E. Hoyer

CSEM-Steel Hybrid Wiggler/Undulator Magnetic Field Studies

Current design of permanent magnet wiggler/ undulators use either pure charge sheet equivalent material (CSEM) or the CSEM-Steel hybrid configuration. Hybrid configurations offer higher field strength at small gaps, field distributions dominated by the pole surfaces and pole tuning. Nominal performance of the hybrid is generally predicted using a 2-D magnetic design code neglecting transverse geometry. Magnetic measurements are presented showing transverse configuration influence on performance, from a combination of models using CSEMs, REC (Hc = 9.2 kOe) and NdFe (Hc = 10.7 kOe), different pole widths and end configurations. Results show peak field improvement using NdFe in place of REC in identical models, gap peak field decrease with pole width decrease (all results less than computed 2-D fields), transverse gap field distributions, and importance of CSEM material overhanging the poles in the transverse direction for highest gap fields.

A Magnetic Monopole Detector Utilizing Superconducting Elements

An electromagnetic detector has been built to extend the search for magnetic monopoles to the lunar sample returned during the Apollo missions. It is sensitive to the minimum magnetic charge allowed by Diracs theory and permits analysis of a sample without changing any of its properties. The apparatus consists of a superconducting niobium sensing coil with a core at room temperature, shorted by a superconducting mechanical switch and protected against the effects of variable ambient magnetic field by an adequate shield made of superconducting lead. Characteristic features, performance, and sample containers are described.

A SOFT X-RAY UNDULATOR BEAMLINE AT THE ADVANCED LIGHT SOURCE WITH CIRCULAR AND VARIABLE LINEAR POLARIZATION FOR THE SPECTROSCOPY AND MICROSCOPY OF MAGNETIC MATERIALS

A new undulator beamline at the Advanced Light Source, Lawrence Berkeley National Laboratory is described. This new beamline has an Apple II type undulator which produces linearly and elliptically polarized X-rays. A high resolution monochromator directs the radiation to two branchlines. The first branchline is optimized for spectroscopy and accommodates multiple endstations simultaneously. The second branchline features a photoemission electron microscope. A novel feature of the beamline is the ability to produce linearly polarized radiation at arbitrary, user-selectable angles. Applications of the new beamline are also described.

Multiple trim magnets, or ‘‘magic fingers,’’ for insertion device field integral correction

Multiple trim magnets (MTMs), also known as ‘‘magic fingers,’’ are an arrangement of magnets for reducing integrated magnetic‐field errors in insertion devices. The idea is to use transverse arrays of permanent magnets, hence the name ‘‘multiple trim magnets,’’ above and below the midplane, to correct both normal and skew longitudinal magnetic‐field integral errors in a device. MTMs are typically installed at the ends of an ID. Adjustments are made by changing either the size, position, or orientation of each trim magnet. Application of the MTMs to the ALS undulators reduced both the normal and skew longitudinal field integral errors, over the entire 20 mm×60 mm ‘‘good field region,’’ of the beam aperture by as much as an order of magnitude. The requirements included corrections of field and gradients outside the multipole convergence radius. Additionally, these trim magnet arrays provided correction of the linear component of the integrated field gradients for particles with trajectories not parallel to ...

Predicting Thermal Distortion of Synchrotron Radiation Mirrors with Finite Element Analysis

High power and high power densities due to absorbed radiation are significant design considerations which can limit performance of mirrors receiving highly collimated synchrotron radiation from insertion devices and bending magnet sources. Although the grazing incidence angles needed for x-ray optics spread the thermal load, localized, non-uniform heating can cause distortions which exceed allowable surface figure errors and limit focusing resolution. This paper discusses the suitability of numerical approximations using finite element methods for heat transfer, deformation, and stress analysis of optical elements. The primary analysis objectives are (1) to estimate optical surface figure under maximum heat loads, (2) to correctly predict thermal stresses in order to select suitable materials and mechanical design configurations, and (3) to minimize fabrication costs by specifying appropriate tolerances for surface figure. Important factors which determine accuracy of results include finite element model mesh refinement, accuracy of boundary condition modeling, and reliability of material property data. Some methods to verify accuracy are suggested. Design analysis for an x-ray mirror is presented. Some specific configurations for internal water-cooling are evaluated in order to determine design sensitivity with respect to structural geometry, material properties, fabrication tolerances, absorbed heat magnitude and distribution, and heat transfer approximations. Estimated accuracy of these results is discussed.

