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Design and test of a high-speed beam monitor for hardon therapy

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). MedAustron.

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Design and test of a high-speed beam monitor for hardon therapy

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  1. Design and test of a high-speedbeam 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)

  2. MedAustron Conventional X-Ray Therapy Ion-Therapy 1 cm 1 cm • Austrian medical accelerator facility • Cancer treatment and non-clinical research with protons and C-ions Protons C-Ions H. Pernegger , E. Griesmayer

  3. Layout Synchrotron Injector 2 Experimental rooms 4 Treatment rooms Preliminary layout H. Pernegger , E. Griesmayer

  4. Parameters • Proton & Carbon Beam • Energy: 60-240 MeV protons and 120-400 MeV/u C-ions • Intensity: 1x1010 protons (1,6 nA) and 4x108 C-ions (0,4 nA) • Beam size: 4x4 mm2 to 10x10 mm2 • Setup • 4 fixed beams and 2 gantries • Field sizes: 40x40 cm2, 25x25 cm2, 4x4 cm2(fixed beams), 20x20 cm2(gantries) • Active scanning • Extraction period: 1 s to 10 s H. Pernegger , E. Griesmayer

  5. 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 H. Pernegger , E. Griesmayer

  6. 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 H. Pernegger , E. Griesmayer

  7. 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) H. Pernegger , E. Griesmayer

  8. Setup and Samples used for tests trigger measured • 2 diamond samples with different pad size + scintilator as “telescopes” • 2.5 x 2.5 mm2 (in trigger) CCD = 190 mm, D= 500 mm • 7.5 x 7.5 mm2 (for analog measurements) CCD = 190 mm, D= 500 mm • Trigger scintilator (5x3mm2) H. Pernegger , E. Griesmayer

  9. 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 1.7mA for MIP • Max (theor.) SNR expected for 55 to 200 MeV protons: 20:1 to 8:1 H. Pernegger , E. Griesmayer

  10. 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 H. Pernegger , E. Griesmayer

  11. Measured pulses • Single signals in diamond (protons at 55 MeV) H. Pernegger , E. Griesmayer

  12. Signal Time Properties Average pulse shape Pulse duration (FWHM) • Rise time : 340ps Duration: 1.4ns H. Pernegger , E. Griesmayer

  13. Diamond signal amplitudes • Amplitudes in the full energy range • r.m.s. noise = 18 mV H. Pernegger , E. Griesmayer

  14. dE/dx in CVD Diamond • Compare measured signal to calculated dE/dx behaviour in diamond • Normalized at 104 MeV for uncertainty in absolute calibration H. Pernegger , E. Griesmayer

  15. First results on Signal-to-Noise • Measured most probable S/N ranges from 15:1 to 7:1 200 MeV 104 MeV 55 MeV H. Pernegger , E. Griesmayer

  16. Preliminary results on Efficiency • Defined as signal with • amplitude > 3 x snoise • tsignal in +/- 3ns window of trigger time • Measured efficiency of 99% to 94% (noise limited) 100% 90% H. Pernegger , E. Griesmayer

  17. 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) H. Pernegger , E. Griesmayer

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