Response times and energy partitioning in electron-beam-excited plasmas

Excimer lasers are typically excited by electron beams (e beams) with initial energies of 100's of keV to a few MeV. The e-beam response time is the interval required for beam electrons and their energetic secondary electrons to slow below the first inelastic thresholds of the buffer gas, below which the electrons thermalize by elastic momentum transfer collisions. In this paper, e-beam response times for rare gases and for gas mixtures typically used for excimer lasers are discussed using results from a Monte Carlo simulation. Issues pertaining to energy partitioning (W values in mixtures and effective electron temperatures) are also discussed. We find that e-beam response times may be >10's of ns in gas mixtures of a few atm. As these times are commensurate with the rise time of e-beam pulses or the width of shorter pulses, beam slowing effects must be considered when modeling these phases of e-beam pumping