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Third generation high brightness light sources are designed to have low emittance and high current beams, which contribute to higher beam loss rates that will be compensated by Top-Off injection. Shielding for these higher loss rates will be critical to protect the projected higher occupancy factors for the users. Top-Off injection requires a full energy injector, which will demand greater consideration of the potential abnormal beam miss-steering and localized losses that could occur. The high energy electron injection beam produces significantly higher neutron component dose to the experimental floor than a lower energy beam injection and ramped operations. Minimizing this dose will require adequate knowledge of where the miss-steered beam can occur and sufficient EM shielding close to the loss point, in order to attenuate the energy of the particles in the EM shower below the neutron production threshold (

Third generation high brightness light sources are designed to have low emittance and high current beams, which contribute to higher beam loss rates that will be compensated by Top-Off injection. Shielding for these higher loss rates will be critical to protect the projected higher occupancy factors for the users. Top-Off injection requires a full energy injector, which will demand greater consideration of the potential abnormal beam miss-steering and localized losses that could occur. The high energy electron injection beam produce significantly higher neutron component dose to the experimental floor than lower energy injection and ramped operations. High energy neutrons produced in the forward direction from thin target beam losses are a major component of the dose rate outside the shield walls of the tunnel. The convention has been to provide thicker 90° ratchet walls to reduce this dose to the beam line users. We present an alternate circular shield wall design, which naturally and cost effectively increases the path length for this forward radiation in the shield wall and thereby substantially decreasing the dose rate for these beam losses. This shield wall design will greatly reduce the dose rate to the users working near the front end optical components but will challenge the beam line designers to effectively utilize the longer length of beam line penetration in the shield wall. Additional advantages of the circular shield wall tunnel are that it's simpler to construct, allows greater access to the insertion devices and the upstream in tunnel beam line components, as well as reducing the volume of concrete and therefore the cost of the shield wall.

One of the most challenging issues for accelerator operations is why and where the beam is lost. This is a major concern for radiation protection at facilities with a large user base, since uncontrolled beam losses could potentially result in unwanted radiation exposures to occupied areas. For NSLS-II the tunnel radiation shield wall has increased attenuation over two lattice cells after the injection region, to shield for the possibility of higher injection losses. This raised the concern over exceeding radiation exposure limits in lesser shielded regions, if similar losses occur in those regions. To address this issue a beam loss control system was designed to limit most beam losses to the more heavily shielded (injection) region. A beam loss monitor system was also designed to verify the fraction of the beam lost in that region and thereby ensure lower levels of exposure around the rest of the ring. The design of these beam loss control and monitoring systems and the NSLS-II operational experience is presented.

The National Synchrotron Light Source II is a third generation light source, which was constructed at Brookhaven National Laboratory. This project includes a highly-optimized 3 GeV electron storage ring, linac preinjector, and full-energy synchrotron injector. Budker Institute of Nuclear Physics built and delivered the booster for NSLS-II. The commissioning of the booster was successfully completed. This paper reviews fulfilled work by participants.

The National Synchrotron Light Source II at Brookhaven National Lab is a third-generation synchrotron radiation facility that has been commissioned in 2014. The facility is based on a 3 GeV electron storage ring, which will circulate 500 mA of beam current at 1 nm rad horizontal emittance. The storage ring is 792 meters in circumference and will accommodate more than 60 beamlines in the final built-out. The beamline sources range from insertion-devices located in straight sections, bending magnets or three-pole-wigglers configured in multiple branches. The NSLS-II storage ring commissioning was successfully completed in July 2014 and the facility delivered the first user light on October 23, 2014. Currently the storage ring reached 300 mA beam current and achieved 1 nm rad of horizontal emittance with 3 sets of Damping Wigglers. At this point six NSLS-II project beamlines are routinely taking photons with beam current at 150 mA. This paper reviews the NSLS-II accelerator design and commissioning experience.

We report the observation of multiparticle coherent emission in the very far infrared from bunched electrons in an electron storage ring. The emission occurs in quasi-periodic bursts, and only when the electron beam current exceeds a threshold value, suggesting an instability-driven modulation of the electron bunch density. For the operating conditions reported, the spectral content of the coherent emission is peaked near a wavelength of 7 mm. This wavelength is much shorter than the nominal electron bunch length, indicating the presence of a density modulation within the bunch.

The lifetime in the NSLS VUV ring is limited by intra-bunch scattering (Touschek scattering). A second RF cavity was added to lengthen the electron bunch, thereby reducing the Touschek loss rate. Initially, the cavity was operated in a “passive” mode. This provided significant lifetime enhancement at higher currents, but also created larger than normal bunch length variations over the range of operating currents. In October 1993, a generator was added to the system to provide greater bunch length control and added lifetime at all operating currents. Recent studies have also been done on bunch shortening with encouraging results. This paper provides a summary of the system, including results from studies and operations.

