Monochromatic x-ray emission of a fully ionized hydrogen plasma.

Subnanosecond emission phenomena have been studied at a modified 1 kJ Mather type plasma focus device. High energy particle beams, nonthermal infrared and microwave emission as well as anisotropic soft x-rays are observed. In the plasma a hydrodynamic instability leads to a final radius of r around 50 My m and a length of 1 = 500 My m through which a current of I = 200 kA is driven. Induced by the high power density, microinstabilities modulate the plasma density periodically. Due to particle-wave interaction, electrons and ions are accelerated to energies beyond 1 MeV. The electron beam is emitted in pulses with a pulse period of about 10 - 30 ps and a pulse width in the range of 1 - 3 ps. Simultaneously, anisotropic emission of soft x-rays at a wavelength of about Lambda = 1 nm into a cone with a half angle Theta = o.2 rad is observed. The relative line width Delta lambda/Lambda = 2 . 10 high -3, indicates a temporal coherent emission of x-radiation by the fully ionized hydrogen plas ma. Assuming an FEL-like process as generation mechanism of the soft x-rays, the period length of the density structure and the relativistic factor Gamma of the electron beam are determined as Lambda about 17 nm and Gamma about 3. The observed phenomena in the plasma can be theoretically described as a selforganization process in terms of a three-wave-coupling model of a beam-plasma system.