‘Multi-color’ optical soft X-ray arrays for MHD and transport diagnostics

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

NSTX Results Review 2004,September, 20 - 21, 2004

Princeton, NJ, USA

AbstractA prototyped “optical” soft x-ray (OSXR) array has been tested in both CDX-U and NSTX, STs at PPPL. Among its benefits over the typical diode SXR arrays are listed, its gain flexibility given by the PMT, its compactness and portability and its insensitivity towards NB-induced noise (given mainly by its neutron transparency).1 In this talk we review the need of a re-entrant ‘multi-color’ “OSXR” system for replacing the USXR diode arrays and for the appropriate application of the ‘multi-color’ technique for MHD mode recognition and associate transport phenomena.

____________________1.- Luis F. Delgado-Aparicio, et al., Rev. Sci. Instrum, 75, 2004.

Why a ‘multi-color’ “OSXR” measurement?Basic diagnostic:• A SXR system (based on filters & photodiode arrays) does tomography in a well defined (and limited) energy range, mainly for diagnostics of core and edge MHD activity.

Current USXR system in NSTX

Why a ‘multi-color’ “OSXR” measurement?Basic diagnostic:• A SXR system (based on filters & photodiode arrays) does tomography in a well defined (and limited) energy range, mainly for diagnostics of core and edge MHD activity.

Limitations:• Due to “layered” structure of the plasma emissivity as a function of energy, important core perturbations are “hidden” by strong peripheral edge emission peel off the peripheral contribution!

Current USXR system in NSTX

408.000407.000 407.200 407.400 407.600 407.800

2/1 + 1/1 E > 0.4 keV (5 µm Be filter)

Mid-plane30 -

120 -

Z (cm)

1/1

t(ms)

E > 1.4 keV (100 µm Be filter)Mid-plane

-120 -

- 30 -

Why a ‘multi-color’ “OSXR” measurement?Basic diagnostic:• A SXR system (based on filters & photodiode arrays) does tomography in a well defined (and limited) energy range, mainly for diagnostics of core and edge MHD activity.

Limitations:• Due to “layered” structure of the plasma emissivity as a function of energy, important core perturbations are “hidden” by strong peripheral edge emission peel off the peripheral contribution!

Current USXR system in NSTX

• Reconstruction of complex structures requires a very large # of chords, therefore, such an array would be prohibitively expensive. Lack of plasma access due to a tight fitting vacuum vessel, access to ports, port space and geometry, and # of ports become an issue. In-vacuum diode SXR cameras have also to sustain elevated bake-out temperatures.

• The NB-high neutron flux induced noise and fast electromagnetic activity (or current ramp up/down), impair the diode arrays.

Solutions: • In order to solve the above problems we proposed to replace the filtered diode system with re-entrant OSXR system.• In addition to overcoming some of the above limitations, such system enables simultaneous time-resolved ‘multi-color’ measurements.

What is a re-entrant multi-color “optical” soft x-ray (rMC-OSXR) array system?

OSXR array head tested on NSTX

MHD results with the “OSXR” shownat HTPD & Rev. Sci. Instrum, 75, 2004

What is a re-entrant multi-color “optical” soft x-ray (rMC-OSXR) array system?

Optimization

OSXR array head tested on NSTX

Rationale of the MC-OSXR array

1. Scintillator2. Reflective coating3. Fiber optic plates (FOP)4. Filter transmission.5. In vacuum fiber optics

6. Fiber optic windows (FOW)7. Atmosphere fiber optics8. PMT and/or APD9. Trans-impedance amplifier10. DAQs

NSTX (2005)

Benefits of the “OSXR” system

• Compactness & portability.• Almost unrestricted plasma accessibility (multiple

toroidal & poloidal locations).• Optically thin to neutron bombardment.

