350 research outputs found
Updated Report Acceleration of Polarized Protons to 120-150 GeV/c at Fermilab
The SPIN@FERMI collaboration has updated its 1991-95 Reports on the
acceleration of polarized protons in Fermilab's Main Injector, which was
commissioned by Fermilab. This Updated Report summarizes some updated Physics
Goals for a 120-150 GeV/c polarized proton beam. It also contains an updated
discussion of the Modifications and Hardware needed for a polarized beam in the
Main Injector, along with an updated Schedule and Budget.Comment: 30 pages, 12 figure
Numerical Modeling of Radiation-Dominated and QED-Strong Regimes of Laser-Plasma Interaction
Ultra-strong laser pulses can be so intense that an electron in the focused
beam loses significant energy due to gamma-photon emission while its motion
deviates via the radiation back-reaction. Numerical methods and tools designed
to simulate radiation-dominated and QED-strong laser-plasma interactions are
summarized here.Comment: 12 pages, 6 figure
Characterization of flowing liquid films as a regenerating plasma mirror for high repetition-rate laser contrast enhancement
In this paper, we characterize a high repetition-rate regenerating plasma mirror produced by the thin film of liquid formed when two laminar streams collide. The use of a flowing liquid film is inexpensive and the interaction surface refreshes automatically, avoiding buildup of on-target debris. The composition of the liquid material and the relative angle of the film-generating nozzles was optimized for this application. Spectra measured in reflection from a water-based plasma mirror showed a blue shift but an optical reflectivity of up to 30%. The thickness of the film was found to be of the order of 2 m, and the stability of the reflected spot was mrad. The reflected beam profile was highly distorted but stable. Further optimization of the nozzles to affect the fluid flow should enable significant improvements in control of the fluid films and increase in the reflectivity of these mirrors
High repetition-rate neutron generation by several-mJ, 35 fs pulses interacting with free-flowing D2O
Using several-mJ energy pulses from a high-repetition rate (1/2 kHz), ultrashort (35 fs) pulsed laser interacting with a 10 lm diameter stream of free-flowing heavy water (D2O), we demonstrate a 2.45 MeV neutron flux of 105/s. Operating at high intensity (of order 1019W/cm2), laser pulse energy is efficiently absorbed in the pre-plasma, generating energetic deuterons. These collide with deuterium nuclei in both the bulk target and the large volume of low density D2O vapor surrounding the target to generate neutrons through dðd; nÞ3 He reactions. The neutron flux, as measured by a calibrated neutron bubble detector, increases as the laser pulse energy is increased from 6 mJ to 12 mJ. A quantitative comparison between the measured flux and the results derived from 2D-particle-in-cell simulations shows comparable neutron fluxes for laser characteristics similar to the experiment. The simulations reveal that there are two groups of deuterons. Forward moving deuterons generate deuterium–deuterium fusion reactions in the D2O stream and act as a point source of neutrons, while backward moving deuterons propagate through the low-density D2O vapor filled chamber and yield a volumetric source of neutrons
Dynamics of Emitting Electrons in Strong Electromagnetic Fields
We derive a modified non-perturbative Lorentz-Abraham-Dirac equation. It
satisfies the proper conservation laws, particularly, it conserves the
generalized momentum, the latter property eliminates the symmetry-breaking
runaway solution. The equation allows a consistent calculation of the electron
current, the radiation effect on the electron momentum, and the radiation
itself, for a single electron or plasma electrons in strong electromagnetic
fields. The equation is applied to a simulation of a strong laser pulse
interaction with a plasma target. Some analytical solutions are also provided.Comment: The original form of this paper was submitted to Phys. Rev. Lett. on
August 3, 2008. The current version of the paper is substantially extended
and includes modifications resulting from points raised during the review
proces
Splitting of the Dipole and Spin-Dipole Resonances
Cross sections for the 90,92,94Zr(p,n) reactions were measured at energies of
79.2 and 119.4 MeV. A phenomenological model was developed to describe the
variation with bombarding energy of the position of the L=1 peak observed in
these and other (p,n) reactions. The model yields the splitting between the
giant dipole and giant spin dipole resonances. Values of these splittings are
obtained for isotopes of Zr and Sn and for 208Pb.Comment: 14 pages, 4 figure
Muon pair creation from positronium in a circularly polarized laser field
We study elementary particle reactions that result from the interaction of an
atomic system with a very intense laser wave of circular polarization. As a
specific example, we calculate the rate for the laser-driven reaction , where the electron and positron originate from a positronium
atom or, alternatively, from a nonrelativistic plasma. We distinguish
accordingly between the coherent and incoherent channels of the process. Apart
from numerical calculations, we derive by analytical means compact formulas for
the corresponding reaction rates. The rate for the coherent channel in a laser
field of circular polarization is shown to be damped because of the destructive
interference of the partial waves that constitute the positronium ground-state
wave packet. Conditions for the observation of the process via the dominant
incoherent channel in a circularly polarized field are pointed out
Ultrafast-ultrafine probing of high-speed electrical waveforms using a scanning force microscope with photoconductive gating
Picosecond photoconductivity in low-temperature-grown GaAs (LT GaAs) has been used to provide temporal resolution both in rigid probes and in scanning force microscope probes. This article reviews the fabrication and use of such probes. 2.5 ps temporal resolution and few microvolts sensitivity are obtained at arbitrary points on circuits with a spatial definition of 100 nm. Rigid probes are tested in application to analogue and digital circuits. As an alternative to electron beam testing, scanning force probes are applied to in situ imaging and waveform measurement. Finally, the use of time-resolved waveform analysis with scanning-force microscopy probes with semiconductor laser sources is demonstrated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43337/1/11082_2004_Article_BF00820152.pd
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