National Spherical Torus Experiment

Facility / Diagnostic Overview

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

Masayuki OnoFor the NSTX Team

46th Annual Meeting of Division of Plasma Physics, American Physical Society

November 15 - 19, 2004Savannah, Georgia

Designed to Study High-TemperatureToroidal Plasmas at Low Aspect-Ratio

Achieved ParametersAspect ratio A 1.27Elongation 2.6Triangularity 0.8Major radius R0 0.85m

Plasma Current Ip 1.5MA

Toroidal Field BT0 0.6T

Solenoid flux 0.7VsAuxiliary heating & current drive:

NBI (100kV) 7 MWRF (30MHz) 6 MWCHI 0.4MA

Pulse Length 1.1sStored Energy 400 kJT ~ 40%

• 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

Research Topics to Achieve Long-Pulse, High Performance Plasmas Are Identified

• Enhanced shaping improves ballooning stability

• Mode, rotation and error field control allows high beta

• NBI and bootstrap sustain most of current

• HHFW heating contributes to bootstrap

• EBW provides off-axis current & stabilizes tearing modes

• Particle and wall control maintains proper density

• Successfully operated for 21.1 weeks with 2460 plasmas– Met the Joule milestone of 18 weeks and programmatic goal of 20 weeks

• Significantly expanded plasma operational regimes toward the NSTX longer term goals:– High ~ 2.5 plasma controlled by faster plasma control system– Simultaneous high T - high j-bootstrap regimes expanded– Effective plasma pulse duration (pulse Ip/ITF) doubled

• Meeting all the FY 04 research milestones:– High beta plasma (T ≥ 25%) sustained for longer than 2 E

– MSE-CIF now yielding core current profile information– Core and edge fluctuations measured and characterized– EBW emission measurement suggests good coupling efficiency– New solenoid-free start-up experiments conducted with “transient” CHI

and with outer PF coils

NSTX had a very productive FY 04 Run

– Gradual joint resistance increase observed in many stressed joints at 4.5 kG

– Further joint monitoring revealed greater than anticipated flag movements

– For machine safety, TF limited to 3 kG during the last month of operation

– Out-of-spec flag movement traced to not-fully-penetrated epoxy fill

– Through R&D, a reliable full-penetration epoxy-fill technique developed

– Other improvements implemented– Appropriate design reviews are

being conducted

TF-Joints issues being resolved

NSTX plasma operations to resume in Feb. 2005

MHD

Tools to reach near ideal MHD limits

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)

Time of peak T

New PF 1A Coils to improve plasma shaping

114465

PF1A

Achieved2004

Goal of2005• Shorter PF 1A is needed to

improve the plasma shaping control ( = 2.5 and = 0.8) for advanced ST operations.

• Due to the success of high operation this year, the new PF 1A coil will be installed this year ahead of schedule.

• Should be available for FY 05 run starting in Feb. 05.

Active Control Will Enable Study of Wall Mode Interactions with Error Fields & Rotation at High T

Columbia U, GA, PPPL

Res

istiv

e W

all M

ode

Gro

wth

Rat

e (s

-1)

Internal Sensors

Conducting Plates

Vacuum Vessel

Ex-Vessel Feedback Control Coil System Status

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• A pair of the Ex-Vessel Feedback Control Coils installed and energized with the preprogrammed power supply in July, 2004.

• Several experiments were performed:

–locked mode control, -plasma rotation control, -error field amplification, - Resistive Wall Modes physics.

Full Ex-Vessel Feedback Control Coil System is scheduled to be available for the FY 05 experimental run.

Transport and Confinement

Measuring Fluctuations to gain understanding of plasma transport

Pfusion ~ H5-7

Measured magnetic field pitch in a ST for the first time

MSE-CIF j(r) diagnostic

MSE Multistage Lyot Filter• Calibrated in situ and achieved the desired statistical errors of 0.2°/0.4° at 4.5/3.0 kG• Initial 8 ch data were collected with 4 ch activated at one time.• MSE data being incorporated into EFIT and other codes.

time(sec)

MSE-CIF measured q(0) and Raxis

• q(0) ~ 0.8 before ~1 after crash• Raxis shift inboard ~ 2 cm after crash• 5 msec resolution

Nova Photonic Inc

8 ch will be available for the FY 05 run and increased to 12 - 14 ch.

Correlation length measurements

Reflectometry Turbulence Measurements

UCLA Reflectometer

• Array of microwave reflectometer horns

• Aligned perpendicular to magnetic flux surfaces

Fast X-ray Camera Reveals Core Electron Dynamics

t=0 t=90s t=180s t=270s

Images with time resolution down to ~ 2 µs

CCD camera

Image intensifierinside magnetic shield

Pinholes andBe foils

PSIImage of core n=1 tearing mode

High k scattering measurements will be developed in FY’ 05

• Initial system will allow range of k measurements in select locations (2 - 20 cm-1)

• Access to ETG possible!

• Major installation this opening.

High k scattering

Luhmann (UC Davis), Munsat (U. Colorado) Mazzucato, Park, Smith (Princeton U.)

