Double layer (DL) formation in laser-produced plasma

Abstract

It is shown that appropriate conditions for DL formation may be created in laser produced plasma. In particular, a ‘feedback’ mechanism is suggested: Wave instabilities → absorption of laser energy → inward heat flux → DL formation → heat flux inhibition → wave instabilities Plasma-target potentials and plasma-currents, produced by Nd. laser intensities (I L ) between 10 12 to 10 15 W/cm 2 , were measured in situ. These measurements seem to be the first direct evidence of DLs in laser produced plasma. Electric fields of E DL ∼ 5 × 10 5 to 5 × 10 6 Volts/cm and widths of 10 to 100 Debye lengths are estimated for the DL. Scaling laws are derived for the measured extremum potentials (V) and currents (I): . Two different slopes were obtained experimentally, one slope equal to α = β = 1·0 for I L < 10 14 W/cm 2 and another of α = β = 0·4 for I L > 10 14 W/cm 2 . These data are explained for temperature scaling law for the low irradiance and for the high irradiance. While the first scaling law is consistent with inverse bremsstrahlung absorption, the second scaling necessitates other absorption processes. Potential and current probes are suggested as useful devices in detecting wave plasma instabilities.