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In this article, possible improvement related to the AGS 6-3-1 bunch merge test is presented. After that, relevant issues for beams with larger longitudinal emittance at RHIC are discussed.

High-order correction terms to the expression of the field of circularly po- larized Gaussian laser are derived. Terms up to seventh order in the small dimen- sionless spatial parameter are explicitly presented. Using the test particle simulation programs, the CAS (Capture & Acceleration Scenario) phenomenon in the circularly polarized field has been proved, and the difference efficiency of CAS scheme between the circularly polarized field and linearly polarized field has been investigated, further more the electron dynamics obtained by the paraxial approximation, the fifth-order correction, and the seventh-order correction are compared in detail. The numerical calculations show that the results of three corrected models coincide with each other very well for kw0>60, and the difference of the three corrected models is very conspic- uously for kw0• 50. Then the ranges of the electron incident momentum for the CAS scheme in circularly polarized field to emerge are examined. This study is of signifi- cance in designing experimental setup to test CAS and helpful in understanding the basic physics of CAS.

Nonlinear polarization vector translation (PVT) is applied in the area of radar anti-jamming in this paper. The processes of real number type and ratio type diagonal matrix PVT are analyzed, pointing out their deficiencies in polarization states separation of the target and jamming. Then exponential diagonal matrix PVT is proposed and show its advantage on both polarization state angle and polarization divergence. The result that Nonlinear PVT separates the target and the jamming on the Poincare sphere can help to improve the filter performance, bringing convenience to subsequent interference suppression, polarimetric target enhancement and recognition.

During the entire period of injector proton study in run 2014, it seems that the beam transverse emittance out of Booster is larger than that in run 2013. The emittance measured at the BtA transfer line and also the transmission from Booster late to AGS late are presented for this argument. In addition to this problem, it seems that the multiturn Booster injection, which defines the transverse emittance, needs more attention. Moreover, for high intensity operations, the space charge effect may be already relevant in RHIC polarized proton runs. With the RHIC proton intensity improvement in the next several years, higher Booster input intensity is needed, therefore, the space charge effect at the Booster injection and early ramp may become a new limiting factor.

The RHIC proton beam polarization can be improved by raising the Booster scraping, which also helps to reduce the RHIC transverse emittance, and therefore to improve the luminosity. By doing this, the beam-beam effect would be enhanced. Currently, the RHIC working point is constrained between 2/3 and 7/10, the 2/3 resonance would affect intensity and luminosity lifetime, and the working point close to 7/10 would enhance polarization decay in store. Run 2013 shows that average polarization decay is merely 1.8% in 8 hours, and most fills have the luminosity lifetime better than 14 hours, which is not a problem. Therefore, even without beam-beam correction, there is room to improve for RHIC polarization and luminosity. The key to push the Booster scraping is to raise the Booster input intensity; for that, two approaches can be used. The first is to extend the LINAC tank 9 pulse width, which has been successfully applied in run 2006. The second is to raise the source temperature, which has been successfully applied in run 2006 and run 2012.

A big problem in RHIC 100 GeV proton run 2009 was the significantly lower luminosity lifetime than all previous runs. It is shown in this note that the beam intensity decay in run 2009 is caused by the RF voltage ramping in store. It is also shown that the beam decay is not clearly related to the beam momentum spread, therefore, not directly due to the 0.7m. β* Furthermore, the most important factor regarding the low luminosity lifetime is the faster transverse emittance growth in store, which is also much worse than the previous runs, and is also related to the RF ramping. In 100 GeV proton run 2012a, the RF ramping was abandoned, but the β* was increased to 0.85m, with more than 20% loss of luminosity, which is not necessary. It is strongly suggested to use smaller β* in 100 GeV polarized proton run 2015/2016

The density profiles were measured in the Hefei tokamak-7 (HT-7) [World Survey of Activities in Controlled Fusion Research, Nuclear Fusion Special Supplement (International Atomic Energy Agency, Vienna, 1997), p. 61] ohmic discharges by means of a new multichannel far-infrared (FIR) laser interferometer. The progress on the extension of the HT-7 ohmic discharge operation region was introduced. The experiment results at the density limit, the multifaceted asymmetric radiation from the edge (MARFE) phenomena, the rf (radio frequency) boronization experiments, and the fueling efficiency studies were reported. The plasma physics in the molecular beam injection (MBI), the pellet injection (PI), and the gas puffing (GP) fueling experiments was studied and discussed.

