Non-Maxwellian electron distributions and continuum X-ray emission in inverse Bremsstrahlung heated plasmas

The heating of a completely ionized plasma by inverse Bremsstrahlung absorption (IB) is studied by numerically integrating the time varying kinetic equation for electrons, and the resulting distribution functions are used to calculate the continuum X-ray emission. The shape of the distribution functions is determined by the competition between IB and electron-electron collisions, and, in all the uniform plasma simulations, the authors find that the distributions are well fitted by the formula Cmexp(-( nu / nu m)m) where m is between 2 and 5. They find the dependence of m on alpha =Z2 nu osc/ nu th2, where Z is the atomic number, nu osc is the oscillation velocity in the laser field and nu th is the thermal velocity: m( alpha )=2+3/(1+1.66/ alpha 0.724). More importantly, in the realistic case of a space and time dependent kinetic simulation of a Be plasma heated by a Nd laser, including heat flow and ion motion, this fit remains valid for electron densities below 0.75 Nc (with constant m), although other effects come into play closer to the critical surface. Thus, these simple results can be used to determine the continuum X-ray spectrum due to Bremsstrahlung (BR) and to direct radiative recombination (DRR).

[1]  M. Rosen,et al.  Hydrodynamics of exploding foil x‐ray lasers , 1986 .

[2]  P. Mora,et al.  Ponderomotive effects and magnetic field generation in radiation plasma interaction , 1979 .

[3]  R. G. Evans,et al.  Electron energy transport in steep temperature gradients in laser-produced plasmas , 1981 .

[4]  P. Jaeglé,et al.  Validity of electron-temperature measurements using continuum plasma emission , 1985 .

[5]  D. Book,et al.  NRL (Naval Research Laboratory) Plasma Formulary. Revised. , 1983 .

[6]  Jacques A. Delettrez,et al.  Electron Heat Flow with Inverse Bremsstrahlung and Ion Motion , 1984 .

[7]  John M. Dawson,et al.  Correct values for high-frequency power absorption by inverse bremsstrahlung in plasmas , 1973 .

[8]  A. Bruce Langdon,et al.  Nonlinear Inverse Bremsstrahlung and Heated-Electron Distributions , 1980 .

[9]  C. T. Dum.  Anomalous Electron Transport Equations for Ion Sound and Related Turbulent Spectra , 1978 .

[10]  J. Virmont,et al.  Density profile modification by light pressure in spherical geometry , 1978 .

[11]  R. D. Jones,et al.  Kinetic theory, transport, and hydrodynamics of a high‐Z plasma in the presence of an intense laser field , 1982 .

[12]  C. T. Dum.  Anomalous heating by ion sound turbulence , 1978 .

[13]  J. R. Albritton.  Laser absorption and heat transport by non-Maxwell-Boltzmann electron distributions , 1983 .

[14]  Hans A. Bethe,et al.  On the Stopping of Fast Particles and on the Creation of Positive Electrons , 1934 .

[15]  J. Virmont,et al.  Nonlocal heat transport due to steep temperature gradients , 1983 .

[16]  W. D. Barfield.  Partial Photoionization Cross Sections and Radiative Recombination Rate Coefficients for Lithium-Like Ions , 1979 .

[17]  P. Jaeglé,et al.  Bremsstrahlung and radiative-recombination emissivity coefficients in non-Maxwellian plasmas , 1984 .

[18]  Matte,et al.  Ionization and recombination rates in non-Maxwellian plasmas. , 1986, Physical review. A, General physics.

[19]  R. H. Pratt,et al.  Direct radiative recombination of electrons with atomic ions: Cross sections and rate coefficients , 1983 .

[20]  E. Goldman.  Numerical modeling of laser produced plasmas: the dynamics and neutron production in dense spherically symmetric plasmas , 1973 .

[21]  Radiodiffusion-télévision Belge,et al.  Rapport d'activite , 1973 .

[22]  P. Mora,et al.  Thermal heat-flux reduction in laser-produced plasmas , 1982 .

[23]  Francis F. Chen,et al.  Amplification and absorption of electromagnetic waves in overdense plasmas , 1974 .

[24]  Gregory A. Moses,et al.  Inertial confinement fusion , 1982 .

[25]  J. Virmont,et al.  A dual treatment of suprathermal electron transport in laser fusion studies , 1979 .

[26]  J. Virmont,et al.  Electron heat transport down steep temperature gradients , 1982 .

[27]  A. R. Bell,et al.  Electron energy transport in ion waves and its relevance to laser‐produced plasmas , 1983 .

[28]  J. Kilkenny,et al.  Electron energy distributions using the time‐resolved free‐bound spectra from coronal plasmas , 1984 .

[29]  Matte,et al.  Amplification of magnetic modes in laser-created plasmas. , 1987, Physical review letters.