The pulsed nature or ‘‘time structure’’ of synchrotron radiation from electron storage rings is used to measure the kinetics of the decay of electronically excited states and is particularly useful because the wavelength of excitation can be chosen at will. However, changes in the length of the pulses of radiation from a storage ring resulting from the gradual decrease of current circulating in the ring during the course of a ‘‘fill’’ limit the duration of data collection, and hence photometric sensitivity. A fourth‐harmonic cavity that was recently added to the vacuum ultraviolet (VUV) storage ring at the National Synchrotron Light Source slows the loss of current during a fill, and thus increases the total number of photons produced. When operated in a passive (unpowered) mode, however, the fourth‐harmonic cavity increases both the average width of the photon pulses and the changes in width that occur during a fill, thus reducing the usefulness of the VUV ring in timing experiments. We demonstrate that ...

A series of beam studies was recently done at NSLS VUV ring to better understand the beam lifetime. Lifetime is dominated by Touschek effect, and both beam measurements and simulations show that the dispersion and small physical aperture limits the survival of the particles in the Touschek scattering. The lifetime is significantly limited by large betachi at injection septum.

NSLS-II at Brookhaven National Laboratory is a new third-generation storage ring light source, whose construction is on the verge of being approved by DOE. When completed, NSLS-II with its ability to provide users with a wide range of spectrum, ranging from IR to ultra-high brightness hard X-ray beams will replace the existing two (20+ years old) NSLS light sources. While presenting an overview of the NSLS-II accelerator system, this paper focuses on the strategy and development of a novel

The National Synchrotron Light Source is performing R&D of a new 3 GeV electron storage ring to be used for the facility upgrade [1]. To satisfy the demands for the brightness and stability of the future light source a state-of-the-art diagnostics system is a necessity. We present our preliminary design with focus on the requirements for instrumentation and technical solutions to achieve them.

The National Synchrotron Light Source at BNL was the first dedicated light source facility and it has now operated for more than 20 years. During this time the user community has grown to more than 2400 users annually. To insure that this vibrant user community has access to the highest quality photon beams, the NSLS is pursuing the design of a new ultra-high brightness (∼1021) electron storage ring, tailored to the 0.3-20 KeV photon energy range. We present our preliminary design and review the critical accelerator physics design issues.

State of the art low emittance light source lattices, require small bend angle dipole magnets and strong quadrupoles. This in turn creates large chromaticity and small value of dispersion in the lattice. To counter the high linear chromaticity, strong sextupoles are required which limit the dynamic aperture. Traditional methods for expanding the dynamic aperture use harmonic sextupoles to counter the tune shift with amplitude. This has been successful up to now, but is non-deterministic and limited as the sextupole strength increases, driving higher order nonlinearities. We have taken a different approach that makes use of the tune flexibility of a TBA lattice to minimize the lowest order nonlinearities, freeing the harmonic sextupoles to counter the higher order nonlinearities. This procedure is being used to improve the nonlinear dynamics of the NSLS-II lattice.

Bursts of coherent radiation are observed from the NSLS VUV ring near a wavelength of 7 mm. The bursts occur when the electron beam current (I) exceeds a threshold value (I/sub th/), which itself varies with ring operating conditions. Beyond threshold, the average intensity of the emission is found to increase as (I-I/sub th/)/sup 2/. With other parameters held nearly constant, the threshold current value is found to increase quadratically with synchrotron frequency, indicating a linear dependence on momentum compaction. It is believed that the coherent emission is a consequence of micro-bunching of the electron beam due to the microwave instability.

Single-bunch current limits were measured for the low-emittance tunes in PEP (Positron-Electron Project) and found to be limited by the transverse mode coupling instability to less than 2.5 mA for RF voltages up to 10.5 MV. The horizontal and vertical transverse impedances appear to be Z/sub x/=1.05 M Omega /m and Z/sub y/=4.2 M Omega /m, respectively, assuming that the average beta functions are equal to those in the RF cavities. At the maximum single-bunch currents, considerable coherent motion of the bunch was observed, probably resulting from the large wakefields caused by residual closed-orbit distortions. The multiple-bunch operation showed large longitudinal and transverse coherent oscillations when bunches were filled to the single-bunch limit. Total currents in excess of 30 mA were obtained by filling widely spaced bunches to less than 1/3 of the single bunch limit. With this method the coherent beam motion was quite small in all dimensions. The results obtained indicate that the lower momentum compaction factor and large beta function variations of the low-emittance lattice (a common feature of all proposed high-energy radiation sources) contribute to enhanced collective effects, limiting the early achievable beam intensity to less than the desired 100 mA. >

