Superconducting Undulator Research Articles

Design, Fabrication, and Testing of a 1.9-m-Long, 16.5-mm Period NbTi Superconducting Undulator for the Advanced Photon Source Upgrade

Superconducting undulator (SCU) technology has been in use at the Advanced Photon Source since 2013. Due to the successful and reliable operation of the existing SCUs, the Advanced Photon Source upgrade project has decided to expand the use of NbTi-based SCUs. The first new magnets to be designed and fabricated are 1.9 m long with a period length of 16.5 mm. NbTi superconductor is used for coil winding and there are four separate coils wound on the mandrel to produce the main undulator field along with end compensation and distributed dipole compensation. The magnetic design, fabrication details, assembly, and testing are described in detail.

Parametric Optimization of Undulator Field for Short Period NI HTS Planar Undulator

There are increasing interests in high temperature superconducting(HTS) undulator with a gradual increase of engineering current density of REBCO conductor. Additionally, no-insulation(NI) winding technique may maximize the undulator field of HTS undulators mainly benefited from its high engineering current density. In this study, we present several design options of an NI HTS undulator to investigate its anticipated performance in terms of magnetic field strength. Specifically, maximum magnetic field along the beam axis depending on the magnetic gap, magnetic period length, winding dimension, and operating temperature is investigated. Then, these results are fitted using a scaling law to easily estimate the anticipated performances of NI HTS undulator at different magnetic gaps and magnetic periods. Finally, a comparison between NI HTS undulator, NbTi based low temperature superconducting undulator, and cryogenic permanent magnet undulator is discussed.

Development and magnetic field measurement of a 0.5-m-long superconducting undulator at IHEP.

Undulators are important devices for accelerator-based light sources whose magnetic field quality determines the photon beam performance. Superconducting-type undulators have been developing rapidly in recent years around the world. The insertion device group at the Institute of High Energy Physics (IHEP) in China started an R&D project to develop prototypes of superconducting undulators (SCUs). A half-meter-long planar SCU has been produced recently. The SCU was designed based on the simulation program OPERA-3D giving a period length of 15 mm and a gap of 7 mm. This prototype was manufactured and fabricated precisely, and was then tested by vertically submerging in liquid helium in a Dewar. After quench training several times, the maximum current in the main coils reached 480 A. The magnetic field was measured by Hall probes mounted on a sledge in the middle of the undulator gap. The peak magnetic field reached 1 T. The measurement results indicate that correction coils with suitable current can not only optimize the magnetic first and second integrals but also reduce the phase error, which is expected bydesign.

Development and cryogenic test of superconducting undulator mock-up coils at IHEP

The insertion device (ID) group at Institute of High Energy started an R&D project one year ago to develop superconducting undulators (SCUs). We produced a short SCU mock-up with 4.5 periods and 15 mm period length. The parameters of the SCU was determined based on the simulation results. Two short mock-up coils had been designed, manufactured and cryogenic tested. With the development of the mock-up, we studied the technology of manufacturing the SCU iron core and winding the NbTi/Cu superconducting wire. A cryogen-free cryostat was built to test the mock-up coils at 4 K temperature. After several times of quench training, the applied current in the coils reached 500 A giving a corresponding magnetic peak field of 1.06 T on axis measured by a hall probe.

Numerical analysis of the end-field with correction coils for the superconducting undulator at IHEP

Superconducting undulators (SCUs) are developing fast around the world. An R&D project is undergoing at Institute of High Energy Physics (IHEP) in China to produce a prototype of 15 mm period length planar undulator with superconducting technology. For undulators, the first and second magnetic field integrals along the longitudinal axis should be zero to avoid disturbing the beam trajectory. By using the finite element program OPERA-3D, we built the SCU model to study the magnetic field distribution on axis. We designed two correction coil pack on each end of the SCU core. The end-field can be adjusted flexibly with different correction currents. Our study in this paper reveals that the magnetic field integrals are highly dependent on the end-field. The relationship between the end-field integrals and the correction currents are given based on polynomial fitting. The optimal correction currents are obtained via numerical analysis.

