Jake Bell with Dan Akerib and Tom Shutt
Capacitive level sensors for use in liquid xenon detectors
The LUX dark matter experiment liquid xenon detector uses an electric field created by grids to increase the drift velocity of electrons into xenon gas causing them to produce additional scintillation photons. These photons combined with the data from the original event photons are used to help determine the location and type of the original event. Electrons accelerate differently in liquid and gas phase xenon. Because of this we need to be sure the grids are level with the liquid-gas boundary. To measure the liquid level capacitive level sensors are used. To remove parasitic capacitance from cables a charge amp is used. The charge amp is capable of removing the capacitance from the cable, but does not remove noise from cabling. To reduce the problem of noise in the cable as much as possible, the charge amp will be connected as closely as possible to the capacitors. The liquid xenon is constantly on the verge boiling, so the liquid-gas boundary is not smooth and needs to be monitored. A system for measuring ripples on the surface of the liquid xenon based on low-noise capacitance measurements will be designed and tested in a chamber similar to the chamber used in the LUX dark matter experiment. The capacitive level meters are used to level the LUX system, but we would like to be able to use the information gained from the level sensors to make sure that the liquid xenon is in a smooth state. If we know that the liquid xenon is in a smooth state then we know that our signal will be properly calibrated.