Overview of recent Spherical results

Presented by Alan Sykes EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon UK

•STs world - wide

Globus-M Pegasus •MAST and NSTX HIT-II MAST HIT-I NSTX START Proto-Sphera CST TS-3 CDX-U TST-M •selected results: HIST Energy confinement ETE Rotamak-ST H-modes, Pthresh HHFW, EBW heating NBI effects density limits beta limits MHD SOL studies •Conclusions CDX-U, PPPL

First : Oct 1993 achieved Major radius R (m) 0.34 Minor radius a (m) 0.22 Elongation < 1.6 Aspect ratio (R/a) >1.5 Plasma current (MA) 0.1 TF rod current (MA) 0.4 Toroidal field at R (T) 0.2 RF Aux. heating (MW) 0.2 Pulse length (s) 0.025 Plasma volume (m 3) 0.5

CDX-U is dedicated to a multi-institutional effort to study liquid lithium effects in spherical torus plasmas participating institutions: PPPL, Johns Hopkins University, UCSD, ORNL, SNL, and LLNL TST-2, Tokyo

First plasma: Sept 1999 TST-2 design (achieved) Major radius R (m) 0.36 (0.36) Minor radius a (m) 0.23 (0.23) Elongation < 1.8 (1.8) Aspect ratio (R/a) 1.6 (1.6) Plasma current (MA) 0.2 (0.11) TF rod current (MA) 0.72 (0.38) Toroidal field at R (T) 0.4 (0.21) Aux. heating HHFW 0.5 (0.001) ( MW) Pulse length (s) 0.05 (0.1) Plasma volume (m 3) 0.5 (0.5)

Key research thrusts: •university research •RF physics •fluctuations and transport HHFW in TST-2

TST-2 Combline CL Antenna has 6 phased straps to excite a unidirectional HHFW

1 m Y. Takase, P1.029 Investigation of current drive techniques

TST-2 has recently investigated the novel ECRH current initiation scheme first demonstrated on CDX-U. flux 1.0 Flux contours and ECRH resonance. Flux 10

surfaces close after BT = 0.088 T 0.5 BT = 0.070 T current is formed BT = 0.062 T 1 (kA) p 0.0 I Z [m] 0.1

HORN ANTENNA -0.5 0.01 10-4 10-3 10-2 10-1 Neutral Pressure (Pa) Driven current as a function of -1.0 filling pressure. Plasma current 0.0 0.2 0.4 0.6 0.8 R [m] up to 1.2kA from 1kW of ECRH ETE, at INPE, BRAZIL

First plasma: November 2000. design (achieved) Major radius R (m) 0.3 (0.3) Minor radius a (m) 0.2 (0.2) Elongation < 2 (?) Aspect ratio (R/a) 1.5 (?) Plasma current (MA) 0.4 (0.03) TF rod current (MA) 0.9 (0.1) Toroidal field at R (T) 0.6 (0.067) Aux. heating - Pulse length (s) 0.1 (0.005) Plasma volume (m 3) 0.35 (?)

Key research objectives: •Investigation of parameter space in ohmic regime •Study of plasma edge physics GLOBUS-M, St Petersburg Parameter Design Achieved value Toroidal magnetic 0.62 0.35 field at vessel axis,Ò Plasma current, ÌÀ 0.5 0.25 Major radius, m 0.36 0.37 Minor radius, m 0.24 0.24 Aspect ratio 1.5 1.5 Vertical elongation 2.2 1.8 Pulse duration, s 0.2 0.06

N.V.Sakharov, P1.020

New results on low-q operation: V.K.Gusev, O23 Pegasus, Univ. Wisconsin

First plasma: June 1999 design (achieved) Major radius R (m) 0.4 (0.45) Elongation < 3 (3.7) Aspect ratio (R/a) >1.16 (>1.1) Plasma current (MA) 0.14 (0.3) TF rod current (MA) 0.2 (0.225) Toroidal field at R (T) 0.1 (0.15) Aux. heating (HHFW, EBW) - (?) Pulse length (s) 0.025 (0.06)

Exploration of A ⇒ 1 regime MAST, Culham

MG, AS & DCR March 2001

MAST team, 2000 NSTX, Princeton

NSTX team, June 2001 NSTX and MAST

•Close-fitting vessel for wall stabilisation •Large vessel for accessibility & flexibility • • ‘Merging/compression’ + solenoid for CHI and solenoid for plasma initiation plasma initiation •HHFW and NBI heating / CD •NBI and ECRH heating / CD MAST and NSTX

MAST NSTX R,m 0.85 0.85 a,m 0.65 0.68 k 3 (2.4) 2.2 (2.5) Ip ,MA 2 (1.05) 1.0 (1.4) B t,T 0.5 0.3-0.6 (0.45) P aux , 5 NBI(2.0) 5 NBI(4.5) τMW +2 EC (1) + 6 FW(4) p , s 5 (0.5) 5 (0.5) Red – achieved (June 2001)

Comparison of large STs with ⇒⇒ MAST and ⇐⇐ conventional aspect ratio NSTX and DIII-D ASDEX-Upgrade of similar size 1MA flat-top discharge in NSTX

Mid-Plane MHD

neL Ip

Te Core SXR

P-NB (1.5 MW)

D.Mueller, P3.022; J.E.Menard, P3.021 MHD-Quiescent Ohmic Plasmas Points to Existence of Pressure Peaking or Internal Barrier Formation

Increasing central Te and ne at constant current!

