B. Kincaid

The Properties of Undulator Radiation

A new generation of synchrotron radiation light sources covering the VUV, soft x-ray, and hard x-ray spectral regions is under construction in several countries. These sources are designed specifically to use periodic magnetic undulators and low-emittance electron or positron beams to produce high-brightness near-diffraction-limited synchrotron radiation beams. Some of the novel features of the new sources are discussed, along with the characteristics of the radiation produced, with emphasis on the Advanced Light Source, a third-generation 1.5 GeV storage ring optimized for undulator use. A review of the properties of undulator radiation is presented, followed by a discussion of some of the unique challenges being faced by the builders and users of the new undulator sources. These include difficult mechanical and magnetic tolerance limits, a complex interaction with the storage ring, high x-ray beam power, partial coherence, harmonics, optics contamination, and the unusual spectral and angular properties of undulator radiation.

Calculation of magnetic error fields in hybrid insertion devices

Abstract The Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory requires insertion devices with fields sufficiently accurate to take advantage of the small emittance of the ALS electron beam. To maintain the spectral performance of the synchrotron radiation and to limit steering effects on the electron beam these errors must be smaller than 0.25%. This paper develops a procedure for calculating the steering error due to misalignment of the easy axis of the permanent-magnet material. The procedure is based on a three-dimensional theory of the design of hybrid insertion devices developed by one of us. The acceptable tolerance for easy axis misalignment is found for a 5-cm-period undulator proposed for the ALS.

Experimental characterization of ALS undulator radiation

The radiation from the 5 cm period undulator at the Advanced Light Source (ALS) has been characterized using a transmission grating spectrometer. Spectral and angular distributions of radiation were measured for deflection parameter K values between 0.45 and 2.12 at low storage ring current (0.1--0.5 mA). From the calibration of the spectrometer, the absolute flux density of the undulator harmonics has been determined together with the spectral linewidth. The electron the beam emittance was determined by analyzing the angular distribution of the red-shifted fundamental. Comparison has been made with radiation calculations based upon the measured magnetic field data of the undulator. Including field errors, electron beam emittance and energy spread, good agreement is found between theoretically and experimentally determined harmonic widths and peak brightness.

The Advanced Light Source U8 beam line, 20--300 eV

The U8 is a beam line under construction at the Advanced Light Source (ALS). The beam line will be described along with calculations of its performance and its current status. An 8 cm period undulator is followed by two spherical collecting mirrors, an entrance slit, spherical gratings having a 15{degree} deviation angle, a moveable exit slit, and refocusing and branching mirrors. Internal water cooling is provided to the metal M1 and M2 mirrors as well as to the gratings. Calculations have been made of both the flux output and the resolution over its photon energy range of 20--300 eV. The design goal was to achieve high intensity, 10{sup 12} photons/sec, at a high resolving power of 10,000. The U8 Participating Research Team (PRT) is planning experiments involving the photoelectron spectroscopy of gaseous atoms and molecules, the spectroscopy of ions and actinide spectroscopy.

First undulators for the Advanced Light Source

The first three undulators, each 4.6 m in length, for the Advanced Light Source (ALS) at Lawrence Berkeley Laboratory (LBL), are near completion and are undergoing qualification tests before installation into the storage ring. Two devices have 5.0-cm period lengths, 89 periods, and achieve an effective field of 0.85 T at the 14 mm minimum magnetic gap. The other device has a period length of 8.0 cm, 55 periods, and an effective field of 1.2 T at the minimum 14 mm gap. Measurements on the first 5 cm period device show the uncorrelated field errors to be 0.23%, which is less than the required 0.25%. Measurements of gap control show reproducibility of /spl plusmn/5 microns or better. The first vacuum chamber, 5.0 m long, is flat to within 0.53 mm over the 4.6 m magnetic structure section and a 4/spl times/10/sup -11/ Torr pressure was achieved during vacuum tests. Device description, fabrication, and measurements are presented.<<ETX>>

