Study of NSTX Electron Density and Magnetic Field Fluctuation using the FIReTIP System K.C. Lee, C.W. Domier, M. Johnson, N.C. Luhmann, Jr. University of California at Davis H. K. Park, E. D. Fredrickson, S. A. Sabbagh, S. Zweben PPPL, Princeton University NSTX Research team Princeton Plasma Physics Laboratory

Abstract The Far Infra Red Tangential Interferometry and Polarimetry (FIReTIP) system on NSTX is capable of simultaneously measuring fluctuations of electron density and magnetic field. Magnetic fields fluctuations (∂B) can be isolated during MHD activity such as internal kinks, since interferometry provides electron density information while polarimetry provides Faraday rotation data along the same beam path. In this paper, a comparison study of the electron density fluctuations with the fluctuations measured by the Gas Puffing Image (GPI) at the boundary plasmas will be discussed. A discussion of the measurements from 3 channels at different tangencies including comparisons with EFIT equilibrium parameters and the structure of MHD modes will be presented. L/H transition study by Gyro-Center Shift and ELMs propagation study are in progress. This work was supported by U.S. DoE Contracts DE-FG02-99ER54518 and DE-AC02-76CH03073

Contents n Overview of FIReTIP system o Introduction o Upgrades of 2005/2006 n TAE, EPM Measurement n Localized Measurements by FIReTIP o Magnetic Field Fluctuation o Comparison with GPI data o ELMs Study by FIReTIP o H-mode transition & Gyro-center shift n Summary

3-D CAD of Far Infra Red Tangential Interferometer Polarimeter

Principle of FIReTIP system on NSTX w LO – w 1 = 4.0±1.0 MHz w LO – w 2 = 6.0±1.0 MHz Rommers & Howard 3-laser system [K.C. Lee et.al., IEEE Trans. on Plasma 32,1721(2004)] Sampling rate: 500kHz (2005)=> ~1MHz (2006)

FIReTIP channels (ch1, ch2, ch3, ch7 for 2005) New for 2005 n Optical components of Ch4 & Ch5 are installed n Test run of Ch5 & heterodyne visible two color compensation for Ch7 are in progress GPI

TAE/f.b.s measurement by FIReTIP Electron density fluctuation spectrum of # ► TAE 150~200kHz compared with Magnetic coil data showed similarity and difference in different channels ► localized fishbones similarity in Ch1, Ch2 & Ch3 due to entire coverage of core plasma of measurement Ch1Ch2 Ch3Ch7

EPM measurement by FIReTIP Electron density fluctuation spectrum of # ► EPM (Energetic Particle Mode) at 0.37~0.4 sec showed higher harmonics up to ~12 th order ► periodic fishbones (0.34~0.37 sec) localized mainly on Ch3 with chirping frequency around 20kHz

time (sec) Faraday rotation measurement by FIReTIP ► Faraday rotation and electron density data on MHD oscillation showed phase difference ► Phase difference => information of magnetic field oscillation ► Different channels showed different pattern of oscillations <= mode structure of MHD

Magnetic fluctuation measurement by FIReTIP (Polarimetry)(Interferometry), where, Polarimetry and interferometry data provide magnetic field fluctuation: In case of constant frequency (MHD) oscillations, Faraday rotation: From measurements,, where

Magnetic fluctuation measurement by FIReTIP θ Phase of magnetic field fluctuation have tendency to increase with beta toroidal.

Comparison FIReTIP and Gas Puffing Image (GPI) ► Periodic Oscillation for the known edge MHD modes (n=2, m=2) ► Phase difference of GPI and FIReTIP edge channel agreed to the mode numbers and location differences of two measurements ► outer channels measure only one poloidal mode peak while the inner channels measure both peaks simultaneously

E r and V p begin to change 10 to 20 ms before L-H transition (here at t ~ sec) H-mode Shot Time (s) V p (km/s) V T (km/s) E r (kV/m) I p (MA) E r (kV/m) H-mode transition study by FIReTIP (2004)

H-mode transition study by FIReTIP (2005) FIReTIP Ch7(edge) Rt=150cm D α (lower) D α (upper) EFIT-Gap (bottom) EFIT-r (mid-out) EFIT-r (mid-in) Te (max) time (sec)

H-mode transition study by FIReTIP (continue)  no E r pre-cursor was showed on 2005 experiment.  electron density of FIReTIP edge channel showed density perturbation (green circles) just before the L/H transition of ohmic plasmas (LSN).  perturbations last ~msec.  among EFIT plasma locations gap-bottom was coincident with transition time => importance of neutral flow at diverter  H-mode transitions occurred while plasma temperature was increasing.  application of Gyro-Center Shift theory* to NSTX is in progress.

ELM propagation measurement by FIReTIP ELMs propagate clockwise

Gyro-Center Shift* by Charge Exchange hot ion neutral core boundary *Submitted to Physics of Plasmas K.C. Lee

Gyro-Center Shift Calculation average gyro-center shift over (-r L ≤ r ≤ r L ) per reaction x reaction rate of an ion with r L and gyro-center at a point average gyro-center shift rate = σv i ∫rf(r)n n (r)dr σv i ∫f(r)n n (r)dr = (½)r L (n + -n - )/(n + +n - ) (½)σv i (n + +n - ) (¼)σv i r L (n + -n - ) current density (charge separation) different from friction[D’lppolito’02] byand

Radial electric field calculation result for DIII-D Gyro-Center Shift Calculation (continue) Gyro-center shift by charge exchange reaction => major source of E r formation

n 2005 measurement and analysis o Localized TAE and f.b.s measurements o Energetic Particle Mode (RPM) measurements with higher order harmonics o Faraday rotation analysis with comparison of electron density fluctuation on MHD oscillations => Study of magnetic field fluctuation o Comparison with GPI data with mode structure of MHD o FIReTIP edge channel density perturbation at the H-mode transition o ELM propagation measurements by FIReTIP n FIReTIP system upgrade and future works o Channel 5 (Rt=132 cm) will be tested for profile reconstruction of electron density o Hetero-dyne visible two color vibration compensation for Ch7 o Application of Gyro-Center Shift theory to NSTX Summary and Future Plan