Threshold for Measuring the Langdon Effect Using Collective Thomson Scattering*

The basis of many transport properties of a laser-produced plasma is contingent upon the understanding of the underlying electron distribution function. A method to infer the electron distribution function in a laser-produced plasma is proposed and applied to identifying flattopped electron distributions produced by inverse bremsstrahlung heating, known as the Langdon effect. The threshold to experimentally distinguish such distributions from Maxwellian is given. By angularly resolving Thomson spectrum over a range of angles, the threshold for identifying the electron distribution function can be reduced. A diagnostic to accomplish this is proposed using an f/3.3 by f/0.5 reflective collector, anamorphic relay, and spectrometer system that will simultaneously measure >100 angularly separated spectrum.