Scintillator-based online detectors for laser-accelerated protons – Concepts and realizations

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

*Dresden laser acceleration source The DRACO laser facility Ti:Sapphire CPA laser rep rate: 10 Hz 2-3 J (on target) I ~1021 W/cm2 ns-ASE contrast 10-10 30 fs -80 -40 0 40 80 time [fs]

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

Proton acceleration at DRACO target changer • RCF @ wheel • 2D • offline • Status • stable high repetition rate lasersystem reliableprotonsource • high degreeof remote controlundervacuum • online optimizationandmonitoringofaccelerationperformance • applicationexperiments • onlinespectrometersforprotons & ions (1D or 2D) online laser parameter control • Thomson parabola • small solid angle • online NEED target manipulation

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

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

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 8.6 mm 182 mm imaging edge polished surfaces polished for efficient reflection edges roughened to avoid reflection spatial resolution

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

Detector setup & proof of principle Measured proton distribution CCD camera image energy p+ • 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 @ 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

Sensitivity calibration

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

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

Detector application online detector proton beam non-invasive online accesstospectraldistributionandyieldofacceleratedprotons beam filter aperture aperture Idocis target laser Phys. Med. Biol. 56 (2011) 1529–1543

Detector application 25 µm out of focus energy optimal 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

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

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

2D detector testing Test matrix optimized for tandetron experiment (12 MeV protons) diam 1.0 mm dist 1.50 mm diam 1.5 mm dist 2.0 mm diam 1.5 mm dist 2.25 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

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

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

Scintillator-based online detectors for laser-accelerated protons – Concepts and realizations