Scintillator-based online detectors for laseraccelerated protons
–
Concepts and realizations
at the DRACO lab
J. Metzkes, K. Zeil, S.D. Kraft, N. Stiller, U. Schramm, L. Karsch, C. Richter,
J. Pawelke, M. Sobiella
Instrumentation for Diagnostics and Control of Laser-Accelerated Proton
(Ion) Beams II
June 7 – 8, 2012
Josefine Metzkes  j.metzkes@hzdr.de  www.hzdr.de  HZDR
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The DRACO laser facility
30 fs
-80 -40 0
40
time [fs]
80
*Dresden laser acceleration source
Ti:Sapphire
CPA laser
rep rate: 10 Hz
2-3 J (on target)
I ~1021 W/cm2
ns-ASE contrast 10-10
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Proton acceleration at DRACO
target changer
RCF @ wheel
 2D
 offline
online laser
parameter
control
Thomson parabola
 small solid angle
 online
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target
manipulation
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Proton acceleration at DRACO
target changer
RCF @ wheel
 2D
 offline
Status
 stable high repetition rate
laser system  reliable
proton source
 high degree of remote
control under vacuum
 online optimization and
monitoring of
acceleration performance
Thomson parabola
 small solid angle
 online
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target
manipulation
 application experiments
NEED
online laser
parameter
control
online spectrometers for
protons & ions (1D or 2D)
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Why plastic scintillators?
Mainly practical reasons:
 easy to handle
 available in nearly any size and thickness  no support necessary
 immediate light emission after excitation  online information
 variable emission wavelength in the visible range
 signal readout with CCD cameras  less EMP issues
 fast decay rates possible  TOF applications
 linear response to particle flux
 light emission saturates with dE/dx  calibration
 light emission degrades with total dose exposition
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Detector setup
1D angularly resolved online
spectrometer for protons
• scintillator stack: 10 layers of BC
418 (Saint-Gobain crystals), maximum
emission @ 391 nm
• resolution of 10 proton energy
ranges
• light guide principle  slim
scintillator unit (15 mm x 76 mm)
• fan-like setup for good spatial
resolution
• detection area: 10 mm x 50 mm
 detection angle as for RCF (~ 26°
half angle )
• compact detector: scintillator and
camera unit only 300 mm x 80 mm
• radiation shielding with Pb
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Detector setup
camera:
◦ 16 bit camera  high dynamic range
◦ 1600 x 1200 px chip size, 4.4 µm pixel size
camera unit directly coupled to the scintillator:
◦ light tight connection  stray light suppression
◦ high light yield
◦ good spatial resolution  7px per layer thickness
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Imaging properties
8.6 mm
182 mm
imaging edge polished
surfaces polished for
efficient reflection
edges roughened to
avoid reflection
spatial resolution
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Detector setup & proof of principle
Measured proton distribution
p+
energy
CCD camera image
proton distribution reconstructed from RCF
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Detector setup & proof of principle
Measured proton distribution
p+
energy
CCD camera image
 sufficient signal-to-noise ratio (>2) for signal
detection  shielding against electron and xray background
 maximum proton energy and yield online
accessible for the full divergence angle of the
proton beam
 online detection of beam inhomogeneities
 improves online beam optimization
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Detector characterization @ Tandetron
6 MV tandetron at the HZDR Ion Beam Center
detector
reference RCF – beam
homogeneity
FC – 25.4 mm diam.
detection surface
 current ~ 100pA
12 MeV p+ beam
beam defining aperture –
10 mm diam.
reference RCF –
beam position
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Sensitivity calibration
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Sensitivity calibration
light transport within the
scintillator case 
correction possible
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condition of
polished
scintillator edge
dE/dx saturation of
scintillator light
output
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Lateral homogeneity
decrease due to imaging properties
• overall lateral homogeneity: ~ 80%
• inhomogeneity due to scintillator conditions  stable
 measured curves give correction factors
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Imaging properties testing
spatial resolution
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imaging properties
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Imaging properties testing
spatial resolution
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imaging properties
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online detector
Detector application
proton beam
non-invasive online
access to spectral
distribution and yield
of accelerated protons
Phys. Med. Biol. 56 (2011) 1529–1543
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energy
Detector application
optimal focus
25 µm out of focus
dispersion
 online optimization &
monitoring of experimental
performance via maximum
proton energy & yield
 shot-to-shot monitoring via
yield (higher sensitivity)
online spectral monitoring
 dosimetry
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1,0
0,4
Idea: mimic an RCF stack  2D spectrum ONLINE
0,7
2D online detector development
C
C`
4,5
1,6
B`
2,1
1,9
profile B-B`
2,5
B
1,4
A`
1,2
A
2,5
profile A-A`
0,7
1,4
2,1
1,0
0,4
1,2
~ 50
1,9
profile C-C`
4,5
~ 50
1,6
2,5
Schnitt B-B`
CCD
camera
2,5
scintillator
Schnitt A-A`
Schnitt C-C`
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2D online detector development
A`
B
B`
C
C`
~ 50
4,5
~ 50
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camera unit
A
4,5
Detector setup
absorber matrix &
scintillator (BC 416,
thickness 260 µm)
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2D detector testing
Test matrix optimized for tandetron
experiment (12 MeV protons)
diam 1.5 mm
dist 2.0 mm
diam 1.5 mm
dist 2.25 mm
diam 1.0 mm
dist 1.50 mm
test with
12 MeV p+
diam 1.5 mm
dist 2.50 mm
diam 1.5 mm
dist 2.75 mm
basic pixel (9 energies): 4.5 x 4.5 mm
 121 pixels on a 50 x 50 mm plate
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2D detector testing
Progress
 final design for basic pixel
 sensitivity calibration @ tandetron
 test of p+ scattering in angled holes
To do
• test of a final design @ DRACO
 performance with background radiation
basic pixel (9 energies): 4.5 x 4.5 mm
 121 pixels on a 50 x 50 mm plate
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… thanks for your attention
(multiple filamentation of a freely
propagating 100 TW beam in air)
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