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
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