UCD

Non-Inductive SustainmentHHFW Off-axis Heating and CD

EBW CD for profile control*

Multiple Roles of HHFW

• Bulk plasma heating to enhance bootstrap currents in advanced ST Operations

• Plasma start-up and current ramp-up

• Super-Alfvénic energetic particle physics (UCI)

- HHFW modification of NBI fast ion distribution function

- TAE mode stablization

• Edge physics for RF- Anomalous edge ion heating- Phase dependent heating

efficiency- Parametric instabilities

&

12 antennas powered by 6 MW sources

ORNL, UCI, MIT, GA, CompX

EBWs Can Generate Critical Off-Axis Current Drive in NSTX at High

NSTX, = 40%

00 1r/a

Charles Kessel (PPPL) Tokamak Simulation Code

Comp-X

• ~ 100 kA of off-axis CD neededto sustain ~ 40% in NSTX

• Cannot use ECCD in NSTX since pe/ce ~ 3-10

• Modeling indicates that EBWCD can provide needed current

• EBWCD may also assist startupand stabilize NTM's

• 4 MW, 28 GHz EBWCD system planned for NSTX

Strong Diffusion Near Trapped-Passing BoundaryEnables Efficient Ohkawa Current Drive

CompX GENRAY/CQL3D

NSTX, T = 42%

1 MW “Proof-of-Principal” EBW System Tests Viability of Heating & Current Drive in NSTX

1 MW

• ~ 750 kW EBW power delivered to plasma--> Use EBWCD to locally

drive 30-40 kA

• If 1 MW system is successful increase RF power to 4 MW with addition of three more gyrotrons, transmission lines & launchers by

--> Provide 3 MW of EBW power in the plasma & Generate > 100 kA

(CPI or Gycom)

Power and Particle Handling

NSTX has largest “P/R” in tokamaks/STs comparable to ITER

viewing area≈ 25x25 cm

spatial resolution≈ 1-2 cm

Gas Puff Imaging Diagnostic

RF limiter

separatrix

Using Princeton Scientific Instruments PSI-5 camera 250,000 frames/sec @ 64 x 64 pixels/frame300 frames/shot, 14 bit digitizer, intensified

Typical image

PSI, Nova Photonics

Fast probe provided edge density and temperarure profile

ne rises faster than Te

UCSD

Outer divertor not detached yetLLNL

Lithium Pellets Injection to Control Particle Recycling

• Capability for injecting solid pellets (<1 – 5 mg) & powder (micro-pellets)

• 10 – 200 m/s radial injection

• 1 – 8 pellets per discharge

• 400 pellet capacity

• Develop optimized scenariosOUTBOARD VIEW

LOAD PORT

PROPELLENT PORT

AXLE FEEDTHRU

400 BARREL TURRET

Lithium “vapor ball” surrounding pellet as it approaches the center-

stack

Lithium vapor spreading along the

center-stack

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In-board gas injector

Lithium Pellet moving through

plasma after entering at 296ms

H. Kugel

Supersonic gas jet penetrates well through a thick scrape-off layer

DEGAS 2 Neutral transport modeling reproduces observed features 114449

camera

CHERS

Preliminary fueling efficiency estimate shows ~ 3 - 4 times improvement over gas puff LLNL

• Quartz microbalance shows time

resolved deposition on NSTX in

geometry typical of a diagnostic

mirror - results show significant

deposition after plasma discharge.

• Novel electrostatic surface particle

detector works well in air and vacuum

environments.

• First time-resolved measurements of

surface dust in tokamaks.

NSTX is developing ITER/BP relevant time resolved surface deposition monitors

temperature

deposition

Deposition over 4 shots 112014-017.

C. Skinner

Solenoid-Free Start-Up

Tokamaks and STs must eliminate OH solenoid

Coaxial Helicity InjectionOuter poloidal field start-up

Capacitor Bank for Transient-CHI Start-Up

Absorber

Injector

• Successfully installed and commissioned new 2 kV, 100 kJ capacitor bank.

• Conducted initial experiments:

-Reduced the required gas pressure for a successful plasma break down by a factor of 3.

- Toroidal plasma currents of up to 150 kA were generated by this technique without induction from the central solenoid.

- High current multiplication ratio; a record current multiplication of 40 was achieved in NSTX for the first time.

• Direct gas and ECH injection into the injector region implemented to facilitate plasma initiation.

Univ. Washington

J. Menard

Improved preionization and PF coil waveforms to be optimized

Solenoid-free Start-up with Outer Poloidal Field CoilsThree scenarios being investigated

Research Tool Development on NSTX

Supports Fusion and Plasma Sciences

• Expand MHD operation space: RWM and PF 1A coil systems

• Understand confinement: Current Profile, X-rays, Fluctuation diagnostics

• Explore super-Alfvenic energetic ion physics: HHFW as a new tool

• Gain understanding of HHFW heating and current drive

• Develop new efficient edge current drive tool: EBW

• Arrays of research tools for heat and particle control

• Develop practical solenoid-free start-up tools: CHI and outer PF coils