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The NSLS-II storage ring is designed to operate with superconducting RF-cavities with the aim to store an average current of 500 mA distributed in 1080 bunches, with a gap in the uniform filling for ion clearing. At the early stage of the commissioning (phase 1), characterized by a bare lattice without damping wigglers and without Landau cavities, a normal conducting 7-cell PETRA-III RF-cavity structure has been installed with the goal to store an average current of 25 mA. In this paper we discuss our analysis of coupled-bunch instabilities driven by the Higher Order Modes (HOMs) of the 7-cell PETRA-III RF-cavity. As a cure of the instabilities, we apply a well-known scheme based on a proper detuning of the HOMs frequencies based upon cavity temperature change, and the use of the beneficial effect of the slow head–tail damping at positive chromaticity to increase the transverse coupled-bunch instability thresholds. In addition, we discuss measurements of coupled-bunch instabilities observed during the phase 1 commissioning of the NSLS-II storage ring. In our analysis we rely, in the longitudinal case, on the theory of coupled-bunch instability for uniform fillings, while in the transverse case we complement our studies with numerical simulations with OASIS , a novel parallel particle tracking code for self-consistent simulations of collective effects driven by short and long-range wakefields.

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.

Recently strong modulation of the electron bunch longitudinal phase space was obtained in the DUVFEL accelerator at NSLS. The chirped beam energy spectra exhibit a spiky structure with a subpicosecond spike separation. A model based on the longitudinal space-charge effect has been suggested as an explanation of the observed effect. For characterization of the structure and comparison with the model we performed several experiments. In this paper we present experimental data and discuss them in relation to the model.

The DUV-FEL facility has been in operation in the High Gain Harmonic Generation (HGHG) mode producing a 266-nm output from 177-MeV electrons for 1 year. In this paper, we present preliminary results of the Chirped Pulse Amplification (CPA) of the HGHG radiation. In the normal HGHG process, a 1-ps electron beam is seeded by a chirped 9 ps long, 800-nm Ti:Sapphire laser. The electron beam sees only a narrow fraction of the seed laser bandwidth. However, in the CPA case, the seed laser pulse length is reduced to 1 ps, and the electron beam sees the full bandwidth. We introduce an energy chirp on the electron beam to match the chirp of the seed pulse, enabling the resonant condition for the whole beam. We present measurements of the spectrum bandwidth for various chirp conditions.

The Deep Ultra Violet FEL (DUV-FEL) experiment is being commissioned in the Source Development Laboratory at NSLS in Brookhaven National Laboratory. The goal of the project is to produce coherent radiation below 100 nm wavelength using High-Gain Harmonic Generation utilizing a seed laser. As a first step of this experiment, self-amplified spontaneous emission (SASE) has been achieved at 400 and 266 nm with electron beam energies at 140 and 171.7 MeV. As an intermediate stage of the experiment, direct seeding with the 266 nm laser also has been accomplished. We report the measurements of the SASE and direct seeding. We measure the FEL properties for various electron beam conditions and discuss the performance of the FEL.

The Deep Ultra-Violet Free Electron Laser (DUVFEL) at the National Synchrotron Light Source consists of a 5 MeV photoinjector, a 200 MeV S-band linear accelerator, a four-magnet chicane compressor and a 10 m wiggler with a 3.9 cm period. The commissioning of the SDL accelerator was completed recently and it is routinely producing a high-quality electron beam with a peak current of ∼400 A and a normalised emittance of 3–4 mm mrad. The first SASE lasing of the DUV FEL has been demonstrated at both 266 and 400 nm. The gain length of the SASE experiments was measured to be 66 cm in both cases and up to 20 nJ per pulse was obtained. A laser seeded FEL at 266 nm is in the very early stages of commissioning and amplification of the laser seed has been observed. The goal of the seeded laser FEL is to saturate the FEL and thereby generate sufficient third harmonic at 89 nm for experimental applications. Here we report the observation and measurements of SASE at 400 and 266 nm and the first results of seeded FEL.

During the commissioning phase 1 of the NSLS-II stor- age ring an option underconsiderationis to install a normal conducting 7-cell PETRA-III cavity structure with a stored average current of 25mA. The aim of this paper is to inves- tigate the effect of coupled-bunch instabilities that may be driven by the Higher Order Modes (HOMs) of the 7-cell PETRA-III cavity.

