Factors affecting the pulse width of capillary discharge soft X-ray laser

Summary form only given, as follows. There are two ways to realize the population inversion in capillary discharge soft X-ray lasers: electron-collisional recombination pumping and electron-collisional excitation pumping schemes. It is possible to enhance the output of laser energy by increasing the gain-length product and the laser pulse width. While the former scheme can extract laser pulses of several tens of ns, the latter scheme can extract only several ns. Pulse widths are determined by the preservation time of optimal plasma condition and the growth time of plasma instability. The object of our study is to reveal the cause which restricts the duration of lasing in the collisional excitation scheme. The device consists of a Marx generator, a pulse transformer, a speed-up capacitor, a gap switch, a capillary and a pre-discharge circuit. The capillary is made of Pyrex glass and is 60 mm in length and 3 mm in inner diameter and is filled with an argon gas of 100-1000 mTorr. Uniformly pre-ionized argon gas in the capillary is excited with the current pulse having an amplitude of 15-60 kA and a first half cycle duration of 100 ns. The plasma photographs were taken from the side and axial directions using a high-speed camera in order to confirm its pinch and the growth of instability. The temporal evolution of the laser energy was measured with a vacuum X-ray diode. The duration of lasing is discussed based on the results of these experiments and MHD simulations of the imploding plasma.