1. 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. Park PPPL, Princeton University S. Sabbagh Columbia University 45th Annual Meeting of the Division of Plasma Physics October 27-31, 2003, Albuquerque, New Mexico

2. Abstract Far 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

3. Contents Introduction Upgrade plans  Visible interferometer for edge channel  Temporal resolution upgrade  Channel expansion Faraday rotation measurement  Error analysis  Para/diamagnetism Conclusions

4. 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

5. 3-D CAD of FIReTIP system

8. Visible Interferometer for Edge Channel Vibration Compensation n 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 n Laboratory test is in progress

9. Temporal Resolution Upgrade n Time Resolution of FIReTIP can be up to ~MHz by using Stark-tuned laser [K.C. Lee et.al., RSI 74,1621(2003)] n Time response of system was limited by the digitizer (100kHz) 2003 Campaign2004 Campaign TypeCAMAC ModulePC Based DAQ Sampling Rate100 kHz1.8 MHz Sampling Channel No.16 Memory1.2 Mbytes256 Mbytes Covering Beam Channel No.47 Upgrade Plan of FIReTIP Digitizer

10. Example of High Time Resolution Physics Study by FIReTIP n FIReTIP measured fish bones (1)~(6) (<50 kHz) n n e fluctuation reduction is indicated after L/H transition n FIReTIP is expected to measure TAE/f.b.s in core plasma (1)(2)(3)(4)(5)(6) L/H transition

11. E.D. Fredrickson, et.al., NSTX Monday Physics meeting (June 16, 2003) FIReTIP ch2 L-mode H-mode Reduction of density fluctuation level after H-mode transition and TAE/f.b.s on spectrum (1)(2) (3) (4)(5)(6)

12. FIReTIP Channel Extension Plan n Construction of Ch4 and Ch5 is in progress

13. Para/diamagnetism Study in Conjunction with EFIT Polarimetry : n n(x) from Thomson scattering data n B T (x) from EFIT01, EFIT02 and Vacuum B-fields Calculation b Tmax = 9%

14. Error Analysis of FIReTIP Faraday Rotation Data n Two sources of noise; (1) Background white noise (>400 Hz) (2) Low frequency oscillation (14~100 Hz) n Error bars were reduced when white noise was filtered out (400Hz) n Smoothing was taken at 14.3 Hz for the removal of low frequency oscillation n Noise suppression of low frequency oscillations is in progress

15. Comparison of 78 points out of 37 shots in 2002 campaign n EFIT calculated higher magnetic fields for most cases n Error bars from low frequency noise of FIReTIP are too big to judge the reliance of EFIT or vacuum magnetic field n FIReTIP measurement showed lower magnetic fields for non- NBI shots (investigation is under going)

16. 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 n Central channels of FIReTIP will improve S/N ratio

17. 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