Beam loading in traveling-wave linear accelerating structures leads to unacceptable spread of particle energies across an extended train of bunched particles due to beam-induced field and dispersion. Methods for modulating the rf power driving linacs are effective at reducing energy spread, but for general linacs do not have a clear analytic foundation. We report here methods for calculating how to modulate the rf drive in arbitrarily nonuniform traveling-wave linacs within the convective-transport (power-diffusion) model that results in no additional energy spread due to beam loading (but not dispersion). Varying group velocity, loss factor, and cell quality factor within a structure, and nonzero particle velocity, are handled.

Beam intensity is a key performance parameter for particle accelerators. Modern high-performance storage rings demand injectors that can deliver large currents per injection cycle, which translates to an increase in machine size and consumed power. Therefore, it is justifiable to look for ways to increase the injector’s performance while minimizing the size increase. We have investigated a number of ways to accumulate charge in a booster synchrotron and applied one of them to the NSLS-II booster. We have designed a scheme to transversely stack two bunch trains from the injector linac in the booster. In this paper we discuss this stacking scheme. The relevant booster dynamics are studied. The charge transport efficiency of the stacking scheme is studied in detail at injection and through a full booster ramp. Pulsed magnet requirements for the injection system and methods to achieve them are discussed. We show that the charge transport efficiency of the stacking scheme is similar to a single bunch train in the booster. This has become a critical design feature of the NSLS-II booster.

In this Letter we report the first experimental characterization of superradiance in a single-pass high-gain free-electron laser (FEL) seeded by a 150 femtosecond (FWHM) Ti:sapphire laser. The nonlinear energy gain after an exponential gain regime was observed. We also measured the evolution of the longitudinal phase space in both the exponential and superradiant regimes. The output FEL pulse duration was measured to be as short as 81 fs, a roughly 50% reduction compared to the input seed laser. The temporal distribution of the FEL radiation as predicted by a numerical simulation was experimentally verified for the first time.

CESR-B type superconducting cavities are under consideration for acceleration of the electron beam in the 3 GeV NSLS-II storage ring. In this paper we present detailed investigation of longitudinal and transverse impedance of CESR-B cavity and transitions. Ferrite material is included in impedance analysis. Its effect on short range wakepotential has been studied using GdfidL code. The summary results of loss factors and kick factors are presented for a 3 mm rms bunch length.

The NSLS-II light source which is a proposed facility to be built at Brookhaven National Laboratory utilizes two synchrotron accelerator rings: the booster and the storage ring (SR). Designing the NSLS-II injector we considered two options for the booster layout, where the rings either a) share the same tunnel, but placed at different horizontal planes or b) booster is located in a separate building. The booster which accepts beam from the linac, accelerates the electron beam to an energy of 3.0 GeV and the beam is extracted to the booster to storage ring (BtS) transport line which transports the beam and injects it into the SR ring. The design procedure for each of the two options of the BtS line and other details about the optics and the magnetic elements of the line are presented in this paper.

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.

Physical review accelerators and beams 8(1), 010701 (2005). doi:10.1103/PhysRevSTAB.8.010701, Published by American Physical Society, College Park, MD

The linac at the NSLS Source Development Lab (SDL) provides a high brightness electron beam for the DUV-FEL project with subpicosecond bunch length and several hundred Amperes peak current by means of a photoinjector and a magnetic bunch compressor. Previous diagnostics of the longitudinal bunch dynamics relied on the rf zero-phasing method and measurements of CTR spectra. In order to have a fast and nonintercepting longitudinal diagnostic available, the electro-optic measurement technique has been implemented with its major component, a synchronized 100 fs Ti:sapphire laser coaligned with the electron beam, already in place as a seed for the FEL. The theoretical temporal resolution for a 100 /spl mu/m thick ZnTe crystal is limited to about 200 fs and the signal contrast to more than 1%. We present preliminary results of multishot scanning measurements and the single-shot diagnostics of the bunch shape as well as its application as a rf-laser jitter monitor.

A new RF control system was designed and implemented to support short pulse High Gain Harmonic Generation (HGHG) experiments, which require subpicosecond synchronization between the laser and the accelerating RF fields. This control system consists of a 81 MHz crystal oscillator to drive both the Ti::Sapphire laser and a 2856 MHz synthesizer, direct vector modulators that control the amplitude and phase of the klystron drive and vector de-modulators for amplitude and phase measurement. RF and electron beam based measurement results of the RF to laser jitter are presented as well as experimental results of synthesizing the RF directly from the 81.6 MHz pump laser pulse train.

