R. Biscardi

Switched detector for beam position monitor

The NSLS (National Synchrotron Light Source) storage rings use sets of four button electrodes to determine the transverse position of the stored electron beam in the vacuum chamber. By means of GaAs switches, the 211 MHz component of the induced signals on each of the four buttons is measured in turn by a single amplifier-detector channel. These signals are then stored in four sample and hold circuits. The measurement cycle is repeated at a rate of 40 kHz. The required sums and differences of these signals are obtained by analog means. The results are normalized with respect to beam intensity by servoing the gain of the amplifier-detector channel such that the sum of the signals from the four buttons is maintained at a fixed value. The prototype receiver provides +or-20 mu m resolution within a 300 Hz bandwidth over a 30 dB dynamic range. The receiver is relatively insensitive to beam energy and to the number of bunches stored in the machine.<<ETX>>

Real time closed orbit correction system

A global closed-orbit feedback experiment based upon a real-time harmonic analysis of both the orbit movement and the correction magnetic fields is described. The harmonic feedback system was constructed and tested on the 750 MeV vacuum ultraviolet ring of the NSLS (National Synchrotron Light Source) and implemented on a real-time basis using relatively simple electronics. The feedback forces the coefficients of a few harmonics near the betatron tune to vanish and significantly improves the global orbit stability. The result of the experiment in the ring using four detectors and four trims, in which maximum observed displacement was reduced by a factor of between three and four, is presented.<<ETX>>

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.

Real time global orbit feedback system for NSLS X-ray ring

The authors report on the design and commissioning of a real-time harmonic global orbit feedback system for the NSLS (National Synchrotron Light Source) X-ray ring. This system uses 8 pick-up electrode position monitors and 16 trim dipole magnets to eliminate 3 harmonic components of the orbit fluctuations. Because of the larger number of position monitors and trim magnets, the X-ray ring feedback system differs from VUV (vacuum ultraviolet) ring system in that the Fourier analysis and harmonic generation networks are comprised of MDAC (multiplying digital-to-analog converter) boards controlled by computer. The implementation of the global feedback system has resulted in a dramatic improvement in orbit stability, by more than a factor of five everywhere. Simultaneous operation of the global and several local bump feedback systems has been achieved.<<ETX>>

NSLS X-ray system RF system upgrade

Presently (Dec. 1992) three RF systems power the electron beam at the NSLS X-ray storage ring to 250 mA at 2.58 GeV. A fourth RF cavity and system is being installed to increase the machine reliability over pre-shutdown operational conditions (3 cavities). It also permits new levels of beam intensity and energy to be achieved in the X-ray ring. Intensities of 500 mA at 2.5 GeV as well as 250 mA at 2.8 GeV are anticipated. A description of the hardware, the installation and the modes of operation will be outlined in this paper. X-ray ring operations are scheduled to resume January 1993. Injection performance and high energy reliability will also be discussed.<<ETX>>

Progress on bunch lengthening at the NSLS VUV ring

The authors describe the basic theory and experimental results on bunch lengthening at the National Synchrotron Light Source (NSLS) vacuum ultraviolet (VUV) ring. Emphasis is placed on results of experiments conducted since the last study. A fourth harmonic cavity was used to provide the necessary conditions for bunch lengthening. Experiments have included using the harmonic cavity in a beam excited mode as well as using an external generator to provide the desired conditions.<<ETX>>

RF system for the NSLS coherent infrared radiation source

The existing NSLS X-ray Lithography Source (XLS Phase I) is being considered for a coherent synchrotron radiation source. The existing 211 MHz warm cavity will be replaced with a 5-cell 2856 MHz superconducting RF cavity, driven by a series of 2 kW klystrons. The RF system will provide a total V/sub RF/ of 1.5 MV to produce /spl sigma//sub L/=0.3 mm electron bunches at an energy of 150 MeV. Superconducting technology significantly reduces the required space and power needed to achieve the higher voltage. It is the purpose of this paper to describe the superconducting RF system and cavity, power requirements, and cavity design parameters such as input coupling, quality factor, and higher order modes.

Commissioning of the phase I Superconducting X-ray Lithography Source (SXLS) at BNL

A report on the performance of phase I of the Superconducting X-Ray Lithography Source (SXLS) storage ring project at the Brookhaven National Laboratory (BNL) is presented. In phase I, low field iron dipoles (B=1.1 T) are being used to study the ring at energies of 200 MeV and below. The basic design parameters of the phase I SXLS ring are listed and the Twiss parameters are shown. The phase I ring was commissioned during the fall of 1990 and the design current of 500 ma has been exceeded. The vacuum system and lifetime, the RF system, and the diagnostics are discussed. Ion clearing electrodes have been essential to storing large currents (I>300 ma) in the ring.<<ETX>>

An active interlock system for the LNLS X-ray ring insertion devices

A description is given of the design and operation of an active interlock system which has been installed in the NSLS (US National Synchrotron Light Source) X-ray electron storage ring to protect the vacuum chamber from thermal damage by missteered high-power photon beams from insertion devices (IDs). The system employs active beam position detectors to monitor beam motion in the 1D straight sections and solid-state logic circuitry to dump the stored beam in the event of a fault condition by interrupting the RF. To ensure a high degree of reliability, redundancy and continuous automatic checking have been incorporated into the design. Overall system integrity is checked periodically with the beam at safe levels of beam current.<<ETX>>

SXLS RF cavity and system

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.<<ETX>>