This work describes tuning methods used at Lawrence Berkeley National Laboratory (LBNL) for hybrid permanent magnet and superconducting undulators (SCUs). The work on the hybrid permanent magnet un...

Author(s): Emma, P; Holtkamp, N; Nuhn, HD; Arbelaez, D; Corlett, J; Myers, S; Prestemon, S; Schlueter, R; Doose, C; Fuerst, J; Hasse, Q; Ivanyushenkov, Y; Kasa, M; Pile, G; Trakhtenberg, E; Gluskin, E | Abstract: Copyright © 2014 CC-BY-3.0 and by the respective authors. Undulators serve as the primary source of radiation for modern storage rings, and more recently for the advent of Free-Electron Lasers (FELs). The performance of future FELs can be greatly enhanced using the much higher magnetic fields of superconducting undulators (SCU) [1]. For example, the LCLS-II hard x-ray undulator can be shortened by up to 70 m using an SCU in place of a PMU (permanent magnet undulator), or its spectral performance can be critically improved when using a similar length. In addition, SCUs are expected to be orders of magnitude less sensitive to radiation dose; a major issue at LCLS-II with its 1-MHz electron bunch rate. We present a funded RaD collaboration between SLAC, ANL, and LBNL, which aims to demonstrate the viability of superconducting undulators for FELs by building, testing, measuring, and tuning two 1.5-m long planar SCU prototypes using two different technologies: NbTi at ANL and Nb3Sn at LBNL. Our goal is to review and reassess the LCLS-II HXR baseline plans (PMU) in July of 2015, after the development and evaluation of both prototypes, possibly in favor of an SCU for LCLS-II.

An analytical expression for prediction of skew harmonics in an iron core combined function regular/skew dipole magnet due to arbitrarily positioned electromagnet coils is developed. A structured approach is presented for the suppression of an arbitrary number of harmonic components to arbitrarily low values. Application of the analytical harmonic strength calculations coupled to the structured harmonic suppression approach is presented in the context of the design of the ALS storage ring corrector magnets, where quadrupole, sextupole, and octupole skew harmonics were reduced to less than 1.0% of the skew dipole at the beam aperture radius r = 3.0 cm.

In Free Electron Lasers (FEL), the electron trajectory through the undulator must meet stringent requirements in terms of trajectory wander and phase variation. This paper analyzes the feasibility of using line current pairs as correctors for superconducting undulators given a set of expected fabrication errors. A tolerance study has first been performed to investigate the impact of geometrical errors on the field quality. These errors are corrected with line currents that increase or decrease the magnetic field locally. Once the uncorrected trajectory is known, an algorithm finds the minimum number of correctors required to fulfill the trajectory specifications, and gives the corrector locations. All the correctors can be powered with the same current, greatly simplifying the implementation. The current then offers a degree of freedom to correct the trajectory and can be tuned dynamically as a function of the magnetic deflection.

The ability to correct magnetic field errors in a superconducting undulator is critical for the successful application of these devices in future and existing light sources. These field errors, which can emanate from sources such as machining and coil winding imperfections, can lead to reduced light source performance by introducing errors in both the electron trajectory and the relative phase relationship between the oscillating electrons and the emitted photons. In this work, correction schemes are presented, which use a single power supply along with a superconducting switch network to define the path for the current during undulator tuning. The basic switching concept was previously designed and successfully tested at Lawrence Berkeley National Laboratory; the approach presented here is a significant advancement in generalizing and scaling that core concept. A new fabrication method is presented here, which uses lithographic methods to produce current paths and switch heaters on a superconducting film. The effect of an example corrector current path design on the magnetic field is investigated using the Finite Element Method, and the results at various undulator and corrector energization levels are presented. Experimental results from the heater switch concept are also presented.

A general modeling framework is introduced that allows for the solution to magnetic field perturbations due to mechanical and magnetic tolerances in hybrid undulators. For example, both geometric pole errors and permanent magnet block geometry and strength errors can be considered. Of particular significance is the scaling of the various errors with variations in the gap of the device. In this work, the perturbation analysis is presented along with specific examples of errors found in hybrid undulators.

A high-performance superconducting undulator concept, incorporating stacked YBa2Cu3O7-δ (YBCO) tapes operating at 4.2 K, is currently under investigation at LBNL as one of many technology options for future FEL applications. The concept is particularly promising for narrow-gap, short period (<;10 mm) regimes, where traditional superconducting and permanent magnet technologies are less-suited. The current path is dictated by etching the YBCO layer using lithography techniques, resulting in a high degree of uniformity from tape to tape as well as a straightforward and highly cost-effective means of production. We describe the approaches being pursued for the tape preparation and the conceptual design of a device. We also provide an initial analysis of the impact of fabrication tolerances in terms of field errors for FEL application.

