The XENONnT Field Cage

The central component of a dual-phase liquid xenon time projection chamber (TPC) is its field cage. This is the structure that establishes the electric field in which electrons drift across the TPC and ensures that this field is homogenious. A new articles, authored by members of Freiburg's astroparticle physics group, describes the field cage of the XENONnT dark matter detector. The field cage was designed by and many of its components were produced in Freiburg.

Detailed view of the XENONnT field cage

The precision in reconstructing events detected in a dual-phase time projection chamber depends on an homogeneous and well understood electric field across the liquid target. In the XENONnT TPC the field homogeneity is achieved through a double-array field cage, consisting of two nested arrays of field shaping rings connected by an easily accessible resistor chain. The topmost field shaping ring can be independently biased, adding a degree of freedom to tune the electric field during operation.

Two-dimensional finite element simulations were used to optimize the field cage, as well as its operation. Simulation results were compared to calibration data. This comparison indicates an accumulation of charge on the panels of the TPC which is constant over time. The simulated electric field was then used to correct the charge signal for the field dependence of the charge yield. This correction resolves the inconsistent measurement of the drift electron lifetime when using different calibrations sources and different field cage tuning voltages.

Publication

Design and performance of the field cage for the XENONnT experiment
E. Aprile et al. (XENON Collaboration)
arXiv:2309.11996