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...

At the heart of the LCLS-II are two undulator lines: the hard x-ray (HXR) line and the soft x-ray line (SXR). The SXR line is comprised of 21 variable gap undulator segments separated by an interspace stands with a cam positioning system capable of positioning in 5 degrees of freedom (DOF). The undulator segment motion control utilizes the Aerotech Ensemble motion controller through an EPICS Soft IOC (input-output controller). Its drive system consists of a Harmonic Drive servo system with feedback from two absolute full-gap encoders. Additional Aerotech motion controllers are used to control the campositioning system and phase shifters of the interspace stand. The HXR line is comprised of 32 undulator segments each including an integrated interspace assembly. The segment girder is placed on two stands with a similar cam-positioning system as in the SXR line allowing for movement in 5 DOF. As one of the design goals of the HXR line was to reuse the original LCLS girder positioning system, the motion control system is an upgraded version of that original system, using RTEMS on VME with Animatics SmartMotors.

The new free electron laser facility Linear Coherent Light Source II (LCLS-II) under construction at SLAC National Accelerator Laboratory will use planar variable gap undulators of hybrid type for the production of free electron laser (FEL) radiation. The LCLS-II will include two FELs with two separate rows of undulators to generate soft and hard x-rays. The soft x-rays will be produced by undulators with 39 mm period length (SXR) and the hard x-rays will be produced by undulators with 26 mm period length (HXR). Both the SXR and the HXR undulators are 3.4 m long and they use a common support structure and frame. In total 21 SXR and 32 HXR undulators will be produced by Lawrence Berkeley National Laboratory in collaboration with SLAC National Accelerator Laboratory. A full-scale prototype with 32 mm period length, called HXU, has been assembled at Lawrence Berkeley National Laboratory (LBNL). The present status of the design, prototyping, and pre-series production of the SXR and HXR undulators are presented in this paper together with the first results from measurements on the full scale HXU prototype.

The Advanced Light Source (ALS) at Berkeley Lab remains one of the brightest sources for soft x-rays worldwide. A multiyear upgrade of the ALS is underway, which includes new and replacement x-ray beamlines, a replacement of many of the original insertion devices and many upgrades to the accelerator. The accelerator upgrade that affects the ALS performance most directly is the ALS brightness upgrade [1], which reduces the horizontal emittance from 6.3 to 2.0 nm (2.5 nm effective). Magnets for this upgrade were installed in late 2012 and early 2013 followed by user operation with the reduced emittance.

The pulsed wire technique is an attractive option for the measurement of undulators where the measurement access is restricted due to, for example, narrow undulator gaps or cryogenic environments in the case of superconducting undulators. Using the pulsed wire technique, direct measurements of the first and second integrals of the magnetic field can be obtained. However, one of the main limitations of this technique is the error introduced by dispersive wave motion, due to the finite flexural rigidity of the wire. For the measurement of the first integral of the magnetic field, an error is also introduced by the use of a current pulse with finite pulse width. In this paper, a general solution is presented for dispersive wave motion in pulsed wire measurements. A method for the measurement of the dispersive wave speed is presented and demonstrated through experimental examples. An algorithm is derived which corrects the dispersion and finite pulse-width errors in the measurement of first magnetic field integrals and the dispersion error in the measurement of second magnetic field integrals. The effectiveness of the correction algorithms is demonstrated through experimental measurements, and the results are compared with Hall probe measurements on a short undulator.

The Advanced Light Source (ALS) at Berkeley Lab while one of the earliest 3rd generation light sources remains one of the brightest sources for soft x-rays worldwide. A multiyear upgrade of the ALS is currently under way, which includes new and replacement x-ray beamlines, a replacement of many of the original insertion devices and many upgrades to the accelerator. The accelerator upgrade that affects the ALS performance most directly is the ALS brightness upgrade, which will reduce the horizontal emittance from 6.3 to 2.2 nm (2.6 nm effective). This will result in a brightness increase by a factor of three for bendmagnet beamlines and at least a factor of two for insertion device beamlines. Magnets for this upgrade are currently in production and will be installed starting later this year.

Forty-eight harmonic sextupole magnets with integrated dipole correctors and skew quadrupole coils will be introduced in the Advanced Light Source Storage Ring. These new magnets are required to allow the ALS to provide the 40 beamline users with higher photon beam brightness (factor of 2 or 3). Introducing new combined-function magnets in an existing storage ring is a challenge due to the limited space available and a balance had to be found between magnet performance and spatial constraints. Consequently four different magnet designs were required. The calculation and simulation results obtained for each design as well as the impact of the different design choices on the magnetic performance are developed in this paper.

