Monitor System

The SVD monitor system consists of temperature monitors using resistive temperature detectors (RTDs), instantaneous radiation monitors based on PIN diodes, total-dose measurements using a RADFET technique (electronic readout) and an alanine dosimeter. These sensors are read using a commercial data logger system [24]. A total of 48 RTDs [25] are attached to the SVD cooling system and the interaction-region (IR) beam pipe. The monitor data has been used as the interlock signal for the cooling systems for SVD and the IR beam pipe. The operation of the cooling system has been highly reliable: no temperature fault condition has been asserted during the past year of operation. The eight sets of unbiased PIN photo diodes (HPK S3590-08) [26] used as real-time radiation monitors are read out by an operational amplifier OPA129 (Burr-Brown). Output signals are recorded by the data logger. The signals are also sent to a discriminator module. When more than two channels indicate an instantaneous radiation dose exceeding 1 Rad/s, the multiplicity logic sends a beam abort request to the KEKB accelerator. The frequency of beam aborts varies with accelerator conditions, but in stable operation is approximately one per day. A RADFET is a MOSFET [27] optimized for radiation measurement. When it is irradiated, the threshold voltage of the FET is shifted due to the accumulation of charge in the gate oxide. Since this mechanism is essentially the same as the mechanism of radiation damage in the VA1 chips, it provides a good measure of radiation damage in those chips. The alanine dosimeters are passive device based on electron spin resonance (ESR) measurement of radiation induced free radicals in an amino acide alanine (CH$_3$-CH-NH$_2$-COOH). They provide a measure of long-term integrated dose and accessible for reading only in conjunction with major detector accesses.