In the HT-7 superconducting tokamak, the onset of a multifaceted asymmetric radiation from the edge (MARFE) usually occurs in the early ohmic discharges of each experimental campaign before wall conditioning. The occurrence and location of a MARFE is identified by different diagnostic systems. An improved confinement mode plasma which was induced by the MARFE is observed, and the global particle confinement time increases 1.9 times. The relaxation time between the MARFE event trigger and the L-H transition is about 1.4 ms, the following L-H transition time is 1.9 ms, and the improved confinement mode phase is maintained for about 40 ms. The MARFE cools the plasma edge, and the electron density profile is observed to become more narrow and peaked. The occurrence of a MARFE is strongly correlated with Zeff but not with the density, and it always occurs at Zeff = 3-8 ohmic discharges. In the case of a good wall condition (Zeff = 1-2), the onset of MARFEs has not been observed before reaching the Greenwald density limit.

High-order correction to the fields of ultrashort, tightly focused laser pulses expressed in power series of e=1∕(ω0t0) and s=1∕(k0w00) (ω0=ck0 the central oscillatory frequency, t0 the pulse duration for half period, w00 the beam waist radius at the central frequency ω0), are derived. These expressions can be used to describe accurately the fields of laser pulses, and are suitable for practical calculations. The first-order correction terms to the fields based on paraxial approximation are explicitly given. They are applied to a simulation study of electron dynamics in laser pulse field with special attention given to the vacuum laser acceleration scheme. We found that as long as ω0t0>20, the zeroth-order approximation (long pulse approximation) is adequate for describing the interaction. For ω0t0

The correlation between the outgoing energy and the scattering angle of electrons accelerated by a laser beam in vacuum has been investigated. Essentially, the single-valued function of the correlation, derived from classical electrodynamics Compton scattering for a plane wave, is broadened to a band. It means electrons with the same outgoing energy will have an angular spread. An equation to describe this correlation has been derived. Dependence of the spread width of scattering angle on laser beam parameters is examined, and physical explanations of these features are given. The results are found to be consistent with the simulation results for a proposed vacuum laser acceleration scheme: the capture and acceleration scenario.

An amplitude modulation reflectometry system with fast-scanning microwave source is designed for edge density profile measurement on the HT-7 superconducting tokamak (R0=1.22 m, a=0.28 m, Bt: 1.8–2.3 T, plasma pulses of 1–20 s). The reflectometer launches microwave power from a very fast-scanning backward wave oscillator in 53–78 GHz to probe the plasma and receive the reflection by the density cutoff layer. It is an extraordinary mode reflectometer, which can measure the edge density profiles in normalized radius r/a from scrape-off layer up to 0.5 when Bt=2.2 T, Ne0=3×1019 m−3 in typical HT-7 operation parameters. The microwave amplitude modulation frequency is 200 MHz. A 2 MHz reference signal and the probing signal are obtained by mixing a 198 MHz local oscillator power with the demodulated microwave signals. Phase comparison is then accomplished at 2 MHz by I/Q phase detector. The scanning time over the full band of 53–78 GHz is about 0.5 ms. The reflectometry will fill in the space left by the five-...

With the EBIS beam and current setting in injector chain, the Au beam at RHIC injection is different from the Tandem beam. The transverse and longitudinal emittance of the EBIS Au beam at RHIC is presented in this note. For further improvements of EBIS and injector settings, this can be used to compare or to justify. Also, based on Run 2012 conditions, the luminosity optimization in RHIC is of interest to study.

