HPD based on Timepix Gisela Anton vLvnT Workshop, Toulon April 23rd, 2008

Demand for photon detectors Air shower telescope Pierre Auger Telesope Gamma ray telescopes HESS and MAGIC Neutrino telescopes IceCube, ANTARES/KM3NeT Demand for several thousand photon detectors!

Standard OM solution

Standard PMT versus HPD

Single Photo Electron (SPE) resolution PMT HPD n=10, g=5 n=1, g=3000 Standard PMT versus HPD: SPE Output signal U :

Examples of existing HPDs 2048 pixels Fast global analog information: 10 nsec. No deadtime free measurement 256 x 32 = 8192 pixels Time resolution: 25 nsec. (40 MHz) Triggered by digital Fast-Or No deadtime free measurement ISPA - tube LHCb - tube Images taken from: Thierry Gys (CERN), Particle Detectors – Principles and Techniques, Lecture 3b, Photo-detection

Analogue and digital read-out Standard PMT versus HPD: electronics amplifier shaper discriminator TDC QDC counter Computer All inclusive

The Medipix development The Medipix2 collaboration members CERN, Geneva, Switzerland IFAE, Barcelona, Spain University of Cagliari, Italy CEA, France Academy of Sciences, Prague CTU Prague, Czech. Republic Universität Erlangen-Nürnberg, Germany ESRF, Grenoble, France Universität Freiburg, Germany University of Glasgow, United Kingdom Medical Research Council, Cambridge Mid-Sweden University, Sweden Università di Napoli, Italy NIKHEF, The Netherlands Università di Pisa, Italy Medipix1 Medipix2 MXR Medipix3 Timepix Medipix2 The Medipix footprints

Medipix/Timepix Semiconductor sensor layer:  Material: 300 µm silicon  Filling factor 100% ASIC/Sensor parameters:  Hybrid design with Pb/Sn bump-bonds  Total sensor area: 14 x 14 mm²  256 rows, 256 columns  Pixel pitch: 55 µm (square)  1 counter per pixel, depth of 14 bits  100 MHz clock frequency

X-ray single photon counting images

Timepix electronics in each pixel Electronics design:  Discriminator and 14-bit counter in each pixel  Clock frequency up to 100 MHz  0.25 µm CMOS AnalogDigital

Time-To-Shutter measurement: time stamp Timepix working principle

Timepix advantage: highly parallel system parallel channels frame time µs

Imaging: Simulations of a cross-focusing electric field Finite Element Simulation (COMSOL) Numerical solution of Poisson’s equation with boundary conditions for the electric potential:  U = -20 kV on photocathode and field shaping electrode  U = 0 kV on sensor surface Sample electron trajectories Equipotential surfaces (1 kV steps)

The angular distribution of the emitted photo-electrons is limiting the spatial resolution of the electron optics Normal emission, E i =1 eV Angular distribution cos(θ), E i =1 eV Further improvement in progress!

Test of concept: HPD set-up at CERN  High voltage discharge lamp  UHV vessel with  Deflection mirror (position adjustable)  CsI photocathode  Accelerating electric field (max. 25 kV)  Timepix chipboard (mounted upside down) Figure from W. Dulinski et al., Nucl. Inst. Meth. A 546 (2005) In collaboration with:  Christian Joram  Jacques Séguinot In collaboration with:  Christian Joram  Jacques Séguinot Experimental set-up at CERN  Timepix energy response function  Electron backscattering at the sensor surface and charge sharing among neighboring pixels  Precision of the timing information of light signals (time resolution) Physics under investigation

Time-To-Shutter measurement: Measured time distribution System works ! But: bad timing!

Time walk Rise time 130 ns !! Rise time 130 ns !!

Charge sharing between pixels Small pixels lead to a distribution of the total charge deposition among multiple neighboring pixels (“charge sharing”). Simulation:  Electron tracking through the sensor using parameterized cross sections for the energy loss  Generation energy of 3.6 eV for one electron- hole pair  Projection of generated carriers onto the pixel matrix taking into account lateral diffusion (2D Gaussian, FWHM 18 µm) Monte Carlo simulations using the GEANT4 framework

energy distribution  time distribution Comparison simulation versus measurement Factors considered for comparison to exp. data:  Digitization error (finite binning)  Uncertainty of time reference (true lamp signal)  Preamplifier gain variation among pixels  Threshold noise among pixels The conversion from the energy to the time distribution is done using a Fermi-like step function for the rising edge of the pulse.

Influence of charge sharing 300 µm 55 µm 100 µm 110 µm

Time distribution Influence of sensor parameters

From Timepix to Photopix TimepixPhotopix Pixel size [µm]55 x x 110 Sensor thickness [µm] Rise time [ns]140tbd Clock [MHz] Counters/pixel1 x 14 bit2 x 20 bit Matrix readoutserialparallel DAQ modeframescontinuous

Planned operating modes of the HPD Time and position resolved measurement of single photons with rates up to several 10 MHz Ultra fast low intensity imager FADC or waveform: photon number per time interval number of photons 10 ns time

Project team, collaborators and funding Gisela Anton Thilo Michel Ulrike Gebert Tilman K. Rügheimer Michael Campbell Xavier Llopart Cudié Christian Joram Jacques Séguinot ECAP, Erlangen (filed a patent) CERN, Geneva (Medipix collaboration) CERN, Geneva (HPD development) Financial support provided by the Studienstiftung des deutschen Volkes

Thank you for your attention!

Electron backscattering has been investigated quantitatively using the GEANT4 framework Overall backscattering probability:Maximum electron penetration depth:  Mean penetration depth of backscattered electrons  0.8 µm  Mean energy of backscattered electrons  12 keV  Backscattering probability of more than 13% over wide energy range

From Timepix to Photopix Timepix Charge sharing: double counting time smearing 1 counter per pixel: deadtime 100 MHz clock: 10 nsec time resolution Read-out time around 265 µsec All counter values are transferred from read-out zone to periphery Requirements „Photopix“ Sensor pixel pitch: 110 µm thickness: 100 µm 2 counters per pixel: no deadtime 500 MHz clock: 2 ns resolution Fast read-out time: 100 µsec Zero-suppression in read-out zone Detected single photon rate of 40 MHz processable (70 µm pitch, pixel, 100 µsec frametime) Detection of each single photon with 2 nsec time resolution