The U5.0 undulator for the advanced light source

The U5.0 Undulator, an 89 period, 5 cm period length, 4.6 m long insertion device has been designed, is being fabricated, and is scheduled for completion in early 1992. This undulator will be the first high brightness source, in the 50 to 1,500 eV range, for the Advanced Light Source at the Lawrence Berkeley Laboratory. A hybrid magnetic configuration using Nd–Fe–B permanent magnet material and vanadium permendur poles has been selected to achieve the field quality needed to meet performance requirements. The magnetic structure is modular with each half consisting of five assembly sections, which provide the periodic structure, and end structures, for entrance and exit correction, mounted on a steel backing beam. Each assembly section consists of 35 half‐period pole assemblies bolted to a mount. The required 0.837 T effective peak field at a 1.4 cm gap has been verified with model measurements. Vertical field integral correction is accomplished with the end structures, each having an arrangement of perman...

Design of the advanced light source elliptical wiggler

Abstract The elliptical wiggler is a circularly polarized light source capable of providing very broad spectral coverage and a high degree of circular polarization. The main features of an elliptical wiggler can be understood through analogy to bending magnet radiation. However, some aspects, such as the end structures influence on the degree of circular polarization, require more elaborate methods to characterize. We present an algorithm based on the stationary-phase method, which allows calculation of radiation properties from an arbitrary electron trajectory, so a non-sinusoidal magnetic fields influence on the radiation performance can be taken into account. We show general radiation properties of an elliptical wiggler and discuss factors affecting the radiation produced. Practical issues encountered during the conceptual design of an elliptical wiggler at the Advanced Light Source are addressed.

Magnet sorting algorithms for insertion devices for the Advanced Light Source

Insertion devices for the Advanced Light Source (ALS) incorporate up to 3000 magnet blocks each for pole energization. In order to minimize field errors, these magnets must be measured, sorted and assigned appropriate locations and orientations in the magnetic structures. Sorting must address multiple objectives, including pole excitation and minimization of integrated multipole fields from minor field components in the magnets. This is equivalent to a combinatorial minimization problem with a large configuration space. Multi-stage sorting algorithms use ordering and pairing schemes in conjunction with other combinatorial methods to solve the minimization problem. This paper discusses objective functions, solution algorithms and results of application to magnet block measurement data. >

REC AND NdFe MAGNETIC MOMENT IRREVERSIBILITY FROM TEMPERATURE CYCLING

Presented are the results of thermal cycling tests carried out on REC and NdFe samples, to determine the irreversible losses in room temperature open circuit magnetic moment. A stabilization prescription was developed for a REC alloy that will allow two 4day/175°C temperature cycles, which simulate two UHV bakeouts, with only a 0.35% average loss and a 0.65% loss variation in the room temperature open circuit magnetic moment after stabilization.

Development of a NdFe-steel hybrid wiggler for SSRL

A NdFe-steel hybrid configured permanent magnet wiggler is being developed for insertion in the SPEAR ring at the Stanford Synchrotron Radiation Laboratory, SSRL. Featuring 15 complete periods, a 12.9-cm magnetic period length, and a peak magnetic field range of 0.01-1.4 Tesla, the wiggler was designed to provide an intense radiation source for the National Laboratory/University of California participating research team (PRT) facility on Beam Line VIII-W. A new permanent magnet material, neodymium-iron (NdFe), is being used in the magnetic structure instead of rare-earth cobalt, REC, used previously in the 27-period wiggler now on Beam Line VI. NdFe advantages include a 16% higher coercive force (10.6-kOe vs. 9.0-kOe) and lower cost. The wiggler design features a thin walled, rigid vacuum chamber with pole pockets on opposing surfaces allowing a 2.1-cm minimum magnetic gap with a 1.8-cm beam vertical aperture. At 3 GeV the wiggler at peak field is expected to radiate approximately two kilowatts in a 5-mrad horizontal fan with a 7.8 keV critical energy. Calculations are in progress to model the wiggler radiation spatial and spectral radiation emission.