The transmission spectrum of cold and thermal neutrons displays sudden intensity changes, known as Bragg edges, whose appearance is connected to the crystallographic structure of the investigated sample. However, many difficulties in interpreting and understanding the detected signal exist, in particular when results are evaluated quantitatively. We measured strain and texture properties of different samples utilizing the Bragg edge method on the CONRAD and VSANS instruments at Helmholtz Centre Berlin as well as on ENGIN-X at ISIS, UK. The different results will be compared and validated with conventional diffraction measurements and theoretical considerations. According to this, a Bragg edge neutron transmission simulation was developed to include instrument effects together with sample characteristics. Therefore, a neutron ray-tracing simulation package was applied to emulate the employed instruments in combination with the Bragg edge transmission technique. A new sample module has been created to realize energy-dependent transmission simulations based on neutron cross sections calculations. Towards the analysis of the conducted experiments the virtual sample features the expected strain and texture parameters. The results of the simulation are in good agreement with the experiments and will be discussed with regard to the prospects and limitations of this measurement method and the utilized instruments.

The present paper investigates the characteristics of the supersonic turbulent flow in a wavy channel by direct numerical simulations. The Mach number, based on the bulk velocity and sound speed at the wall, is 1.5 and the Reynolds number, based on the bulk velocity, the channel half‐width and the kinetic viscosity at the wall is 3 460. The wave amplitude to wavelength ratio is 0.05. To validate the numerical algorithms, a weak compressible flow at Mam = 0.33 is also simulated and the results agree well with available experimental measurements and results of DNS. The statistic quantities and flow structures for the supersonic flow are compared with those for the low Mach number case. It is found that, the statistic quantities profile for supersonic flow differs substantially from profile for the incompressible case as the appearance of the shock waves and their interaction with the turbulent flow field.

Beam‐gas collision created experimental background, i.e., singles, has affected heavy ion and polarized proton operations in Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The gas molecules in interaction region are mainly caused by the electron induced gas desorption, and the electrons are produced from the beam induced electron multipacting, or called electron cloud. The background has a dependence on the usual electron cloud related parameters, such as the bunch intensity, bunch spacing, and the solenoid field. With the RHIC upgrade plan, the experimental background may become a luminosity limiting factor. Mitigations are discussed.

During Run‐8, the Relativistic Heavy Ion Collider (RHIC) provided collisions of spin‐polarized proton beams at two interaction regions. Physics data were taken with vertical orientation of the beam polarization, which in the “Yellow” RHIC ring was significantly lower than in previous years. We present recent developments and improvements as well as the luminosity and polarization performance achieved during Run‐8, and we discuss possible causes of the not as high as previously achieved polarization performance of the “Yellow” ring.

With the significant beam intensity improvement in RHIC polarized proton run 2005 and run 2006, the emittance growth becomes a luminosity limiting factor. The beam emittance growth has a dependence on the dynamic pressure rise, which in RHIC proton runs is mainly caused by the electron cloud. The dependence of the emittance growth on other electron cloud related parameters is also identified. The beam instability is usually absent, and the emittance growth rate is much slower than the ones typically caused by the head-tail instability. It is suspected that the emittance growth is caused by the electron cloud below the instability threshold. A discussion follows.

The gold beam transverse emittance in Run 2007 was about 20% larger than in Run 2004. Since the gold beam transverse emittance was a dominant factor in terms of luminosity in deuteron-gold run 2003, it is of interest in deuteron-gold run 2008. Some studies are proposed.

The proton beam emittance growth in RHIC Run5 and Run6 has a dependence on the dynamic pressure rise, which is caused by the electron cloud and peaked at the end of the beam injection and early acceleration. At store, the electron cloud is not significant, it seems that the emittance growth is dominated by the beam-beam effect.

The influence of nonradiative recombination on the photoluminescence (PL) decay dynamics in GaInNAs/GaAs quantum wells is studied by time-resolved photoluminescence under various excitation intensities. It is found that the PL decay process strongly depends on the excitation intensity. In particular, under the moderate excitation levels the PL decay curves exhibit unusual nonexponential behavior and show a convex shape. By introducing a new parameter of the effective concentration of nonradiative recombination centers into a rate equation, the observed results are well simulated. The cw PL data further demonstrate the nonradiative recombination effect on the optical properties of GaInNAs/GaAs quantum wells. (c) 2006 American Institute of Physics.

