Design, construction, and testing of the PandaX-xT cryogenics system

TL;DR

This work presents a scalable cryogenics design for the PandaX-xT detector, addressing the challenge of safely cooling ~43_t of liquid xenon. It combines two AL600 GM cryocoolers operating as dual cooling towers with a dedicated $LN_{2}$ coil for emergency protection, validated on a test tower and a 1-tonne LXe vessel. Key results show ~1900 W cooling at $178$ K and emergency cooling capacity >$1500$ W at LXe temperature, along with long-term xenon pressure stability near $210$ kPa and fluctuations within ~1 kPa. The findings demonstrate a robust, redundant, and scalable cryogenics solution suitable for the next-generation PandaX-xT program and other large LXe detectors.

Abstract

The PandaX-xT is a next-generation experiment with broad scientific goals, including the search for dark matter, Neutrinoless Double Beta Decay, and astrophysical neutrinos, using a dual-phase time projection chamber with about 43 tons of liquid xenon. A new cryogenics system of the PandaX-xT is described in this paper. It is developed to handle large mass of liquid xenon efficiently and safely, including two cooling towers for normal operation and one liquid-nitrogen coil for emergency case. Each cooling tower equipped with an AL600 Gifford-McMahon cryocooler features a 1300 W heater, specifically designed to maintain the cold finger's temperature at the desired setpoint. The performance of the cooling tower and the coil has been tested. The cryogenics system with two cooling towers has achieved about 1900~W cooling power at 178~K. The liquid nitrogen coil provides emergency cooling power of more than 1500~W at liquid xenon temperature. For the prototype of a 1-tonne liquid xenon detector, the fluctuation of xenon saturated vapor pressure remains below 1 kPa over one month, while the pressure is around 210~kPa.

Figures (10)

• Figure 1: Schematic view of the PandaX-xT cryogenics system prototype. The diagram shows the installation locations of the main components: an emergency $LN_2$ cooler, two coldheads, test tower with its heater, 1-tonne liquid detector vessel, sensor connections, and backup connections for future equipment. The inner chamber ports and outer vacuum chamber ports are intended for connecting pump systems. The blue lines represents the liquid xenon pipes, the black denotes the inner chambers (gas xenon pipes), and the purple indicates the outer vacuum chambers. Liquid xenon pipes are partially routed outside the inner chambers for easy installations.
• Figure 2: A photograph of the PandaX-xT cryogenics system prototype. The cooling bus, mounted on the upper yellow platform, liquefies xenon gas, which then flows downward by gravity into the 1-tonne liquid xenon detector vessel housed on the lower yellow platform.
• Figure 3: The section view of the cooling tower with AL600 coldhead. The two cooling towers have identical structures. Gas xenon is liquefied on the cold finger and then directed through a funnel into the liquid pipe. The isolated vacuum chamber which control by DN80 pneumatic valve allowing independent maintenance of each cooling tower without disrupting the operation of the other.
• Figure 4: Design of heater and position of temperature sensors. Cartridge heaters are evenly distributed across the heater to ensure uniform heating, while PT100 sensors are arranged within the same quadrant for ease of installation and replacement.
• Figure 5: The section view of emergency $LN_{2}$ cooling tower. When the pressure exceeds a preset threshold, the electronic valve opens, allowing $LN_{2}$ to flow into the stainless steel coil. The $LN_{2}$ absorbs heat from the gas xenon and exits through the outlet. A PT100 temperature sensor monitors the cooling process in real time.