standard THGEM versus FLOWER Progress on THGEM-based photon detectors for COMPASS RICH-1 Fulvio Tessarotto, INFN – Sezione di Trieste On behalf of an Alessandria-Aveiro-Freiburg-Liberec-Prague-Torino-Trieste Collaboration OUR THGEMS ARE PRODUCED BY INDUSTRY: THGEM – based PD’s RICH-1 upgrade project IT IS POSSIBLE TO USE THE STANDARD PCB TECHNOLOGY TO PRODUCE THE ELEMENTS OF A DETECTOR OF SINGLE PHOTONS: THGEMS ARE PRINTED BOARDS WITH AN ARRAY OF HOLES: IN THE SPECTROMETER OF THE COMPASS EXPERIMENT AT CERN SPS HADRON IDENTIFICATION IS PROVIDED BY: AND CsI COATED AT CERN: 300 mm x 300 mm PD prototype MWPC’s with CsI are successfully used, but: - the effective gain is moderate (~10,000  p.e. detection eff. ~70%) - the quantum efficiency is challenged by aging (~1 mC/cm2) - the signal is slow, coming from the ions drift (~100 ns) - for larger gains the electrical stability in the experimental environment is limited and the recovery time after a detector trip is long (~1 d) Performances in terms of rate capability and noise rejection cannot be increased without a change of technology. The new photon detectors will allow to: - avoid photon feedback - reduce the ion backflow to the CsI layer - detect signals from electron drift (few ns) - use simple and robust components THE PHOTON DETECTOR ARCHITECTURE IS: IT PROVIDES LARGE GAIN FOR UV PHOTONS, IN ORDER TO COPE WITH THE CHALLENGES OF THE MEASUREMENTS FORESEEN BY COMPASS AN UPGRADE OF THE PHOTON DETECTORS IS PROPOSED BY THE COLLABORATION: MWPC’s + CsI THGEMs + CsI 1500 mm 650 mm Detector cross section: THGEMs Anode pads CsI HIGH RATE CAPABILITY AND GOOD TIME RESOLUTION TEST PRODUCTION OF 600 mm x 600 mm THGEM: Conclusions THGEMs represent a good choice for single UV photon detectors: pcb technology is o.k. provided appropriate parameters are chosen Almost all principle aspects have been validated and understood using small size prototypes: effective single photon detection, large and stable gain, fast signals Optimization still to be performed on many details and open points Many challenges to overcome before achieving large size, cheap, robust, fast, high gain, high rate, magnetic insensitive single photon detectors, but we are progressing COMPASS RICH-1 will probably be the first to use THGEM-based PDs DURING 4 YEARS OF STUDIES WE PERFORMED: Ion backflow: standard THGEM versus FLOWER Characterisation of small size (30 x 30 mm2) THGEM prototypes - Single layer arrangement - Multiple layer arrangement - Using X-ray sources - Using UV light sources - With Cherenkov light at the test beams - Analog read-out, single channel - Digital read-out, 1 channel per anode pad - Read-out of the current on the various electrodes More than 50 different THGEM samples characterised Towards large sizes - Production of large size THGEM samples, up to 600 x 600 mm2 - Study of specific engineering aspects with dedicated arrangements Construction and test of a large size detector, 300 x 300 mm Collaborators: IBF down to few % for FLOWER THGEM