scintillator-based online detectors for laser-accelerated protons – concepts and realizations

Mitglied der Helmholtz-GemeinschaftJosefine Metzkes j.metzkes@hzdr.de www.hzdr.de HZDR

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

Seite 2 Mitglied der Helmholtz-GemeinschaftJosefine Metzkes j.metzkes@hzdr.de www.hzdr.de HZDR

The DRACO laser facility

time [fs]

-80 -40 0 40 80

Ti:SapphireCPA laserrep rate: 10 Hz2-3 J (on target)I ~1021 W/cm2

ns-ASE contrast 10-10

Proton acceleration at DRACORCF @ wheel2Doffline

target changer

targetmanipulation

Thomson parabolasmall solid angleonline

online laser parameter control

Proton acceleration at DRACORCF @ wheel2Doffline

target changer

targetmanipulation

Thomson parabolasmall solid angleonline

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 performanceapplication experiments

online spectrometers for protons & ions (1D or 2D)

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 calibrationlight emission degrades with total dose exposition

Detector setup1D 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

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

Imaging properties

edges roughened to avoid reflection

imaging edge polished

spatial resolution

surfaces polished for efficient reflection

182 mm

8.6 mm

Detector setup & proof of principle

proton distribution reconstructed from RCFp+

Measured proton distribution

CCD camera image

Detector setup & proof of principle

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

Detector characterization @ Tandetron6 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

Sensitivity calibration

dE/dx saturation of scintillator light output

light transport within the scintillator case correction possible

condition of polished scintillator edge

Lateral homogeneity

lateral position

decrease due to imaging properties

• overall lateral homogeneity: ~ 80%

• inhomogeneity due to scintillator conditions stable measured curves give correction factors

Imaging properties testing

spatial resolution imaging properties

Imaging properties testing

spatial resolution imaging properties

Detector application

Idocisap

erture

beam fil

targetlas

proton beam

Phys. Med. Biol. 56 (2011) 1529–1543

non-invasive online access to spectral distribution and yield of accelerated protons

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

2D online detector development

profile A-A`

profile B-B`

profile C-C`

Idea: mimic an RCF stack 2D spectrum ONLINE

Schnitt A-A`

Schnitt B-B`

Schnitt C-C`

CCD camera

2D online detector development

absorber matrix & scintillator (BC 416, thickness 260 µm)

Detector setup

2D detector testing

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 mmdist 2.0 mm diam 1.5 mm

dist 2.25 mm

diam 1.5 mmdist 2.50 mm

Test matrix optimized for tandetronexperiment (12 MeV protons)

2D detector testing

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 calibration @ tandetron test of p+ scattering in angled holes

• test of a final design @ DRACO

performance with background radiation

(multiple filamentation of a freely propagating 100 TW beam in air)

… thanks for your attention

scintillator-based online detectors for laser-accelerated protons – concepts and realizations

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