# Characterization of a double Time-Of-Flight detector system for accurate velocity measurement in a storage ring using laser beams

## TL;DR

This paper presents a novel laser-based method to precisely measure the distance and timing between double Time-Of-Flight detectors in a storage ring, enhancing velocity measurement accuracy for exotic nuclei in isochronous mass spectrometry.

## Contribution

The study introduces a new laser range finder technique for calibrating double TOF detectors, improving velocity resolution in storage ring mass spectrometry.

## Key findings

- Measured detector distance with 20 mm precision
- Achieved velocity resolution of 4.4×10⁻⁴
- Calibrated time delay difference to 99 ps

## Abstract

The Isochronous Mass Spectrometry (IMS) is a powerful tool for mass measurements of exotic nuclei with half-lives as short as several tens of micro-seconds in storage rings. In order to improve the mass resolving power while preserving the acceptance of the storage ring, the IMS with two Time-Of-Flight (TOF) detectors has been implemented at the storage ring CSRe in Lanzhou, China. Additional velocity information beside the revolution time in the ring can be obtained for each of the stored ions by using the double TOF detector system. In this paper, we introduced a new method of using a 658 nm laser range finder and a short-pulsed ultra-violet laser to directly measure the distance and time delay difference between the two TOF detectors which were installed inside the $10^{-11}$ mbar vacuum chambers. The results showed that the distance between the two ultra-thin carbon foils of the two TOF detectors was ranging from 18032.5 mm to 18035.0 mm over a measurable area of 20$\times$20 mm$^2$. Given the measured distance, the time delay difference which comes with signal cable length difference between the two TOF detectors was measured to be $\Delta t_{delay1-2}=99$(26) ps. The new method has enabled us to use the speed of light in vacuum to calibrate the velocity of stored ions in the ring. The velocity resolution of the current double TOF detector system at CSRe was deduced to be $\sigma(v)/v=4.4\times 10^{-4}$ for laser light, mainly limited by the time resolution of the TOF detectors.