Energy Confinement Scaling in the Low Aspect Ratio National Spherical Torus Experiment (NSTX) S. M. Kaye, M.G. Bell, R.E. Bell, E.D. Fredrickson, B.P. LeBlanc, K.C. Lee, S. Lynch and S.A. Sabbagh 47 th APS – DPP Meeting Oct 24-28, 2005 Denver, Co. Supported by Office of Science Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAERI Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec College W&M Colorado Sch Mines Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin

SMK – APS-DPP Scaling Experiments Performed to Assess Effect of Aspect Ratio on Energy Confinement Data from 2004 experiments (ELM-free and ELMy H-mode) I p = MA, B T = T, n e =1.5- 7e19 m -3, P NBI =1.5-7 MW,  = Data from 2005 experiments being analyzed NSTX extends parameter space –Allows for exploration of confinement trends at high- , low-  –Connect to conventional aspect ratio database for assessment of R/a International H-mode Confinement Database NSTX  correlation

SMK – APS-DPP Results of Systematic Parametric Scans Indicate Some Scalings Similar to Those at Conventional R/a ~ Linear current scaling (correlated with density) Slightly weaker power degradation than at conventional R/a B T =0.45 T  E,thermal calculated in TRANSP

SMK – APS-DPP Data Exhibits a B T Dependence and Significant Shot – Shot Variability H-factor depends on ELM severity and inversely on plasma shaping  98y,2 ~  0.8

SMK – APS-DPP Statistical Analyses Indicate a Stronger B T but Weaker I p Dependence Than Exhibited at Conventional Aspect Ratio B  ~     B  ~     Variation in power scaling exponents among methods leads to range of  -scaling dependences (from null to unfavorable) B T and  scaling to be studied in future experiments through dedicated scans (strong   –  correlation in present NSTX dataset) Principal Component – Error in Variables Ordinary Least Squares Regression

SMK – APS-DPP NSTX Confinement Data In the International H-mode Database Has Been Used to Determine Aspect Ratio Scaling   E,th IPB98(y,2) ~ I p 0.93 B T 0.15 n e 0.41 P L,th  0.78 M 0.19 R 1.97  0.58 B  ~    2.7  -0.9   0.01   E,th fit ~ I p 0.73 B T 0.36 n e 0.39 P L,th R 2.14  1.03 B  ~    2.78    0.12 ITER98PB(y,2) and other scalings developed with data from  <0.5 do not describe low R/a data well Scalings developed with low R/a data exhibit stronger  and less unfavorable  dependences  –  correlated in database: leads to difficulty in establishing these dependences uniquely

SMK – APS-DPP NSTX Confinement Studies Have Been Carried Out Systematic scans indicate current, power scaling similar to those at higher aspect ratio –Density increases with plasma current –Weaker current scaling using statistical methods –Scalings show B  ~  0 to  (  –   correlation) Data shows scaling with B T and significant shot – shot variability –Some variability can be attributed to the effects of shaping, ELM amplitude, density fluctuation amplitude (weak) More studies need to be done –Assess B T dependence through dedicated scans –Perform dedicated  and shape (  ) scans –Complete analysis of more recent data

SMK – APS-DPP Shot – Shot Confinement Variability Studied in Context of Other Plasma Variations No dependence on rotation or MHD activity (at any frequency) Weak dependence on density fluctuation amplitude