Development of a Multichannel Spectrometer for the Thomson Scattering Diagnostic on Pegasus
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Development of a Multichannel
Spectrometer for the Thomson
Scattering Diagnostic on Pegasus
N. L. Schoenbeck, A.S. Dowd, R.J. Fonck, J.I. Moritz,
D.J. Schlossberg, and G.R. Winz
APS - DPP
Nov. 16, 2011
University of PEGASUS
Wisconsin-Madison Toroidal Experiment
Abstract
• Motivation: Explore electron transport in helicity-driven discharges and
investigate edge stability
• Source: Red-shifted scattered light from frequency doubled Nd:YAG
laser (532-632 nm)
• Spectrometer Components:
– New high throughput volume phase holographic (VPH) grating technology
– New high quantum efficiency image intensified CCD cameras (ICCD)
• Design:
– 2 temperature ranges: 10eV-100eV and 100eV-500eV
– Up to 8 spatial channels per spectrometer
• Result: A compact, simplified system
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011
Pegasus Toroidal Experiment
High-stress Ohmic Experimental Parameters
Equilibrium Field Coils heating solenoid Parameter To Date
A 1.15 – 1.3
R(m) 0.2 – 0.45
Ip (MA) ≤ .21
IN (MA/m-T) 6 – 12
li 0.2 – 0.5
κ 1.4 – 3.7
Vacuum τshot (s) ≤ 0.025
Vessel βt (%) ≤ 25
PHHFW (MW) 0.2
RF Heating
Antenna
Toroidal
Field Coils
Ohmic Trim Coils Plasma
Limiters
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011
Thomson Scattering Background info
• Elastic scattering of EM
radiation off free electrons in
the plasma
• Low energy limit of Compton
scattering
• Results in temperature
dependent spectrum of
Gaussian shape about the
laser wavelength
– At high temperatures there is a
slight relativistic blue shift
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011
Thomson Scattering On Pegasus
• Preliminary calculations of
scattering light on Pegasus
yields an average of ~3600
scattered photons per laser
pulse in the direction of our
viewing optics
– For more info see Dave
Schlossberg PP9.00008
3
80x10
• To improve data analysis at
various temperatures, the
60
spectrometer has been
Intensity (AU)
40 designed for low (10-100eV)
20
and high (100eV-500eV)
ranges
0
480 500 520 540 560 580
nm
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011
Implementation of a Thomson Scattering
Diagnostic
Laser Test
See Dave Schlossberg PP9.00008 Setup
• Selection and testing laser
– 2J 532 nm Nd:YAG laser with
~10ns pulse length
• Scattering calculations and
reduction of stray light within
Pegasus Tokamak Background
– Beam line baffles Channel Locations
– Beam dump
• Viewing port and
background channels
Beam Dump
Design
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011
Pegasus Thomson Scattering System
Key Components
• Frequency doubled Nd:YAG laser @ 532 nm
Spectrometer exit Fast-gated
• Beam Dump lens ICCD
VPH transmission
• Collection Lens & Fiber Optics: dispersion grating
– 136mm clear aperture with an 80 cm field of view along the laser Spectrometer
entrance lens
– Fiber optic bundles to image plasma location to spectrometer
Fiber optic bundle
(one spatial channel)
• Spectrometer
– Achromatic lens at spectrometer input Collection
lens
– Cut-on filter to block laser wavelength
Beam
– Volume phase holographic (VPH) grating steering Scattered
mirror light
• New high efficiency, >70%, transmission gratings Beam
dump
• Simplifies spectrometer design and reduces stray
light from reflections
Plasma
– Camera lens at spectrometer output
– Image intensified CCD (ICCD) cameras
Nd:YAG
• High quantum efficiency (QE ~45%) laser
• Low Noise
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011
Thomson System Location on Pegasus
Laser
Collection Lens
