Pulsed discharge in a large diameter tube with long-lasting pre-ionization

The evolution of a nitrogen plasma discharge in a tube with an inner diameter of 9.2 mm, excited by a particular pulse shape, is studied to suppress ablation from the inner wall. Excitation is realized by two current pulses. The first one is a long pre-ionization pulse, which guarantees the stability of the plasma column, and the second one is a higher current pulse, which causes the detachment of the discharge plasma from the wall. The evolution of plasma in the tube is modeled using the magneto-hydrodynamic code NPINCH in two approximations: (1) non-ablative and (2) strongly ablative walls. The time dependences of the optical radiation power in the direction along the discharge tube axis are measured and compared with simulated experimental results in non-ablative and ablative approaches. Time dependence of the measured optical radiation emission corresponds to the non-ablative model. In the selected large diameter capillary, the development of the pinching plasma is not significantly affected by the ablation of the material from the capillary walls.