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Faraday cup ion detectors are widely used in the investigation of laser-produced plasmas. However, it is well known that these detectors are susceptible to space charge distortion of the ion signal. Although an analytical model describing the threshold condition for distortion was developed in 1970 by Green, this model has never been tested experimentally. In the present investigation, it is found that the analytic model derived by Green appears to be inadequate when compared in detail to experiments performed using KrF (248 nm, 15 ns) laser pulses incident on a graphite target at an intensity of 1.7×1010 W/cm2. By comparing the results of particle-in-cell (PIC) simulations with these experiments, it has been discovered that electrons play an important role in the space charge distortion phenomenon.
Date of Publication: April 2006