122169147
Microscopic self-consistent study of neon halos with resonant contributions
Recent reaction measurements have been interpreted as evidence of a halo structure in the exotic neutron-rich isotopes Ne-29,Ne-31. While theoretical studies of Ne-31 generally agree on its halo nature, they differ significantly in their predictions of its properties and underlying cause (e.g., that Ne-31 has an inverted ordering of p-f orbitals). We have made a systematic theoretical analysis of possible Neon halo signatures - the first using a fully microscopic, relativistic mean field approach that properly treats positive energy orbitals (such as the valence neutron in Ne-31) self-consistently with bound levels, as well as the pairing effect that keeps the nucleus loosely bound with negative Fermi energy. Our model is the analytical continuation of the coupling constant (ACCC) method based on a relativistic mean field (RMF) theory with Bardeen-Cooper-Schrieffer (BCS) pairing approximation. We calculate neutron- and matter-radii, one-neutron separation energies, p- and f-orbital energies and occupation probabilities, and neutron densities for single-particle resonant orbitals in Ne27-31. We analyze these results for evidence of neutron halo formation in Ne-29,Ne-31. Our model predicts a p-orbit in halo structure for Ne-31, based on a radius increase from Ne-30 that is 7-8 times larger than the increase from Ne-29 to Ne-30, as well as a decrease in the neutron separation energy by a factor of similar to 10 compared to that of Ne27-30. In contrast to some other studies, our inclusion of resonances yields an inverted ordering of p and f orbitals for spherical and slightly deformed nuclei. Furthermore, we find no evidence of an s-orbit in halo in Ne-29 as recently claimed in the literature. (C) 2014 The Authors. Published by Elsevier B.V.
55611929
A PEPPER-POT BASED DEVICE FOR DIAGNOSTICS OF THE SINGLE-SHOT BEAM
In order to measure the peak current and the beam transversal distribution of an ampere-scale microsecond single-pulse ion beam, a novel single shot beam diagnostic device based on pepper-pot technique, which is a combination of Faraday cup and pepper-pot measurement facility, was developed at Peking University (PKU) [1]. It consists of a main Faraday cup with a pepper-pot mask at its bottom, and a Faraday cup array locating 3 mm away from the pepper-pot mask. This device has been tested at the PKU LEBT test bench and the measurement results are consistent with the results acquired by the Allison scanner. By replacing the Faraday cup array with a fluorescent screen and a CCD camera, this device becomes a facility that not only has the ability to measure the total beam current and the beam profile, but also has the capability to measure the beam emittance for CW or pulsed ion beams. Details will be presented in this paper.
124768645
Development of high intensity beam emittance measurement unit
Three sets of High Intensity Beam Emittance Measurement Units (HIBEMUs) are being developed at Peking University. They are HIBEMU-2 (slit-wire type, one direction), HIBEMU-3 (Allison scanner type, one direction) and HIBEMU-4 (slit-wire type, two directions). For HIBEMU-2 and HIBEMU-3, more recent work has been done on software redesign in order to measure beam emittance and to draw phase diagram more efficiently and precisely. Software for control and data processing of them were developed in Labveiw environment, trying to improve calculation rationality and to offer user-friendly interface. Mechanical modification was also done for HIBEMU-3, mainly concentrating on the protection of Faraday cups from being overheated by the high intensity beam and also from interference of secondary electrons. This paper will also cover the mechanical structure as well as the software development of HIBEMU-4, which is a two-direction emittance scanner newly designed and manufactured for the high energy beam transport (HEBT) of Peking University Neutron Imaging FaciliTY (PKUNIFTY). At the end of this paper, comparison and analysis of the three HIBEMUs are given to draw forth better design of the future emittance measurement facility.
