1. 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