Spectrometer N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011
Collection Lens Designed to Collect Full
Field of View
• Design Criteria:
– Collect 80 cm flat field of view 72cm from lens
– Resolution sufficient to collect a scattering area ~1.3cm x 0.3 cm
• Curved image plane with open locations for fiber placement
• Image Plane: F# 2.1 with a focal length of 20.2cm
• Resolution: 100um
• Magnification ~1/3
Collection Lens
Field
of Fiber Optic
View Bundles Transmit
(FOV) Light to
Spectrometer
Image Plane
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011
Fiber Optic Bundles Map to1.4cm of Light
Along Laser Beam
• Each spatial channel:
– 0.3 cm tall (across the laser) by 1.4 cm along the laser in the plasma
– With demagnification this gives .98mm x 4.50mm fiber dimensions
• Fibers will be stationary with plans to populate more plasma
locations in the future
– Repositioning fibers for different data points done manually as needed
– Initial measurement will be done with 8 spatial channels: 4 data points with
corresponding background channels
– Plans to expand to 24 spatial channels
532 nm Laser fi
Beam THE FIBER O
Fiber Optic
N.L. Schoenbeck, APS Division of
Plasma Physics 11/16/2011 BundlesThomson Spectrometer Layout N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011
Large diameter Input Lens & Filter to
Reduce Walk-off
• Input Lens: Achromat
Transmission
from Wright Scientific
%
90.00001
– F# 1.8 with 124mm focal 80.00001
length 70.00001
• Images collimated light 60.00001
XR3002
onto 3” cut-on filter 50.00001 "1.5 degree tilt"
"3 degree tilt"
"4.5 degree tilt"
40.00001
– Block wavelengthsVPH Grating Designed for High
Throughput in 2 Temperature Regimes
• Two gratings
– 2971 lines/mm for low
temperatures (~10eV-100eV)
– 2072 lines/mm for high
temperatures (~100eV-500eV)
• 3” gratings to minimize
walk-off
• Dispersion selected such
that camera width is J. Arns KOSI
limiting the etendu
• Spectrometers will be
built at two input angles
– 54 degrees
– 36 degrees
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011VPH Grating Mount Designed for Flexibility
with 2 Blaze Angles
• Kinematic mount designed to clip in appropriate grating for a
given temperature range
• 3 degrees of freedom (roll, tilt, & yaw) built in for fine
adjustments
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011Detector Area Sets System Etendu & Size of
Fiber Optic Bundles
• Design Criteria: • 8 legs are bundled together
– Eight spatial channels vertically – Bundled length ~1’ (30cm) to simplify strain
• Depends on camera detector relief at spectrometer
height and magnification of
spectrometer
• Minimum spacing to maximize use
of detector area
– 10 spectral bins horizontally
– ~0.25mm gaps between fiber channels
• Based on camera detector
width and dispersion of grating • Light from fiber channels collimated
– Total area must be conserved by entrance lens
– Central 2 channels nearly parallel
– Others will be collimated at slight angles
CCD Detector Chip
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011Exit Lens & Camera Aligned such that
532nm Light Misses Detector !
!
!
!
!
• Camera aligned such that laser light is not!"#$#%&'(&)*+,-.&/0&
detected !
• Photography lens used as the exit lens
!
!
– High resolution
– Small demagnification given input lens
• Camera stage designed for 2 input angles. !
!! !
!
01#23%14& &
! B/+!C09-!C$"3?!0D+5-(5+!D5.@(,+9!)582/-!8>02+9!! !"#$%&$'()*+,-./&0(-+-1'&
+E+1!(1@+5!@8CC8,(6-!682/-812!,.1@8-8.19! K+0-(5+9!9D+,806!9,5+02+9!.E+5!-/+!+1-85+!C50>+! 9+--8129!069.!81!5.(2/!
! F5+,89+!>01(06!C.,(9812! 98-(0-8.193!
!
! G.)(9-!C(66H>+-06!,.19-5(,-8.1!