55354069
NUMERICAL METHODS TO THE SPACE CHARGE COMPENSATION (SCC) EFFECT OF THE LEBT BEAM
Numerical simulation as well as experimental researches on space charge compensation for high intensity, low energy ion beam has been done at Peking University (PKU). In this paper we will describe the simulation model proposed at PKU and use it on the PKU ECR single-charged ion source. It consists of a new concept of equivalent density and more consideration of physical process. A series of arithmetical equations is gained through theoretical derivation. Although no numerical solutions have been carried out from our computation, it is foreseeable that the final result will be achieved soon.
32125097
PRELIMINARY RESULTS OF H2+ BEAM GENERATED BY A 2.45 GHZ PERMANENT MAGNET ECR ION SOURCE AT PKU
To obtain high-yield H2 ion beam, experimental and theoretical study was carried out on the 2.45 GHz Peking University permanent magnet electron cyclotron resonance ion source (PKU PMECRIS). With PMECR II [1], studies on the size of discharge chamber and the operation pressure were carried out to increase H2 ion fraction. Beam analysis results prove that the H2 can reach 47.7% with suitable operation parameters. More details will be presented in this paper. INTRODUCTION The creation of molecular ion H2 is an essential process in hydrogen gas plasma. For proton ion source, H2 ions are undesirable in the final extract beam. But recently, the demand to build an ion source to generate high current hydrogen molecular ion H2 beam has been growing rapidly. For example, H2 ion can be used as a pilot beam of the intense deuteron beam during the commissioning of linear accelerators to minimize the activation of components.[2][3] Also it is an effective way to improve the output current of cyclotrons by accelerating H2 and stripping it into H at the exit of accelerator, instead of accelerating H beam directly.[4][5] R. F. King et al. proposed a one-dimensional plasma model for a volume arc source, which is expected to produce 140 mA of ion beam with H2 species ratio around 73% in theory, but it wasn’t realized.[6] N. Joshi et al. developed a volume type ion source at Frankfurt University, and about 91% H2 was extracted with current intensity of 2.84 mA.[7] Obviously, the fraction of H2 is definitely high, but the current is not enough for some applications. With a 2.45 GHz permanent magnet ECR ion source PMECR II [1][8][9] (Fig. 1), the fraction and current intensity of molecular ion H2 were improved at PKU. Theoretical study indicates that, to optimize the production of H2, it is helpful to increase the electron temperature in the source and avoid attachment with neutral H2 which lead to fast destruction of H2.[6] In our PMECRIS, these were achieved by changing the size of discharge chamber and operation pressure in the source. The experimental results will be presented.
43842936
Study of the Energy Modulated Electron Cyclotron Resonance Ion Source for the Coupled RFQ-SFRFQ Cavity
The coupled RFQ and SFRFQ cavity has been manufactured and tested recently. According to the beam dynamic design, the input He beam within 120° phase width is designed for the cavity to achieve over 98% transmission efficiency. An energy modulated electron cyclotron resonance (ECR) ion source was proposed and simulated. To achieve the 1% energy modulation on the 30keV direct current (DC) beam, two simplified RF power feeding structures for beam bunching were studied. The simulations show positive results as well as the bunched beam is achieved by the energy modulated ECR ion source.
92987620
Vertices, vortices & interacting surface operators
A bstractWe show that the vortex moduli space in non-abelian supersymmetric $ \mathcal{N} = \left( {{2},{2}} \right) $ gauge theories on the two dimensional plane with adjoint and anti-fundamental matter can be described as an holomorphic submanifold of the instanton moduli space in four dimensions. The vortex partition functions for these theories are computed via equivariant localization. We show that these coincide with the field theory limit of the topological vertex on the strip with boundary conditions corresponding to column diagrams. Moreover, we resum the field theory limit of the vertex partition functions in terms of generalized hypergeometric functions formulating their AGT dual description as interacting surface operators of simple type. Analogously we resum the topological open string amplitudes in terms of q-deformed generalized hypergeometric functions proving that they satisfy appropriate finite difference equations.
