SMK – IAEA ‘04 1

Stanley M. Kayefor the NSTX Research TeamPPPL, Princeton University, U.S.A.

20th IAEA Fusion Energy ConferenceVilamoura, Portugal

November 2004

Progress Towards High Performance Plasmas in the National Spherical Torus

Experiment (NSTX)

Supported by

Columbia UComp-X

General AtomicsINEL

Johns Hopkins ULANLLLNL

LodestarMIT

Nova PhotonicsNYU

ORNLPPPL

PSISNL

UC DavisUC Irvine

UCLAUCSD

U MarylandU New Mexico

U RochesterU Washington

U WisconsinCulham Sci Ctr

Hiroshima UHIST

Kyushu Tokai UNiigata U

Tsukuba UU Tokyo

JAERIIoffe Inst

TRINITIKBSI

KAISTENEA, Frascati

CEA, CadaracheIPP, Jülich

IPP, GarchingU Quebec

SMK – IAEA ‘04 2

NSTX Is Designed To Study Toroidal Confinement Physics at Low Aspect Ratio and High T

Aspect ratio A 1.27

Elongation 2.5

Triangularity 0.8

Major radius R0 0.85m

Plasma Current Ip 1.5MA

Toroidal Field BT0 0.6T

Pulse Length 1s

Auxiliary heating:

NBI (100kV) 7 MW

RF (30MHz) 6 MW

Central temperature1 – 3 keV

Aspect ratio A 1.27

Elongation 2.5

Triangularity 0.8

Major radius R0 0.85m

Plasma Current Ip 1.5MA

Toroidal Field BT0 0.6T

Pulse Length 1s

Auxiliary heating:

NBI (100kV) 7 MW

RF (30MHz) 6 MW

Central temperature1 – 3 keV

Establish physics database for future Spherical Torus (ST) devices

Non-solenoidal current generation/sustainment key element of program

SMK – IAEA ‘04 3

• Ip flattop ~ 3.5skin

• W flattop ~ 10 E

• T>20%, N>5, E/E,L>1.5 for ~10 E

• IBS/Ip = 0.5, IBeam/Ip = 0.1

Operational and Physics Advances Have Led to Significant Progress Towards Goal of High-T, Non-Inductive Operation

fBS = IBS/Ip = 0.5 1/2 pol

T = <p>/(BT02/20)

H-mode plasma

SMK – IAEA ‘04 4

Improved Plasma Control System Opened Operating Window During 2004 Campaign

Reduced latency improved vertical control at high-, high-T

Capability for higher allowed higher IP/aBT

Significantly more high-T

(N=6.8 %mT/MA achieved)

More routine high Longer current flattop duration pulse = (>0.85 Ip,max)

SMK – IAEA ‘04 5

T Can Be Limited by Internal Modes – Rotation Dynamics Important

• Flow shear/diamagnetic effects slow internal mode growth• Coupled 2/1, 1/1 modes eventually reduce rotation T collapse

Menard EX/P2-26

SMK – IAEA ‘04 6

Resistive Wall Modes Can Limit T at Low q

Newly installed active coils for error field/RWM control will provide means to stabilize external modes

Sabbagh EX/3-2

10% above no-wall limit for manywall times (wall ~ 5 msec)

n=1-3 components measured bynew internal magnetic sensors

- first observation of n>1

NSTX exhibits a broad spectrum of instabilities driven by fast ion resonance

Fredrickson EX 5-3

N

(G)

(G)

(G)

Bp(n=1)(deg

)B

z(G

)

n=1 no wall unstable

n=2,3

|Bp|(n=1)

|Bp|(n=2)

|Bp|(n=3)

(f<40 kHz, odd-n)

0.22 0.24 0.26 0.28t(s)

-20-10010200

100200300010

20300102030400204060

02

46

0.18 0.20 0.22 0.24 0.26 0.28t(s)

-20-10010200

1002003000

10

20010

20300102030

02

46

114147

FIG. 1

114452

Critical rotation frequency ~ 1/q2

SMK – IAEA ‘04 7

Systematic Scans Reveal Stored Energy Increases With Plasma Current in NBI Discharges

~ Linear dependence at fixed BT, Pinj

0

5

0.0 0.1 0.2 0.3 0.4 0.50

100

Time (s)

0

5

0

1

0.5 1.0 1.5Radius (m)

Ip [MA]

PNB [MW]

WMHD [kJ]

We [kJ]

100200

300

0

1

0

ne [1019m-3]

Te [keV]

ne [1019 m-3]

Te [keV]