A 5 GeV superconducting radiofrequency (SCRF) linac for the dual application of FEL driver and top-off injector for a storage ring is described. Starting from the FEL drive beam requirements of subpicosecond bunch lengths and kiloamp peak current the choice of frequency, gradient and operating modes of the linac are presented. Magnetic optics and RF system descriptions follow to provide the specified beam parameters. Accelerator design issues are identified for future studies.

Saturation of a high-gain harmonic-generation free-electron laser (HGHG-FEL) at 266 nm has been accomplished at the Brookhaven National Laboratory/Deep Ultra Violet Free Electron Laser Facility (BNL/DUV-FEL) by seeding with an 800 nm Ti:sapphire laser. We describe the diagnostics used to characterize the electron beam and the FEL output. Analytic and simulation calculations of the HGHG output are presented and compared with the experimental data. We also discuss the chirped pulse amplification of a frequency chirped seed by an energy chirped electron beam. The third harmonic at 88 nm accompanying the 266 nm fundamental has been used in an ion pair imaging experiment in chemistry, the first application of the BNL/DUV-FEL.

The Deep Ultra Violet Free Electron Laser (DUV-FEL) experiment has reached a milestone by saturating the Free Electron Laser using High Gain Harmonic Generation (HGHG) method in the Source Development Laboratory (SDL) at NSLS. It utilizes the 10 m long, 3.9 cm period NISUS wiggler. The goal of the project is to produce radiation at a wavelength less than 100 nm, utilizing the HGHG method. HGHG at 266 nm has been accomplished by seeding with the 800 nm Ti:Sapphire laser and observed saturation. The third harmonic at 88 nm accompanying the 266 nm is being used in an ion pair imaging experiment in chemistry. We discuss the measurement of energy, gain, spectrum, and pulse length of the FEL output. We also describe the diagnostics used for operating the FEL.

The performance and future upgrade of the XUV at the Brookhaven DUV-FEL facility are presented in this report. The High Gain Harmonic Generation (HGHG) Free Electron Laser (FEL) at the DUV-FEL now routinely produces fully coherent 266 nm radiation with the 800 nm seed, and the output energy of the HGHG is about 100 uJ with 1 ps pulse duration (FWHM) [1], The first three harmonics of the HGHG from the nonlinear harmonic generation process were experimented characterized. The third harmonic (89 nm, 14 eV) of the HGHG has been explored for chemical science applications [2]. To further expand the DUV-FEL user base and explore its unique potential, it is proposed that the DUV-FEL to be upgraded to produce XUV (< 100 nm) at the HGHG fundamental. Several options are now under consideration to upgrade the DUV-FEL for XUV radiation generation; which including the electron beam energy upgrade to 300 MeV and installing the shorter period VISA undulator. PACS: PACS codes: 42.72.Bj, 41.60.Cr, 41.60-m

We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti:sapphire laser has been used to produce saturated amplified radiation at the 266 nm third harmonic. The results confirm the predictions for HGHG FEL operation: stable central wavelength, narrow bandwidth, and small pulse-energy fluctuation.

The design of a 700 MeV superconducting compact electron storage ring for applied X-ray lithography is in its final stage. This succeeds a 200 MeV warm dipole model constructed and now in operation at Brookhaven National Laboratory (BNL). RF cavities and systems in both machines are discussed. The authors present cavity design parameters, construction, and the kind of mode suppression as well as the type of tuner and input window to provide 300 kV of accelerating voltage at 211.54 MHz. A 65 kW, RF power source is described. >

In the National Synchrotron Light Source (NSLS) Vacuum Ultraviolet (VUV) ring, a beam instability occurred as a function of cavity tuner position, restricting the operating range of the tuner and requiring the cavity to operate at an elevated temperature to compensate. The cavity mode responsible for the instability was diagnosed and subsequently damped with a tuned probe terminated in 50 Omega . The instability was cured, and has not been observed up to the design current of 1-A stored beam. >

The RHIC Accelerating System runs at 26.7 MHz and is required to have an operating range of 85 kHz during the acceleration cycle. Since it also must provide sufficient range to cover manufacturing errors and temperature variation, a requirement of 300 kHz has been specified. A mechanical approach acting on the cavity accelerating gap has been chosen for financial reasons over a ferrite approach. A prototype has been constructed and fully tested on the existing test cavity, using the tuning loop feedback circuitry developed for this task. Results from both the loop response and the power tests of the prototype indicate that this design will successfully meet the performance requirements for the RHIC Accelerating Cavity.

