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SU‐GG‐T‐462: Observation of Quasi‐Monoenergetic Laser Accelerated Proton and Carbon Beams
Author(s) -
Litzenberg D,
Dollar F,
Bulanov S,
Brantov A,
Bychenkov V,
Chvykov V,
Kalintchenko G,
Matsuoka T,
McGuffey C,
Yanovsky V,
Krushelnick K,
Maksimchuk A
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3468860
Subject(s) - proton , coulomb explosion , laser , atomic physics , materials science , plasma , ion , spectral line , optics , physics , nuclear physics , ionization , quantum mechanics , astronomy
Purpose : To perform preliminary experiments to achieve the Directed Coulomb Explosion (DCE) regime of proton acceleration to therapeutic energies in high‐intensity laser‐matter interactions. Method and Materials : Particle‐in‐Cell (PIC) simulations of the planned experiments at HERCULES laser at the University of Michigan have predicted a new regime of attainable laser‐target interactions for proton acceleration. The laser was recently upgraded to 300 TW with Amplified Spontaneous Emission (ASE) intensity contrast ratio of 10 −11 , allowing intensities of 2×10 22 W/cm 2 to be achieved in a near diffraction limited, 1.3 micron, focal spot. Dual plasma mirrors have been installed and characterized to reduce the prepulse at < 30 ps (from the uncompensated dispersion of optical elements during the pulse compression) before the main pulse providing 3 orders of magnitude contrast improvement. This allowed experiments on thin foil membranes (50 nm) with 50TW temporally clean pulses without compromising the target. Results : We found for the first time that for all target thicknesses proton spectra exhibit quasi‐monoenergetic features, which are more pronounced for ultra‐thin (50 nm Si 3 N 4 ) targets resulted in AE/E∼30%. Moreover for these Si 3 N 4 targets spectra for all the charge states of carbon ions C 3+ ‐C 6+ are also found to be quasi‐monoenergetic. Maximum proton energy drops from 6 MeV for 1 ⌈ m Mylar foil to 4 MeV for 50 nm Si 3 N 4 membranes. Conclusion : Implementation of dual plasma mirrors substantially improved laser contrast and created more favorable proton and carbon flux‐energy distributions. Further improvements to the plasma mirrors are required, using better antireflection coatings on glass substrates, to achieve the DCE regime of proton acceleration.