Development of a Test Cryostat for a Superconducting Undulator Prototype at the SSRF

The superconducting undulator (SCU) is a trend to be applied for future light sources to obtain the higher light brilliance. A planar SCU prototype with a period of 16 mm, a magnetic gap of 9.5 mm and 50-periods magnet has been under development at the Shanghai Synchrotron Radiation Facility (SSRF) since late 2013. The key technologies including magnet cooling, coil winding, low-temperature alignment of magnet and beam tube, and cryogenic magnetic field measurement have been investigated. A cryocooler-cooled test cryostat was developed for the purpose of both experimentally studying the key technologies and testing the performance of the SCU prototype. Two-stage cryocoolers were applied for cool down, helium liquefaction and keeping the SCU cooled at operation. The SCU magnet and the UHV beam tube were cooled separately. The magnet working at 4.2 K is cooled by thermosiphon-driven liquid helium flowing through the piping in the magnet mandrel. The beam tube, thermal shields and binary leads were conduction-cooled. The beam tube will work at between 4.2 K and 20 K up to dynamic loads generated by the SSRF beam. A set of improved self-centered support assembly for the magnet was developed in order to avoid the complex alignment at low temperature and lower down the machining cost. A cooling approach to effectively cool the junction of the binary lead made of copper and HTS lead commonly used in cryocooler-cooled superconducting systems was adopted and validated. The cryostat was successfully debugged and run at the early of 2016. This paper describes the design details of the cryostat including new approaches to cool the SCU and the binary leads, its fabrication and test results.

Fast and efficient critical state modelling of field-cooled bulk high-temperature superconductors using a backward computation method

A backward computation method has been developed to accelerate modelling of the critical state magnetization current in a staggered-array bulk high-temperature superconducting (HTS) undulator. The key concept is as follows: (i) a large magnetization current is first generated on the surface of the HTS bulks after rapid field-cooling (FC) magnetization; (ii) the magnetization current then relaxes inwards step-by-step obeying the critical state model; (iii) after tens of backward iterations the magnetization current reaches a steady state. The simulation results show excellent agreement with the H -formulation method for both the electromagnetic and electromagnetic-mechanical coupled analyses, but with significantly faster computation speed. The simulation results using the backward computation method are further validated by the recent experimental results of a five-period Gd–Ba–Cu–O (GdBCO) bulk undulator. Solving the finite element analysis (FEA) model with 1.8 million degrees of freedom (DOFs), the backward computation method takes less than 1.4 h, an order of magnitude or higher faster than other state-of-the-art numerical methods. Finally, the models are used to investigate the influence of the mechanical stress on the distribution of the critical state magnetization current and the undulator field along the central axis.

Conceptual Design of a Conduction-Cooled Superconducting Undulator

In superconducting undulators (SCUs) that are currently operating at the Advanced Photon Source, the undulator magnets are indirectly cooled with liquid helium penetrating through channels in the magnet cores. The liquid helium is stored in a tank that is cooled by cryocoolers. However, a cryogen-free version of a superconducting undulator in which the undulator magnets are conduction-cooled is also possible, as has been realized in the SCUs developed at ANKA. We are currently working on a conceptual design of a conduction-cooled planar superconducting undulator. The measured load lines of cryocoolers and the measured thermal conductance of various thermal links are used in the thermal analysis. Also, various materials for the undulator magnet cores are being considered. This paper reports the thermal design of a conduction-cooled planar SCU.

Fabrication and Testing of 10-Pole Short-Period Nb3Sn Superconducting Undulator Magnets

NbTi superconducting undulators (SCUs) are currently reliably operating at the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). These devices have significantly enhanced x-ray flux and brightness at the high energy spectrum. As NbTi SCU technology is close to its full potential, further performance enhancement requires using different superconducting materials. Nb3Sn is a promising candidate to achieve that goal. Recently the APS has started developing a Nb3Sn superconducting undulator compatible with the APS storage ring. The completed device is planned to be installed in the APS storage ring. To develop the Nb3Sn SCU technology, a series of short SCU models has been previously fabricated and successfully tested. In this study, the design has been further optimized to address previously unresolved problems. Several 10-pole, 4.5-period models were fabricated and tested. All of the fabricated models have reached the maximum operating current; however, one of the model, MM4, has failed right after reaching the maximum design current. The details of quench and training performances are presented.

