Stanley M. KayePPPL, Princeton University

ITPA MeetingLisbon, Portugal8-10 November 2004

Confinement Scaling Experiments on NSTX

Confinement Scaling Experiments Planned and Carried Out

• H-mode scaling– Part of NSTX/MAST identity experiment– Examine specific parametric trends– Use results from systematic scans + other discharges to

develop scalings• Also L-mode

• Dimensionless scaling– t,

– (NSTX/DIII-D similarity)

NSTX Device Characteristics and Parameters

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

Systematic Parameter Scans in H-mode Plasmas Performed

• Run as part of NSTX/MAST identity experiment– Plan to run in DND, ~1.9, ~0.4

– DND not viable due to high PLH threshold

– Lower not viable at high power (disruptive)– LSN w/ PF1b (~2.1)

• Ip scan at fixed P, BT (0.45 T)– 0.6 to 1.2 MA in 4 steps– Scans at both 2 and 3 NBI sources

• P scans at fixed Ip, BT (0.45 T)

– Full scans at Ip=0.8, 1.0 MA

– Used modulated NBI if necessary to establish low power H-mode between 1 and 2 steady sources (i.e., 1 ½ sources)

Stored Energy Increases Linearly With Plasma Current

2 NBI Sources

Linear Ip scaling for three sources as well

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]

Some Confinement Trends Found to be Similar to Those at Conventional Aspect Ratio

Expand database to include other dischargesStudy global dependences of global confinement time (EFIT)

(~10% “random” uncertainty on Emag)

Thermal Confinement Times Exhibit Similar Parametric Trends

Thermal E determined by TRANSP(126 discharges ‘TRANSPed”)

~25% uncertainty on E,th

BT Dependence Observed For Both Global and Thermal Confinement

Are magnetic fluctuations important?

Core Density Fluctuations Influenced Strongly by Magnetic Fluctuations

• Long- turbulence measured in core for first time in an ST through correlation reflectomtery

• High correlation between magnetic and reflectometer phase fluctuations

• Turbulence correlation lengths long• Lcr, ne/ne larger at lower BT

Lcr scales as s

~0.45-0.7

~0.45

Transition from e-s to electromagnetic dominated core in finite-T NSTX?

Strong BT and Weaker Ip Dependence In Regressions

Ip0.65 BT

0.45 for both if dataset constrained to BT>0.31 T

Ip1.0 BT0

0.95 ne0.05 P-0.50 Ip

1.1 BT01.50 P-0.50 (no error)

Ip0.79 BT0

0.71 ne0.16 P-0.49 Ip

0.66 BT01.07 P-0.36 (error)

(Principal Component Analysis)

Comparison With “New” H-mode Scalings (from Cordey IAEA)

tauthC1

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

tauthC1

tau

th

tauthC

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

tauthCta

uth

Eth (

sec)

ELMy H-mode scalings - Cordey

P-0.61 P-0.45

All data

Global L-mode Scaling Also Exhibits Strong BT Dependence (all BT), And Linear Ip Dependence

Database not complete enough for Eth scaling

Transport Properties of NSTX Plasmas Are Also Being Studied

• Electrons dominate loss in most H-modes– NCLASS ≤ i << e – Electron transport higher at lower BT? Ion transport lower?

• CHERS recalibration continuing

Magnetic Shear Can Modify Plasma Transport Properties and Lead to Internal Transport Barriers

Low Density (ne0~21019 m-3) L-mode

TRANSP magneticdiffusion

To Do

• Combine 2004 data with previous data to try to verify BT scaling– Quantify MHD activity

– Understand difference between systematic scan and MLR Ip dependence

• Other hidden parameter dependences– ELMs– Rotation

• Compare to MAST results at similar powers, currents– Later this year

• Recalibration of CHERS data (Ti, ….)

– Recalculate E,thermal, s, and submit to ITPA database

TF Limited to ≤ 0.45 T in 2004 Campaign

• BT scan (fixed Ip and fixed q) not carried out

– Required BT ~ 0.55 T

• Dimensionless Scaling Experiments Planned But Not Carried Out – Study dependence of confinement and transport

on , holding other dimensionless variables fixed as much as possible

• Understand basis for observed transport– Differentiate between electrostatic and electromagnetic

turbulence induced transport

• Gain confidence in predictions to larger devices

• Be,th ~ *0.35-0.35

* Scan

• Change * by varying n and BT (assuming concomitant change in Te with BT)

– Adjust PNBI in order to maintain T, * (i.e., T ~ B2)

I) High *, low T (“high” n)

BT = 0.55 T, Ip = 1.1 MA, PNBI = 2 to 3 sources

II) Low *, low T (“low” n)

BT = 0.35 T, Ip = 0.7 MA, PNBI = 1 sources

Scan

Change Ip/BT (fixed q, geometry) at constant beam power

I) Low T (from * scan)

BT = 0.55 T, Ip = 1.1 MA, PNBI = 2 to 3 sources

II) High T

BT = 0.35 T, Ip = 0.7 MA, PNBI = 2 to 3 sources

III) Medium T

BT = 0.45 T, Ip = 0.9 MA, PNBI = 2 to 3 sources

LSN, ~ 1.9, ~ 0.6