Speaker
Mr
Hao Liu
(State Key Laboratory of Partical Detection and Electronics, University of Science and Technology of China)
Description
The Circular Electron Positron Collider (CEPC) is one of next generation colliders aim at huge amount of the Higgs, W and Z bosons generation and its 70 cm × 70 cm × 40 layers AHCAL (Analog Hadron Calorimeter) prototype is under construction. The prototype AHCAL is a sampling calorimeter with steel as the absorber and scintillator tiles and SiPM (Silicon Photomultiplier) as sensitive medium and contains about 12,000 40 mm × 40 mm scintillators. The uniformity of scintillator light yield is a vital factor which greatly influences the energy linearity and resolution of the calorimeter. This paper describes a test platform which can measure the light yield of every scintillator used in the AHCAL prototype.
The test platform which runs in a dark box to shield environmental light consists of a PC, a readout electronic system, and a 90Sr radioactive source on a stepping motor. The whole test platform is designed based on 4 SPIROC2E chips, a low-noise front-end chip with 36 SiPM readout channels. There’re 144 scintillator positions on the test platform, each of which contains a SiPM and an electronic readout channel. The stepping motor is programmed to move above the scintillators by a self-written software. When a test is started, each channel is ready to collect, sample, digitize the incident signal and then sends the charge and timing information to PC, while the 90Sr radioactive source is controlled to stay on the top of the first tested scintillator. After a fixed interval, 10 minutes for example, charge information is enough to extrapolate the light yield of the current scintillator and the source is moved to the next scintillator for another test unless all scintillators tested. Since the valid digital data from SPIROC2E chips is characterized with a “hit” signal, offline analysis is easy to be carried out and the light yield of every scintillator is obtained. In that way the whole test process for all scintillators will work out automatically without redundant intervention.
SiPM gain difference, which could result from production and using damage, should be controlled strictly in order to test the light yield of scintillators. Even the same type SiPMs have distinctive gain, and are strongly dependent on temperature. So temperature monitoring system is established based on temperature sensors located evenly in all SiPM cells. Thanks to the internal DAC of SPIROC2E chip, the bias voltage for each SiPM can be tuned to minimize the gain difference according to the feedback from the temperature monitors.
Summary
A SPIROC2E-based scintillator test platform for the AHCAL prototype has been developed, including the dark box, the stepping motor, the radioactive source, the readout electronics system and temperature monitors. It makes it practical to test and eliminate the light yield difference which is significant for the energy linearity and resolution of the calorimeter.
Primary author
Mr
Hao Liu
(State Key Laboratory of Partical Detection and Electronics, University of Science and Technology of China)
