Design, construction and commissioning of a high-flow radon removal system for XENONnT Article Swipe
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· 2022
· Open Access
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· DOI: https://doi.org/10.1140/epjc/s10052-022-11001-9
· OA: W4311730467
A high-flow radon removal system based on cryogenic distillation was developed and constructed to reduce radon-induced backgrounds in liquid xenon detectors for rare event searches such as XENONnT. A continuous purification of the XENONnT liquid xenon inventory of 8.4 tonnes at process flows up to 71 kg/h (200 slpm) is required to achieve a radon reduction by a factor larger than two for radon sources inside the detector. To reach such high flows, the distillation column’s design features liquid xenon inlet and outlets along with novel custom-made bath-type heat exchangers with high liquefaction capabilities. The distillation process was designed using a modification of the McCabe–Thiele approach without a bottom product extraction. The thermodynamic concept is based on a Clausius–Rankine cooling cycle with phase-changing medium, in this case the xenon itself. To drastically reduce the external cooling power requirements, an energy efficient heat pump concept was developed applying a custom-made four cylinder magnetically-coupled piston pump as compressor. The distillation system was operated at thermodynamically stable conditions at a process flow of $$({91\pm 2})\,\mathrm{kg/h}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>(</mml:mo> <mml:mrow> <mml:mn>91</mml:mn> <mml:mo>±</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> <mml:mo>)</mml:mo> <mml:mspace/> <mml:mrow> <mml:mi>kg</mml:mi> <mml:mo>/</mml:mo> <mml:mi>h</mml:mi> </mml:mrow> </mml:mrow> </mml:math> (( $$258\pm 6$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>258</mml:mn> <mml:mo>±</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> </mml:math> ) slpm), 30% over design. With this flow, a "Image missing" activity concentration $$<1\,\upmu $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo><</mml:mo> <mml:mn>1</mml:mn> <mml:mspace/> <mml:mi>μ</mml:mi> </mml:mrow> </mml:math> Bq/kg is expected inside the XENONnT detector given the measured radon source distribution.
