The Lee code is applied to characterize the plasma focus in two
plasma focus devices UNU/ICTP PFF and Amirkabir plasma focus
device (APF),
and for optimizing the nitrogen soft x-ray yields based on bank,
tubes and operating parameters. It is foun
d that the soft x-ray yield
increases with changing pressure until it reaches the maximum
value for each plasma focus device, with keeping the bank
parameters, operational voltage unchanged but systematically
changing other parameters.