Development of multi-color optical soft X-ray arrays for MHD and transport diagnostics in fusion experiments

1. Development of ‘multi-color’ optical soft X-ray arrays for MHD and transport diagnostics in fusion experiments L. F. Delgado-Aparicio, D. Stutman, K. Tritz, G. Suliman and M. Finkenthal The Plasma Spectroscopy Group The Johns Hopkins University R. Kaita, L. Roquemore and D. Johnson Princeton Plasma Physics Laboratory

2. Abstract We are developing fast (? 100kHz), “multi-color” (multi-energy) optical soft x-ray arrays as an improved alternative to conventional photodiode arrays for MHD and transport diagnostic. Tests of a “single-color” array on NSTX show that the optical device has SNR and immunity to noise, superior to those of conventional diode arrays, while having similarly fast time response [1]. In addition, the optical design enables improved plasma access and spatial coverage at reduced cost, making possible large channel-count, “multi-color” tomographic systems. Due to the “layered” structure of the plasma emissivity, such systems would enable simultaneous imaging from the plasma edge to the core. A re-entrant “multi-color” OSXR array will be prototyped on NSTX, where it will also augment the coverage of the existing diode system. The optimization of this diagnostic is discussed and applications of the “multi-color” technique illustrated with NSTX results and numerical simulations. [1] Luis F. Delgado-Aparicio, et al., Rev. Sci. Instrum, 75, 4020, (2004).

3. “Classical” soft x-ray (SXR) photodiode arrays

4. “Classical” soft x-ray (SXR) photodiode arrays

5. “Classical” soft x-ray (SXR) photodiode arrays

6. Classical” soft x-ray (SXR) photodiode arrays

7. What is an “optical” soft x-ray (OSXR) array system? [1] Luis F. Delgado-Aparicio, et al., Rev. Sci. Instrum, 75, 4020, (2004).

8. Components of the “optical” SXR Array 0.3 ?m Ti and 0.5, 5, 50 and 100 ?m Be foils Columnar (crystal growth) CsI:Tl (30 ?m) deposited on a 2mm fiber optic plate (FOP, NA ? 1). 40 mm in diameter, 1/3” thickness UHV fiber optic window (6” CF). Hi throughput, multi-clad, non-scintillating, 1.5 m long fiber optics (NA ? 0.7 ?T ? 40%). Current pre-amplifiers (104 - 1011 V/A). Current detector: Bi-alkali (Sb-Rb-Cs, Sb-K-Cs), multi-anode, low cross talk, high gain (? 106) Hamamatsu photo-multiplier tube (PMT). Magnetic shielding is necessary! Future candidate: Advanced Photonix’s large area avalanche photodiode (APD). One channel, 5 mm in diameter, modified, hi quantum efficiency (? 90%), high internal gain (? 300), internally amplified, cooled (-20 to 0 oC) module.

9. “Optical” array installation in NSTX (PPPL)

10. Results from NSTX (PPPL) Ro= 85 cm a = 68 cm A = Ro/a ~ 1.25 BT(0) = 0.3 - 0.6 T Ip < 1.5 MA

11. Test of a “single-color” array in NSTX (PPPL)

12. Benefits of the “OSXR” system (I)

13. Benefits of the “OSXR” system (II)

14. Benefits of the “OSXR” system (III)

15. What is a re-entrant (in vacuum) “optical” SXR array? Scintillator Reflective coating Fiber optic plates (FOP) Filter transmission. In vacuum fiber optics Fiber optic window (FOW) Atmosphere fiber optics PMT and/or APD Trans-impedance amplifier DAQs

16. What is a re-entrant “multi-color” OSXR system?

17. What can a re-entrant multi-color OSXR can do? Multi-color (2-3 color) tomographic reconstructions. Time & space dependent transport measurements of intrinsic (e-, ions and C) and injected (neon) impurities; including SGI. MHD mode recognition (ELMs & RWMs) and their effects on core & edge plasma parameters. ELMs characterization & perturbative effects (see K. Tritz, et al., poster JP1.031). ‘Two -color’ modeling of Te perturbations during MHD events (NEXT SLIDE).

18. “Two -color” modeling of Te perturbations during MHD events

19. Tangential multi-color OSXR for NSTX

20. Poloidal multi-color OSXR for NSTX

21. Components 30 ?m CsI:Tl (RMD, Inc) deposition on a 2 mm FOP (Collimated Holes, Inc). Ti and Be filters (Lebow, Inc) Vacuum compatible fiber optic bundle (L=0.5 - 2.1 m) with epoxied NA=0.64, 50 ?m individual fiber optics (Collimated Holes, Inc). Fiber optic window (XRSINC) 1.5 m, NA=0.74, fiber optic canes (Bicron - Saint Gobain). AXUV (IRD, Inc) and/or PMT (Hamamatsu) In-vacuum fiber optic test

22. In-vacuum fiber optic test (II)

23. In-vacuum fiber optic test (III)

24. Conclusions A single-color “OSXR” array has been successfully tested on NSTX. The time response of the system is in the order of 2 - 5 ?s, thus the system would be able to be sampled at frequencies in the order of 100 - 400 kHz. The NB-induced noise in the diode system seems to be due to elastic and inelastic scattering of 2.5 MeV DD neutrons in the photo-diode’s silicon lattice. The “optical” SXR array appears to be “thin” to neutron bombardment in comparison to the photo-diode (silicon) based arrays. A re-entrant ‘multi-color’ OSXR array has been proposed to replace the photo-diode based USXR system in NSTX and thus, correctly apply the ‘multi-color’ technique for MHD mode recognition and transport measurements. Tests of in-vacuum fiber optic bundles have been done at the JHU laboratories for NSTX and NCSX applications.

25. Current applications Comparison between PMT and APD technologies. Time response and sensitivity for UV/visible light. Test with columnar CsI:Tl (0.05 - 1 MHz). Development of optical array for turbulent SXR measurements (see G. Suliman, et. al. poster BP1.088). RWMs, ELMs and neutron impact studies. Correlation between the “optical” array (NSTX Bay J) and the diode arrays (NSTX Bay G).

26. Acknowledgments The Johns Hopkins University: Scott Spangler and Steve Patterson. Princeton Plasma Physics Laboratory: Robert Majeski, Jeff Spaleta, Tim Gray, Jim Taylor, John Timberlake (CDX-U). James Kukon, Brent Stratton, Joe Winston and Bill Blanchard (NSTX). This work was supported by The Department of Energy (DOE) grant No. DE-FG02-86ER52314ATDOE

27. Preprints