The authors summarize the results of a task group that studied the vacuum-chamber thermal protection problem for the Advanced Photon Source (APS). It is pointed out that the high-power-density photon beams in the proposed next generation of synchrotron light sources introduce new risks to the integrity of the ring vacuum chambers. In these machines, power densities are such that vacuum chamber cooling is unable to reduce the risk of rapid penetration of the chamber. Two general methods have been studied for providing passive protection of the vacuum chamber. These include limiting of the power supplies that could missteer the beam and insertion of limiting apertures using beam scrapers that prevent the photon beam from illuminating the vacuum chamber. The APS uses the former during construction and will be able to implement the latter at a future time if the potential risk to the chamber warrants additional protection. >

The individual quadrupole gradients, undulator focusing, beam position monitor (BPM) gains, and orbit steering magnet calibrations in the NSLS VUV Ring were determined by analyzing the measured orbit response matrix with the computer code LOCO (Linear Optics from Closed Orbits). The measured orbit response matrix is the change in orbit at the BPMs with changes in steering magnet excitation. The analysis showed beta function distortions of /spl plusmn/35% and /spl plusmn/25% horizontally and vertically. The design periodicity of the optics was restored by adjusting the quadrupole gradients to restore the periodicity of the response matrix. This lead to an increase of about 18 percent in the beam lifetime at 500 mA with a slight (3 and 7 percent) decrease in both the horizontal and vertical electron emittances as determined from the beam sizes measured using a synchrotron light monitor.

Studies have demonstrated that an 862 MHz RF cavity higher order mode (HOM) causes longitudinal coupled-bunch (LCB) dipole and quadrupole oscillations at specific RF tuner positions with associated increases in longitudinal, horizontal, and vertical electron beam sizes. In the XRF2 cavity a reconfiguration of damping antennae removed the 862 MHz HOM. High speed I(t) stripline measurements showed that a strong quadrupole oscillation resulted when the HOM was induced in the XRF3 cavity. The reason that a symmetric six bunch pattern was found to be effective in damping this mode is explained.

A "fast" beam position monitor capable of measuring the position of a circulating bunch in the VUV electron storage ring is presently under development. This monitor will collect data at a rate of about 6/spl times/10/sup 6/ measurements/sec per channel. We describe the design and operation of the monitor and the processing of the acquired data.

We describe a major paradygm shift in in the approach to the production of synchrotron radiation This change will considerably improve the scientific capabilities of synchrotron light sources. We introduce plans for an upgrade of the National Synchrotron Light Source (NSLS). This upgrade will be based on the Photoinjected Energy Recovering Linac (PERL). This machine emerges from the union of two technologies, the laser-photocathode RF gun (photoinjector) and superconducting linear accelerators with beam energy recovery (Energy Recovering Linac). The upgrade will bring the NSLS users many new insertion device beam lines, brightness greater than 3rd generation light-source's and ultra-short pulse capabilities, not possible with storage ring light sources.

Observations of coherent infrared (IR) light emissions from /spl sim/30 cm long electron bunches at the NSLS VUV ring have been reported. The emissions occurred above some current threshold and had a maximum spectral content near 42 GHz, leading to speculations that they were due to a longitudinal instability creating a /spl sim/7 mm modulation of the bunch density. To check this experimentally we performed streak camera measurements recording a large number of beam profiles taken both during and between the coherent emission bursts. In the course of our studies we have directly proven that the longitudinal beam density indeed experiences a significant modulation when coherent emission bursts occur.

The synchrotron radiation emitted from the NSLS VUV ring is found to contain significant spectral structure at long wavelengths (/spl lambda/ > 0.5mm), suggesting multiple beam interference effects. A predominant pattern occurs as a result of direct radiation interfering with radiation reflected from the curved outer wall of the electron beam dipole chambers. This structure appears for both normal incoherent synchrotron radiation emission and coherent emission, the latter resulting from an instability-driven density modulation within the electron bunch.

Coherent synchrotron radiation from the NSLS VUV ring has been detected and partially characterized. The observations have been performed at the new far infrared beamline U12IR. The coherent radiation is peaked near a wavelength of 7mm and occurs in short duration bursts. The bursts occur only when the electron beam current (I) exceeds a threshold value (I{sub th}), which itself varies with ring operating conditions. Beyond threshold, the average intensity of the emission is found to increase as (I-I{sub th}). The coherent emission implies micro-bunching of the electron beam due to a longitudinal instability.

