Asymptotics of block Toeplitz determinants and the classical dimer model

We compute the asymptotics of a block Toeplitz determinant which arises in the classical dimer model for the triangular lattice when considering the monomer-monomer correlation function. The model depends on a parameter interpolating between the square lattice ($t=0$) and the triangular lattice ($t=1$), and we obtain the asymptotics for $0<t\le 1$. For $0<t<1$ we apply the Szeg\"o Limit Theorem for block Toeplitz determinants. The main difficulty is to evaluate the constant term in the asymptotics, which is generally given only in a rather abstract form

Small-angle fragmentation of carbon ions at 0.6 GeV/n: a comparison with models of ion-ion interactions

Momentum distributions of hydrogen and helium isotopes from 12C fragmentation at 3.5° were measured at 0.6 GeV/nucleon in the FRAGM experiment at ITEP TWA heavy ion accelerator. The fragments were selected by correlated time of flight and dE/dx measurements with a magnetic spectrometer with scintillation counters. The main attention was drawn to the high momentum region where the fragment velocity exceeds the velocity of the projectile nucleus. The momentum spectra of fragments span the region of the fragmentation peak as well as the cumulative region. The differential cross sections cover six orders of magnitude. The distributions measured are compared to the predictions of three ion-ion interaction models: BC, QMD and LAQGSM03.03. The kinetic energy spectra of fragments in the projectile rest frame have an exponential shape with two temperatures, being defined by their slope parameters

Inclusive pion double charge exchange on Oxygen(16) at 0.6-1.1 GeV

The inclusive pion double charge exchange (DCX) on oxygen nuclei has been measured in the region where additional pion production is kinematically forbidden. The experiment was performed at ITEP PS at incident pi- kinetic energies T_0= 0.59, 0.75 and 1.1 GeV. The integrated forward differential cross section was found to decrease with energy slowly. At 1.1 GeV it exceeds the theoretical prediction within the conventional sequential single charge exchange mechanism with a neutral pion in the intermediate state (Glauber elastic rescattering) by about half an order of magnitude. The sequential mechanism with two pions in the intermediate state (Glauber inelastic rescatterings), which was proposed recently, seems to be able to explain the observed slow energy dependence and allows to predict the DCX cross section for higher energies.Comment: 27 pages, 13 figures. Minor corrections, one figure added. Accepted in NP

On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

Splitting of fragmentation peaks of light ions in

The FRAGM experiment at the ITEP-TWA heavy ion facility has a unique opportunity of measuring the momentum distributions of nuclear fragments. We present the results of 56Fe fragmentation into light ions on 9Be target at 0.23 GeV/nucleon. The momentum spectra of projectile like fragments were measured with a high resolution beam line spectrometer. In contrast to the carbon fragmentation, where the momentum spectra have Gaussian-like shapes, in the emission of the light fragments the shapes have a double-humped structure. This splitting is most pronounced in proton spectra. The possibility of describing this effect by asymmetric fission and multifragmentation is discussed. A comparison is made with the results of the FRS measurements at GSI. The obtained experimental data are in a reasonable agreement with the predictions of several transport codes such as BC, INCL and LAQGSM

Splitting of fragmentation peaks of light ions in 56Fe + 9Be collisions at 0.23 GeV/nucleon

The FRAGM experiment at the ITEP-TWA heavy ion facility has a unique opportunity of measuring the momentum distributions of nuclear fragments. We present the results of 56Fe fragmentation into light ions on 9Be target at 0.23 GeV/nucleon. The momentum spectra of projectile like fragments were measured with a high resolution beam line spectrometer. In contrast to the carbon fragmentation, where the momentum spectra have Gaussian-like shapes, in the emission of the light fragments the shapes have a double-humped structure. This splitting is most pronounced in proton spectra. The possibility of describing this effect by asymmetric fission and multifragmentation is discussed. A comparison is made with the results of the FRS measurements at GSI. The obtained experimental data are in a reasonable agreement with the predictions of several transport codes such as BC, INCL and LAQGSM

Cumulative protons in

In the FRAGM experiment at heavy ion accelerator complex TWAC-ITEP, the proton yields at an angle 3.5° have been measured in fragmentation of carbon ions at T0 = 0.3, 0.6, 0.95 and 2.0 GeV/nucleon on beryllium target. The data are presented as invariant proton yields on cumulative variable x in the range 0.9 < x < 2.4. Proton spectra cover six orders of invariant cross section magnitude. They have been analyzed in the framework of quark cluster fragmentation model. Fragmentation functions of quarkgluon string model are used. The probabilities of the existence of multi-quark clusters in carbon nuclei are estimated to be 8–12% for six-quark clusters and 0.2–0.6% for ninequark clusters