High-power excimer laser systems

Two-high power excimer laser systems with square (25 × 25 cm) and circular (with a diameter of 40 cm) cross sections of the output laser beam are described. The first (second) system consists of four (five) excimer lasers. The experimental results on the generation of the high-quality high-power laser pulses are presented. Laser beams with a pulse duration of 1–250 ns, a divergence of 0.01 mrad, a spectral line width of 0.01 cm⁻¹, and a pulse energy of up to 330 J are obtained. Original Text ? Astro, Ltd., 2006.     

How to measure the pomeron phasein diffractive dipion photoproduction

The study of charge asymmetry of pions in the high-energy process ep → eπ⁺π^-p (γp → π⁺π^-p) at very small dipion momenta offers a method to measure the phase of the forward hadronic (quasi-) elastic amplitude γp → ρp. We estimate the potential of such measurements at HERA. Received: 19 February 2004, Revised: 1 August 2005, Published online: 3 November 2005     

Analogue of a spin flop phase transition for an array of magnetic moments with dipole interaction

In a two-dimensional array of magnetic moments with planar magnetization and relatively weak anisotropy in the basal plane, a stepwise phase transition is induced by an external magnetic field parallel to the easy axis of the system. This transition is similar to the spin flop phase transition in weakly anisotropic Heisenberg antiferromagnets with the significant difference that it is accompanied by the rearrangement of the sublattice structure of the magnet; i.e., it can be interpreted as a topological transition. The transition should manifest itself for arrays of submicron magnetic particles (magnetic dots) on nonmagnetic substrates, which have recently become the object of intensive research.     

Transfer of CIDNP among coupled spins at low magnetic field

Coherent polarization transfer among groups of dynamically polarized spins is explored and applied to field cycling experiments where spin evolution proceeds at low magnetic field while observation is performed at high field. The case of two nonequivalent spins-1/2 with scalar spin coupling is considered theoretically in detail for the cases of sudden and adiabatic field change. The criterion for efficient polarization transfer is derived theoretically and consistently confirmed experimentally for three photochemical reactions, involving spin systems of increasing complexity that exhibit chemically induced dynamic nuclear polarization: (1) the two polarized protons of the purine base of adenosine monophosphate; (2) four coupled indole protons of tryptophan; and (3) long-range polarization transfer among the aliphatic protons of cycloundecanone. The importance of polarization transfer in other cases with non-equilibrium population of the nuclear spin levels and the possibility of its utilization in field cycling NMR studies are discussed.     

Ground-state energy of pionic hydrogen to one loop

We investigate the ground-state energy of the atom (pionic hydrogen) in the framework of QCD + QED. In particular, we evaluate the strong energy-level shift. We perform the calculation at next-to-leading order in the low-energy expansion in the framework of the relevant effective field theory. The result provides a relation between the strong energy shift and the pion-nucleon S-wave scattering lengths - evaluated in pure QCD - at next-to-leading order in isospin-breaking and in the low-energy expansion. We compare our result with available model calculations. Received: 11 June 2002 / Published online: 9 October 2002     

Observation of weak impact of a stochastic magnetic field on fast-ion confinement

Fast ions are observed to be very well confined in the Madison Symmetric Torus reversed field pinch despite the presence of stochastic magnetic field. The fast-ion energy loss is consistent with the classical slowing down rate, and their confinement time is longer than expected by stochastic estimates. Fast-ion confinement is measured from the decay of d-d neutrons following a short pulse of a 20 keV atomic deuterium beam. Ion confinement agrees with computation of particle trajectories in the stochastic magnetic field, and is understood through consideration of ion guiding center islands.     

Optimum conditions for pumping laser transitions of cadmium ions by various processes in a hollow-cathode discharge

The interaction of electrons of various energies with helium and cadmium atoms in a hollow-cathode discharge is analyzed. On the basis of the results of this analysis the conclusion is made that helium is ionized predominantly by electrons moving from the cathode wall to the cavity axis and having energies 70<ε<300 eV, whereas helium and cadmium are ionized predominantly by electrons with energies 9<ε<70 eV which move chaotically. For each of these energy ranges, the kinetic equation is solved and the electron energy distribution function (EDF) is determined, which is used for calculating pumping rates for laser transitions of cadmium ions. The conclusion is made that the rate of population of laser transitions through charge transfer is determined by electrons having a predominant direction of motion and an anisotropic EDF. The population rate associated with electron impact and the Penning ionization is determined by electrons moving chaotically and having an isotropic EDF. The analysis of the EDF made it possible to explain differences in discharge conditions (helium and cadmium pressures) providing optimum lasing for lines pumped by different processes. Radial profiles of pump rates obtained from the analysis made it possible to calculate and explain the dependence of the laser output power on the cathode diameter.     

On the role of strong turbulence in low-pressure rf discharges in a magnetic field

The results of an experimental and theoretical investigation of strong turbulence produced by an external rf field in the plasma of a beam-plasma discharge are presented. The modulation instability of a rf electric field, perpendicular to a constant magnetic field, in the frequency range between the lower-hybrid and ionic Langmuir frequencies, has been investigated. It is shown that the low-frequency fields can be used to control beam relaxation. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 9, 608–612 (10 November 1996)     

Nonequilibrium plasma produced by microwave nanosecond radiation:parameters, kinetics, and practical applications

The results of the investigation of nonequilibrium plasma produced by powerful microwave nanosecond radiation is reviewed. Nanosecond microwave discharge is a new branch of gas discharge physics. At present, this type of discharge is intensively investigated. Interesting properties and peculiarities of such a discharge and various its applications are discussed, first of all for the creation of an artificial ionized layer (AIL) in the earth's atmosphere. The laboratory experiments performed and the new effects which appear in nanosecond microwave discharge are briefly summarized. Different applications of AIL are analyzed on the basis of the experimental modeling     

Structure and phase composition of the intermetallide Ni3Al+0.5 at.% B synthesized under pressure

We have used x-ray structural analysis, together with transmission and scanning electron microscopy, to study the phase composition, structure, and elemental distribution in the intermetallide Ni₃Al+0.5 at.% B, produced by self-propagating high-temperature synthesis under pressure. It is shown that the synthesized material is an ordered alloy of the type L1₂. The phase composition of the alloy Ni₃Al+0.5 at.% B is represented by the phases Ni₃Al (the fundamental phase), grains of a layered NiAl composition, and inclusions of Ni₃B. The latter is found inside the Ni₃Al grains, in the form of surrounded particles, and at dislocations and at grain boundaries in the NiAl phase. Institute for the Physics of Strength and Materials Production. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 59–64, September, 1996.