1,776 research outputs found
Production of high energy particles in laser and Coulomb fields and e^+e^- antenna
A strong laser field and the Coulomb field of a nucleus can produce
e^{+}e^{-} pairs. It is shown for the first time that there is a large
probability that electrons and positrons created in this process collide after
one or several oscillations of the laser field. These collisions can take place
at high energy resulting in several phenomena. The quasielastic collision
e^{+}e^{-} -> e^{+}e^{-} allows acceleration of leptons in the laser field to
higher energies. The inelastic collisions allow production of high energy
photons e^{+}e^{-}-> 2 gamma and muons, e^{+}e^{-} -> mu^{+}mu^{-}. The yield
of high-energy photons and muons produced via this mechanism exceeds
exponentially their production through conventional direct creation in laser
and Coulomb fields. A relation of the phenomena considered with the
antenna-mechanism of multiphoton absorption in atoms is discussed.Comment: 4 page
Polarization of the electron and positron produced in combined Coulomb and strong laser fields
The process of production in the superposition of a Coulomb and a
strong laser field is considered. The pair production rate integrated over the
momentum and summed over the spin projections of one of the particles is
derived exactly in the parameters of the laser field and in the Born
approximation with respect to the Coulomb field. The case of a monochromatic
circularly polarized laser field is considered in detail. A very compact
analytical expression of the pair production rate and its dependence on the
polarization of one of the created particles is obtained in the quasiclassical
approximation for the experimentally relevant case of an undercritical laser
field. As a result, the polarization of the created electron (positron) is
derived.Comment: 16 pages, no figure
Fast Switching Ferroelectric Materials for Accelerator Applications
Fast switching (< 10 nsec) measurement results on the recently developed
BST(M) (barium strontium titanium oxide composition with magnesium-based
additions) ferroelectric materials are presented. These materials can be used
as the basis for new advanced technology components suitable for high-gradient
accelerators. A ferroelectric ceramic has an electric field-dependent
dielectric permittivity that can be altered by applying a bias voltage.
Ferroelectric materials offer significant benefits for linear collider
applications, in particular, for switching and control elements where a very
short response time of <10 nsec is required. The measurement results presented
here show that the new BST(M) ceramic exhibits a high tunability factor: a bias
field of 40-50 kV/cm reduces the permittivity by a factor of 1.3-1.5. The
recently developed technology of gold biasing contact deposition on large
diameter (110 cm) thin wall ferroelectric rings allowed ~few nsec switching
times in witness sample experiments. The ferroelectric rings can be used at
high pulsed power (tens of megawatts) for X-band components as well as at high
average power in the range of a few kilowatts for the L-band phase-shifter,
under development for optimization of the ILC rf coupling. Accelerator
applications include fast active X-band and Ka-band high-power ferroelectric
switches, high-power X-band and L-band phase shifters, and tunable
dielectric-loaded accelerating structures.Comment: 7 pages, 6 figures, submitted to Proceedings of 2006 Advanced
Accelerator Concepts Worksho
Experimental studies of thorium ions implantation from pulse laser plasma into thin silicon oxide layers
We report the results of experimental studies related to implantation of
thorium ions into thin silicon dioxide by pulsed plasma fluxes expansion.
Thorium ions were generated by laser ablation from a metal target, and the
ionic component of the laser plasma was accelerated in an electric field
created by the potential difference (5, 10 and 15 kV) between the ablated
target and SiO2/Si(001) sample. Laser ablation system installed inside the
vacuum chamber of the electron spectrometer was equipped with YAG:Nd3+ laser
having the pulse energy of 100 mJ and time duration of 15 ns in the Q-switched
regime. Depth profile of thorium atoms implanted into the 10 nm thick
subsurface areas together with their chemical state as well as the band gap of
the modified silicon oxide at different conditions of implantation processes
were studied by means of X-ray photoelectron spectroscopy (XPS) and Reflected
Electron Energy Loss Spectroscopy (REELS) methods. Analysis of chemical
composition showed that the modified silicon oxide film contains complex
thorium silicates. Depending on local concentration of thorium atoms, the
experimentally established band gaps were located in the range of 6.0 - 9.0 eV.
Theoretical studies of optical properties of the SiO2 and ThO2 crystalline
systems have been performed by ab initio calculations within hybrid functional.
Optical properties of the SiO2/ThO2 composite were interpreted on the basis of
Bruggeman effective medium approximation. A quantitative assessment of the
yield of isomeric nuclei in "hot" laser plasma at the early stages of expansion
has been performed. The estimates made with experimental results demonstrated
that the laser implantation of thorium ions into the SiO2 matrix can be useful
for further research of low-lying isomeric transitions in 229Th isotope with
energy of 7.8(0.5) eV
Electron-muon heat conduction in neutron star cores via the exchange of transverse plasmons
We calculate the thermal conductivity of electrons and muons kappa_{e-mu}
produced owing to electromagnetic interactions of charged particles in neutron
star cores and show that these interactions are dominated by the exchange of
transverse plasmons (via the Landau damping of these plasmons in
nonsuperconducting matter and via a specific plasma screening in the presence
of proton superconductivity). For normal protons, the Landau damping strongly
reduces kappa_{e-mu} and makes it temperature independent. Proton
superconductivity suppresses the reduction and restores the Fermi-liquid
behavior kappa_{e-mu} ~ 1/T. Comparing with the thermal conductivity of
neutrons kappa_n, we obtain kappa_{e-mu}> kappa_n for T>2 GK in normal matter
and for any T in superconducting matter with proton critical temperatures
T_c>3e9 K. The results are described by simple analytic formulae.Comment: 15 pages, 5 figures, to appear in Phys. Rev.
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