R. Gaglione

MICROMEGAS chambers for hadronic calorimetry at a future linear collider

Prototypes of MICROMEGAS chambers, using bulk technology and analog readout, with 1 ? 1 cm2 readout segmentation have been built and tested. Measurements in Ar/iC4H10 (95/5) and Ar/CO2 (80/20) are reported. The dependency of the prototypes gas gain versus pressure, gas temperature and amplification gap thickness variations has been measured with an 55Fe source and a method for temperature and pressure correction of data is presented. A stack of four chambers has been tested in 200 GeV/c and 7 GeV/c muon and pion beams respectively. Measurements of response uniformity, detection efficiency and hit multiplicity are reported. A bulk MICROMEGAS prototype with embedded digital readout electronics has been assembled and tested. The chambers layout and first results are presented.

Beam test of a small MICROMEGAS DHCAL prototype

A sampling hadronic calorimeter with gaps instrumented with thin MICROMEGAS chambers of small pad size and single bit readout is a candidate for an experiment at a future linear collider. Several MICROMEGAS chambers with 1 cm2 anode pads were fabricated using the Bulk technology. Some prototypes equipped with analog readout GASSIPLEX chips were developed for characterisation at the CERN/PS facility. A stack of four chambers and stainless steal absorber plates was used to assess the behaviour of MICROMEGAS in 2 GeV electron showers. Longitudinal and transverse shower profile are shown. The Bulk fabrication process was adapted to laminate a mesh on anode PCBs with front-end chips connected on the backside. It is well suited for the construction of a 1 m3 DHCAL-MICROMEGAS prototype as large and thin chambers can be made. Such chambers with digital readout chips (HARDROC or DIRAC) were fabricated and tested in a beam. First results are presented.

HARDROC1, readout chip of the Digital HAdronic CALorimeter of ILC

HARDROC (HAdronic Rpc Detector ReadOut Chip) is the very front end chip designed for the readout of the RPC or Micromegas foreseen for the Digital HAdronic CALorimeter (DHCAL) of the future International Linear Collider. The very fine granularity of the ILC hadronic calorimeters (1cm2 pads) implies a huge number of electronics channels (4 105 /m3) which is a new feature of “imaging” calorimetry. Moreover, for compactness, the chips must be embedded inside the detector making crucial the reduction of the power consumption to 10 µWatt per channel. This is achieved using power pulsing, made possible by the ILC bunch pattern (1 ms of acquisition data for 199 ms of dead time). HARDROC readout is a semi-digital readout with two or three thresholds (2 or 3 bits readout respectively in hardroc1 and hardroc2) which allows both good tracking and coarse energy measurement, and also integrates on chip data storage. The 64 channels of the 2nd prototype, HARDROC2, are made of: • Fast low impedance preamplifier with a variable gain over 8 bits per channel • A variable slow shaper (50-150ns) and Track and Hold to provide a multiplexed analog charge output up to 15pC. • 3 variable gain fast shapers followed by 3 low offset discriminators to autotrig down to 10 fC up to 10pC. The thresholds are loaded by 3 internal 10 bit- DACs and the 3 discri outputs are sent to a 3 inputs to 2 outputs encoder • A 128 deep digital memory to store the 2*64 encoded outputs of the 3 discriminators and bunch crossing identification coded over 24 bits counter. • Power pulsing and integration of a POD (Power On Digital) module for the 5MHz and 40 Mhz clocks management during the readout, to reach 10µW/channel The overall performance of HARDROC will be described with detailed measurements of all the characteristics. Hundreds of chips have indeed been produced and tested before being mounted on printed boards developed for the readout of large scale (1m2) RPC and Micromegas prototypes. These prototypes have been tested with cosmics and also in testbeam at CERN in 2008 and 2009 to evaluate the performance of different kinds of GRPCs and to validate the semi-digital electronics readout system in beam conditions.

MICROROC: MICRO-mesh gaseous structure Read-Out Chip

MICRO MEsh GAseous Structure (MICROMEGAS) and Gas Electron Multipliers (GEM) detectors are two candidates for the active part of a Digital Hadronic CALorimeter (DHCAL) as part of a high energy physics experiment at the International Linear Collider. Physics requirements lead to a highly granular hadronic calorimeter with up to thirty million channels with probably only hit information (digital calorimeter). To validate the concept of digital hadronic calorimetry, a cubic meter technological prototype, made of 40 planes of one squared meter each, is compulsory. Such a technological prototype involves not less than 400 000 electronic channels, thus requiring the development of ASIC. Based on the experience of previous ASICs (DIRAC and HARDROC) and on multiple testbeam results, a new ASIC, called MICROROC (MICRO mesh gaseous structure Read-Out Chip), is currently beeing jointly developped at IN2P3 by OMEGA/LAL and LAPP microelectronics goups. It should be submitted to foundry in june 2010, and prototypes are expected to be delivred at the beginning of september. MICROROC is a 64 channel mixed-signal integrated circuit based on HARDROC manufactured in AMS 350 nm SiGe technology. Analog blocks and the whole digital part are reused from HARDROC, but the very front-end part, ie the preamplifier and shapers, has been especially re-designed for one square meter MICROMEGAS detectors, which require HV sparks robustness for the electronics and also very low noise performance to detect signals down to 2fC with an anode capacitance of. Each channel of the MICROROC chip is made of a fixed gain charge preamplifier, two different adjustable shapers, three comparators and a random access memory used as a digital buffer. Other blocks, like 12-bit DAC, configuration registers, bandgap voltage reference and LVDS receiver are included. All these blocks are power-pulsed, thus reaching a power consumption equal to zero in standby mode. After characterisation of the MPW prototypes, a low volume production will be packaged in TQFP160 with the same pinout as the HARDROC chip. Therefore bulk MICROMEGAS detectors with embedded MICROROC will be straightforward built, using HARDROC previously designed PCBs and the same data acquisition system.

Micromegas for imaging hadronic calorimetry

The recent progress in R&D of the Micromegas detectors for hadronic calorimetry including new engineering-technical solutions, electronics development, and accompanying simulation studies with emphasis on the comparison of the physics performance of the analog and digital readout is described. The developed prototypes are with 2 bit digital readout to exploit the Micromegas proportional mode and thus improve the calorimeter linearity. In addition, measurements of detection efficiency, hit multiplicity, and energy shower profiles obtained during the exposure of small size prototypes to radioactive source quanta, cosmic particles and accelerator beams are reported. Eventually, the status of a large scale chamber (1 ? 1 m2) are also presented with prospective towards the construction of a 1 m3 digital calorimeter consisting of 40 such chambers.

Test in a beam of large-area Micromegas chambers for sampling calorimetry

The application of Micromegas for sampling calorimetry puts specific constraints on the design and performance of this gaseous detector. In particular, uniform and linear response, low noise and stability against high ionisation density deposits are prerequisites for achieving good energy resolution. A Micromegas-based hadronic calorimeter was proposed for an application at a future linear collider experiment and three technologically advanced prototypes of 1×1 m2 were constructed. Their merits relative to the above-mentioned criteria are discussed on the basis of measurements performed at the CERN SPS test-beam facility.