“Optical” SXR array head

Shot #114021, 0.8 MA, 4 MW NBI, 1.51014 n/s

Benefits of the “OSXR” system

• Compactness & portability.• Almost unrestricted plasma accessibility (multiple

toroidal & poloidal locations).• Optically thin to neutron bombardment.

“Optical” SXR array at CDX-U, PPPL

Shot #114022, 0.8 MA, 2-4 MW NBI, 1.01014 n/s

Benefits of the “OSXR” system

• Compactness & portability.• Almost unrestricted plasma accessibility (multiple

toroidal & poloidal locations).• Optically thin to neutron bombardment.

“Optical” SXR array at CDX-U, PPPL

Noise evaluation on the re-entrant USXR and the OSXR arrays

NS

TX

Sho

t # 1

1402

2 (2

- 4

MW

NB

)

Benefits of the “OSXR” system

• Compactness & portability.• Almost unrestricted plasma accessibility (multiple

toroidal & poloidal locations).• Optically thin to neutron bombardment.

“Optical” SXR array at CDX-U, PPPL

• Less expensive than the diode system.• Electronics far away of the machine.• The initial photon statistics is conserved due to

optimized scintillation (CsI:Tl) properties.• The gain of the system can be remotely changed by

the use of a PMT and/or an APD.• The time response of the OSXR system is

comparable to that of the AXUV photodiodes(2-5s).

Benefits of the “OSXR” system

• Compactness & portability.• Almost unrestricted plasma accessibility (multiple

toroidal & poloidal locations).• Optically thin to neutron bombardment.

“Optical” SXR array at CDX-U, PPPL

• Less expensive than the diode system.• Electronics far away of the machine.• The initial photon statistics is conserved due to

optimized scintillation (CsI:Tl) properties.• The gain of the system can be remotely changed by

the use of a PMT and/or an APD.• The time response of the OSXR system is

comparable to that of the AXUV photodiodes(2-5s).

Fast ELM measured with Hup diode array

Chord#

t (ms)

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10

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t (ms)

OSXR

What can a rMC-OSXR array system do?• Time dependent transport measurements of intrinsic (e-, ions and C) and

injected (Ne) impurities • MHD mode recognition and their effects on core & edge plasma parameters. • ELMs characterization & perturbative effects (see K. Tritz, et al., Tuesday, 9/21/04).

• ‘Two -color’ modeling of Te perturbations during MHD events (see D. Stutman, et al., Thursday, 9/23/04).

• The ratio of low to high energy USXR signals is Te sensitive (MPTS)• USXR profiles modeled using C, O and B coronal equilibrium radiative coefficients.

Chord #

t (ms)

Te (

keV

)

R (cm)

How sensitive is this method ?

First assessment (proof of principle, using a type-I ELM)

MPTS

USXR

What can a rMC-OSXR array system do?• Time dependent transport measurements of intrinsic (e-, ions and C) and

injected (Ne) impurities • MHD mode recognition and their effects on core & edge plasma parameters.• ELMs characterization & perturbative effects (see K. Tritz, et al., Tuesday, 9/21/04).

• ‘Two -color’ modeling of Te perturbations during MHD events (see D. Stutman, et al., Thursday, 9/23/04).

The correct application of the powerful ‘multi-color’ technique requires imaging the SAME plasma region, rather than piecing together images from different plasma regions at

different energies.

Chord #

t (ms)

Te (

keV

)

R (cm)

How sensitive is this method ?

First assessment (proof of principle, using a type-I ELM)

MPTS

USXR

Conclusions

• The “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 seem to be due to elastic and inelastic 2.5 MeV DD neutron scattering in the photo-diode’s silicon lattice.

• The “optical” SXR array is “thin” to neutron bombardment in comparison to the diode based arrays. The levels of “induced neutron noise” are a fourth to a fifth of the noise in the USXR diode system.

• A re-entrant ‘multi-color’ OSXR array has been proposed to replace the photo-diode based USXR system in NSTX and correctly applied the ‘multi-color’ technique for MHD mode recognition and transport measurements.

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