The authors calculate the transient voltage induced in a radio frequency cavity by the injection of a relativistic bunched beam into a circular accelerator. A simplified model of the beam induced voltage, using a single tone current signal, is generated and compared with the voltage induced by a more realistic model of a point-like bunched beam. The high Q limit of the bunched beam model is shown to be related simply to the simplified model. Both models are shown to induce voltages at the resonant frequency {omega}{sub r} of the cavity and at an integer multiple of the bunch revolution frequency (i.e. the accelerating frequency for powered cavity operation) h{omega}{sub {omicron}}. The presence of two nearby frequencies in the cavity leads to a modulation of the carrier wave exp(h{omega}{sub {omicron}}t). A special emphasis is placed in this paper on studying the modulation function. These models prove useful for computing the transient voltage induced in superconducting rf cavities, which was the motivation behind this research. The modulation of the transient cavity voltage discussed in this paper is the physical basis of the recently observed and explained new kinds of longitudinal rigid dipole mode which differs from the conventional Robinson mode.

Data on diffractive ππ scattering in the reactions π + p → π + π 0 p, π + p → π + π + n and π + n → π + π − p are presented and discussed in terms of a factorized double-exchange model involving OPE and Pomeranchuk plus exchange-degenerate ϱ, f contributions.

We have observed an I =1 resonance decaying into π − η , in the reaction K − n→ Λπ − η , (η decaying into neutrals), at a mass of 0.98±0.01 GeV with a Γ of 60±30 GeV. The production cross section is (15±3) μ b.

We have measured the production and decay angular distributions of the reaction π+p→πOΔ++ at 13.1 GeV/c incident momentum. For −t > 0.1 (GeV/c)2 the data is well described by M1 ϱ-exchange models, the best results being obtained from a weak cut model with a wrong signature nonsense zero. For −t < 0.1 (GeV/c)2 there is evidence for the existence of other exchange mechanisms.

During the past year the authors have conducted a series of tests on the LBL prototype 1-2 GHz and 2-4 GHz stochastic cooling electrodes at Argonne Chemistry Division's electron LINAC. The electrode geometries are illustrated in Figures 1 and 2. Using the test electron beam, the 16-loop arrays were operated as beam current pickups and their sum and difference mode coupling impedances were measured.

Experimental studies have been performed on the PEP storage ring run at 7.1 GeV in the low-emittance mode. The motivation for this work is to explore the capability of PEP as a dedicated synchrotron radiation source. The long straight sections and low emittance available at PEP make its use for this purpose very attractive, and would produce a source of very high brightness x-ray beams for the scientific community. During the studies, single-bunch current limitations were measured as a function of RF voltage. Thresholds were in the range of 1-2 mA per bunch, which is lower than expected based upon transverse impedance estimates from the PEP collider optics. An increase in threshold current by about 50% was realized by modifying the optics to reduce the magnitude of the horizontal beta functions in the straight sections and at the RF locations. The reason for the lower than expected thresholds has not been resolved. To permit its effective use as a synchrotron radiation source, a beam current of 50-100 mA is desired, which will require that PEP be run in the multibunch mode. Our goal in this study was to investigate the multibunch operating mode to ascertain that reasonable beam intensities weremore » possible. By utilizing many low intensity (0.1-0.25 mA) bunches, stable and reproducible currents of 15-20 mA were achieved. In an attempt to improve this value, one of the idle RF stations was operated in a tune-splitting mode, with only partial success. By adjusting the tuner positions of the unused RF stations, up to 33 mA was ultimately stored, albeit with some evidence for instability. Possible approaches to improving the multibunch stability are discussed.« less

The discussion of the status of the Z$sub 1$* covers the substantial improvement in the differential cross section data for K$sup +$p elastic scattering and an improved energy dependent analysis based on the K-matrix formalism, which in order to fit the data, requires a P/sub $sup 3$/$sub 2$/- resonance pole. (JFP)

Beams from high energy accelerators are constrained to have very small emittances. To be useful for large volume proton therapy they must be spread out in space to illuminate the entrance portal uniformly. This could be done by letting the beam diverge (either from its own angular spread or by defocusing it with quadrupoles) and then collimating the beam to a uniformity of the spatial density of particles to yield the required dose uniformity. However, this technique is very inefficient on the use of incident beam. Although scanning the beam magnetically could yield high efficiency and highly uniform dose, considerable development would be necessary to develop the technique and its required reliability. The use of multiple scattering foils simplifies the treatment planning and verification, since the size and uniformity are determined only by the properties of the materials and not by the variables (current, temperature, hysteresis, etc.) in magnetic scanning devices.

To address the growing needs of the NSLS user community we are aggressively pursuing R&D towards a facility upgrade. The present goals are a 3 GeV ultra-low emittance storage ring, tailored to the 5-20 keV photon energy range, that will triple the present NSLS ID capacity, and provide three orders of magnitude increase in brightness over the present brightest NSLS beamlines. To achieve these goals we propose a 24 period TBA lattice, with extensive use of super-conducting small gap undulators. This paper reviews our preliminary design and the key accelerator physics issues.