543 research outputs found
Helium-3 and Helium-4 acceleration by high power laser pulses for hadron therapy
The laser driven acceleration of ions is considered a promising candidate for
an ion source for hadron therapy of oncological diseases. Though proton and
carbon ion sources are conventionally used for therapy, other light ions can
also be utilized. Whereas carbon ions require 400 MeV per nucleon to reach the
same penetration depth as 250 MeV protons, helium ions require only 250 MeV per
nucleon, which is the lowest energy per nucleon among the light ions. This fact
along with the larger biological damage to cancer cells achieved by helium
ions, than that by protons, makes this species an interesting candidate for the
laser driven ion source. Two mechanisms (Magnetic Vortex Acceleration and
hole-boring Radiation Pressure Acceleration) of PW-class laser driven ion
acceleration from liquid and gaseous helium targets are studied with the goal
of producing 250 MeV per nucleon helium ion beams that meet the hadron therapy
requirements. We show that He3 ions, having almost the same penetration depth
as He4 with the same energy per nucleon, require less laser power to be
accelerated to the required energy for the hadron therapy.Comment: 8 pages, 3 figures, 1 tabl
Three Dimensional Relativistic Electromagnetic Sub-cycle Solitons
Three dimensional (3D) relativistic electromagnetic sub-cycle solitons were
observed in 3D Particle-in-Cell simulations of an intense short laser pulse
propagation in an underdense plasma. Their structure resembles that of an
oscillating electric dipole with a poloidal electric field and a toroidal
magnetic field that oscillate in-phase with the electron density with frequency
below the Langmuir frequency. On the ion time scale the soliton undergoes a
Coulomb explosion of its core, resulting in ion acceleration, and then evolves
into a slowly expanding quasi-neutral cavity.Comment: 5 pages, 6 figures;
http://www.ile.osaka-u.ac.jp/research/TSI/Timur/soliton/index.htm
Radiation Pressure Dominate Regime of Relativistic Ion Acceleration
The electromagnetic radiation pressure becomes dominant in the interaction of
the ultra-intense electromagnetic wave with a solid material, thus the wave
energy can be transformed efficiently into the energy of ions representing the
material and the high density ultra-short relativistic ion beam is generated.
This regime can be seen even with present-day technology, when an exawatt laser
will be built. As an application, we suggest the laser-driven heavy ion
collider.Comment: 10 pages, 4 figure
Current sheets at three-dimensional magnetic nulls:effect of compressibility
The nature of current sheet formation in the vicinity of three-dimensional
(3D) magnetic null points is investigated. The particular focus is upon the
effect of the compressibility of the plasma on the qualitative and quantitative
properties of the current sheet. An initially potential 3D null is subjected to
shearing perturbations, as in a previous paper [Pontin et al., Phys. Plasmas,
in press (2007)]. It is found that as the incompressible limit is approached,
the collapse of the null point is suppressed, and an approximately planar
current sheet aligned to the fan plane is present instead. This is the case
regardless of whether the spine or fan of the null is sheared. Both the peak
current and peak reconnection rate are reduced. The results have a bearing on
previous analytical solutions for steady-state reconnection in incompressible
plasmas, implying that fan current sheet solutions are dynamically accessible,
while spine current sheet solutions are not.Comment: to appear in Physics of Plasmas. This version contains updated
figures and references, additional discussion, and typos are fixed. This is
the second in a series of papers - the first of which (by the same authors)
is located at astro-ph/0701462. A version with higher quality figures can be
found at http://www.maths.dundee.ac.uk/~dpontin
Proton acceleration in analytic reconnecting current sheets
Particle acceleration provides an important signature for the magnetic collapse that accompanies a solar flare. Most particle acceleration studies, however, invoke magnetic and electric field models that are analytically convenient rather than solutions of the governing magnetohydrodynamic equations. In this paper a self-consistent magnetic reconnection solution is employed to investigate proton orbits, energy gains, and acceleration timescales for proton acceleration in solar flares. The magnetic field configuration is derived from the analytic reconnection solution of Craig and Henton. For the physically realistic case in which magnetic pressure of the current sheet is limited at small resistivities, the model contains a single free parameter that specifies the shear of the velocity field. It is shown that in the absence of losses, the field produces particle acceleration spectra characteristic of magnetic X-points. Specifically, the energy distribution approximates a power law ~ξ-3/2 nonrelativistically, but steepens slightly at the higher energies. Using realistic values of the “effective” resistivity, we obtain energies and acceleration times that fall within the range of observational data for proton acceleration in the solar corona
Numerical calculations of a high brilliance synchrotron source and on issues with characterizing strong radiation damping effects in non-linear Thomson/Compton backscattering experiments
A number of theoretical calculations have studied the effect of radiation
reaction forces on radiation distributions in strong field counter-propagating
electron beam-laser interactions, but could these effects - including quantum
corrections - be observed in interactions with realistic bunches and focusing
fields, as is hoped in a number of soon to be proposed experiments? We present
numerical calculations of the angularly resolved radiation spectrum from an
electron bunch with parameters similar to those produced in laser wakefield
acceleration experiments, interacting with an intense, ultrashort laser pulse.
For our parameters, the effects of radiation damping on the angular
distribution and energy distribution of \emph{photons} is not easily
discernible for a "realistic" moderate emittance electron beam. However,
experiments using such a counter-propagating beam-laser geometry should be able
to measure such effects using current laser systems through measurement of the
\emph{electron beam} properties. In addition, the brilliance of this source is
very high, with peak spectral brilliance exceeding
photonssmmmrad% bandwidth with
approximately 2% efficiency and with a peak energy of 10 MeV.Comment: 11 figures, 11 page
Lorentz-Abraham-Dirac vs Landau-Lifshitz radiation friction force in the ultrarelativistic electron interaction with electromagnetic wave (exact solutions)
When the parameters of electron - extreme power laser interaction enter the
regime of dominated radiation reaction, the electron dynamics changes
qualitatively. The adequate theoretical description of this regime becomes
crutially important with the use of the radiation friction force either in the
Lorentz-Abraham-Dirac form, which possess unphysical runaway solutions, or in
the Landau-Lifshitz form, which is a perturbation valid for relatively low
electromagnetic wave amplitude. The goal of the present paper is to find the
limits of the Landau-Lifshitz radiation force applicability in terms of the
electromagnetic wave amplitude and frequency. For this a class of the exact
solutions to the nonlinear problems of charged particle motion in the
time-varying electromagnetic field is used.Comment: 14 pages, 5 figure
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