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 β N, β 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 β, high fast particle content ( β FAST up to 20%), Alfvén 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 β (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 β 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 β 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) Dα emission

IAEA ST workshop 2008, Roma19 Model is validated against MAST data INVERTED D  IMAGE Observed Dα 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%, β 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, β N =6, C : long pulse, f NI >1, β N =6.7, reduced TF D : high β T, I p =2MA, q0~1, test fast particle β limit E : 'touch-base', high l i, low β F : high  =0.6, β limit and confinement scaling G : high thermal β T (β N up to 7), I p =2MA, n g =1, β limit testing Common parameters: Ip=1.2MA κ=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 <150 Hz mode Growth rate (s -1 ) Resonant frequency (Hz) derivative gain proportional gain

IAEA ST workshop 2008, Roma29 Pulse length limitations Scenariopulse lengthτRτR limiting factor A11.8s0.5sTF joints I 2 t A TF joints I 2 t B2.40.9TF joints I 2 t C4.70.9TF joints I 2 tfully NI D2.61.2Solenoid I 2 tless NI current E3.4Solenoid I 2 t" F2.40.8TF joints I 2 t G1.90.5Solenoid I 2 t"

IAEA ST workshop 2008, Roma30 ELM control coils Poloidal magnetic spectrum for the n=3 configuration of the dipole (left) and monopole (right) coil sets. Superimposed as the blue crosses are the q=m/3 rational surfaces of the CTF-like equilibrium. The dipole set is closer to resonance. Alternative ELM control coil geometries - both ex-vessel. (left, preferred) n=3 dipole (right) n=3,4,6 monopole

IAEA ST workshop 2008, Roma31 1MW 18GHz EBW heating/current drive Harmonic accessibility via O-X-B mode conversion. Midplane resonance topology with Doppler broadening. (shot #8694, B φ = 0.55T at R=0.8m.) This diagram is calculated for present day MAST, will need to be scaled for higher TF. Shows optimum access at ~18GHz

IAEA ST workshop 2008, Roma32 In conclusion, addressing CTF goals Indicative values (not all simultaneous) MAST today Divertor Steady state Stability Transport step size Fast particles No  * extrapolation Upgrade exceeds most physics parameters of CTF:

IAEA ST workshop 2008, Roma33 Upgraded MAST is a key facility to progress fusion The MAST team welcomes international partners to help explore the exciting new physics we will reach with the upgrade and remembering the synergy with ITER/DEMO physics priorities,

IAEA ST workshop 2008, Roma34 This work was funded jointly by the United Kingdom Engineering and Physical Sciences Research Council and by the European Communities under the contract of Association between EURATOM and UKAEA. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

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IAEA ST workshop 2008, Roma36 High  N High f BS High q 0 Low l i High  Hollow j(R) Improves MHD stability Improves vertical stability Physics basis of a long pulse ST I rod : limited by engineering and economics I p : maximise for confinement... but competes with f BS - required for off-axis current drive, and optimisation

IAEA ST workshop 2008, Roma37  AIpIp I rod q min q0q0 l i (3)n/n G NN f NI T e,i0 n eo MA keV10 19 m -3 A A B C D E F G Main parameters All the scenarios have 4 beams at 2.5 MW each (1 on-axis, 2 off-axis, 1 cntr.) Scenarios A.2, B, and C differ mainly in I rod and the assumed fast ion diffusion. –“low” density  almost fully non-inductive. Scenario D and G are high plasma current I p = 2 MA.