The RHIC RF systems must capture the injected beam, accelerate it through transition to top energy, shorten the bunches prior to rebucketing, and store the beam for 10 hours in the presence of strong intra-beam scattering. These different functions are met by three independent systems. An accelerating system at 26.7 Mhz (h=342), a storage system at 196.1 MHz (h=2508), and a wideband system for the damping of injection errors.

The accelerating system for RHIC operates at 26.7 MHz (h=342) and must capture the injected beam, accelerate it to top energy, and shorten the bunches prior to rebucketing into the storage (h=2508) system. These different functions set the design parameters of the cavity. The frequency of 26.7 MHz has been chosen in order to provide large enough buckets to capture the injected beam from the AGS and a large linear region for debunching during a bunch rotation at top energy. Provision of the large linear region also dictates the voltage requirement of 400 kV per cavity. The cavity must be tuned /spl sim/90 kHz to compensate for the change in speed of the gold beam.

The 28 MHz accelerating system consists of a quarter wave cavity driven by an inductively coupled 100 kW tetrode amplifer and 1 kW solid state driver amplifer. 40 dB of RF feedback closed around the cavity and amplifiers reduces small perturbations within the loop by a factor of 100, and reduces the time required to shift the phase at transition by a factor of 10, limited by the saturation of the drive chain. The cavity is tuned over a 200 kHz range by a mechanical tuner which varies the gap capacitance. Broadband HOM damping is provided by two orthogonal loop coupled high pass filters. Design parameters and commissioning results are presented.

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.

The DUVFEL electron linac is designed to produce sub-picosecond, high brightness electron bunches to drive an ultraviolet FEL. The accelerator consists of a 1.6 cell S-band photoinjector, variable pulse length Ti:Sapp laser, 4 SLAC-type S-band accelerating sections, and 4-dipole chicane bunch compressor. In preparation for FEL operation, the compressed electron beam has been fully characterized. Measurement of the beam parameters and simulation of the beam are presented.

The DUVFEL photoinjector consists of a 1.6 cell BNL gun IV with copper cathode, variable pulse length Ti:Sapp laser, and solenoid magnet. The beam dynamics and the electromagnetic fields in the photoinjector have been characterized by producing a short electron beam with very low charge that is used as a field probe. The transverse beam size and divergence are measured as a function of the initial RF phase and the initial spot size and compared with simulations using the code HOMDYN. The electromagnetic fields used in the simulations are produced by SUPERFISH, and have been verified with RF measurements. The simulations and measurements of beam dynamics are presented.

The DUVFEL accelerator in the Source Development Lab of NSLS/BNL generates a high brightness electron beam from a laser driven electron source and a magnetic bunch compressor. This beam is used for different FEL experiments in SASE and future HGHG configurations. The compression of the electron beam to high peak current while preserving the transverse properties is of great importance to the performance goals of these FELs. In this paper we report on the experimental methods to characterize the longitudinal properties of the electron beam and the measured results for various settings of the DUVFEL accelerator. The observed effects on the electron beam spectra and time profiles during compression are most likely due to coherent effects while their exact origin is still subject of ongoing investigation.

Measurements of the thermal emittance of an electron beam produced by photoemission from the copper cathode of a high power RF cavity are presented. The RMS normalized emittance has been measured as a function of laser spot size, applied surface field, and polarization of the laser beam at normal incidence. Local field enhancement due to surface effects is found to increase the emittance substantially beyond that expected for a perfect planar surface.

The 1.6 cell S-band photoinjector cavity has been in operation at the DUVFEL at BNL for the past year. The initial beam measurements indicated a higher than expected emittance and beam divergence at the exit of the gun field. The imbalance in the two cells was suspected, but lack of field probes in the cavity prohibited direct confirmation. A detailed SUPERFISH model was constructed of the cavity assembly. The field balance as a function of cathode plate and tuner position was determined using the model. A series of calibrated measurements of both the cavity RF properties and the delivered RF power was undertaken. Electron beam properties were also measured as a function of cavity tune. Significant improvements in beam quality were achieved. The simulations and measurements are presented.