MH D

nel Ip

Teo Typical H-mode discharge in MAST

Plasma current ⇐Plasma current ~ 500kA

Line integral density ⇐ rapid density rise in H-mode

D α signal ⇐ Da signal indicates ELMs and ELM-free periods (shaded)

Homodyne reflectometer signal ⇐ apparent reduction in turbulence

Edge poloidal rotation ⇐ edge poloidal rotation increases after transition Soft X-ray ⇐ SXR signal: H-mode triggered by

EBW emission sawtooth crash

⇐ jump in EBW emission produced by steep edge density gradient R.J.Akers P 2.026 V Shevchenko P3.101 Energy Confinement

STs are now contributing to τ ITER FEAT E (s) 10 the International Databases

DIII-D • START data gives 1 JET confidence in the robustness MAST Predicted full of the ITER98pby2 scaling 0.1 H-mode performance of MAST • Preliminary and projected 0.01 MAST L-mode MAST data shown

START 0.001 0.001 0.01 0.1 1 10 τ ITER98Y2(s) TOK ASDEX AUG CMOD COMPAS D3D JET JFT2M JT60U PBXM PDX STARTS TCV Energy Confinement in START and MAST

100 • MAST energy confinement H-mode (MAST) is typically over 10x greater L-mode (MAST) H-mode (START) than that in START L-mode (START) • Both START and MAST

E 10 τ support ITERpby2 scaling

• MAST data shows a clear increase in τE at transition to H-mode; START data 1 does not 1 10 100 τE ( ITER IPB98(y,2) )

R. Akers, P2.026 Early transport studies on NSTX reveal exciting trends

2x 100 1x •Energy confinement time is

) typically 2x ITER89P L-mode c

e prediction s

m 0.5x

( 50

E

τ τ H-Mode •Max. E to date ~120ms MHD-Quiescent Time Time of Max W stored 0 0 50 100 τ 89P (msec ) J.Menard, P3.021 L-H transition in MAST

1.4 All DND H-Mode discharges from Campaign I

1.2 Ohmic

1.0 NBI Discharges 0.8 Ohmic DND 0.6

0.4

Greenwald number G 0.2 at L - H transition at H - L transition 0 0.1 0.2 0.3 0.4 0.5 0.6

Plasma current (MA) L-H transition in MAST

• Pthresh scaling law predictions L-H transition Power threshold in STs:[1,2] for L-H transition in a typical MAST EXP vs ITER scaling MAST shot range from 10kW to MAST CPTM vs ITER scaling NSTX EXP #104312 100kW

2.0 • To date, Pthresh required in MAST ITER

,MW =13*P PEXP and NSTX is much greater

1.5 EXP P 1.0 [1] J. A. Snipes, 24th EPS Conference, Berchtesgaden (1997), Vol 21A,EPS (1997) p961

0.5 [2] ITER Physics Basis, Nucl. Fusion 39 (1999) p.2196 (5 scalings)

0.0 0.00 0.02 0.04 0.06 0.08 0.10

ITER P ,MW L-H transition in MAST

• Pthresh scaling law predictions L-H transition Power threshold in STs:[1,2] for L-H transition in a typical MAST EXP vs ITER scaling MAST shot range from 10kW to MAST CPTM vs ITER scaling NSTX EXP #104312 100kW

MAST Ohmic #3893 2.0 • To date, Pthresh required in MAST ITER

,MW =13*P PEXP and NSTX is much greater

1.5 EXP P 1.0 [1] J. A. Snipes, 24th EPS Conference, Berchtesgaden (1997), Vol 21A,EPS (1997) p961

0.5 [2] ITER Physics Basis, Nucl. Fusion 39 (1999) p.2196 (5 scalings)

0.0 0.00 0.02 0.04 0.06 0.08 0.10

ITER P ,MW Te and Ti profile measurement in MAST

Electron and ion temperature profiles, #3873 Te profile from 40-point Thomson 1500 TS @ 290ms CX @ 278-285ms Scattering

1000 Ti profile from CX spectroscopy Temperature / eV

500 Electron and ion temperatures 0 0.2 0.4 0.6 0.8 1.0 1.2 Radius / m over 1keV are routinely obtained in both NSTX and MAST

ne, Te, Pe profiles at edge of ELM-free H- Comparison of NPA and CX estimates of mode in MAST E.Arends,P2.028 ion temperature is ongoing New Energetic Ion-Induced MHD Data Speaks to New Science