Superconducting undulators are currently under development at a number of light sources to serve as the next generation of insertion devices, with higher fields providing enhanced spectral range for users. Most of these devices are designed with wire-based technologies appropriate for periods greater than 10mm. New undulator concepts yielding very short-period, high-field devices with periods of a few millimeters and a K ∼ 1 have the potential to significantly reduce the cost and enhance the performance of FEL’s. Here we describe a design using high temperature superconductor tapes that are commercially avail able, and that promise a cost-effective fabrication proces s using micromachining or lithography.

Superconducting insertion devices using Nb3Sn conductors offer the potential of higher brightness photon beams and enhanced spectral range over existing permanent magnet technology. However, Nb3Sn is a low temperature superconductor that must be operated at temperatures near 4.2 K. At these temperatures, any small heat dissipation can potentially be sufficient to lose the superconducting state of a section of a superconducting electromagnet. To quantify the amount of power deposited on the winding emanating from beam-induced heating on a storage ring, we propose a diagnostic calorimeter that will be temporarily integrated into the synchrotron ring. The design of the calorimeter is discussed and the various heat input sources, expected to disturb the operation of a superconducting electromagnet, are reviewed.

A magic angle rotating field (MARF) NMR/MRI magnet has been designed and built, demonstrating future potential to realize vivo measurement of the chemical composition of specific biological tissues and organs, This proof of principle prototype opens the possibility for in situ magic angle scanning of stationary, living, biological specimens. Magnetic design strategy and performance capability are described.

The positron and electron damping rings for the International Linear Collider will contain long straight sections consisting of twenty wiggler/quadrupole pairs. The wigglers will be based upon the CESR superconducting design. There are a number of challenges associated with the design of the wiggler straight vacuum system, in particular, the absorption of photon power generated by the wigglers. This paper will present the overall conceptual design of the wiggler straight vacuum system developed for the ILC Reference Design Report. Particular emphasis will be placed on photon power load calculations and the absorber design.

Shimming systems are required to provide sufficient field homogeneity for high resolution nuclear magnetic resonance (NMR). In certain specialized applications, such as rotating-field NMR and mobile ex situ NMR, permanent magnet-based shimming systems can provide considerable advantages. We present a simple two-dimensional shimming method based on harmonic corrector rings which can provide arbitrary multipole order shimming corrections. Results demonstrate, for example, that quadrupolar order shimming improves the linewidth by up to an order of magnitude. An additional order of magnitude reduction is in principle achievable by utilizing this shimming method for z-gradient correction and higher order xy gradients.

The possibility exists of achieving significantly lower emittances in an electron storage ring by increasing the horizontal betatron tune. However, existing magnet locations and strengths in a given ring may be inadequate to implement such an operational mode. For example, the ALS storage ring[1] could lower its emittance to one third of the current value by increasing the horizontal tune from 14.25 to 16.25. Nevertheless, this would come with the cost of large chromaticities that could not be corrected with our existing sextupole magnets. We discuss such operational issues and possible solutions in this paper.

Three elliptically polarizing undulators (EPU) are installed and operational at the Advanced Light Source (ALS); the most recent was installed in April '05. Operational experience has shown a variation in electron beam size which correlates with the EPU's magnetic quadrant shifts used to vary polarization. Storage ring electron dynamics studies pointed to the existence of a shift dependent skew quadrupole (SQ) component generated within the EPU's. Detailed magnetic and mechanical measurements demonstrated that the field errors were the result of systematic individual magnetic block displacements which vary with quadrant shift. This paper will discuss the results of electron dynamics studies, magnetic and mechanical measurements, design modifications planned for future EPU's to eliminate the SQ source, and the design and implementation of SQ compensation coils

An R&D effort is underway at Lawrence Berkeley National Laboratory (LBNL) to develop the technology of Nb3Sn superconducting undulators (SCUs). Issues relating to the selection of the appropriate conductor are discussed. The design and fabrication of SCUs using Nb3Sn is presented. Two prototype devices have been designed and fabricated at LBNL. The first device concentrated on basic fabrication issues and on magnet protection, a key concern due to extremely high copper current densities during a quench. Test on the first prototype demonstrated that such devices can be passively protected in a scalable manner. The second device incorporated design improvements as well as trim coils that are designed to serve as the basic element of a future active phase error correction approach. Preliminary tests on the second device are presented. The trim coils were successfully tested at a variety of field levels. Two quench runs were performed, both occurring at similar to 70% of short-sample J(c). Stability issues associated with flux-jumps and possible epoxy cracking are discussed.

Superconducting insertion devices, which produce periodic magnetic fields, have been built and installed in a number of synchrotron-light source storage-rings. For the most part, these devices have been wigglers, which have relatively long period lengths. This report concerns itself with the special cryogenic issues associated with short period undulators. The motivation for considering the incorporation of superconducting technology in insertion device designs is to achieve higher magnetic fields than can be achieved with more conventional permanent magnet technology. Since the peak field decreases sharply with increased magnet gap to period ratio, the cryogenic design of the magnet system is crucial. In particular, the insulation required for a warm vacuum bore device is impractical for short period undulators. This report describes the issues that are related to a cold bore ({approx}4 K) and an intermediate temperature bore (30 to 70 K) designs. The criteria for the use of small cryocoolers for cooling a short period undulator are presented. The problems associated with connecting small coolers to an undulator at 4.2 K are discussed.

