IAEA ST workshop 2008, Roma1 An upgrade for MAST G. Cunningham for the MAST team EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK. IAEA ST workshop 2008, Roma2 MAST stands on two legs CTF DEMO physics IAEA ST workshop 2008, Roma3 Strategic objective number 1: ST based component test facility (CTF) Tritium consumption0.6kg yr CANDU stock for 10 yr in parallel with ITER major, minor radius0.84, 0.54 m Elongation2.4 I p, I TF 6.5, 10.5 MA P aux 40 MW N, T 3.5, 16% f NI 100% (40% bootstrap) Indicative ST-CTF parameters: IAEA ST workshop 2008, Roma4 Strategic objective number 2: ITER and DEMO physics basis EFDA missionMAST upgrade contribution Burning plasmasHigh , high fast particle content ( FAST up to 20%), Alfvn mode physics First wall materials, divertor designHigh, but adjustable, heat load, flexible magnetic design, accessible target area Technology and physics of long pulse steady state... NB current drive, variable NBI geometry, q profile control, density control Predicting fusion performanceConfinement scaling, high rotation, high (RWM), fast particle effects,... IAEA ST workshop 2008, Roma5 Features Vacuum vessel and main PF coils retained, Closed, and pumped, divertor for long pulse density control, Extensive set of divertor coils for plasma shaping and divertor control, Fatter centre column for increased TF and flux, Increased NBI power, Off-axis NBI and on-axis counter-current NBI for q profile and rotation control, 1MW EBW heating and current drive Continuous pellet injector IAEA ST workshop 2008, Roma6 NBI geometry (plan view) 2 double PINI boxes (1 on-axis, 1 off-axis PINI per box) 1 on-axis counter-current PINI IAEA ST workshop 2008, Roma7 Design process (and talk outline) Non-inductive steady state (>> resistive timescale), NB drive Bootstrap drivendirect NB current drive High q profile control Strong shaping ( ) Lower density High T Active pumping Reduce J 0 Substantial input power Adequate divertor power handling off-axis/counter NBI Higher elongation Higher density Lower li IAEA ST workshop 2008, Roma8 Divertor magnetic design IAEA ST workshop 2008, Roma9 Elongation is a function of l i, and control system At suitable l i (l i (2)=0.65 here), and by optimising the divertor current, k>2.5 is achievable. However such li is not readily sustained, and vertical control is demanding An additional 'X point' coil increases triangularity, improves vertical control, and raises limit. The confinement region is now satisfactory, but the divertor is problematic. IAEA ST workshop 2008, Roma10 New array of divertor coils Array of divertor coils takes strike point out to larger radius and gives good compensation for solenoid field. Also, solenoid is enlarged to increase volt-seconds Startup (merging- compression) coil is removed Radial field coil is relocated to admit off-axis NBI IAEA ST workshop 2008, Roma11 Wide range of divertor control The divertor strike point location can be moved considerably, allows higher power density operation for divertor target testing, and low power density for long pulse. The divertor is remote from the main plasma, allowing closed divertor operation. IAEA ST workshop 2008, Roma12 the same philosophy can be extended... Possible DEMO divertor solution, Possible thanks to large MAST vessel, Known in the US as 'super-X', Ongoing development - collaborations welcome (simplification is no doubt possible!) IAEA ST workshop 2008, Roma13 Central shaping coil gives further versatility Large centre column leaves space for a small central shaping coil gives access to increased triangularity IAEA ST workshop 2008, Roma14 Divertor power handling 10 MW m -2 considered the limit for 5s operation Experiment has found most of the power goes to the outboard divertor outboard/inboard