Cryogenic loss monitors with FPGA TDC signal processing

TL;DR

This paper presents the design and testing of radiation-hard helium gas ionization chambers with FPGA-based TDC signal processing for cryogenic beam loss monitoring in particle accelerators.

Contribution

It introduces a novel FPGA-based TDC scheme for fast, high-resolution beam loss detection in cryogenic environments, suitable for use in superconducting RF facilities.

Findings

Successful operation at temperatures from 5K to 350K

Achieved current measurement resolution better than 10 bits

Demonstrated fast response suitable for beam loss monitoring

Abstract

Radiation hard helium gas ionization chambers capable of operating in vacuum at temperatures ranging from 5K to 350K have been designed, fabricated and tested and will be used inside the cryostats at Fermilab's Superconducting Radiofrequency beam test facility. The chamber vessels are made of stainless steel and all materials used including seals are known to be radiation hard and suitable for operation at 5K. The chambers are designed to measure radiation up to 30 kRad/hr with sensitivity of approximately 1.9 pA/(Rad/hr). The signal current is measured with a recycling integrator current-to-frequency converter to achieve a required measurement capability for low current and a wide dynamic range. A novel scheme of using an FPGA-based time-to-digital converter (TDC) to measure time intervals between pulses output from the recycling integrator is employed to ensure a fast beam loss response along with a current measurement resolution better than 10-bit. This paper will describe the results obtained and highlight the processing techniques used.