!"#$2%&$'3,.,4(&0(-+-1'&
Detector Active ! I@+1-8,06!,.6.5!5+D5.@(,-8.1!.C!066!>.@+69!!
099(5+9!-/+!J(068-A!.C!D5.@(,-9!>+09(5+@!!
K+0-(5+9!9D+,806!,.0-812!C.5!
Area )A!/(+!@8CC+5+1,+!
.D-8>8=+@!D+5C.5>01,+!81!
1+05H81C505+@!0DD68,0-8.193!
! K.5!81@(9-5806!,0>+509!>3! 5.64,.&71)'+*&
! L.(1-9!01@!.D-8,06!,.0-8129!,01!)+!! :E0860)6+!C.5!.-/+5!,0>+50!
>.@8C8+@!.1!5+J(+9-! >.(1-9!9(,/!09!QKR!S!.5!
! L?M!9,5+.(1-3!
to spectrometer
"#$#%!&!'()*+,-!-.!,/012+3! ! 4056!7+899!:;!&!ICCD Detectors Chosen for High Gain &
,&#'(! 1(,+4,%&#/(! +,4%! )0(! $%&'(! $#)(#*$+$(,! 5=())(,! )0&#! ;G! =$)78! 94! +>,)0(,! (#0&#/(! )0(! 1(,+4,%&#/(! 4+!
"HEIJ!KDDE*:!)0(!DDE*!&,(!)0(,%4(2(/),$/&223!/442(-8!
!
Low Noise Qualities
"#!&2)(,#&)$.(!/4>12$#'!%()04-!$*!)4!>*(!&!2(#*!=()B((#!)0(!4>)1>)!4+!)0(!$%&'(!$#)(#*$+$(,!&#-!)0(!DDE!L!&!
M2(#*N/4>12(-!KDDEO8!90$*!0&*!)0(!&-.&#)&'(!4+!&224B$#'!)0(!$%&'(!$#)(#*$+$(,!)4!=(!,(%4.(-:!)0>*!(#&=2$#'!
)0(! DDE! )4! =(! >*(-! &24#(! +4,! >#$#)(#*$+$(-! &112$/&)$4#*8!P$)0! &! *>$)&=23! 0$'0! Q>&2$)3! $%&'(! $#)(#*$+$(,:! )0(!
Manufacturer’s
2(#*N/4>12(-! &,,&#'(%(#)! Specifications:
/&#! &2*4! 1,4->/(! Andor
&! =())(,! Q>&2$)3! $%&'(! &*! )0(!iStar 734.&,$&)$4#*! &#-!
+$=,(N)4N+$=,(!
=2(%$*0(*! &,(! ,(%4.(-! +,4%! )0(! *3*)(%8! E$*&-.&#)&'(*! 4+! 2(#*N/4>12(-! *3*)(%*! &,(! 2&,'(,! 103*$/&2! *$6(:!
Effective Active Area (mm) 13.3 x 13.3
24B(,!'&$#!2(.(2:!$#/,(&*(-!*/&))(,:!&#-!$#/,(&*(-!-$*)4,)$4#8! Effective Pixel Size (um) 19.5 x 19.5
!
Read Noise As low as 2.9 e-
"--$#'!&#!$%&'(!$#)(#*$+$(,!)4!&!DDE!'$.(*!)B4!%&$#!&-.&#)&'(*R! Active Pixels 1024 x 1024
;8! K#/,(&*(-!*(#*$)$.$)3@!*$#'2(!104)4#!(.(#)*!/&#!=(!-()(/)(-!B0(#!)0(!%$/,4!/0&##(2!12&)(!5SDT7!$*!
120 - 1090
Spectral Range (nm)
41(,&)(-!&)!0$'0!.42)&'(*8!
Photocathode QE (max) Up to 45%
))(,$#'!)4!#*(/4#-!2(.(28!
Minimum Optical Gate Width As low as 1.2ns Image Intensifier Gain >200
!