This report describes a new heavy ion pre-injector for the Relativistic Heavy Ion Collider (RHIC) based on a high charge state Electron Beam Ion Source (EBIS), a Radio Frequency Quadrupole (RFQ) accelerator, and a short Linear accelerator (Linac). The highly successful development of an EBIS at Brookhaven National Laboratory (BNL) now makes it possible to replace the present pre-injector that is based on an electrostatic Tandem with a reliable, low maintenance Linac-based pre-injector. Linac-based preinjectors are presently used at most accelerator and collider facilities with the exception of RHIC, where the required gold beam intensities could only be met with a Tandem until the recent EBIS development. EBIS produces high charge state ions directly, eliminating the need for the two stripping foils presently used with the Tandem. Unstable stripping efficiencies of these foils are a significant source of luminosity degradation in RHIC. The high reliability and flexibility of the new Linac-based pre-injector will lead to increased integrated luminosity at RHIC and is an essential component for the long-term success of the RHIC facility. This new pre-injector, based on an EBIS, also has the potential for significant future intensity increases and can produce heavy ion beams of all species including uraniummore » beams and, as part of a future upgrade, might also be used to produce polarized {sup 3}He beams. These capabilities will be critical to the future luminosity upgrades and electron-ion collisions in RHIC. The proposed pre-injector system would also provide for a major enhancement in capability for the NASA Space Radiation Laboratory (NSRL), which utilizes heavy-ion beams from the RHIC complex. EBIS would allow for the acceleration of all important ion species for the NASA radiobiology program, such as, helium, argon, and neon which are unavailable with the present Tandem injector. In addition, the new system would allow for very rapid switching of ion species for NSRL experiments, reducing delays due to the interference with RHIC injection operations, and allowing enhanced mixed field radiation studies. The new RFQ and Linac that are used to accelerate beams from the EBIS to an energy sufficient for injection into the Booster are both very similar to existing devices already in operation at other facilities. Injection into the Booster will occur at the same location as the existing injection from the Tandem.« less

Electron cloud and ion desorption are currently intensity limit of several hadron machines in operation, and possibly of concern for several accelerators in construction and planning. In this summary, the background, the progress, and the working session discussion of this aspect are reported.

The RHIC warm section electron cloud is distinguished from normal short bunch electron cloud, observed in many machines, by the much longer bunch spacing and non‐uniform distribution in the ring. It is suspected that the beam halo scraping produced positive ions may help secondary electrons to stay longer. Local desorption leading to more residual gas being ionized by the beam may be important too. Anti‐grazing ridges are designed to counteract these mechanisms. This article reviews the RHIC warm section electron cloud, the beam scraping effect, and the test of anti‐grazing ridges.

The ion desorption has a long history of intensive studies by many physical societies. Recently, it has been found responsible to the intensity limitation of several low energy heavy ion accelerators, and it is also of concern for high energy hadron accelerators, such as RHIC, LHC, and GSI FAIR. This article reviews the relevant observations at RHIC.

In the gold operation of RHIC Run 2004, the experiment background of PHOBOS had limited the beam intensity, and hence the luminosity. This background was caused by the pressure rise at the beam rebucketing. In this note, the effect of the vertical orbit bump at the PHOBOS on the rebucketing pressure rise is reviewed. If proven effective, then it may be applied to the Run 2005 copper operation for luminosity improvement.

(Received 3 December 2003; published 2 March 2004)We describe a mechanism using clearing electrodes and solenoids to remove the electron cloud in theSpallation Neutron Source’s accumulator ring. Simulation indicates that strong multipacting couldhappen at median clearing fields. A similar phenomenon was reported in an experimental study at LosAlamos Laboratory’s Proton Storage Ring. A weak solenoid is proven to be a good remedy forsuppressing multipacting by confining electrons near the chamber wall’s surfaces. We investigatedthe clearing mechanism using both electrodes and solenoids.

Effects of the beam loss, ion and electron gas desorption on the RHIC vacuum pressure bump have been reviewed. The beam loss and ion desorption are probably not the dominant factors in the RHIC vacuum problem. On the other hand, electron desorption, given the electron multipacting, can cause serious vacuum problem. In general, the electron multipacting was not predicted for the RHIC according to the present understanding of the mechanism. However, beam loss created ions can extend electron lifetime during the bunch gap, and electron multipacting becomes possible at the RHIC. Also, the pressure rise in the RHIC Gold beam run was much worse than the usual electron cloud induced vacuum pressure rise, which was observed in many machines. One possibility is that the beam loss created ions have raised the electron density saturation limit and, therefore, contributed to further pressure rise. Some complications in diagnostics of electron multipacting by coherent tune shift in bunches will be discussed. Electron collection may indicate the coincidence between the electron multipacting and the pressure rise. It also can help to determine the electron density.

