DESIGN STUDIES ON 100MeV / 100kW ELECTRON LINAC FOR NSC KIPT NEUTRON SOURCE ON THE BASE OF SUBCRITICAL ASSEMBLY DRIVEN BY LINAC
In NSC KIPT, Kharkov, Ukraine a neutron source based on a subcritical assembly and driven by a 100 MeV/100kW electron linac is under design and development. Design and construction of such a linac with high average beam current, low emittance and low beam losses are challenging tasks. In this paper the linac physical design with beam simulation results are described, the accelerating structures and some key technical solutions are presented.

title: Study on the characteristics of linac based THz light source
abstract: There are many methods based on linac for THz radiation production. As one of the options for the Beijing Advanced Light, an ERL test facility is proposed for THz radiation. In this test facility, there are 4 kinds of methods to produce THz radiation: coherent synchrotron radiation (CSR), synchrotron radiation (SR), low gain FEL oscillator, and high gain SASE FEL. In this paper, we study the characteristics of the 4 kinds of THz light sources.

title: Beam dynamics studies on the 100 MeV/100 kW electron linear accelerator for NSC KIPT neutron source
abstract: We designed a 100 MeV/100 kW electron linear accelerator for NSC KIPT, which will be used to drive a neutron source on the basis of subcritical assembly. Beam dynamics studies have been conducted to reach the design requirements (E = 100 MeV, P = 100 kW, dE/E < 1% for 99% particles). In this paper, we will present the progress of the design and the dynamic simulation results. For high intensity and long beam pulse linear accelerators, the BBU effect is one big issue; special care has been taken in the accelerating structure design. To satisfy the energy spread requirement at the linac exit, the particles with large energy difference from the synchronous particle should be eliminated at a low energy stage to ease the design of the collimation system and radiation shielding. A dispersion free chicane with 4 bending magnets is introduced downstream of the 1st accelerating section; the unwanted particles will be collimated there.

title: Design study of a L-band DC photocathode gun
abstract: In this paper, we the design study of a L-band DC photocathode gun injector for the ERL (Energy Recovery Linac) test facility. The main parameters of the injector are energy of 2.3 MeV, a bunch length of 2 ps, and a normalized emittance of 2.1 mm·mrad.

title: Experimental studies on the photoelectron instability in the Beijing Electron Positron Collider
abstract: A vertical coupled-bunch instability was observed for a positron beam at the Beijing Electron Positron Collider (BEPC). The experimental results show that the instability has similar characteristics as that observed in the Photon Factory of KEK several years ago. The instability at BEPC can be explained by the effect of an electron cloud which is produced in the beam chamber by synchrotron light hitting the wall.

title: Travelling wave accelerating structure design for TESLA positron injector linac
abstract: A modified cup-like TW accelerating structure for TESLA Positron Pre-Accelerator (PPA) is designed by optimizing the structure geometry and by changing the iris thickness cell by cell in a section. This structure has high shunt-impedance and a large iris radius to meet with the requirements of high gradient and large transverse acceptance. The beam dynamics in the structure with the optimum solenoid focus held are studied. A satisfactory positron beam transmission and the beam performance at the PPA output have been obtained. In this paper the accelerating structure design is described in detail and the results are presented.

title: PROTON BRANCH OF MODIFIED URCA PROCESS IN STRONG MAGNETIC FIELD AND SUPERFLUIDITY OF NEUTRON STAR CORES
abstract: The modified URCA process produces efficient neutrino energy losses in neutron star cores, and has been shown to go via neutron and proton branches. Based on the improved electron chemical potential and critical temperature of superfluidity, the effects of strong magnetic field and superfluidity on the proton branch of modified URCA process are investigated simultaneously in this paper. The results show that strong magnetic field enhances the neutrino emissivities compared to the case in zero magnetic field, and superfluidity reduces the emissivities significantly. For the total neutrino emissivities, the magnetic field is dominant at the initial stage of neutron star cooling, but the superfluidity becomes crucial as the temperature drops below the critical temperature.

