design and test of a high-speed beam monitor for hardon therapy h. pernegger on behalf of erich...
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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)
CERN RD42 meeting H. Pernegger , E. Griesmayer 2
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 meeting H. Pernegger , E. Griesmayer 3
Layout
Synchrotron
2 Experimental rooms
4 Treatment rooms
Injector
Preliminary layout
CERN RD42 meeting 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
CERN RD42 meeting 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
Protonen: 2826 100.1100.1 mmspmmsp ⋅⋅<<⋅⋅ ++φC-Ionen: 2624 100.4100.4 mmsCmmsC ⋅⋅<<⋅⋅ ++φ
Maximum rates up to 6x larger during RF cycle
CERN RD42 meeting 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
RF-Amp
n Bit
CVD-DetectorCounter
CERN RD42 meeting 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)
CERN RD42 meeting H. Pernegger , E. Griesmayer 8
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)
trigger measured
CERN RD42 meeting 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 1.7A for MIP– Max (theor.) SNR expected for 55 to 200 MeV protons: 20:1 to
8:1
CERN RD42 meeting 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
PECL Trigger
8 BitPECL Zähler
DAC
24 BitCMOS Zähler
analogin Lat ch und
Re -ad out
Δ u
Δ t
Δ t
Δ u
analogin
PECLout
CERN RD42 meeting H. Pernegger , E. Griesmayer 11
Measured pulses
• Single signals in diamond (protons at 55 MeV)
CERN RD42 meeting H. Pernegger , E. Griesmayer 12
Signal Time Properties
• Average pulse shape • Pulse duration (FWHM)
• Rise time : 340ps Duration: 1.4ns
CERN RD42 meeting H. Pernegger , E. Griesmayer 13
Diamond signal amplitudes
• Amplitudes in the full energy range– r.m.s. noise = 18 mV
CERN RD42 meeting 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
CERN RD42 meeting H. Pernegger , E. Griesmayer 15
First results on Signal-to-Noise
• Measured most probable S/N ranges from 15:1 to 7:1
200 MeV104 MeV55 MeV
CERN RD42 meeting H. Pernegger , E. Griesmayer 16
Preliminary results on Efficiency
• Defined as signal with – amplitude > 3 x noise
– tsignal in +/- 3ns window of trigger time
• Measured efficiency of 99% to 94% (noise limited)
90%
100%
CERN RD42 meeting 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)