Development and operating experience of a 1.2-m long helical superconducting undulator at the Argonne Advanced Photon Source

Development of superconducting undulators (SCUs) continues at the Advanced Photon Source (APS). Several planar SCUs were designed and built, and two of them are currently in operation at the APS. In January 2018 a new helical SCU (HSCU) was installed on the storage ring at the APS. It has a 1.2 m-long magnet with bifilar winding that generates on its axis a single harmonic of about 6 keV x-rays. The magnet is housed in the newly designed compact cryostat equipped with four cryocoolers. The HSCU was extensively tested prior to its installation on the APS storage ring, and it demonstrated cryogenic and magnetic performance in accordance with the design specifications. The HSCU was rapidly and successfully commissioned, and in February 2018 it was transferred to user operations. Its performance as an x-ray radiation source has been studied and spectral characteristics confirmed. The HSCU is currently used to support unique scientific program at the APS.

Thermal Analysis of a Superconducting Undulator Cryostat for the APS Upgrade

The Advanced Photon Source Upgrade includes four 4.8-m-long superconducting undulator (SCU) cryostats, each containing two planar undulator NbTi magnets up to 1.9 m long. The cooling is provided by six cryocoolers arranged in three thermal circuits. The magnets are indirectly cooled with LHe penetrating through channels in the magnet cores. This 4 K circuit, which also includes a LHe tank, is cooled by five 4 K cryocooler 2nd stages. A beam vacuum, which is thermally isolated from the magnets, is cooled by one 10 K cryocooler 2nd stage. A thermal shield and warm parts of current leads are cooled by the 1st stages of all six cryocoolers. This paper presents an ANSYS-based thermal analysis of the new SCU cryostat including all thermal circuits. The benchmarked thermal conductance between the cryocooler cold heads and the LHe tank are used in the calculations as well as the measured cryocooler load lines. The model predicts temperatures in the system, total 4 K heat loads, and excess cooling power for various operational modes of the undulator.

A New Superconducting Undulator Cryostat for the APS Upgrade

The Advanced Photon Source (APS) is in the midst of a major facility upgrade including both a new electron storage ring (SR) and many new insertion devices (IDs) providing x-ray photon beams to a new suite of experimental end stations. Included among the new IDs are four 4.8-meter superconducting undulator (SCU) cryostats, each containing two 1.8-meter planar undulator magnets operating at 4.2 K in either a phase shifted or canted configuration. We describe a new, compact cryocooler-based cryostat design which supports the magnets and associated subsystems and also fits the space constraints of the SR ID straight sections. The design is an evolution of earlier single-magnet 2-meter cryostats, retaining some subsystem commonality while incorporating lessons learned and several features unique to the challenge of supporting two independently operable undulator magnets in a single device.

Cooling Design for the Magnetic Structure of SHINE Superconducting Undulator

Forty planar superconducting undulators (SCUs) of 4 m length will be used in Shanghai High Repetition rate XFEL and Extreme Light (SHINE) facility. As the longest SCU in developing of the worldwide, they could generate photon in energy range of 10-25 keV. NbTi/Cu wires with the diameter 0.6 mm and the ratio of Cu to NbTi 0.9 have been chosen as the fundamental element of superconducting coils. Coils temperature must be below 5 K when operating current reaches 400 A. Meanwhile, the magnetic gap need to be less than 5 mm to obtain the peak field of 1.58 T. Therefore, beam chamber installation is infeasible in such a small gap. Two parallel copper foils close to the surface of magnetic poles have been designed to shield beam heat load. Furthermore, four liquid Helium tubes located symmetrically around magnetic structure have been designed to cool the copper foils used as beam channel. There is no cryocooler on the SCU because liquid Helium is provided by the cryogenic plant of SHINE.

Superconducting undulator coils with period length doubling

Only since few years it has been demonstrated experimentally that NbTi based superconducting undulators (SCUs) have a higher peak field on axis for the same gap and period length in operation with electron beam with respect to permanent magnet undulators (even the ones in vacuum and cooled to cryogenic temperatures). Another advantage of NbTi based SCUs with respect to permanent magnet devices is radiation hardness, widely demonstrated for NbTi magnets, which is and will become an increasingly important issue with the small gaps in the newest machines as round beam storage rings and FELs. Moreover, SCU technology allows switching of the period length by changing the current direction in one of separately powered subset of winding packages of the superconducting coils. This feature further broadens the energy range of the emitted photons, required by the different beamlines. To this end a 0.41 m long superconducting undulator coil with switchable period length between 17 mm and 34 mm has been developed. In this contribution we describe the design and report on the quench tests, as well as on the magnetic field measurementsThe first section in your paper.