ratio, Roi up to 30 IAEA ST workshop 2008, Roma15 P NBI = 10 MW, P RAD = 3 MW, target = 90, SOL = 1 cm, flux = 4 INNER TARGET Power deposition at the inner target (high ) Even R strike ~0.3m is OK in DND IAEA ST workshop 2008, Roma16 P NBI = 10 MW, P RAD = 3 MW, target = 30, SOL = 1 cm, flux = 4 OUTER TARGET R strike >0.8m is OK... outer target, declined plate IAEA ST workshop 2008, Roma17 Divertor - active pump design IAEA ST workshop 2008, Roma18 Closed divertor with active (cryo-) pumping Closed divertor gives factor 5 reduction in vessel pressure, active pumping a further 50% decrease. (OSM/Eirene) MAST, EXPERIMENT MAST MAST-U, PUMP OFF MAST-U, PUMP ON R(m) D emission IAEA ST workshop 2008, Roma19 Model is validated against MAST data INVERTED D IMAGE Observed D image Abel inverted image Model calculation IAEA ST workshop 2008, Roma20 Plasma scenario design 8 scenarios developed (2 discussed here), Transp (including Nubeam) is the main design tool (run until profiles are relaxed), Non-inductive current fraction 40% to 100%, N from 3.7 to 6.7. IAEA ST workshop 2008, Roma21 Most scenarios have CTF-like shape Three shapes in total CTF like high (F) MAST (E) Most scenarios have CTF like shape. A,B,C,D,G Off-axis beams require high . IAEA ST workshop 2008, Roma22 Objective: Test the confinement and stability of a monotonic q-profile with q>2 Avoid all low m/n MHD Major problem in current STs No sawteeth crashes No 2/1 and 3/2 NTMs Requires high TF to keep q > 2 I rod = 3.2 MA Scenario is ideally stable even without rotation. Neoclassical transport increases with q safe to use ITER scaling? but recent ST results suggest stronger B t and weaker Ip scaling, giving greater benefit from TF enhancement than has been assumed. Scenario A (CTF-like q profile) A1 : A2 : + IAEA ST workshop 2008, Roma23 Two ways to scenario A A1: High density: n/n G = 0.5 Conservative approach. N ~ 3.7 > N ITER =2.2 ( N th = 3.1) Balance on-axis Ohmic current with off- axis NBCD classical fast-ion diffusion Flat top: ft 1.8s 3.7 R 37 E limited by TF to 2.2s A2: Low density:n/n G = 0.2 Almost non-inductive f NI = 0.8 N = 4.8, with high fast particle pressure N fast =2.7, N th = 2.1 Dominated by NBI current anomalous fast-ion diffusion D fi = 0.3 m 2 /s. Flat top: ft 1.8 s 2 R 45 E limited by TF to 1.8s IAEA ST workshop 2008, Roma24 Flexible machine - range of scenarios A1,A2 : baseline, CTF-like q profile, 2 density variants B : high fast particle content - confinement, f NI =0.9, N =6, C : long pulse, f NI >1, N =6.7, reduced TF D : high T, I p =2MA, q0~1, test fast particle limit E : 'touch-base', high l i, low F : high =0.6, limit and confinement scaling G : high thermal T ( N up to 7), I p =2MA, n g =1, limit testing Common parameters: Ip=1.2MA =2.5 A=1.6 li(3)=0.5 (except where stated otherwise) IAEA ST workshop 2008, Roma25 Main limiting instability: n=1 internal kink Pressure driven internal n=1 kink in the low magnetic shear region (infernal mode) is the limiting instability in most scenarios (except G). Mode is strongly stabilised by rotation. Mode is stabilised by fast particles. Wall has little influence on the stability. C C B D Effect of rotation on reference scenarios Toroidal rotation on axis (km/s) Growth rate / Alfven IAEA ST workshop 2008, Roma26 MHD stability - MISHKA analysis Once the internal mode is stabilised, the next least stable mode is an external kink, which is amenable to wall stabilisation. Stabilising plates are under consideration. IAEA ST workshop 2008, Roma27 Vertical position control High elongation is a major objective Little passive stabilisation close to plasma on LFS (NBI and diagnostic access) IAEA ST workshop 2008, Roma28 Vertical position control Rigid plasma analysis (RZIP) stable operating zone >1kHz mode