Damping of electromagnetic waves due to electron-positron pair production

The problem of the backreaction during the process of electron-positron pair production by a circularly polarized electromagnetic wave propagating in a plasma is investigated. A model based on the relativistic Boltzmann-Vlasov equation with a source term corresponding to the Schwinger formula for the pair creation rate is used. The damping of the wave, the nonlinear up-shift of its frequency due to the plasma density increase and the effect of the damping on the wave polarization and on the background plasma acceleration are investigated as a function of the wave amplitude.Comment: 11 pages, 5 figures; revtex

Bright ultra-broadband fiber-based biphoton source

In this Letter, we report a first experimental realization of bright ultra-broadband (180 THz) fiber-based biphoton source with widely spectrally separated signal and idler photons. Such a two-photon source is realized due to the joint use of broadband phase-matching of interacting light waves and high optical nonlinearity of a silica-core photonic crystal fiber. The high performance of the developed fiber source identifies it as an important and useful tool for a wide range of optical quantum applications

Investigation of proton relaxation in live plant tissues by the spin echo method

The method of spin echo n.m.r. has been used to study the times of proton relaxation and the rate of proton exchange in various plant tissues. We have evaluated the possible mechanisms of the relaxation and shown that the times of proton relaxation in the main are determined by the interactions within the proton system consisting of three fractions exchanging between themselves. It has been established that in the test systems there is rapid (T22k12 > 1) exchange between the protons of the hydrate and free water with slow (k13T23 < 1) exchange between the protons of the OH groups of the cell walls and the protons of water. From the experimental values of the relaxation times we have estimated the amount of hydrate water (V) and its mobility (τC) and from the dependence of the spin relaxation time on tCP-the lifetimes of the protons of the OH groups of the cell walls for various plant tissues. © 1970

Application of bent crystals at IHEP 70-GeV accelerator to enhance the efficiency of its usage

Bent crystal was extracting 70-GeV protons with average intensity 4*10^11 (as measured in external beamline) per spill of 1.6 s duration, in parallel to the simultaneous work of two internal targets in the accelerator ring. An additional crystal, placed in the external beamline, was deflecting a small part of the extracted beam with intensity 10^7 protons toward another physics experiment. Crystal-extracted beam had a typical size of 4 mm by 4 mm fwhm at the end of the external beamline. Measurements for the extraction efficiency and other characteristics at the simultaneous work of four experimental set-ups are presented. With crystal working in the above-said regime during one month, no degradation of channeling was observed. The studies of extraction efficiency have been continued with new crystals.Comment: 6pp. Presented at EPAC 200

The Investigations Of Beam Extraction And Collimation At U-70 Proton Synchrotron Of IHEP By Using Short Silicon Crystals

The new results of using short (2-4mm) bent crystals for extraction and collimation of proton beam at IHEP 70 Gev proton synchrotron are reported. A broad range of energies from 6 to 65 GeV has been studied in the same crystal collimation set-up. The efficiency of extraction more than 85% and intensity more than 10E12 were obtained by using crystal with the length 2-mm and the angle 1 mrad. The new regime of extraction is applied now at the accelerator to deliver the beam for different experimental setups within the range of intensity 10E7-10E12ppp.Comment: Presented at EPAC 2002 (Paris, June 3-7), 3p