Properties of high-pressure discharge plasmas

Plasma properties during and immediately after electrical breakdown in a hi gh-pressure gas are investigated. A simple scaling law of electrical discha rge at high pressure is obtained. Introducing the normalized net ionization rate xi, the electron temperature at breakdown is described uniquely in te rms of the ionization properties of the gas, the second ionization coeffici ent gamma at the cathode, and the parameter pd, where p is the gas pressure and d is the system dimension. The electron attachment process plays a dec isive role in the breakdown phenomenon for a high-pressure gas, whereas it is not important in low-pressure discharges. An analytical expression for t he high-pressure plasma density is obtained by making use of the electron r ate equation. A simple analytical expression for plasma generation in a hig h-pressure gas provides important scaling laws in the d.c. electrical disch arge system, where the electron attachment process is negligible. It is fou nd that the logarithm of the electron density at breakdown is proportional to the discharge time tau (b), and is inversely proportional to the pulse r isetime and the gap distance d between the two electrodes. The plasma densi ty at breakdown is also an increasing function of the gas ionization energy epsilon (i).