Fast 2-D Tangential Imaging of Edge Turbulence: Neon Mantle (draft XP) R. J. Maqueda, S. J. Zweben, J. Strachan C. Bush, D. Stutman, V. Soukhanovskii Goal: measure the edge turbulence structure vs. time during controlled impurity puff experiments. Approach: use Gas Puff Imaging with new Phantom 7 camera while increasing neon puff up to doubling the total radiated power (“radiative mantle”).

Why study “blobs”? “Blob”: 2-D cross-section (poloidal vs. radial plane) of filamentary structures which posses a very long parallel wavelength relative to total magnetic field. Intermittent, convective transport. Localized deposition of energy on plasma facing components. Apparent result of “non-linear” phase of edge turbulence. In NSTX Correlation lengths: ~4 cm. Auto correlation times:  s. Velocity: up to 3 km/s.

Proposed XP is part of a more general study on edge turbulence, H-mode physics and ELMs Poloidal distribution of edge turbulence Is the turbulence suppressed by “good” curvature? What are the characteristics in the X-point region? Look for, and measure, turbulent structures on high-field side gas puff, shoulder gas puff, and divertor (X-point) region. L-H mode transitions Where do the transitions begin? Does it depend on divertor configuration? Observe transitions with fish-eye view at > frames/s. Look for sheared/zonal flows in the divertor region.

ELM physics Are the “blobs” observed at the edge “micro” ELMs? Where are the ELMs born? Does it depend on the type of ELM? Observe evolution of ELM structures with tangential GPI. Observe ELM structures with fish-eye view and fast frame rates. New for 2005 campaign *** Phantom 7 fast-framing digital camera *** 64 pixels x 64 pixels at frames/s Up to frames/shot 12 bit digitization...most of these measurements can be done in piggyback mode Proposed XP is part of a more general study on edge turbulence, H-mode physics and ELMs (cont.)

Gas Puff Imaging (GPI) I  n o n e f(n e,T e ) Main diagnostic for proposed XP Non-perturbing, deuterium or helium puff “Automatic” blob detection

Why impurity puff experiments? (part 1) Physics of blobs depends on both local (“blob”) and background plasma characteristics Highly radiating mid-Z impurities may “radiatively condense” blob affecting its characteristics and movement.

Why impurity puff experiments? (part 2) Enhanced confimenent regimes have been achieved in other experiments through the addition of medium Z impurities: “ radiative mantles ”, “ RI-mode ”, etc. In general, impurities showed no accumulation in the core while an enhancement factor relative to empirical L-mode scaling laws was achieved. TEXTOR, “Messiaen, A.M. et al, Nucl. Fus. 1994”

Proposed experimental run plan Target plasma 1 MA, 0.45 T LSN discharges (...or similar lower B versions). Reduce inner gap (“almost” IWL) to prevent H-mode access. NBI power such that H-mode is achieved if inner gas is increased. Use “shoulder puff” to fuel discharge. Experiment Add controlled amounts of neon soon after NBI is turned on (outer miplane gas puff). Increase neon puff in successive discharges until doubling total radiated power. Perform GPI measurement at two times (different discharges): 1) as neon puff is being established 2) once “steady state” is reached (time permitting) Increase inner gap to obtain H-mode and add neon puff.

Proposed experimental run plan Summary Development of target plasma:3 shots 5 neon puff strengths (from no puff to 100 % radiation increase)x 2 GPI gas puff timingx 2 discharge statistics= 20 shots Additional shots (H-mode discharges)5 shots Total discharges 28 shots Diagnostics GPI Other edge fluctuation measurements: reflectometer, reciprocating probe. Spectroscopy: spectrometers and filter scopes, soft X-ray measurements for neon, plasma TV with neon filter(s) available on wheel. Neon effects: Z eff, total radiation bolometer arrays.

Phantom 7 camera