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Description
A robust and reliable vacuum degradation detection system is essential to identify leaks in the cryostat of superconducting tokamaks [1]. This Vacuum Monitoring System (VMS) must be able to function in the harsh environment encountered near superconducting magnets, while also measuring vacuum pressure as low as 2E-8 mbar, with a response time in the order of few seconds [2]. Commercial vacuum gauges struggle to operate in such harsh condition due to the significant effect of the magnetic field on the pressure measurement. However, Cold Cathode Gauges (CCG) are known to be able to operate in ultra-high vacuum and under intense external magnetic fields as the field itself sustains the sensor discharge [3]. In this contribution, the design and benchmark of a custom Penning CCG has been carried out. Sensor’s assembly and acquisition systems have been tailored for its application in the the JT-60SA cryostat [2]. The sensor response, delay ignition time and gauge characteristic under intense magnetic field and at cryogenic temperatures have been carried out at ENEA Frascati laboratories using fields up to 4 T at liquid Nitrogen temperatures, and at LNCMI Grenoble using fields up to 2 T at liquid Helium temperatures.
The experimental work on the CCG discharge identified critical conditions for sensor operation and the combined and isolated effect of temperature and field on the plasma current as well as the effect of charge-promotion strategies to reduce ignition delay times.
[1] K. Hamada et al. IEEE Transactions on Applied Superconductivity, 2023
[2] K. Fukui et al. IEEE Transactions on Applied Superconductivity, 2025
[3] H. C. Hseuh et al Journal of Vacuum Science & Technology, 1994
