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

US DEPARTMENT OF ENERGY

DOE UC DAVISDEPARTMENT OF APPLIED SCIENCE

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 teamPrinceton 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

Overview of FIReTIP system Introduction Upgrades of 2005/2006

TAE, EPM Measurement

Localized Measurements by FIReTIP Magnetic Field Fluctuation Comparison with GPI data ELMs Study by FIReTIP H-mode transition & Gyro-center shift

Summary



3-D CAD of FarInfraRedTangentialInterferometerPolarimeter



Principle of FIReTIP system on NSTX

wLO – w1 = 4.0±1.0 MHz

wLO – w2 = 6.0±1.0 MHz

FIR Laser

NSTX Plasma /4

Plate

Reference Mixer

Signal Mixer

Polarizer

1

Stark Laser

2

LO

R L

Polarizers

S R S L

FIR Laser

x 2.6 10 132 n( x )BT ( x )d x o

x

x 2.8 10 15 n( x )d x o

x

ifdt

td

)(

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

Optical components of Ch4 & Ch5 are installed

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 #113655

►TAE 150~200kHzcompared withMagnetic coil data showed similarity and difference in different channels

►localized fishbonessimilarity in Ch1, Ch2 & Ch3 due to entire coverage of core plasma of measurement

Ch1 Ch2

Ch3 Ch7



EPM measurement by FIReTIP

Electron density fluctuation spectrum of #113114

►EPM (Energetic Particle Mode)at 0.37~0.4 secshowed higher harmonics up to ~12th 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



)cos(~

taF

F

Magnetic fluctuation measurement by FIReTIP

(Polarimetry) tbn

n

e

e cos~

(Interferometry)

)cos(~

tAB

B

T

T, where cos222 abbaA ,

Polarimetry and interferometry data provide magnetic field fluctuation:

In case of constant frequency (MHD) oscillations, Faraday rotation:

From measurements

,dlnB eTF TTT BBB~

0 eee nnn ~0 ,

,

where

A

ba

coscos



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



Er and Vp begin to change 10 to 20 ms before L-H transition (here at t ~ 0.220 sec)

H-mode

Shot 113350

Time (s)

Vp (km/s)

VT (km/s)

Er (kV/m)

Ip (MA)

0.16 0.20 0.24 0.28

1.00.8

0.4

0.0-0.5

-1.0

-10

5

0

-5

-1.5

-2.0

-2.5

-1550

-10

-15

-5

Er (kV/m)

H-mode transition study by FIReTIP (2004)



H-mode transition study by FIReTIP (2005)FIReTIPCh7(edge)Rt=150cm

Dα(lower)

Dα(upper)

EFIT-Gap(bottom)

EFIT-r(mid-out)

EFIT-r(mid-in)

Te (max)

time (sec)



H-mode transition study by FIReTIP (continue)

no Er 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

bou

nd

ary

*Submitted to Physics of PlasmasK.C. Lee



Gyro-Center Shift Calculation average gyro-center

shift over(-rL ≤ r ≤ rL)per reaction

xreaction rate of an ion with rL and gyro-center

at a point

average gyro-center

shift rate

=

σvi ∫rf(r)nn(r)drσvi ∫f(r)nn(r)dr= (½)rL(n+-n-)/(n++n-)

(½)σvi(n++n-)(¼)σvirL(n+-n-)

current density (charge separation) different from friction[D’lppolito’02]

r

nrv n

Li

2

2

1

r

nv

Bq

TnmJ n

ii

iiiGCSr

2

Bq

vmr

i

iL

i

i

m

Tv

2by and

r

nrvenJ n

LiiGCS

r

2

2

1



Radial electric field calculation result for DIII-D

Gyro-Center Shift Calculation (continue)

Gyro-center shift by charge exchange reaction => major source of Er formation

r

nv

Bq

TnmJ n

ii

iiiGCSr

2



2005 measurement and analysis Localized TAE and f.b.s measurements Energetic Particle Mode (RPM) measurements with higher order

harmonics Faraday rotation analysis with comparison of electron density

fluctuation on MHD oscillations

=> Study of magnetic field fluctuation Comparison with GPI data with mode structure of MHD FIReTIP edge channel density perturbation at the H-mode transition ELM propagation measurements by FIReTIP

FIReTIP system upgrade and future works Channel 5 (Rt=132 cm) will be tested for profile reconstruction of

electron density Hetero-dyne visible two color vibration compensation for Ch7 Application of Gyro-Center Shift theory to NSTX

Summary and Future Plan

Documents

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