Electro-optic analysis of the influence of target geometry on electromagnetic pulses generated by petawatt laser-matter interactions
Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, United Kingdom
2 ENEA – C.R. Frascati, Dipartimento FSN, Via E. Fermi 45, 00044 Frascati, Italy
3 Dipartimento di Ingegneria Industriale, Università di Roma Tor Vergata, Via del Politecnico 1, I-00133 Roma, Italy
* Corresponding author: email@example.com
Published online: 9 January 2018
We present an analysis of strong laser-driven electromagnetic pulses using novel electro-optic diagnostic techniques. A range of targets were considered, including thin plastic foils (20-550 nm) and mass-limited, optically-levitated micro-targets. Results from foils indicate a dependence of EMP on target thickness, with larger peak electric fields observed with thinner targets. Spectral analysis suggests high repeatability between shots, with identified spectral features consistently detected with <1 MHz standard deviations of the peak position. This deviation is reduced for shots taken on the same day, suggesting that local conditions, such as movement of metal objects within the target chamber, are more likely to lead to minor spectral modifications, highlighting the role of the local environment in determining the details of EMP production. Levitated targets are electrically isolated from their environment, hence these targets should be unable to draw a neutralization current from the earth following ejection of hot electrons from the plasma, in contrast to predictions for pin-mounted foils in the Poyé EMP generation model. With levitated targets, no EMP was measurable above the noise threshold of any diagnostic, despite observation of protons accelerated to >30 MeV energies, suggesting the discharge current contribution to EMP is dominant.
© The Authors, published by EDP Sciences, 2018
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