2110716
Single-bunch instability estimates for the 1-nm APS storage ring upgrade with a smaller vacuum chamber
We recently studied a lattice achieving 1 -nm emittance at the APS storage ring [1]. The successful design required very strong sextupoles in order to tune the machine to the desired positive chromaticity. A preliminary design of such magnets indicated saturation in the poles unless the vacuum chamber gets smaller by a factor of two compared to the existing APS chamber. Since the resistive wall impedance scales as 1/b3, where b is the radius of the chamber, we questioned how much current we can store in a single bunch at the 1-nm storage ring. In order to answer this question quantitatively, we calculated all wake potentials of impedance elements of the existing APS storage ring with the transverse dimension properly scaled but with the longitudinal dimension kept unchanged. With the newly calculated impedance of a smaller chamber, we estimated the single- bunch current limit. It turned out that the ring with a smaller chamber would not diminish the single-bunch current limit substantially. We present both wake potentials of 1-nm and the existing rings followed by the simulation results carried out for determining the accumulation limit to the ring.
22794424
Dipole and spin-dipole resonances in charge-exchange reactions on 12C.
The [sup 12]C([ital n],[ital p])[sup 12]B reaction was studied using the white neutron source at the Los Alamos Meson Physics Facility/Weapon Neutron Research Center with a continuous incident neutron energy from 60 to 260 MeV. Double differential cross sections were measured in the angular range 11[degree][le][theta][sub lab][le]37[degree]. Using the neutron time-of-flight facility at the Indiana University Cyclotron Facility, we also studied the [sup 12]C([ital p],[ital n])[sup 12]N reaction at [ital E][sub [ital p]]=186 MeV and the [sup 12]C([ital [rvec p]],[ital [rvec n]])[sup 12]N reaction at [ital E][sub [ital [rvec p]]]=160 and 186 MeV. Double differential cross sections were measured between [theta][sub lab]=0[degree] and [theta][sub lab]=50[degree] in 5[degree] steps. Spin observables [ital D][sub [ital N][ital N]], [ital A][sub [ital Y]], and [ital P] were measured at [theta][sub lab]=5[degree],9[degree],13[degree] with [ital E][sub [ital [rvec p]]]=160 MeV and [theta][sub lab]=15[degree],20[degree] with [ital E][sub [ital [rvec p]]]=186 MeV. Angular distributions of differential cross section and spin observables for low-lying transitions in the residual nuclei are compared with disorted-wave impulse approximation (DWIA) calculations. A multipole decomposition analysis was performed to study the giant dipole and giant spin-dipole resonances. The contributions of the quasifree reaction in the giant resonance region was subtracted. The empirical results ofmore » energy distributions for dipole ([Delta][ital L]=1) transition are compared with DWIA calculations using nuclear structure information obtained with a conventional shell model and also with a random phase approximation.« less
41167320
Status of the CAMD Light Source
In parallel with the increasing diversity of its research program, the CAMD Light Source has improved its beam brightness and quality. Using a well calibrated model of the lattice, the ring optic has been refined to generate a lower beam emittance of 150 nm. rad and this has been confirmed by measuring the beta values with the modulated quadrupole shunt system. The beam sizes have also been measured with an X-ray pinhole camera and compared to the calculated emittance. The beam orbit is corrected to a standard position referenced to the quadrupole centers to a precision better than 0.5 mm, using a suite of well localized bumps which can also flexibly steer the user photon beams to their requirements. Beam reliability has been improved by bringing into use a VME control system for the energy ramp.
120316681
Experimental results of the betatron sum resonance
The experimental observations of motion near the betatron sum resonance, /spl nusub x/+2/spl nusub z/=13, are presented. A fast quadrupole (Panofsky-style ferrite picture-frame magnet with 8 pulsed power supplies) producing a betatron tune shift of the order of 0.03 at rise time of 1 /spl mu/s was used. This quadrupole was used to produce betatron tunes which jumped past and then crossed back through a betatron sum resonance line. The beam response as function of initial betatron amplitudes were recorded turn by turn. The correlated growth of the action variables, J/sub x/ and J/sub z/, was observed. The phase space plots in the resonance frame reveal the features of particle motion near the nonlinear sum resonance region.<<ETX>>
10177650
Clarification of the three-body decay of 12C (12.71 MeV).
Using beta decays of a clean source of 12N produced at the IGISOL facility, we have measured the breakup of the 12C (12.71 MeV) state into three alpha particles with a segmented particle detector setup. The high quality of the data permits solving the question of the breakup mechanism of the 12.71 MeV state, a longstanding problem in few-body nuclear physics. Among existing models, a modified sequential model fits the data best, but systematic deviations indicate that a three-body description is needed.
1289258
Energetic electrons associated with magnetic reconnection in the magnetic cloud boundary layer.
Here is reported in situ observation of energetic electrons (∼100-500 keV) associated with magnetic reconnection in the solar wind by the ACE and Wind spacecraft. The properties of this magnetic cloud driving reconnection and the associated energetic electron acceleration problem are discussed. Further analyses indicate that the electric field acceleration and Fermi-type mechanism are two fundamental elements in the electron acceleration processes and the trapping effect of the specific magnetic field configuration maintains the acceleration status that increases the totally gained energy.
