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XP414: Aspect Ratio Effects near the High b p Equilibrium Limit

XP414: Aspect Ratio Effects near the High b p Equilibrium Limit. Goals Examine aspect ratio dependence of rotation effects at high b p Maximize D Shafranov /a = 1/(2A)*( b p (1 + 5/6 M 2 ) + 1/4); (High A limit) Test strong theoretical dependence of (R Pmax – R axis )/a on aspect ratio

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XP414: Aspect Ratio Effects near the High b p Equilibrium Limit

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  1. XP414: Aspect Ratio Effects near the High bp Equilibrium Limit • Goals • Examine aspect ratio dependence of rotation effects at high bp • Maximize DShafranov/a = 1/(2A)*(bp(1 + 5/6 M2) + 1/4); (High A limit) • Test strong theoretical dependence of (RPmax– Raxis)/a on aspect ratio • Produce maximum bp and bN in NSTX • Approach (reach?) the equilibrium limit (ebp > 1.8 based on 110184) • Reach bN = 8 (conceptual design milestone) • potential for bN = 10 in best case scenario • Test equilibrium reconstruction at maximum bp • Determine global stability / confinement in new equilibrium regime • Increased diamagnetism and omnigeniety; drift reversal • test theoretical expectation of improved confinement

  2. Set up equilibria of various aspect ratio Scan bp by scanning Ip at max NBI power Utilize Ip ramp-down to produce maximum bN, bp Shot 110184 had maximum bN = 6.8 during Ip ramp Diamagnetism increased in this phase Rotational shift of pressure contours has strong aspect ratio dependence Run plan "Tokamak Equilibria with Toroidal Flows" by M. Furukawa, et al. (RPmax – Raxis) / a (%) On–axis Mach = 0.2 A

  3. Vertical field at inboard midplane reduced by more than a factor of 4 at highest bp High bp phase reached with only two NBI sources (3.3 MW power)! High bp plasma slightly diamagnetic Highest bp plasma is approaching the equilibrium limit Bp > 0.20 T Z (m) Bp at Z = 0 (T) 110184 t = 0.325 s bp = 0.95 ebp = 0.66 Bp < 0.05 T Z (m) Bp at Z = 0 (T) 110184 t = 0.583 s bp = 2.3 ebp = 1.8

  4. Shafranov shift maximized at high bp Rotational shift of pressure contours (Rpmax– Raxis)/a = 8% Maximum bp configurations will test EFIT rotation reconstructions Poloidal flux and pressure 40 2 30 20 Pkinetic (kPa) 10 1 0 0 0.5 1.0 1.5 2.0 Z(m) 0 R(m) 5 108420 t = 0.403 s 4 -1 3 Pdynamic (kPa) 2 1 -2 0 0.5 1.0 1.5 2.0 0.8 1.0 1.2 1.4 1.6 R(m) R(m)

  5. XP414: Aspect Ratio Effects at High bp - Run plan • Scan aspect ratio and poloidal beta (40 shots) Task Number of Shots A) Use shot 110184 as template, Bt = 4.5 kG, maintain fixed, lowest aspect ratio ~ 1.27; late Ip ramp-down to 0.6 MA, full NBI power (i) Set up initial Ip = 0.8 MA; attain H-mode (at bN > 6) 4 (ii) Initial Ip = 0.6 MA; 2 (iii) Initial Ip = 1.0 MA 2 (iv) Attempt initial Ip = 1.2 MA 4 B) Repeat with A increasing to 1.6 by increasing inner gap 8 C) Repeat with A increasing to 1.6 to maximum by increasing inner gap 8 D) Get one more aspect ratio or vary Mach number 8 Total shots: 36

  6. High bp equilibria can be investigated at several points (schematic only: timing not accurate) • Aspect ratio in 110184 increased in time – vary A in similar way 6 X10 1.2 MA 1.0 1.0 MA Plasma current 0.8 MA 0.6 MA Amps 0.5 “standard” high bp scan taken here “ultra” high bp taken here 0 0 0.1 0.2 0.3 0.4 0.5 3 Default NBI timing Bt = 4.5 kG Source C 2 (arb) Source A 1 Source B 0 0 0.1 0.2 0.3 0.4 0.5 Time (Seconds)

  7. Duration and Required / Desired Diagnostics • XP could be completed in 1.5 run days • Required • CHERS toroidal rotation measurement (with increased resolution) • Internal RWM sensors • Thomson scattering • Diamagnetic loop • USXR • Desired • Advanced USXR diagnostics • Toroidal Mirnov array • Fast camera

  8. Xp 414 should be run, and early in the 2004 • Why run it? • First documentation of ultra-high bp ST plasma • Investigation of an operational regime only produced theoretically • Several physics topics to investigate • Significant extension of NSTX stable operating space • Extreme test of equilibrium reconstruction with rotation • Good way to publish equilibrium reconstructions with rotation • Never published. New publication in collaboration with Lang Lao • Not a transient plasma – object is to maintain for several tE • Why run it early? • Fits into short-term goal of reaching high-beta early in run • Required machine conditions similar to high bt run • Possible candidate for IAEA publication • Abstracts due to US committee usually due late Feb, early March • RWM feedback work will occur too late for independent IAEA paper • Tight timeline for RWM passive stabilization work to make IAEA • RWM rotation physics paper possible for independent IAEA paper

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