anthony Field, IEA ‘ 04, WS 59, San Diego, 14. 02. 05