N.L. Schoenbeck
APS-DPP 11/16/2011 From Andor iStar 734 Manual
!New Gen 3 Image Intensifiers Have
Improved Quantum Efficiency
• New technology has
made it possible to
make a simplified
detector system
• Gen 3 ICCD cameras
have ~45% QE across
visible region
• Motivated switch to 532
frequency doubled
Nd:YAG laser to take
advantage of this
technology
From Andor iStar 734 Manual
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011Dark Noise Testing Indicates Low Read
and Low Dark Current Noise
Andor iStar 734 ICCD Camera (S/N 4075) Dark Noise
14
31kHz Digitization (32us Read Time per Pixel)
1MHz Digitization (1us Read Time per Pixel)
Digitization Measured
62kHz kHz Digitization (16us Read Time per Pixel) Rate Read Noise
RMS Counts per Pixel
12
500kHz Digitization (2us Read Time per Pixel)
(RMS per Pixel)
10
31 kHz 6.65 ± 0.10
8 62 kHz 9.66 ± 0.02
6
500 kHz 8.61 ± 0.02
1 MHz 8.39 ± 0.01
0 20 40 60
Exposure Time (ms)
1.0
Normalized Average Counts per Pixel
!!!"#$ ! ! !!!"#$!!"##$%& !
0.8
• CCD dark noise ~ 0.6
• Read noise dominates dark signal 0.4
– Can be reduced by hardware binning 0.2
0.0
• Additional noise sources include electron 0 2 4 6 8
Hardware Bin Size (Bins are Square)
10
background illuminescence (EBI)
– Expected at < .2 electrons/pixel/sec
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011Camera Sensitivity Appears Linear with
Intensity
• Preliminary test of the camera response with a steady white
light source
• Variable gating collects light
• Background signals level ~800 (programmed by Andor)
0 200 400 600 800 1000 0 200 400 600 800 1000
0
0
2000 50us Light Collection 100us Light Collection
2400
200
200
2400
Average Counts per Pixel
2200 2200
1800 2000 2000
400
400
1800 1800
1600 1600
600
600
1400
1600
1400
1200 1200
1000 1000
800
800
800 800
1400
1000
1000
0 200 400 600 800 1000 0 200 400 600 800 1000
1200
0
0
500us Light Collection 1000us Light Collection
200
200
2400 2400
2200
1000
2200
2000 2000
400
400
1800 1800
1600 1600
800
600
600
1400 1400
1200 1200
200 400 600 800 1000
1000
800
800
1000
800
800
Integration Time (us)
1000
1000
N.L. Schoenbeck, APS Division of Plasma Physics
11/16/2011Thomson Data Analysis Using ICCD
Camera
• Image data: All 8 spatial
Average Counts per Pixel
822
channels into a single file
for Bin Shown
820
818
• Background fluctuations 816
subtracted for each shot 0 200 400 600 800 1000
Pixel Number
• Spatial & spectral bins are 0 200 400 600 800 1000
0
created in software
– 3nm spectral bins for 10-100eV
200
– 6nm spectral bins for 100eV-500eV 880
400
• Individual bins searched for 860
cosmic rays 600
840
• Fitting routines will determine 820
800
plasma temperature and
density 800
1000
Dark Noise Image from S/N 4075
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011Summary
• A new Thomson Scattering system has been designed for the
Pegasus Toroidal Experiment
– Novel spectrometer components include:
• Transmission VPH grating
– High efficiency (>70%)
• ICCD camera as detector
– High gain
– Fast gating
– Low Noise
• Testing of individual components is underway
• Preliminary data expected early next year
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011Acknowledgements & Website
Work supported by US DOE Grant DE_FG02_96ER54375
For a pdf version of this poster please visit:
http://pegasus.ep.wisc.edu/Technical_Reports/Conferences.htm
Or Contact Nikki: NSCHOENBECK@WISC.EDU
N.L. Schoenbeck, APS Division of Plasma Physics 11/16/2011You can also read
