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, Belgium2 TERA Foundation, Novara, Italy3 University and INFN, Torino, Italy

outlineMechanical structure of the pixel ionisation chamberRead-out: electronics and performancesData Acquisition SystemResults from test with protons at PSIResults from test with C+6 at GSI (2000)Preliminary results from test with C+6 at GSI (2002)

The pixel chamberparallel 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

Detector designThe detector has to be thin to minimize the effects on the beam energy and shapeAnode and cathode are glued to frames in order to assure the mechanical rigidity and the gap thicknessWater equivalent thickness < 1 mm

Front-end electronicslocated around the chamber

we have developed a full custom chip (TERA05)

every chip has 64 channels that convert the collected charge into counts

Linearity at 100 fC charge quantum20 pA < I < 0.6 ALinearity better than 0.7 %

Linearity at 600 fC charge quantum10 pA < I < 2 ALinearity better than 0.3 %

Reproducibility of charge quantumI = 49.96 nAQc = 600 fC24 C < T < 27 C1 month6 measures

Data acquisitionSignals (RS422 standard) are delivered via twisted pair flat cables (100 m maximum length)max transfer rate = 10 MHz = 40 Mbyte/sread out transfer time = 50 sread out cycle total time = 100 sreal time operating system

Beam test at PSIPSI test with a 138 MeV proton beam7 mm FWHM beamSpot-scanning

Beam test at GSIBeam characteristicsraster-scan delivery systemC+6, beam dimension = 8.8 mm (FWHM)data acquisition synchronized with raster-scanAimsspatial resolutionhomogeneity of response

Spatial resolution

Homogeneity of the response

PMCFIFOCPUPixel chamberPCOUT16 bitOperative Systen VxWorks with Tornado II environment1024 pixel4chip4 chip4 chip4 chipDAQ- test gsi 2002

49 pixels map The map follows the beam...Daq with 49 pixels map

Beam intensity dependence 1 single voxel treated with several beam intensities Deviation from linearity is within 1%

Spatial resolution 14x14 cm2 field ~2100 voxels DAQ: 7x7 map that follows the beamSpatial resolution < 0.2 mm

Detector designThick 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.

TERA05Very Large Scale Integration (VLSI)if conversionoutput Qint100 fC

Read out electronicsRecycling Integrator architecture.

Spread of charge quantaI = 49.96 nA26 chips

Data acquisitionconnection by twisted pair flat cables (100 m max)max rate transfer = 1 MHz = 2 Mbyte/sread out transfer time = 1 msPCI DAQ cardLabVIEW softwarecheap solutioneasy to handleSlow data acquisition