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

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

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

Proton acceleration at DRACO RCF @ 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

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

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

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

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

Sensitivity calibration

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

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

Imaging properties testing spatial resolution imaging properties

Imaging properties testing spatial resolution imaging properties

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

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

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

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

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)

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 calibration @ tandetron test of p+ scattering in angled holes To do test of a final design @ DRACO  performance with background radiation

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