Effect of gas injection location on initiation of magnetic arcades in WIRX

Gaseous arc discharges enable the study of magnetic arcades, flux ropes and loops. The Wheaton Impulsive Reconnection Experiment (WIRX) uses two long parallel copper electrodes to make magnetic arcades. We investigate how arcade initiation is affected by diffuse and localized gas injection in WIRX. Using photodiode arrays and ICCD cameras, we identify the location on the electrodes where the plasma first forms. This location depends on gas injection configuration. Most setups lead to the plasma quickly (1-2 μs) moving away from this initial location but a combination of diffuse and localized fueling anchors it longer (10-20 μs) and increases reproducibility. This effect is stronger for higher magnetic fields. The optimal delay between the gas valve opening and the discharge is an important parameter that varies between fueling configurations (2-4 ms). Plasma voltage and fast-ion gauge measurements reveal that these changes are due to different rates of gas flow. Gas injection from both anode and cathode significantly encourages consistent plasma behavior at arc initiation. These results will guide next-step arcade experiments.