The paper presents an improving computer code of solving the LC net circuit used in inertial confinement fusion and accurately indicates the instantaneous property of large bore flashlamp discharge. We considered the expansion of plasma arc during a pulse basic on the well known MEH theory. It is shown that the early part of the expansion is independent of the lamp diameter. However

at some point in the expansion

the presence of the flashlamp wall becomes important

and the current pulse is dependent of the arc expansion. But under the condition of large energy and long pulse the plasma arc may fill the flashlamp bore.