The Advanced Light Source (ALS) is a third-generation light source in operation since 1993. This light source is providing state-of-the-art performance to more than 40 beamlines and their users, due to the upgrades that have been completed over the last few years. The storage ring upgrade project that is developed here will allow the ALS to provide the 40 beamline users with higher photon beam brightness (factor of 2 or 3) by having its storage ring lattice modified. Forty-eight harmonic sextupole magnets with integrated dipole correctors and skew quadrupole coils will be introduced, which will require a level of installation activity not seen at the ALS since its original construction in 1991. Introducing new combined-function magnets in an existing storage ring is a challenge due to the limited space available and a balance had to be found between magnet performance and spatial constraints. After an introduction reviewing the characteristics of the three design families of the 48 combined-function magnets, the magnet fabrication and installation are developed along with analyses based on the magnetic measurements and the ALS storage ring commissioning results.

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.

The Advanced Light Source (ALS) at Berkeley Lab is one of the earliest 3rd generation light sources. Over the years substantial upgrades have been implemented to keep the facility at the forefront of soft x-ray sources. A multiyear upgrade is currently under way, which includes new and replacement x-ray beamlines, a replacement of many of the original insertion devices and many upgrades to the accelerator. The accelerator upgrade that affects the ALS performance most directly is the ALS brightness upgrade, which will reduce the horizontal emittance from 6.3 to 2.2 nm (2.6 nm effective). This will result in a brightness increase by a factor of three for bend magnet beamlines and at least a factor of two for insertion device beamlines and will keep the ALS competitive with newer sources.

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.

An upgrade of the Advanced Light Source to enable top-off operation has been completed during the last four years. The final work centered around radiation safety aspects, culminating in a systematic proof that top-off operation is equally safe as decaying beam operation. Commissioning and transition to full user operations happened in late 2008 and early 2009. Top-off operation at the ALS provides a very large increase in time-averaged brightness (by about a factor of 10) as well as improvements in beam stability. The following sections provide an overview of the radiation safety rationale, commissioning results, as well as experience in user operations.

Superconducting undulator (SCU) technology has the potential to significantly enhance the performance of synchrotron radiation sources for storage ring and FEL applications. Since 2002, our team at Lawrence Berkeley National Laboratory has been performing R&D on superconducting undulators, including the fabrication of three Nb3Sn prototypes. We have demonstrated experimentally the possibility to provide the prototype with trim coils that could be used for phase error correction. The research effort that we report here demonstrates the possibility to add degrees of freedom to the field correction provided by these coils in a cryogenic environment. By means of bridge of superconducting switches, we can modify the current direction through a trim coil. Here we describe the design of the experimental bridge we fabricated, the results we obtained and finally the generalized concept one could plan to apply to correct the phase errors with trim coils connected to a network of superconducting bridges.

Heat load on beamline optics is a serious obstacle for devices designed to generate pure linearly polarized photons in third generation synchrotron radiation facilities. For permanent magnet undulators, this problem can be overcome by implementing a figure-eight design configuration. As yet there has been no good method to tackle this problem for electromagnetic elliptical undulators. Here, a novel design and operational mode is suggested, which can generate pure linearly polarized photons with very low on-axis heat load. Additionally, the minimum photon energy capability of linearly polarized photons can be significantly extended by this method.

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 total of three permanent magnet chicane magnets have been installed at the Advanced Light Source (ALS) at the Lawrence Berkeley National Laboratory. The magnet de- sign incorporates an annular array of counter-rotating per- manent magnet pairs (PMs) with supplemental fast trim coils (EMs). The purpose is to provide a fixed angular sep- aration between two successive elliptically polarizing un- dulator (EPU) photon fans (with the PMs) and to correct steering perturbation resulting from EPU polarization state and gap changes (with the hysteresis-freeEMs). This paper presents a method for fine tuning relative orientation set- tings of the rotors in the presence of initial uncertainty of the exact PM rotor geometrical and magnetization param- eters by performing magnetic measurements with rotating coils. The measurement method will be developed and il- lustrated with experimental data from the measurement of a 16 cylinder permanent magnet harmonic corrector ring.

An upgraded femtosecond slicing facility has been commissioned successfully at the Advanced Light Source. In contrast to the original facility at the ALS which pioneered the concept, the new beamline uses an undulator (the first in-vacuum undulator at the ALS) as the radiator producing the user photon beam. To spatially separate the femtosecond slices in the radiator, a local vertical dispersion bump produced with 12 skew quadrupoles is used. The facility was successfully commissioned during the last 1.5 years and is now used in routine operation.

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.

The advanced light source is currently being upgraded for top-off operation. This major facility upgrade will provide an improvement in brightness from soft X-ray undulators of about one order of magnitude and keep the ALS competitive with the newest intermediate energy light sources. Major components of the upgrade include making the booster synchrotron capable of full energy operation, radiation safety studies, improvements to interlocks and collimation systems, diagnostics upgrades as well as emittance improvements in the main storage ring. Most hardware necessary as part of the upgrade has been installed and commissioned. The radiation safety studies are making good progress and have passed a first outside peer review successfully.