The interaction of short intense pulses with solid targets is known for the acceleration of ions by the target normal sheath acceleration mechanism. After the ions are accelerated they are assumed to drift in space towards the detector. During this time, the temperature of the plasma is understood to be significantly high such that recombination is prevented and all the ions that are accelerated are assume to retain their charge state till detection. Experiments carried out to study the recombination of accelerated protons from a solid target show a 200 times higher than expected neutral atoms and can contribute to nearly 80% of the accelerated ions at 10 keV which then falls rapidly at higher energies. Neither charge transfer with the background gas nor electron ion recombination in the plasma is sufficient to explain the spectral form of the neutral atoms obtained. We have developed a model where the ions co-propagate with a dense bunch of electrons resulting in spectrally-similar characteristics of fast neutral atoms detected. The model presented here provides insights about the closely linked dynamics of ion acceleration which results in the further release of electrons from the target as the ions are accelerated. These electrons released then co-propagate with the ion bunch allowing electron-ion recombination to take place and resulting in the formation of fast neutral atoms. To further understand the neutralization process, we have also carried out novel experiments to probe the distance after which the ions are converted into fast neutral atoms. The study of neutralization along with the model presented here provides insights into the strongly coupled dynamics of electrons and ions taking place long after the ions are accelerated.
|Working group||Laser-driven ion acceleration|