L. Solomon

Fabrication of a high-field short-period superconducting undulator

Abstract The visible free electron laser (FEL) experiment at the accelerator test facility (ATF) at Brookhaven National Laboratory is designed to utilize the high brightness beam from a laser-photocathode rf gun injected into a 50 MeV S-band linac in conjunction with a 8.8 mm period undulator. The undulator is designed to provide a 0.5 T field on axis which is reached at a current 15% below the quench current. It consists of 3 contiguous sections. We discuss the field errors by evaluating the trajectory wander and the optical phase error. Whereas undulator sections with low errors can be built as machined without any shimming or trimming, special care has to be taken during the assembly of a full length device.

Development of an in-vacuum minipole undulator array for National Synchrotron Light Source In-Vacuum UNdulator

An in-vacuum minipole (short period) insertion device has been developed in a collaboration between SPring-8 and the National Synchrotron Light Source (NSLS). The magnetic arrays were assembled, field measured, corrected, and vacuum tested by SPring-8 and were installed in an NSLS-developed chamber with mechanical parts in the NSLS X-Ray Ring (E=2.584 GeV) in May 1997 and a successful commissioning of the device was carried out in June 1997. The device is made of permanent magnets with 30.5 periods and a period length of 11 mm. It is designed to produce fundamental radiation at 4.6 keV, and with a modest value of deflection parameter (K=0.7 at 3.3& mm gap) enables higher harmonics to be used as well, for a variety of experiments. A detailed description of the mechanical support and vacuum chamber will be reported elsewhere. We describe technical challenges encountered in constructing this type of device, and present an outline of our collaboration.

Small-gap undulator experiment on the NSLS X-ray ring

We report results of an on-going experiment being carried out in the X13 straight section of the NSLS X-ray Ring which explores the limits of the operation of small-gap undulators. In particular, we discuss measurements of stored electron beam lifetime as a function of the vertical aperture presented by a 4-jaw scraper or a variable-aperture vacuum vessel. At an electron beam current of 300 mA the variable-aperture vacuum chamber was dosed to an inner aperture of 3.8 mm with no effect on the electron beam lifetime. Measurements of the output radiation spectrum of a 16 mm period undulator at a magnet gap of 7.5 mm are also described.

Initial results from an in-vacuum undulator in the NSLS X-ray ring

A short-period in-vacuum undulator for the NSLS X-ray Ring has been developed in a collaboration between SPring-8 and the NSLS, and has achieved its project design goals during commissioning studies. The device is called IVUN (in-vacuum undulator) and employs magnet arrays (31 periods, with an 11 mm period) developed at SPring-8, while the requisite vacuum chamber and mechanical systems were developed at the NSLS. At a magnet gap of 3.3 mm, IVUN produces 4.6 keV radiation in the fundamental, with useful photon fluxes in both the second and third harmonics. The magnet gap is adjustable between 2 and 10 mm. A brief overview of IVUN is presented, together with initial commissioning results: the dependence of electron-beam lifetime and bremsstrahlung on magnet gap, and the output radiation spectrum.

Orbit stability improvement at the NSLS X-ray ring

We describe recent improvements in both the short and long-term orbit stability at the NSLS X-ray Ring. The short-term stability has been improved by increasing the gain and the bandwidth of the global harmonic feedback systems. The long-term horizontal orbit drift over the course of a fill has been reduced by including the RF-frequency in the orbit feedback. Work is in progress to further reduce orbit drift by compensating for thermally induced mechanical motions of the beam position monitors.

Chamber motion measurements at the NSLS X-ray ring

Work has been ongoing at the NSLS to improve the orbit stability of the X-ray ring by accounting for the thermal motion of the vacuum chamber, which supports the electron beam position monitors (BPMs). In-situ contact measurements of the vacuum chamber motion have been carried out using support stands that have been designed and extensively tested to reduce errors associated with thermal changes in the stands themselves. Using this chamber motion as a correction to the orbit motion measured by the BPMs, the precise location of the radiation beam can be predicted. These predictions are compared with actual radiation beam measurements on the experimental floor, and with predictions based solely on BPM measurements of the electron beam position. This paper reviews this work including stand design and performance, chamber motion measurements, predictions based on these data, and results.

Magnetic field measurements of a superconducting undulator for a harmonic generation FEL experiment at the NSLS

An 18 mm period, 0.54 Tesla, 8 mm gap superconducting undulator with both horizontal and vertical focusing has been-built and tested. This magnet, which is fabricated in 25 cm length sections, is being tested for use in the radiator section (total magnet length of 1.5 m) of the Harmonic Generation Free Electron Laser experiment at the National Synchrotron Light Source-Accelerator Test Facility at Brookhaven National Lab, in collaboration with Grumman Corp. The measurement system is outlined, sources and estimates of errors are described, and some magnetic field data are presented and discussed.<<ETX>>

A superconducting short period undulator for a harmonic generation FEL experiment

A three stage superconducting (SC) undulator for a high gain harmonic generation (HGE) FEL experiment in the infrared is under construction at the NSLS in collaboration with Grumman Corporation. A novel undulator technology suitable for short period (6-40 mm) undulators will be employed for all three stages, the modulator, the dispersive section and the radiator. The undulator triples the frequency of a 10.4 /spl mu/m CO/sub 2/ seed laser. So far a 27 period (one third of the final radiator) prototype radiator has been designed, built and tested.<<ETX>>

Magnetic measurements of permanent magnet insertion devices at the BNL-NSLS

Since June 1988, three permanent magnet insertion devices of the hybrid type have been installed into the X-ray ring at the National Synchrotron Light Source at Brookhaven National Laboratory as part of the Phase II facility upgrade. The three magnets consist of a soft X-ray undulator (SXU) and two hybrid wigglers, with peak fields of 0.35 and 1.2 T, respectively. Some results of point and integral magnetic measurements performed on these magnets are presented.<<ETX>>

The status of the high-gain harmonic generation free-electron laser experiment at the Accelerator Test Facility

The Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL) is an accelerator and beam physics user facility capable of producing a high-brightness, 70-MeV electron beam. Currently, a high-gain harmonic generation (HGHG) free-electron laser (FEL) experiment is underway at the ATF. This is a collaborative effort between BNL and the Advanced Photon Source (APS). The experiment consists of two phases: 1) self-amplified spontaneous emission (SASE) and 2) HGHG. Here, a brief introduction to the HGHG theory, measurements in the SASE phase, the recent modifications in preparation for the HGHG phase, and future plans will be discussed.