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Dimensionless Parameter Scans in H-mode Plasmas

Dimensionless Parameter Scans in H-mode Plasmas. S.M. Kaye et al. 11 June 2004. Objective of XP. Study dependence of confinement and transport on b , holding other dimensionless variables fixed as much as possible Understand basis for observed transport

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Dimensionless Parameter Scans in H-mode Plasmas

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  1. Dimensionless Parameter Scans in H-mode Plasmas S.M. Kaye et al. 11 June 2004 1

  2. Objective of XP • Study dependence of confinement and transport on b, 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 2

  3. Justification • b-scaling of confinement at present is uncertain • Parameter scans from individual devices (DIII-D, JET) show weak dependence Bt~b-0.1 • Statistical analysis (ITER databases) show much stronger dependences • Bt~b-0.5 (L-mode) • Bt~b-1.1 (H-mode) • NSTX can provide a larger range of bT, bN than conventional tokamaks • May reside in different regime than JET, DIII-D owing to high-bT • Strong degradation with bT? 3

  4. Approach • Vary one dimensionless parameter while keeping others fixed as much as possible (global and local) • Global parameters (fix a, R, k) • b ~ nT/B2 • r* ~ T1/2/B • n* ~ nq/T2 • For fixed q (BT/Ip=constant), this means • r* = constant  T ~ B2 • n* = constant  n ~ B4 (at constant r*) • b = constant  T ~ B2 • Issue: n* may vary during b-scan • Need to determine n* dependence separately 4

  5. n* Scan • Change n* by varying n and BT (assuming concomitant change in Te with BT) • Adjust PNBI in order to maintain bT, r* (i.e., T ~ B2) • High n*, low bT (“high” n) BT = 0.55 T, Ip = 1.1 MA, PNBI = 2 to 3 sources II)Low n*, low bT (“low” n) BT = 0.35 T, Ip = 0.7 MA, PNBI = 1 sources 5

  6. b Scan • Change Ip/BT (fixed q, geometry) at constant beam power I) Low bT (from n* scan) BT = 0.55 T, Ip = 1.1 MA, PNBI = 2 to 3 sources II)High bT BT = 0.35 T, Ip = 0.7 MA, PNBI = 2 to 3 sources III)High bT BT = 0.45 T, Ip = 0.7=9 MA, PNBI = 2 to 3 sources LSN, k ~ 1.9, d ~ 0.6 6

  7. Long development time • First attempt to see if (and how) desired conditions and matching can be achieved (1 day XP) • Only a few conditions • Additional run time, with modified expt’l approach, may be required at a later date (FY05?) • Issues (for development of follow-on XP) • How fixed is r* (relation of change of T to change of B)? • How fixed are local parameters? • W, Ti/Te, Te’, …… • What is the level of MHD activity at higher bT? • Avoid b-limiting MHD activity 7

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