326670
Limits on sizes of fundamental particles and on gravitational mass of a scalar
We review the experimental limits on mass of excited fundamental particles and contact interaction energy scale parameters Λ for QCD, QED and electroweak reactions. In particular we have focused on the QED reaction measuring the differential cross-sections for the process e+e−→γγ(γ) at the energies from 91 GeV to 202 GeV using the data collected with the L3 detector from 1991 to 1999. With a global fit we set lower limits at 95% CL on Λ>1687 GeV, which restricts the characteristic QED size of the interaction region to Re<1.17×10−17 cm. All the interaction regions are found to be smaller than the Compton wavelength of the fundamental particles. This constraint is used to estimate a lower limit on the size of a fundamental particle related to gravitational interaction, applying the model of self-gravitating particle-like structure with the de Sitter vacuum core. It gives rτ⩾2.3×10−17 cm and re⩾1.5×10−18 cm, if leptons get masses at the electroweak scale, and rτ⩾3.3×10−27 cm,re⩾4.9×10−26 cm, as the most stri...
118632272
Multidimensionally-constrained relativistic mean-field models and potential-energy surfaces of actinide nuclei
Background: Many different shape degrees of freedom play crucial roles in determining the nuclear ground state and saddle point properties and the fission path. For the study of nuclear potential energy surfaces, it is desirable to have microscopic and self-consistent models in which all known important shape degrees of freedom are included. Purpose: By breaking both the axial and the spatial reflection symmetries simultaneously, we develop multidimensionally-constrained relativistic mean field (MDC-RMF) models. Methods: The nuclear shape is assumed to be invariant under the reversion of x and y axes, i.e., the intrinsic symmetry group is V-4 and all shape degrees of freedom beta(lambda mu) with even mu, such as beta(20), beta(22), beta(30), beta(32), beta(40), ..., are included self-consistently. The single-particle wave functions are expanded in an axially deformed harmonic oscillator (ADHO) basis. The RMF functional can be one of the following four forms: the meson exchange or point-coupling nucleon interactions combined with the nonlinear or density- dependent couplings. The pairing effects are taken into account with the BCS approach. Results: The one-, two, and three-dimensional potential energy surfaces of Pu-240 are illustrated for numerical checks and for the study of the effect of the triaxiality on the fission barriers. Potential energy curves of even-even actinide nuclei around the first and second fission barriers are studied systematically. Besides the first ones, the second fission barriers in these nuclei are also lowered considerably by the triaxial deformation. This lowering effect is independent of the effective interactions used in the RMF functionals. Further discussions are made about different predictions on the effect of the triaxiality between the macroscopic-microscopic and MDC-RMF models, possible discontinuities on PES's from self-consistent approaches, and the restoration of broken symmetries. Conclusions: MDC-RMF models give a reasonably good description of fission barriers of even-even actinide nuclei. It is important to include both the nonaxial and the reflection asymmetric shapes simultaneously for the study of potential energy surfaces and fission barriers of actinide nuclei and of those in unknown mass regions such as, e.g., superheavy nuclei.
119135529
Orbifold Vortex and Super Liouville Theory
We study the nonabelian vortex counting problem on $\mathbb{C}/\mathbb{Z}_p$. At first we calculate vortex partition functions on the orbifold space using localization techniques, then we find how to extract orbifold vortex partitions function from orbifold linear quiver instanton partition functions. Finally, we study the AGT like relation between orbifold SU(2) vortices and $\mathcal{N} = 1$ super Liouville theory in the mixed R/NS sector by fixing the dictionary among parameters in the common hypergeometric functions system.
109283317
Design and implementation of the NaI(Tl)/CsI(Na) detectors output signal generator
We designed and implemented a signal generator that can simulate the output of the NaI(Tl)/CsI(Na) detectors' pre-amplifier onboard the Hard X-ray Modulation Telescope (HXMT). Using the development of the FPGA (Field Programmable Gate Array) with VHDL language and adding a random constituent, we have finally produced the double exponential random pulse signal generator. The statistical distribution of the signal amplitude is programmable. The occurrence time intervals of the adjacent signals contain negative exponential distribution statistically.