Design and test of a high-speed beam monitor for hardon therapy H. Pernegger on behalf of Erich Griesmayer Fachhochschule Wr. Neustadt/Fotec Austria (H. Frais-Koelbl, E. Griesmayer, H. Kagan, H. Pernegger)

CERN RD42 meetingH. Pernegger, E. Griesmayer2 MedAustron Conventional X-Ray Therapy Ion-Therapy C-Ions 1 cm Protons 1 cm Austrian medical accelerator facility Cancer treatment and non-clinical research with protons and C-ions

CERN RD42 meetingH. Pernegger, E. Griesmayer3 Layout Synchrotron 2 Experimental rooms 4 Treatment rooms Injector Preliminary layout

CERN RD42 meetingH. Pernegger, E. Griesmayer4 Parameters Proton & Carbon Beam –Energy: MeV protons and MeV/u C-ions –Intensity: 1x10 10 protons (1,6 nA) and 4x10 8 C-ions (0,4 nA) –Beam size: 4x4 mm 2 to 10x10 mm 2 Setup –4 fixed beams and 2 gantries –Field sizes: 40x40 cm 2, 25x25 cm 2, 4x4 cm 2 (fixed beams), 20x20 cm 2 (gantries) –Active scanning –Extraction period: 1 s to 10 s

CERN RD42 meetingH. Pernegger, E. Griesmayer5 High speed beam monitor Initial goal: Develop a detector for beam diagnostic Measure intensity & structure of extracted beam by counting individual particles (no integration) –Short pulses with good time resolution for high-speed counting –Resolve beam time structure (measure number of extracted particles for each revolution) –1D or 2D position sensitivity to provide beam profile Rates: counting single particles at rates close to the GHz/channel-range Maximum rates up to 6x larger during RF cycle

CERN RD42 meetingH. Pernegger, E. Griesmayer6 Beam Monitor Concept Segmented CVD diamond as detector material –High drift velocity + short charge lifetime give short signals –Radiation hard –Variable segmentation possible on thin solid stage detector RF-amplifier and parallel counting –Direct amplification of ionization current pulse (no current integration) –discriminator and pulse counter to parallel readout

CERN RD42 meetingH. Pernegger, E. Griesmayer7 Test of first prototype Tested a first prototype of detector and electronics at Indiana University Cyclotron Facility –Tested with protons (worse case: smaller signal) –Tested in energy range for proton therapy (55-200MeV) –Variable intensity Main focus: measure analog signal characteristics –Signal time properties –Amplitude properties –Energy scan and dE/dx in diamond –Efficiency Tested with first prototype of –2 samples of CVD diamond –First prototype for analog amplification stages –First tests of digital electronics (in progress)

CERN RD42 meetingH. Pernegger, E. Griesmayer8 Setup and Samples used for tests 2 diamond samples with different pad size + scintilator as “telescopes” –2.5 x 2.5 mm2 (in trigger) CCD = 190  m, D= 500  m –7.5 x 7.5 mm2 (for analog measurements) CCD = 190  m, D= 500  m –Trigger scintilator (5x3mm2) triggermeasured

CERN RD42 meetingH. Pernegger, E. Griesmayer9 RF amplifier stage 3-stage current amplification Parameters (per stage) –Bandwidth 2GHz –Amplification 20dB, Noise 2.7dB Some signal estimates: –Max. current peak from diamond 1.7  A for MIP –Max (theor.) SNR expected for 55 to 200 MeV protons: 20:1 to 8:1

CERN RD42 meetingH. Pernegger, E. Griesmayer10 Digital readout stage Disriminator –Discriminate on voltage and time difference –Baseline restoration with delay line –Implemented in PECL Counting & readout –Count in fast 8-bit and latch to 24 bit counters –Allows to store full “pulse trains” for fast rate vs time measurement in SDRAM

CERN RD42 meetingH. Pernegger, E. Griesmayer11 Measured pulses Single signals in diamond (protons at 55 MeV)

CERN RD42 meetingH. Pernegger, E. Griesmayer12 Signal Time Properties Average pulse shape Pulse duration (FWHM) Rise time : 340ps Duration: 1.4ns

CERN RD42 meetingH. Pernegger, E. Griesmayer13 Diamond signal amplitudes Amplitudes in the full energy range –r.m.s. noise = 18 mV

CERN RD42 meetingH. Pernegger, E. Griesmayer14 dE/dx in CVD Diamond Compare measured signal to calculated dE/dx behaviour in diamond –Normalized at 104 MeV for uncertainty in absolute calibration

CERN RD42 meetingH. Pernegger, E. Griesmayer15 First results on Signal-to-Noise Measured most probable S/N ranges from 15:1 to 7:1 200 MeV 104 MeV 55 MeV

CERN RD42 meetingH. Pernegger, E. Griesmayer16 Preliminary results on Efficiency Defined as signal with –amplitude > 3 x  noise –t signal in +/- 3ns window of trigger time Measured efficiency of 99% to 94% (noise limited) 90% 100%

CERN RD42 meetingH. Pernegger, E. Griesmayer17 Next steps Diamond and dedicated electronics seems to be ideally suited for beam diagnostics Achieved very promising results for beam diagnostics with protons –SNR 7:1 to 15:1 in the typical energy range for proton therapy –Risetime of 350ps and pulse width 1.4ns –Efficiency 94% to 99% (electronics noise limited) Since then –Worked on optimizing SNR for even lower signals (MIP range) and achieved lower noise with modified electronics –Recently tested with C ions (3 weeks ago) and large surface (3x1cm pad)