Stephen L. Kramer

Bunch length control in the NSLS VUV ring

Abstract 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.

Photoinjected energy recovery linac upgrade for the National Synchrotron Light Source

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-sources and ultra-short pulse capabilities, not possible with storage ring light sources.

Investigation of coherent emission from the NSLS VUV ring

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.

Status of the visible Free-Electron Laser at the Brookhaven Accelerator Test Facility

Abstract The 500 nm free-electron laser (FEL) at the accelerator test facility (ATF) of the Brookhaven National Laboratory is reviewed. We present an overview of the ATF, a high-brightness, 50-MeV, electron accelerator and laser complex which is a users facility for accelerator and beam physics. A number of laser acceleration and FEL experiments are under construction at the ATF. The visible FEL experiment is based on a novel superferric 8.8 mm period undulator. The electron beam parameters, the undulator, the optical resonator, optical and electron beam diagnostics are discussed. The operational status of the experiment is presented.

NSLS upgrade concept

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.

Time-resolved fluorescence using synchrotron radiation excitation: A powered fourth-harmonic cavity improves pulse stability

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 ...

NSLS II: The Future of the NSLS

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.

NSLS-II Injection Concept

Currently the facility upgrade project is in progress at the NSLS (at Brookhaven National Laboratory). The goal of the NSLS-II is a 3 GeV ultra-low-emittance storage ring that will increase radiation brightness by three orders of magnitude over that of the present NSLS X-ray ring. The low emittance of the high brightness ring’s lattice results in a short lifetime, so that a top-off injection mode becomes an operational necessity. Therefore, the NSLS-II injection system must provide, and efficiently inject, an electron beam at a high repetition rate. In this paper, we present our concept of the NSLS-II injection system and discuss the conditions for, and constraints on, its design.

NSLS VUV ring lifetime study

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.

Beam induced RF cavity transient voltage

Abstract We calculate the transient voltage induced in a radio frequency (RF) 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 ωr of the cavity and at an integer multiple of the bunch revolution frequency (i.e. the accelerating frequency for powered cavity operation) hω0. The presence of two nearby frequencies in the cavity leads to a modulation of the carrier wave exp(jhω0t). 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 kind of longitudinal rigid dipole mode which differs from the conventional Robinson mode.