Natural circulation loop using liquid nitrogen for cryo-detection system
The natural circulation loop is designed for the cryogenic insert in a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Sensitivity is the key parameter of a FTICR mass spectrometer and the cryo-cooling of the pre-amplifier can reduce the thermal noise level and thereby improve the signal-to-noise ratio. The pre-amplifier consisted of non-magnetic materials is thermally connected to the cooling loop which is passing through the flange maintaining ultra-high vacuum in the ion cell. The liquid nitrogen passes through inside of the loop to cool the pre-amplifier indirectly. At the end, a cryocooler is located to re-condense nitrogen vapor generated due to the heat from the pre-amplifier. The circulating fluid removes heat from the pre-amplifier and transports it to the cryocooler or heat sink. In this paper the natural circulation loop for cryogenic pre-amplifier is introduced for improving the sensitivity of cryo-detector. In addition, the initial cool-down of the system by a cryocooler is presented and the temperature of the radiation shield is discussed with respect to the thickness of shield and the thermal radiation load.