We present the concepts for an electron storage ring dedicated to and optimized for the production of stable coherent synchrotron radiation (CSR) over the far-infrared terahertz wavelength range from 200 μm to about 1 cm. CIRCE (Coherent InfraRed CEnter) will be a 66 m circumference ring located on top of the ALS booster synchrotron shielding tunnel and using the existing ALS injector. This location provides enough floor space for both the CIRCE ring, its required shielding, and numerous beamlines. We briefly outline a model for CSR emission in which a static bunch distortion induced by the synchrotron radiation field is used to significantly extend the stable CSR emission towards higher frequencies. This model has been verified with experimental CSR results. We present the calculated CIRCE photon flux where a gain of 6–9 orders of magnitude is shown compared to existing far-IR sources. Additionally, the particular design of the dipole vacuum chamber has been optimized to allow an excellent transmission of these far-infrared wavelengths. We believe that the CIRCE source can be constructed for a modest cost.

We present the concepts for an electron storage ring dedicated to and optimized for the production of stable coherent synchrotron radiation (CSR) over the far-infrared terahertz wavelength range from 200 pm to about one cm. CIRCE (Coherent InfraRed CEnter) will be a 66 m circumference ring located on top of the ALS booster synchrotron shielding tunnel and using the existing ALS injector. This location provides enough floor space for both the CIRCE ring, its required shielding, and numerous beamlines. We present the calculated CIRCE photon flux where a gain of 6 - 9 orders of magnitude is shown compared to existing far-IR sources. Additionally, the particular design of the dipole vacuum chamber has been optimized to allow an excellent transmission of these far-infrared wavelengths. We believe that the CIRCE source can be constructed for a modest cost.

ALS Superbend Magnet Performance S. Marks, J. Zbasnik, W. Byrne, D. Calais, M . Chin, R. DeMarco, M . Fahmie, A . Geyer, J. Krupnick, F. Ottens, J. A . Paterson, P. Pipersky, D. A . Robin, R. D. Schlueter, C. Steier, A . Wandesforde results; Section III will summarize cryogenic test results. The design, requirements, and Superbend project have been 'Abstract— The Lawrence Berkeley National Laboratory has discussed elsewhere [3], [4], [5]. been engaged in the design, construction and testing of four superconducting dipoles (Superbends) that are installed in three arcs of the Advanced Light Source (ALS), with the fourth magnet as a spare. This represents a major upgrade to the A L S providing an enhanced flux and brightness at photon energies above 10 keV. In preparation for installation, an extensive set of tests and measurements have been conducted to characterize the magnetic and cryogenic performance of the Superbends and to fiducialize them for accurate placement in the A L S storage ring. The magnets are currently installed, and the storage ring is undergoing final commissioning. This paper will present the results of magnetic and cryogenic testing. i. INTRODUCTION II. MAGNETIC PERFORMANCE A. Magnetic Measurement Setup Figure 1 below, shows a picture of Superbend #1 installed around an alignment fixture on the test stand. Both the cryostat and the alignment fixture are mounted with six struts allowing for adjustment in all degrees of freedom. he Advanced Light Source (ALS) at the Lawrence Berkeley National Laboratory (LBNL) is a national user facility producing high brightness synchrotron radiation, primarily in the vacuum ultraviolet and soft x-ray regimes (6 eV to 10 keV). The A L S has engaged in a major upgrade to meet the growing demand for bright hard x-ray sources with photon energies above 10 keV. The upgrade consists of replacing three of the total of 36 conventional storage ring bending magnets with three superconducting bend magnets (Superbends). The increase in peak field from 1.34 T, corresponding to the conventional bend magnets, to 5.74 T, for the Superbends, results in almost an order of magnitude increase in both flux and brightness at 10 keV, and nearly two orders of magnitude at 20 keV for an electron beam energy of 1.9 GeV. Experimental uses for the new sources will include protein crystallography, x-ray tomography and powder diffraction. In the initial R & D phase of the Superbend project a conceptual design of a magnet that could be incorporated into the A L S was developed, and a robust superconducting coil was produced and tested[l], [2]. The second phase of the project, a joint venture between L B N L and Wang N M R , involved detailed design and fabrication of four magnets. Following fabrication, each magnet underwent extensive magnetic and cryogenic testing. This paper will report the results of the tests. Section II will summarize magnetic test Manuscript received September 24, 2001. This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division, of the U . S. Department of Energy, under Contract No. DE-AC03-76F00098. Authors are with Larwence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, California, U S A . T Fig. 1 Magnet #1 installed on the test stand. The alignment fixture serves several important functions in the testing process [4]. A cylindrical bore coincident with the