title: Young Stellar Groups around Herbig Ae/Be Stars: A Low-Mass YSO Census
abstract: We present near-IR and mid-IR observations of eight embedded young stellar groups around Herbig Ae/Be stars (HAEBEs) using archived Spitzer IRAC data and 2MASS data. These young stellar groups are nearby (≤1 kpc) and still embedded within their molecular clouds. In order to identify the young stellar objects in our sample, we use the color-color diagram of J - [3.6] versus Ks - [4.5]. The Spitzer images of our sample show that the groups around HAEBEs, spectral types earlier than B8, are usually associated with bright infrared nebulosity. Within this, there are normally 10-50 young stars distributed close to the HAEBEs (<1 pc). Not only are there young stars around the HAEBEs, there are also young stellar populations throughout the whole cloud, some of which are distributed and some of which are clumped. The groups around the HAEBEs are substructures of the large young population within the molecular cloud. The sizes of groups are also comparable with those substructures seen in massive clusters. Young stars in groups around HAEBEs have generally larger SED slopes compared to those outside, which suggests that the young stars in groups are probably younger than the distributed systems. This might imply that there is usually a higher and more continuous star-forming rate in groups, that the formation of groups initiates later, or that low-mass stars in groups form slower than those outside. Finally, there is no obvious trend between the SED slopes and the distance to the HAEBEs for those young stars within the groups. This suggests that the clustering of young stars dominates over the effect of massive stars on the low-mass young stars at the scale of our study.

title: Fermion Damping in a Fermion-Scalar Plasma
abstract: In this article we study the dynamics of fermions in a fermion-scalar plasma. We begin by obtaining the effective in-medium Dirac equation in real time which is fully renormalized and causal and leads to the initial value problem. For a heavy scalar we find the novel result that the {ital decay} of the scalar into fermion pairs in the medium leads to damping of the fermionic excitations and their in-medium propagation as quasiparticles. That is, the fermions acquire a width due to the decay of the heavier scalar in the medium. We find the damping rate to lowest order in the Yukawa coupling for arbitrary values of scalar and fermion masses, temperature and fermion momentum. An all-order expression for the damping rate in terms of the exact quasiparticle wave functions is established. A kinetic Boltzmann approach to the relaxation of the fermionic distribution function confirms the damping of fermionic excitations as a consequence of the induced decay of heavy scalars in the medium. A linearization of the Boltzmann equation near equilibrium clearly displays the relationship between the damping rate of fermionic mean fields and the fermion interaction rate to lowest order in the Yukawa coupling directly in real time. {copyright}more » {ital 1999} « less

title: Partial wave analysis of $J/\psi \to \gamma \eta \eta$
abstract: Based on a sample of $2.25\times 10^{8}$ $J/\psi$ events collected with the BESIII detector at BEPCII, a full partial wave analysis on $J/\psi\to\gamma\eta\eta$ was performed using the relativistic covariant tensor amplitude method. The results show that the dominant $0^{++}$ and $2^{++}$ components are from the $f_0(1710)$, $f_0(2100)$, $f_0(1500)$, $f_2'(1525)$, $f_2(1810)$ and $f_2(2340)$. The resonance parameters and branching fractions are also presented.

title: Measurement of branching ratio and $B_s^0$ lifetime in the decay $B_s^0 \rightarrow J/\psi f_0(980)$ at CDF
abstract: We present a study of Bs0 decays to the CP-odd final state J/ψ f0(980) with J/ψ → µ+µ- and f0(980) → π+π-. Using pp collision data with an integrated luminosity of 3.8 fb-1 collected by the CDF II detector at the Tevatron we measure a Bs0 lifetime of τ(B0s → J/ψ f0(980)) = 1.70-0.11+0.12(stat) ± 0.03(syst) ps. This is the first measurement of the Bs0} lifetime in a decay to a CP eigenstate and corresponds in the standard model to the lifetime of the heavy Bs0 eigenstate. We also measure the product of branching fractions of B0s → J/ψ f0(980) and f0(980) → π+π- relative to the product of branching fractions of B0s → J/ψφ and φ→K+K- to be Rf0/ψ = 0.257 ± 0.020(stat) ± 0.014(syst), which is the most precise determination of this quantity to date.