Crystal X

One of the major unsolved problem in our understanding of the Universe is the dark matter (DM) detection. While many evidence for DM come from cosmology and astronomy, the smoking-gun is still missing. The primary candidate for DM is a kind of elementary particle named WIMP: Weakly-Interacting Massive Particle. WIMPs are one of the most motivated dark matter candidate and currently many experiments around the world are searching for them. The most successful class of direct detection experiments searching for WIMPs with masses from a few GeV/c2 to TeV/c2 have utilized liquid xenon (LXe) time projection chambers (TPCs).

 

To date the most stringent limit on the WIMP-nucleon spin-independent elastic scattering cross-section for WIMP masses above 6 GeV/c2 is set by XENON1T expreiment, which is installed in Italy under the Gran Sasso massif at a depth of about 1400 m of limestone rock, and corresponds to 4.1∙10-47 cm2 for a mass of 30 GeV/c2. Hypothetical WIMPs interacting in LXe are expected to release a tiny fraction of energy via nuclear recoils which can then be converted to measurable signals by photodetectors. Because of the low interaction rate and the small number of photons produced per interaction it is imperative that backgrounds are kept to a minimum.

 

To perform tests with LXe for R&D purposes, we designed and built, in partnership with a Italian company, a cryogenic system for changing the physical state of xenon, from the gas phase into the liquid phase,  and possibly also for purifying it. The cryogenic facility is named CRYSTALX which stands for CRYogenic Setup for Tests At Liquid Xenon temperature. The cooling power is provided by evaporation of liquid nitrogen (LN). Xenon gas can be continuosly circulated through a hot SAES getter hosting a zirconium cartridge to remove electronegative impurities from the gas. The xenon chamber, where the condensation occurs, is made of a 16 liters stainless steel vessel with vacuum insulation. In normal working conditions, when the system is in thermodynamic equilibrium, the chamber is kept at a temperature of about−98°C, corresponding to a pressure of the vapour phase of about 2 barA.

 

 

  • The circuitry for the cooling system
  • The installation for the Crystal X experiment
  • Electro-chromatic valve for the cryogenic application
  • The inner vessel which contains Xenon
  • A detailed picture of differential pressure sensor
  • Variable frequency driver
  • Pump for the Xenon circulation loop