Liverpool LAr Facility

Dr Mavrokoridis established the Liverpool LAr Facility in 2009, with the aims of performing research and development studies into the progression of LAr TPC technologies which would feed into future neutrino detectors. A wide variety of studies have been performed, such as on:

• the use of MicroMegas devices in LAr (in collaboration with SACLAY, France)
• development of high voltage feed-throughs
• characterisation of cryogenic web-cams for internal detector monitoring purposes
• purification and recirculation, including the development of a novel 2-bellow cryogenic pump
• the use of silicon photomultipliers (SiPMs) for optical readout (in collaboration with FBK, Italy)
• the use of CCD and EMCCD cameras as an alternative readout method
• the use of TPX cameras as an alternative readout method

Much of this research has been carried out utilising a very flexibly designed 40 litre TPC - the original proof-of-concept demonstrator for the ARIADNE program - which can be operated both in gas and liquid.

The 40 litre demonstrator consists of an 8-inch Hamamatsu cryogenic PMT coated with wavelength shifter looking upwards towards the fiducial volume, which is defined by a 20 cm high field cage. This field cage is capped by the extraction region, above which various charge multiplication devices, such as THGEMs and MicroMegas, can be mounted. When running the demonstrator in photographic mode, a single THGEM is placed above the extraction region, and an EMCCD or TPX camera, is mounted outside the detector, looking at the top of the THGEM via a view port at a distance of ~1 m from the THGEM.

When an incoming particle passes through the LAr, it creates prompt scintillation light and ionisation. The prompt scintillation light is detected immediately by the PMT, whereas the free ionisation electrons are drifted to the surface of the liquid through a typical electric field of 0.5 kV/cm. At the surface of the liquid, the electrons experience a higher electric field (~3 kV/cm) in order to be extracted to the gas phase. Once in the gas phase, the electrons enter the THGEM's 500 μm diameter copper-clad holes, in which an electric field of around 40 kV/cm is generated - causing electron avalanches and secondary scintillation light. This light is captured by the PMT, and additionally by the externally mounted EMCCD camera. This set-up resulted in beautiful photographic images of cosmic rays, and paved the way for the current ERC-funded program.

A 250 litre pilot vessel was assembled to allow for performance evaluation and quality assurance of the components and systems that were installed in ARIADNE. This includes our next-generation purification and recirculation system and a cryo-cooler head.