SMK – IAEA ‘04 8

Parametric Dependences of NSTX Energy Confinement Time Established

Some tokamak trends reproduced in thermal and global E’s

• E exceeds tokamak scalings• L~H; L more transient• BT dependence observed

E,th/pby2 = 0.5 to 1.4

Global E from magnetics

SMK – IAEA ‘04 9

Long-Wavelength Turbulence Measured in Core for First Time in an ST Through Correlation Reflectometery

Core density fluctuations influenced strongly by magnetic fluctuations – radial correlation lengths long

Lc, ne/ne larger at lower BT

~0.45-0.7

Lc scales as s

SMK – IAEA ‘04 10

NSTX Has Investigated Regimes of ReducedElectron Transport

• Electron transport generally dominant (neo≤i<<e in H-mode)• Produced electron ITBs using fast current ramp, early NBI in low density (ne0~21019 m-3) L-modes

ETG modes predicted to be linearly stable in region of reversed shear(gyrokinetic calculations)

Stutman EX/P2-8

TRANSP magneticdiffusion

Reverse shear corroborated by observation of double-tearing modes

SMK – IAEA ‘04 11

NSTX Has Developed MSE for Current Profile Measurements at Low BT

• Preliminary reconstructions performed• Agreement with TRANSP modeling good

Equilibrium reconstruction with MSE constraint

SMK – IAEA ‘04 12

Toroidal Current Generated Without a Solenoid

1) PF-only startup 2) Transient Co-Axial Helicity Injection

- 20 kA generated - Ip up to 140 kA, Ip/Iinjector up to 40

Goal is to maintain plasma onoutside where Vloop is high

Goal is to extend Ip beyondduration of Iinjector

Non-solenoidal current generation/sustainment essential in future ST

4 5 8 10 12 146 7 9 11 13Time (ms)

1

0

100

0

0

2

4ICHI (kA)

Ip (kA)

VCHI (kV)

114374

SMK – IAEA ‘04 13

Hot component

Cold component

New Diagnostics/Experiments Leading to Better Understanding of HHFW Absorption

k||=14 m-1 80% 7 m-1 (ctr) 70% -7 m-1 (co) 40% -3 m-1 ~10%

Edge ion heating observed during HHFW

Impact of edge heating on HHFW absorption being studied

Absorption deficit observed during HHFW heating - Dependent on wave phase

% Absorption

Edge ion heating associated with parametric decay of HHFWinto IBW

SMK – IAEA ‘04 14

70 to 90% of Power Accounted for inNBI Discharges

• Most power to divertor plates (35%)

• Inner divertor detachment for ne 21019 m-3

– Reduced heat flux: 1 MW/m2

• Outer divertor always attached– qheat up to 10 MW/m2

– Attempt to detach with higher nedge &/or Prad,div

SMK – IAEA ‘04 15

A New Type of ELM With Minimal Energy Loss/Power Loading Has Been Observed

Maingi EX/2-2

D (au) Wstored (kJ)

Type “V”

Mixed Type I + Type “V”

Different ELMs reside in different regimes

SMK – IAEA ‘04 16

Significant Progress Made in Addressing ST Physics Goals and in Increasing Our Understanding of Toroidal Confinement Physics

• Improved plasma control and routine high elongation• High T and enhanced confinement for long duration (several E)

– T up to ~40%, N up to 6.8 %m T/MA– Developing understanding of -limits and methods to control MHD

modes– Developing integrated understanding of plasma transport and methods

to reduce transport• Non-solenoidal plasma startup• Regimes of reduced power loading • Current flattops for several current relaxation times

– Significant sustained non-inductive current at high-T (60% of total)

• Integration of achievements form basis for moving forward with ST concept– Many NSTX accomplishments consistent with requirements for ST

Component Test Facility (Wilson FT/3-1a,b)

SMK – IAEA ‘04 17

Backup

SMK – IAEA ‘04 18

Longer Duration High-T Achieved With Edge Density Control

• He pre-conditioning to control recycling

•Early NBI and pause in Ip ramp trigger early H-mode

• T max at IP/ITF ~ 1

T >30 % for ~2E

Large flow shear and strong gradients

observed at time of peak T 0 1 2

R (m)

Z (

m)

0

1

2

-2

-1

1.0 1.50.5R (m)

ne [1020m-3]

Ti, Te [keV]

0

1

vi [km/s]

0

0.5

0

100

200

112600, 0.55s 112600, 0.55s

0 1 2R (m)

Z (

m)

0

1

2

-2

-1

1.0 1.50.5R (m)

ne [1020m-3]

Ti, Te [keV]

0

1

vi [km/s]

0

0.5

0

100

200

112600, 0.55s 112600, 0.55s

L-H