Upgrade Plan of FIReTIP System and Toroidal Magnetic Field Measured by Polarimetry on NSTX* K.C. Lee, C.W. Domier, M. Johnson, H. Chen, N.C. Luhmann, Jr

US DEPARTMENT OF ENERGY

DOE UC DAVISDEPARTMENT OF APPLIED SCIENCE

Upgrade Plan of FIReTIP System and Toroidal Magnetic Field Measured by

Polarimetry on NSTX*

K.C. Lee, C.W. Domier, M. Johnson, H. Chen, N.C. Luhmann, Jr.University of California at Davis

B. LeBlanc, H. K. ParkPPPL, Princeton University

S. Sabbagh Columbia University

45th Annual Meeting of the Division of Plasma PhysicsOctober 27-31, 2003, Albuquerque, New Mexico



AbstractFar Infra Red Tangential Interferometry and Polarimetry (FIReTIP) has been successfully operated and simultaneously measures electron density and toroidal magnetic field on the National Spherical Torus Experiment (NSTX). Up to now, four channels have been in full operation and the full seven channel operation will commence when the required access is provided. Both density and Faraday rotation measurements are extensively studied. Comparison study of the Faraday rotation data with the calculated values of EFIT equilibrium code is partly completed using Thomson electron density profile data to address para/dia magnetic effects in spherical torus plasmas. This includes a detailed analysis of noise and errors. In this paper, the full system upgrade plan will be discussed with a possible improvement of polarimetry S/N to be useful as a real time signal.

*Supported by U.S. DoE Contracts DE-FG03-99ER54518 and DE-AC02-76CH03073



Contents

Introduction

Upgrade plans Visible interferometer for edge channel Temporal resolution upgrade Channel expansion

Faraday rotation measurement Error analysis Para/diamagnetism

Conclusions



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-D CAD of FIReTIP system







Visible Interferometer for Edge Channel Vibration Compensation

Edge channel (ch7) S/N ratio is ~1/40 of core channels

Homodyne visible (l=0.6328 mm) HeNe laser interferometry will be installed on channel 7

Laboratory test is in progress



Temporal Resolution Upgrade

Time Resolution of FIReTIP can be up to ~MHz by using Stark-tuned laser [K.C. Lee et.al., RSI 74,1621(2003)]

Time response of system was limited by the digitizer (100kHz)

2003 Campaign 2004 Campaign

Type CAMAC Module PC Based DAQ

Sampling Rate 100 kHz 1.8 MHz

Sampling Channel No. 16 16

Memory 1.2 Mbytes 256 Mbytes

Covering Beam Channel No. 4 7

Upgrade Plan of FIReTIP Digitizer



Example of High Time Resolution Physics Study by FIReTIP

FIReTIP measured fish bones (1)~(6) (<50 kHz)

ne fluctuation reduction is indicated after L/H transition

FIReTIP is expected to measure TAE/f.b.s in core plasma

(1) (2) (3) (4) (5) (6)

L/H transition



E.D. Fredrickson, et.al., NSTX Monday Physics meeting (June 16, 2003)

FIReTIP ch2

L-mode

H-modeReduction of density fluctuation level after H-mode transition and TAE/f.b.s on spectrum

(1) (2)

(3)

(4)(5)(6)



FIReTIP Channel Extension Plan

Construction of Ch4 and Ch5 is in progress



Para/diamagnetism Study in Conjunction with EFIT

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

x

Polarimetry :

n(x) from Thomson scattering data

BT(x) from EFIT01, EFIT02 and Vacuum B-fieldsCalculation

bTmax= 9%



Error Analysis of FIReTIP Faraday Rotation Data

Two sources of noise;

(1) Background white noise (>400 Hz)

(2) Low frequency oscillation (14~100 Hz)

Error bars were reduced when white noise was filtered out (400Hz)

Smoothing was taken at 14.3 Hz for the removal of low frequency oscillation

Noise suppression of low frequency oscillations is in progress



Comparison of 78 points out of 37 shots in 2002 campaign

EFIT calculated higher magnetic fields for most cases

Error bars from low frequency noise of FIReTIP are too big to judge the reliance of EFIT or vacuum magnetic field

FIReTIP measurement showed lower magnetic fields for non-NBI shots (investigation is under going)



3

2

1

0

-1

0 50 100 150Tangency Radius (cm)

Diff

eren

ce in

Rot

atio

n A

ngle

(D

eg) =0.1

=2.0=3.0

=0.5=1.0

Calculated values of Difference in Faraday rotation angle between vacuum field and presence of diamagnetic effects (~0.5 kG)

Real time polarimetry data of FIReTIP including time evolution of dia/paramagnetism are expected to be EFIT input for accuracy improvement

Central channels of FIReTIP will improve S/N ratio



Conclusion Upgrade plans

A visible interferometer will be installed for edge channel vibration compensation

Temporal resolution will be increased up to ~1MHz by PC based DAQ which enables FIReTIP to provide high time resolution data for MHD(TAE/f.b.s) and electron density fluctuation studies

Four channel operation is expected in ’04 (ch1, ch2, ch3, ch7)

Faraday Rotation Measurement Error and noise were analyzed for the plasma shots of 2002

campaign Para/diamagnetism of NSTX plasmas was compared by using EFIT

calculation and vacuum B-field with FIReTIP measurement Residual low frequency noise source is under investigation Development of FIReTIP polarimetry as EFIT input data is in

progress

Documents

Upgrade Plan of FIReTIP System and Toroidal Magnetic Field Measured by Polarimetry on NSTX* K.C. Lee, C.W. Domier, M. Johnson, H. Chen, N.C. Luhmann, Jr