∝ 1/2 Frequency B /ne 103932/103936 • Rich variety of modes 6 0.5 TF

– Likely Compressional Alfven ) ne 2 Eigenmodes (AE’s) 4 0.4 cm

– Multiple bands 15 Tesla

– Measure effects on fast ions L (10 2 0.3 e (TRINITI) n TF • New physics regime? 0 0.2 0.00.2 0.4 –Vbeam >> VAlfven 2.5 –Vth ~ VAlfven at high beta • New theory 2.0

• DIII-D/NSTX comparison 1.5 should be revealing 1.0 – Role of aspect ratio (UC Irvine) 0.5 – Different gap structure at low A Frequency (MHz)

0.0 0.1 0.2 0.3 D. Darrow, P3.023, R.Bell, P3.024, Time (sec) E. Fredrickson, P3.019 Ongoing work by R.Akers, C.Byrom, M.Tournianski, F.Zaitsev, P.Helander, F.Cherneyshev

Neutral Particle Analyser spectra from MAST C.Byrom, P2.027 R.Akers, P2.028

18 #2889, 170-175ms, range:1.3-13.7KeV P.Helander & R.Akers 16 #2891, 170-175ms, range:2.6-27.4KeV Slab model analytic approximation 14 assuming slowing only on the electrons

12) (A.U.) 1/2 10 LACS tail D (fuel ions) ln(flux/E 8

6 H (NBI ions) T~450eV i Ti~1600eV 4 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 E (keV)

Large Angle Coulomb Scattering (LACS), routinely omitted from the multiple small- angle scattering approximation of the Fokker LACS Tail F(ξ) = δ(1-ξ) ie. Delta fn. (beam) Planck collision operator. PAPER IN PREPARATION

Full 3D Fokker Planck modelling is in progress HHFW provides effective electron heating

M. Ono (1995): Fast wave decay (absorption) rate: k 3 ~ n/ B ~ ε / B, ⊥im e ε = ω 2/ ω 2 ~ 102 pe ce

(J. Wilson, et al., PPPL, D. Swain, et al. ORNL)

J C Hosea, P3.064 Density limits in STs

June 2000 • To date, STs seem resilient to June 2001 H−Mode major disruptions at high MARFE density • Also, confinement does not appear to degrade as the Greenwald limit is approached • However, MAST data from campaign 1 was at low plasma current • Data from M2 campaign extend high-density operation space

(S. You, P2.025) 50 Beta in Spherical Tokamaks 40

1996 = 6 1997 β N 1998 30

Pegasus, β DIII-D, #80108 β = 3.5 START attained world record T , % 20 2001 N NSTX,2001 tokamak beta values by a conventional (Troyon limit) combination of high shape factor 10 tokamak β (~ I/aB) and high N.

0 0246810 B The high shape factor is a feature p /a T β of STs; can high N be achieved in normalised plasma current, I large, collisionless STs?

J.E.Menard, P3.021 n=1 magnetics (a.u.) observation of neo-classical H mode 2,1 mode tearing modes in an ST?

n=2 magnetics (a.u.) •In both NSTX and MAST, MHD appears to β set in at p ~ 0.5, triggered by large sawteeth

•On MAST, this MHD has been identified as 3,2 mode (3,2) and (2,1) tearing modes SXR (a.u.)

sawteeth (H mode) 3730 β 0.5 p ELM 0.5 ELMs 0.4 β 0.4 p 0.3

0.3 n=2 island size (a.u.) [magnetic amplitude]0.5 β The MHD tracks p, 0.2 island decays β below critical p suggestive of NTMs NBI (a.u.)

220 240 260 280 Explores NTM physics in the ST: Time (ms) see RJB poster P2.030 this afternoon! R.J. Buttery et al, P2.030; J.E.Menard, P3.021 Edge Physics Studies

In-out power asymmetries and the L-H transition

• Large inboard to outboard pressure difference observed at target Langmuir probes

• OSM2 modelling shows pressure difference B mainly driven by B - large in STs

Explores physics of ITER-relevant collisional SOL

A.Kirk, P1.053; J-W Ahn, P1.054; G Counsell, P1.055 Halo Currents in MAST & NSTX Have Been Very Modest

• Lower and more symmetric halo currents anticipated in ST than in tokamak [1,2]

[1] POMPHREY, N, BIALEK, J M & PARK, W, 38 o (1998) 449. [2] CALOUTSIS, A and GIMBLETT, C G, NSTX MAST Nuclear Fusion 38 (1999) 1487.

R.Buttery, P2.030

(ITER Physics Basis, Nuclear Fusion 39 (1999) 2137) H-mode in NBI heated 0.6MA shot #3909

(last shot before EPS) Conclusions

Research on STs is progressing fast

Insight being gained into: • Basis physics of tokamaks; plasma heating; MHD; SOL etc • ST contributing to tokamak databases (confinement, Pthresh, halo current etc) • Possibilities of ST as a route to fusion being explored

H-mode in MAST