Performances of a pixel ionization chamber to monitor a voxel scan hadron beam

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Performances of a pixel ionization chamber to
monitor a voxel scan hadron beam

• A.Boriano 3, F.Bourhaleb 2,3, R. Cirio 3, M.
  Donetti 2,3,
• F. Marchetto 3, C. Peroni 3, C.J. Sanz Freire 1,3
  
• 1 Ion Beam Applications, Louvain la-Neuve,
  Belgium
• 2 TERA Foundation, Novara, Italy
• 3 University and INFN, Torino, Italy

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outline

• Mechanical structure of the pixel ionisation
  chamber

• Read-out electronics and performances

• Data Acquisition System

• Results from test with protons at PSI

• Results from test with C6 at GSI (2000)

• Preliminary results from test with C6 at GSI
  (2002)

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The pixel chamber

• parallel plate ionization chamber
• anode segmented in 1024 square pixels
• pixel dimension 7.5 X 7.5 mm2
• sensitive area 24 X 24 cm2
• 1 mm water equivalent thickness
• front-end electronics, located around the
  chamber, to perform analog to digital conversion

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Detector design

• The detector has to be thin to minimize the
  effects on the beam energy and shape
• Anode and cathode are glued to frames in order to
  assure the mechanical rigidity and the gap
  thickness
• Water equivalent thickness lt 1 mm

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Front-end electronics

• located around the chamber
• we have developed a full custom chip (TERA05)
• every chip has 64 channels that convert the
  collected charge into counts

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Linearity at 100 fC charge quantum

• 20 pA lt I lt 0.6 ?A
• Linearity better than 0.7

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Linearity at 600 fC charge quantum

• 10 pA lt I lt 2 ?A
• Linearity better than 0.3

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Reproducibility of charge quantum

• I 49.96 nA
• Qc 600 fC
• 24 ºC lt T lt 27 ºC
• 1 month
• 6 measures

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Data acquisition

• Signals (RS422 standard) are delivered via
  twisted pair flat cables (100 m maximum length)
• max transfer rate 10 MHz 40 Mbyte/s
• read out transfer time 50 ?s
• read out cycle total time 100 ?s
• real time operating system

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Beam test at PSI

• PSI test with a 138 MeV proton beam
• 7 mm FWHM beam
• Spot-scanning

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Beam test at GSI

• Beam characteristics
• raster-scan delivery system
• C6, beam dimension 8.8 mm (FWHM)
• data acquisition synchronized with raster-scan

• Aims
• spatial resolution
• homogeneity of response

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Spatial resolution
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Homogeneity of the response
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DAQ- test gsi 2002
Pixel chamber
PMC
4 chip
CPU
PC
1024 pixel
4 chip
4 chip
F I F O
OUT 16 bit
4 chip
Operative Systen VxWorks with Tornado II
environment
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Daq with 49 pixels map
49 pixels map
The map follows the beam...
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Beam intensity dependence

• 1 single voxel treated with several beam
  intensities
• Deviation from linearity is within 1

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Spatial resolution

• 14x14 cm2 field
• 2100 voxels
• DAQ 7x7 map that follows the beam

Spatial resolution ? lt 0.2 mm
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Detector design
Thick version When used in plastic phantom the
detector can be thick. With photon or electron
beam air gap has to be minimized. Anode and
cathode are glued to a plastic slab, which is a
grid of 1024 holes. Each hole can be considered
as an independent sensitive volume.
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TERA05

• Very Large Scale Integration (VLSI)
• i?f conversion
• output ? Qint
• 100 fCltcharge quantumlt800 fC
• Imax 4 ?A
• 64 channels
• 16 bit wide counters
• multiplexed digital output
• dead-time free readout
• max read out rate 10 MHz

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Read out electronics
Recycling Integrator architecture.
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Spread of charge quanta

• I 49.96 nA
• 26 chips

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Data acquisition
Slow data acquisition

• connection by twisted pair flat cables (100 m
  max)
• max rate transfer 1 MHz
• 2 Mbyte/s
• read out transfer time 1 ms
• PCI DAQ card
• LabVIEW software
• cheap solution
• easy to handle