Insertion device magnet measurements for the Advanced Light Source

Allowable magnetic field errors for the 4.6 m long insertion devices for the Advanced Light Source (ALS) are extremely small and are driven by electron beam and radiation requirements. Detailed measurements and adjustments of each insertion device are performed to qualify them for installation in the ALS. To accomplish this, a high speed, precision magnetic measurement facility has been designed and built. Hall probe mapping equipment, capable of completing a 2500 sample, 6 m scan with precision axial position monitoring using a laser interferometer in under one minute, is used to obtain both local and integrated field information. A 5.5 m long, 1 cm wide coil is used to measure the field integral through an entire insertion device. This paper describes magnetic measurement equipment, and results of measurements on IDA, the first of the ALS insertion devices.<<ETX>>

Analysis of insertion device magnet measurements for the Advanced Light Source

The Advanced Light Source (ALS), which is currently being commissioned at Lawrence Berkeley Laboratory, is a third generation light source designed to produce XUV radiation of unprecedented brightness. To meet the high brightness goal the storage ring has been designed for very small electron beam emittance and the undulators installed in the ALS are built to a high degree of precision. The allowable magnetic field errors are driven by electron beam and radiation requirements. Detailed magnetic measurements and adjustments are performed on each undulator to qualify it for installation in the ALS. The first two ALS undulators, IDA and IDB, have been installed. This paper describes the program of measurements, data analysis, and adjustments carried out for these two devices. Calculations of the radiation spectrum, based upon magnetic measurements, are included. Final field integral distributions are also shown. Good field integral uniformity has been achieved using a novel correction scheme, which is also described.

Correlation between measured undulator magnetic fields and x‐ray spectraa)

Electron storage ring insertion devices, especially undulators, are designed using ideal device theory and the resulting x‐ray spectra are reasonably close to predictions in most cases. However, magnetic field errors result in nonideal x‐ray spectra. These effects can be calculated theoretically, and may also be measured. Here we present a study of an undulator whose magnetic fields and x‐ray spectra have been measured carefully. We compare experiment and theory and explain the deviation from ideal of the shape of the undulator’s spectral peaks in terms of magnet errors.

Diagnostic beamline for a third generation storage ring

A knowledge of the position, size, and stability of the source and the angle of emission of synchrotron radiation (SR) from the storage ring are essential for optimizing the operation of storage ring, insertion devices and monochromators. Berkeley’s Advanced Light Source (ALS) has a natural emittance of 3.4×10−9 mrad, and has beam sizes σh and σv (assuming a 10% emittance ratio into the vertical direction) in bending magnet 1 (BM1) of 44 and 83 μm, respectively. Simple diffractive optical calculations show that imaging this beam using visible light optics is not feasible and imaging must be performed using photon energies greater than 50 eV. This will be the same for all third generation low emittance storage rings. The synchrotron radiation diagnostics at ALS will consist of an imaging system for 200 eV photons and a ‘‘white beam’’ port with a streak camera to obtain the timing information. The imaging system will employ two crossed spherical mirrors in a Kirkpatrick–Baez configuration, to eliminate asti...

The U5.0 Undulator Design for the Advanced Light Source at LBL

Abstract The U5.0 undulator, currently under design, is the first in a series of insertion devices planned for the Advanced Light Source at LBL. U5.0 parameters include a 5-cm period and a 5-m length with an 0.837-T maximum field at a 14-mm gap. A hybrid configuration utilizing NdFeB permanent magnet material and vanadium permendur poles is used for the magnetic structure. Construction is modular with many pole assemblies attached to a pole mount, which in turn is fastened onto one of the backing beams. Vertical field integral correction at the ends is accomplished with permanent magnet rotators. The support structure features a four-post configuration, a rigid base with three kinematic floor supports, and two rigid 5-m long backing beams that fit within the 2.4-m-high accelerator enclosure. The drive system is computer-controlled using a stepper motor and shaft encoder coupled to a roller-screw/nut and chain drive train. Vacuum chamber design is a rigid configuration with a 10 mm vertical by 218 mm horizontal aperture of 5.5 m length. Chamber fabrication features a two-piece welded chamber of 5083 H321 aluminum. Pumping is with ion and titanium sublimation pumps.