1. Scintillator-based online detectors for laser-accelerated 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
Experiments at draco laser HZDR

2. The DRACO laser facility
time [fs]
30 fs
-80
-40 40 80
Ti:Sapphire
CPA laser
rep rate: 10 Hz
2-3 J (on target)
I ~1021 W/cm2
ns-ASE contrast 10-10
*Dresden laser acceleration source

3. Proton acceleration at DRACO
wheel 2D
offline
target changer
target
manipulation
Thomson parabola
small solid angle
online
online laser parameter control

4. Proton acceleration at DRACO
wheel 2D
offline
target changer
target
manipulation
Thomson parabola
small solid angle
online
online laser parameter control
Status
stable high repetition rate laser system  reliable proton source
high degree of remote control under vacuum
online optimization and monitoring of acceleration performance
application experiments
online spectrometers for protons & ions (1D or 2D)
NEED

5. 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

6. Detector setup 1D angularly resolved online spectrometer for protons
scintillator stack: 10 layers of BC 418 (Saint-Gobain crystals), maximum 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

7. 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

8. Imaging properties 182 mm imaging edge polished
surfaces polished for efficient reflection
edges roughened to avoid reflection
spatial resolution

9. Detector setup & proof of principle
proton distribution reconstructed from RCF p+
energy
Measured proton distribution
CCD camera image

10. Detector setup & proof of principle
energy
Measured proton distribution
CCD camera image
sufficient signal-to-noise ratio (>2) for signal detection  shielding against electron and x- ray 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

11. Detector characterization @ Tandetron
6 MV tandetron at the HZDR Ion Beam Center
12 MeV p+ beam
FC – 25.4 mm diam. detection surface
 current ~ 100pA
detector
reference RCF – beam homogeneity
beam defining aperture – 10 mm diam.
reference RCF – beam position

12. Sensitivity calibration

13. Sensitivity calibration
dE/dx saturation of scintillator light output
light transport within the scintillator case  correction possible
condition of polished scintillator edge

14. Lateral homogeneity overall lateral homogeneity: ~ 80%
lateral position
decrease due to imaging properties
overall lateral homogeneity: ~ 80%
inhomogeneity due to scintillator conditions  stable
measured curves give correction factors

15. Imaging properties testing
spatial resolution
imaging properties

16. Imaging properties testing
spatial resolution
imaging properties

17. Detector application online detector proton beam
Idocis
aperture
beam filter
target
laser
online detector
proton beam
Phys. Med. Biol. 56 (2011) 1529–1543
non-invasive online access to spectral distribution and yield of accelerated protons

18. Detector application dispersion
optimal focus
25 µm out of focus
dispersion
energy
online optimization & monitoring of experimental performance via maximum proton energy & yield
shot-to-shot monitoring via yield (higher sensitivity)
online spectral monitoring  dosimetry

19. 2D online detector development
profile A-A`
profile B-B`
profile C-C`
2,5
0,4
0,7
1,0
1,9
2,1
1,2
1,4
1,6
Idea: mimic an RCF stack  2D spectrum ONLINE
~ 50
4,5 A A` B B` C C`
Schnitt A-A`
Schnitt B-B`
Schnitt C-C`
CCD camera
scintillator

20. 2D online detector development
~ 50
4,5 A A` B B` C C`
camera unit
absorber matrix & scintillator (BC 416, thickness 260 µm)
Detector setup

21. 2D detector testing Test matrix optimized for tandetron
test with 12 MeV p+
basic pixel (9 energies): 4.5 x 4.5 mm
 121 pixels on a 50 x 50 mm plate
diam 1.5 mm
dist 2.0 mm
dist 2.25 mm
dist 2.50 mm
dist 2.75 mm
diam 1.0 mm
dist 1.50 mm
Test matrix optimized for tandetron
experiment (12 MeV protons)

22. 2D detector testing Progress final design for basic pixel
basic pixel (9 energies): 4.5 x 4.5 mm
 121 pixels on a 50 x 50 mm plate
Progress
final design for basic pixel
sensitivity tandetron
test of p+ scattering in angled holes
To do
test of a final DRACO
 performance with background radiation

23. … thanks for your attention
(multiple filamentation of a freely
propagating 100 TW beam in air)
… thanks for your attention