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

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Layout

Synchrotron

2 Experimental rooms

4 Treatment rooms

Injector

Preliminary layout

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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

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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

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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

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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)

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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

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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

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Measured pulses

• Single signals in diamond (protons at 55 MeV)

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Signal Time Properties

• Average pulse shape • Pulse duration (FWHM)

• Rise time : 340ps Duration: 1.4ns

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Diamond signal amplitudes

• Amplitudes in the full energy range– r.m.s. noise = 18 mV

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dE/dx in CVD Diamond

• Compare measured signal to calculated dE/dx behaviour in diamond– Normalized at 104 MeV for uncertainty in absolute calibration

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First results on Signal-to-Noise

• Measured most probable S/N ranges from 15:1 to 7:1

200 MeV104 MeV55 MeV

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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%

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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)