Creating a Strong, Uniform Electric Field for ProtoDUNE Field Cage

ProtoDUNE is the prototype of the Deep Underground Neutrino Experiment at Fermilab and CERN. One experiment is the Dual-Phase Field Cage consisting of both liquid and gaseous argon. The field cage consists of 98 levels of aluminum bars supported by fiber reinforced plastic. Neutrinos are detected by their interaction with electrons of the liquid argon and extracted in gaseous argon above. To direct electrons, the interior of the cage is held to a uniform electric field of 300V/cm. The uniform field is created by applying a 300kV potential at the cathode and allowing the voltage to be divided evenly across the cage. To accomplish this, a series of resistors and varistors are placed on a board and placed on the cage. Resistors are used to reduce the current and divide the voltage, and varistors protects the resistors by allowing currents to only flow at electrical surges. Quality assurance of the parts used are conducted by testing these parts individually ensuring a uniform voltage drop among each part. Rigorous testing and strict selections ensures both a uniform electric field is created, and any power supply used will not be damaged by high currents.