The RHIC resistive wall coupled bunch instability is reviewed for gold and proton beams at the injection, top energy, and storage. The gold beam around the transition is also discussed. The strongest resistive wall coupled bunch instabilities are at the injection, for both gold and proton beams. With proper set-up of the machine chromaticity, however, most of these instabilities can be eliminated, or significantly reduced.

One of the most important factors in the electron cloud build-up is the secondary electron (SE) survival in the bunch gap. In addition to the energy distribution, SE also has an angular distribution. In this note, the SE survival in the bunch gap is modified to include the SE angular distribution. It is shown that with this effect, the survival rate is substantially extended. Some related issues in concerns of the RHIC electron cloud are also discussed. For 120 bunches in the RHIC ring, the electron cloud has little chance to build-up. However, for more than 120 bunches, the chance becomes large.

A proposed new heavy ion preinjector for RHIC is described. The progress made at BNL on the development of an Electron Beam Ion Source (EBIS) has increased our confidence that one can build a preinjector meeting RHIC requirements using an EBIS producing intermediate charge state heavy ions. A new RFQ and Linac will be required to accelerate beams from this source to an energy sufficient for injection into the AGS Booster. These are both straightforward devices, very similar to ones already in operation at other laboratories. Injection into the Booster will occur at the same location as the existing heavy ion injection from the Tandem Van de Graaff.

Brookhaven National Laboratory, Upton, New York 11973~Received 24 August 1999; published 15 March 2000!Secondary-electron yields were investigated for 28-MeV protons, 126-MeV oxygen-ions, and 182-MeVgold ions incident on 304 stainless-steel surfaces. The dependence on the incidence angle was studied in detail,and a system was developed which allows accurate measurements to be performed over a wide angular rangeextending to nearly grazing collisions. Electron yield estimates of interest for future accelerator applications aredeveloped for 1-GeV protons, and the possible mitigation of deleterious effects by using serrated rather thanflat surfaces is analyzed.PACS number~s!: 79.20.Rf, 34.90.1q.I. INTRODUCTION

The impedance and beam instability issues of the SNS storage ring is reviewed, and the effort toward solutions at the BNL is reported. Some unsettled issues will be raised, indicating the direction of planned works.

The impedance working group was charged to reply to the following 8 questions relevant to the design of high-intensity proton machines such as the SNS or the FNAL driver. These questions were first discussed one by one in the whole group, then each ne of them assigned to one member to summarize. On the lst morning these contributions were publicly read, re-discussed and re-written where required—hence they are not the opinion of a particular person, but rather the averaged opinion of all members of the working group. (AIP)

In the Spallation Neutron Source (SNS) storage ring, the machine cycle is dominated by the multiturn injection. Therefore, the beam loading issues are quite different from the conventional beam loading. The evolution of the particle distribution due to beam loading needs attention. If not corrected, the beam loading effect will lead to a bunch to bucket mismatch in the injection, causing bunch leakage into the interbunch gap. The bunch leakage will increase the extraction beam loss, and lower the e-p instability threshold. On the other hand, the control of bunch leakage necessitates the beam loading factor to be small. Therefore, beam stabilities associated with the beam loading automatically satisfied. In this article, the simulation of the SNS beam loading effect (together with the space charge effect) will be presented. Same method has been applied to the PSR, where some beam loading effect is shown.

For high intensity proton runs, emittance blow-up is often accompanied with nontrivial beam loss. It has been suggested [10] that the largest portion of the Booster to AGS (BTA) transfer loss is located in the AGS end. It was also found that the space charge tune spread, immediately after the bunched beam enters the AGS ring, is large enough for the envelope resonance and emittance blow-up [11]. It was decided, in 1997 high intensity proton run, to raise the BTA transfer kinetic energy from 1.54 GeV to 1.9 GeV. The transfer efficiency was increased, as expected. The beam emittance in the AGS ring did not increase, even the AGS acceptance was enlarged [12], which is probably because of the reduced space charge tune spread.