D. Humphries

Pure permanent magnet harmonics corrector ring

Abstract A concept for creating any desired harmonics mix in a pure permanent magnet (PM) corrector ring is presented. Useful for nulling various harmonics simultaneously, such a device is versatile for many accelerator applications. The harmonic mix can be changed without redesign or replacement by a new ring or parts and, if desired, can be accomplished in situ via remote control of cylinder motors. Harmonics suppression of greater than a factor of 100 or even 1000 are possible; exact functional dependencies of harmonics suppresion capability versus magnet geometry are given. Sensitivity to positioning and corrector ring PM errors are given, and shown to be themselves nullable.

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.

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.

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.

Modeling and measurement of the ALS U5 undulator end magnetic structures

The end structures for the ALS U5.0 undulators utilize a system of dual permanent magnet rotors intended to establish gap independent field performance. They may also be used for tuning of the first and second magnetic field integrals of these devices. The behavior of these structures has been studied by means of two dimensional modeling with the POISSON Group of computer codes. A parametric study of the magnetic field distribution and first and second integrals of the fields has been conducted. In parallel, magnetic measurements of the final completed structures have been performed using an automated Hall probe measurement system. Results of the modeling and measurements are compared. Implications for tuning of the ends of the devices within the context of the electron beam parameters of the ALS are discussed.<<ETX>>

The U5.0 undulator for the ALS

The U5.0 undulator, an 89-period, 5-cm-period-length, 4.6-m-long insertion device, has been designed and is in fabrication. This undulator will be the first high-brightness source, in the 50-1500-eV range, for the Advanced Light Source (ALS) and is scheduled for completion in 1992. A modular hybrid configuration utilizing Nd-Fe-B permanent magnet material and vanadium permendur is used. It achieves a 0.837-T effective peak field. Correction of the vertical field integral is achieved with permanent magnet rotors at the ends. Gap adjustment is done with an arrangement of roller screws, chain drives, a gear reduction unit, and a stepper motor driven by a closed-loop control system. The vacuum chamber design is a two-piece, machined and welded 5083-H321 aluminum construction of 5.1-m length. Magnetic design, subsystem design, and fabrication progress are presented.<<ETX>>

Insertion devices for the Advanced Light Source at LBL

The Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory (LBL) will be the first of the new generation of dedicated synchrotron light sources to be put into operation. Specially designed insertion devices will be required to realize the high-brightness photon beams made possible by the low emittance of the electron beam. The complement of insertion devices on the ALS will include undulators with periods as short as 3.9 cm and one or more high field wigglers. The first device to be designed is a 5-m-long, 5-cm-period, hybrid undulator. The goal of very high brightness and high harmonic output imposes unusually tight tolerances on the magnetic field quality and thus on the mechanical structure. The design process, using a generic structure for all undulators, is described.<<ETX>>

Wigglers at the Advanced Light Source

Two 3.4 m long wigglers are being designed and constructed at Lawrence Berkeley Laboratorys (LBL) Advanced Light Source (ALS). A 19 period planar wiggler with 16.0 cm period length is designed to provide photons up to 12.4 keV for protein crystallography. This device features a hybrid permanent magnet structure with tapered poles and designed to achieve 2.0 T at a 1.4 cm magnetic gap. An elliptical wiggler is being designed to provide circularly polarized photons in the energy range of 50 eV to 10 keV for magnetic circular dichroism spectroscopy. This device features vertical and horizontal magnetic structures of 14 and 14 1/2 periods respectively of 20 cm period length. The vertical magnetic structure is a 2.0 T hybrid permanent magnet configuration. The horizontal structure is an iron core electromagnetic design, shifted longitudinally 1/4 period with respect to the vertical magnetic structure. A maximum horizontal peak field of 0.1 T at an oscillating frequency up to 1 Hz will be achieved by excitation of the horizontal poles with a trapezoidal current waveform.