56005177
Inclusive J production in Z0 decays
Abstract Inclusive J production in Z0 decays is observed via the leptonic decay mode J → l+l− (l = e,μ). We measure the branching ratio Br(Z0 → J + X) = (4.1 ± 0.7 (stat.) ± 0.3 (sys.)) × 10−3. We have calculated the fraction of the J mesons from b-hadron decay and find a branching ratio of Br(b → J + X)= (1.3±0.2(stat.)±0.2(sys.)) × 10−2. We determine the average fractional energy of bottom hadrons 〈XE > = 0.70±0.03 (stat.)+0.02−0.01 (sys.) using the momentum spectrum of the J mesons. From a study of the angle between the J and the most energetic jet, we set an upper limit on the branching ratio Br ( Z 0 → q q g ∗ ; g ∗ → J + X ) −4 at 90% confidence level.
105752539
The preliminary explanation of a new working model on 10GHz ECR2 source
A new working model and a new magnetic field configuration were employed on the 10GHz ECR2 source of the heavy ion research facility in Lanzhou(HIRFL). That resulted in an obvious enhancement of beam currents of ECR2 ion source, the beam current of Ar9+ increase from 125 e mu A to 320 e mu A, for Ar11+ ion beam increase from 40 e mu A to 80 e mu A. In this paper, primary analysis and explanation of this working model is presented, we will also discuss the action of low energy electrons in ECR plasma and get an important conclusion, which the low energy electrons injection is more effective in the extraction region of ECR ion sources.
73704898
A New Design for ILC 3.2 km Damping Ring Based on FODO Cell
In this paper, we made a new design for ILC 3.2 km damping ring with 2 arcs based on FODO cell and 2 straight sections which are nearly the same as the new version of the 6.4 km ring DCO4 [1]. This new lattice uses less magnets than DCO4 and less quadrupoles than the present SuperB like lattice [1], and has a freely tunable momentum compaction factor. The work of lattice design and dynamic aperture study will be presented in detail. INTRODUCTION After ILC enter the Technical Design Phase 1 by the end of 2008, the Minimum Machine study [2] based on RDR baseline was launched as the essential strategy of cost-reduction. The term “minimum machine” which try to redesign the machine does not refer to any definable true minimum, but instead is a euphemism for higher level alternative design concepts which promise significant cost-reduction while maintaining the machine performance. With the new machine parameter, a reduction in the number of bunches by a factor of two allows a reduction by the same factor in the circumference of the damping ring, while keeping the current (bunch spacing) in the rings constant. To first order, this could result in a reduction of the damping rings’ cost by almost a factor of two. However, the actual cost savings will depend on the exact lattice design. The design study of ILC 6 km damping ring has started very early and gone through intense competition. The 6.4 km DCO4 based on FODO arc cell is the final version adopted by RDR baseline in 2008. But for the 3.2 km ring, the study which was started by the end of 2008 seems to be immature. The only existent design for the smaller ring is DSB3 based on SuperB lattice. Considering the advantage of FODO lattice such as smaller number of quadrupoles and sextupoles per cell, freely tuable momentum compaction, and better dynamic aperture, we try to make a new design for the smaller ring using FODO arc cell which can also provide a reference for DSB3 design. We named our new design as DMC1 for convenience. GLOBAL CONSIDERATION AND PARAMETER CALCULATION In our design, we adopted the racetrack structure as the 6.4 km baseline design (DCO4). The layout of our 3.2 km damping ring is shown in Figure 1 with the electron and positron beams counter-rotating in the two rings. The advantage of this kind of structure is that the ————————————— injection and extraction beam lines for e+ and erings can be in the same tunnel. Also, the rf section and wigglers are located near each other in order to minimize cryogenic transfer lines, while the rf section must be upstream to avoid the radiation damage. Figure 1: Layout of the 3.2 km ILC damping ring. The first parameter should be considered before lattice design is the damping time. ILC damping ring has a very fast damping time (about 25 ms) which is decided by the 5 Hz machine repetition rate. The damping time for a damping ring is given by [3]
111161553
Vacuum monitoring system of HLS storage ring
The vacuum monitoring system of Hefei Light Source (HLS) storage ring is a subsystem of the upgraded HLS control system, which is based upon EPICS. There are 6 Varian vacuum Multi-Gauges controllers around the storage ring of HLS to monitor the pressure of 15 positions. An Industrial PC is used as Input/Output Controller (IOC) and it connects the 6 Varian vacuum Multi-Gauge controllers with serial communication (RS485 mode). The pressure values are displayed in a PC with Linux, which is used as operator interface (OPI). The pressure values are archived in a database and some data analyses are also done.
121485651
Aging test of a real-size high rate MRPC for CBM-TOF wall
A new kind of low-resistivity glass has been developed. Its volume resistivity is on the order of 1010 Ω cm and multi-gap resistive plate chambers (MRPCs), once assembled with it, can be operated at a charged particle flux in excess of 25 kHz/cm2, with very small charge build-up at the plates. This new technology has a wide range of application in high energy physics experiments such as FAIR-CBM, LHC-ATLAS or Jlab-SOLID, to mention some. In this paper we report on results related to its long-term behavior (aging). A 6 × 2-pad CBM module has been irradiated by X-rays at a mips-equivalent flux of 15 kHz/cm2, for 300 hours and for a released charge totaling 0.22 C (50 mC/cm2). Tested in an electron beam before and after exposure, no degradation of the detector performances could be appreciated. As expected, compared to common glass MRPCs, the newly developed high rate counter also responds faster to sudden irradiation.