Analysis of experiments on energetic ions from laser produced plasmas with reference to hot electrons and pulsation

The need for highly charged heavy ions from projected particle accelerators has recently led to a re-evaluation of the complex processes of ion production in laser generated plasmas. Possible mechanisms for the production of intense beams of high charge state ions are investigated as is the experimental evidence for these mechanisms. The hypothesis that 20 keV ions are driven by 'hot electrons' is not supported by experimental work to date. This work, on the other hand, suggests that 30 ps pulsation is the basic mechanism for the acceleration of tantalum ions up to charge state 8+; their energy increases linearly with charge state up to 24 keV. For long pulses and charge states between 8+ and 18+, it appears that there is a secondary mechanism of electron impact ionization by plasma electrons of approximately 200 eV in the plasma in front of the target, resulting in ions whose energy of around 24 keV is independent of the charge state. (author) 3 figs., 4 refs