5 research outputs found
Generation of GeV protons from 1 PW laser interaction with near critical density targets
The propagation of ultra intense laser pulses through matter is connected
with the generation of strong moving magnetic fields in the propagation channel
as well as the formation of a thin ion filament along the axis of the channel.
Upon exiting the plasma the magnetic field displaces the electrons at the back
of the target, generating a quasistatic electric field that accelerates and
collimates ions from the filament. Two-dimensional Particle-in-Cell simulations
show that a 1 PW laser pulse tightly focused on a near-critical density target
is able to accelerate protons up to an energy of 1.3 GeV. Scaling laws and
optimal conditions for proton acceleration are established considering the
energy depletion of the laser pulse.Comment: 26 pages, 8 figure
Accelerating Protons to Therapeutic Energies with Ultra-Intense Ultra-Clean and Ultra-Short Laser Pulses
Proton acceleration by high-intensity laser pulses from ultra-thin foils for
hadron therapy is discussed. With the improvement of the laser intensity
contrast ratio to 10-11 achieved on Hercules laser at the University of
Michigan, it became possible to attain laser-solid interactions at intensities
up to 1022 W/cm2 that allows an efficient regime of laser-driven ion
acceleration from submicron foils. Particle-In-Cell (PIC) computer simulations
of proton acceleration in the Directed Coulomb explosion regime from ultra-thin
double-layer (heavy ions / light ions) foils of different thicknesses were
performed under the anticipated experimental conditions for Hercules laser with
pulse energies from 3 to 15 J, pulse duration of 30 fs at full width half
maximum (FWHM), focused to a spot size of 0.8 microns (FWHM). In this regime
heavy ions expand predominantly in the direction of laser pulse propagation
enhancing the longitudinal charge separation electric field that accelerates
light ions. The dependence of the maximum proton energy on the foil thickness
has been found and the laser pulse characteristics have been matched with the
thickness of the target to ensure the most efficient acceleration. Moreover the
proton spectrum demonstrates a peaked structure at high energies, which is
required for radiation therapy. 2D PIC simulations show that a 150-500 TW laser
pulse is able to accelerate protons up to 100-220 MeV energies.Comment: 26 pages, 6 figure
Ion acceleration with few cycle relativistic laser pulses from foil targets
Ion acceleration resulting from the interaction of 11 fs laser pulses of ~35
mJ energy with ultrahigh contrast (<10^-10), and 10^19 W/cm^2 peak intensity
with foil targets made of various materials and thicknesses at normal
(0-degree) and 45-degree laser incidence is investigated. The maximum energy of
the protons accelerated from both the rear and front sides of the target was
above 1 MeV. A conversion efficiency from laser pulse energy to proton beam is
estimated to be as high as ~1.4 % at 45-degree laser incidence using a 51
nm-thick Al target. The excellent laser contrast indicates the predominance of
vacuum heating via the Brunels effect as an absorption mechanism involving a
tiny pre-plasma of natural origin due to the Gaussian temporal laser pulse
shape. Experimental results are in reasonable agreement with theoretical
estimates where proton acceleration from the target rear into the forward
direction is well explained by a TNSA-like mechanism, while proton acceleration
from the target front into the backward direction can be explained by the
formation of a charged cavity in a tiny pre-plasma. The exploding Coulomb field
from the charged cavity also serves as a source for forward-accelerated ions at
thick targets.Comment: 12 pages, 7 figures
Effects of ionization in a laser Wakefield accelerator
Experimental results are presented from studies of the ionization injection process in laser wakefield acceleration using the Hercules laser with laser power up to 100 TW. Gas jet targets consisting of gas mixtures reduced the density threshold required for electron injection and increased the maximum beam charge. Gas mixture targets produced smooth beams even at densities which would produce severe beam breakup in pure He targets and the divergence was found to increase with gas mixture pressure
Effects of ionization in a laser Wakefield accelerator
Experimental results are presented from studies of the ionization injection process in laser wakefield acceleration using the Hercules laser with laser power up to 100 TW. Gas jet targets consisting of gas mixtures reduced the density threshold required for electron injection and increased the maximum beam charge. Gas mixture targets produced smooth beams even at densities which would produce severe beam breakup in pure He targets and the divergence was found to increase with gas mixture pressure