Development of Short-Period Nb3Sn Superconducting Planar Undulators

NbTi-based superconducting undulators (SCUs) have been developed and proven to increase the brightness by an order of magnitude at high X-ray energies at the ANL's Advanced Photon Source (APS). Nb 3 Sn has the potential to further enhance the performance of SCUs. A new project, aiming to fabricate a full-length, 3-m-long Nb 3 Sn SCU, compatible with the storage ring, has started at the APS. To develop the technology, three Nb 3 Sn short prototype magnets were fabricated and tested in liquid helium. These prototypes were used to incrementally improve the original design. The final short model magnet reached 100% of the short sample limit. The achieved current level in this magnet is 75% higher than what an NbTi wire can deliver.

Full-Scale Conduction-Cooled Superconducting Undulator Coils—Training, Stability, and Thermal Behavior

For several years, the Institute for Beam Physics and Technology (IBPT) at the Karlsruhe Institute of Technology (KIT) has collaborated with its industrial partner Babcock Noell GmbH (BNG) on the development of superconducting undulators (SCUs) for the electron storage ring ANgstromquelle KArlsruhe (ANKA), the test facility and synchrotron radiation source run by the IBPT, as well as low-emittance synchrotron radiation sources. After the successful test of the first full scale, 1.5-m-long, superconducting undulator with 15-mm period length in the ANKA storage ring, the collaboration is at present primarily working on an SCU with 20-mm period length (SCU20), foreseen to be installed at ANKA. The 1.5-m-long undulator coils have been tested in a horizontal, conduction-cooled measurement setup developed at the IBPT. This paper describes the training, stability, and thermal behavior of the coils.

The potential role of cryogenics in insertion magnets

Most of the insertion magnets that are used for storage rings and free-electron lasers are room temperature permanent magnets. Superconducting wiggler and undulator magnets have been built, but their performance has been limited by the engineering current density and stability of the coils. Superconducting undulators must have a small gap and cell length, which can be a hindrance even when the beam vacuum chamber is at room temperature. Beam heating is also an issue. To control, the heat leak at low temperature, the beam vacuum chamber should be cooled to a temperature between 20 and 40 K. Permanent magnets fabricated from Nd-Fe-B can be cooled to cryogenic temperatures with an increase in the magnetic field within the magnet gap. This permits the magnet gap to be reduced considerably when the vacuum chamber is at the same temperature as the permanent magnet. This paper discusses the cryogenic cooling of both superconducting and cryogenic permanent magnet wigglers and undulators.

A second-generation superconducting undulator cryostat for the APS

A second-generation cryocooler-based cryostat has been designed and built to support a new helically wound superconducting undulator (SCU) magnet for the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). The design represents an evolution of existing SCU cryostats currently in operation in the APS storage ring. Value engineering and lessons learned have resulted in a smaller, cheaper, and simpler cryostat design compatible with existing planar magnets as well as the new helically wound device. We describe heat load and quench response results, design and operational details, and the “build-to-spec” procurement strategy.

Thermal Model of a Quench in Superconducting Undulators

Currently there are two 1.1 m long planar superconducting undulators (SCUs) in operation in the Advanced Photon Source storage ring. Their NbTi magnets are cooled with liquid Helium (LHe) penetrating through a channel in the magnet coil formers. In this scheme, the latent heat of LHe provides an effective energy buffer that allows the magnet to return to normal operation within minutes. An FEA-based dynamic thermal model of the SCU is being developed to analyze the behavior of the SCU cryogenic systems during a quench. In this paper, preliminary results of these FEA-based calculations and a comparison with the current operation of SCUs are presented.

Hard X-ray Sources for the Mexican Synchrotron Project

One of the principal tasks for the design of the Mexican synchrotron was to define the storage ring energy. The main criteria for choosing the energy come from studying the electromagnetic spectrum that can be obtained from the synchrotron, because the energy range of the spectrum that can be obtained will determine the applications available to the users of the future light source. Since there is a public demand of hard X-rays for the experiments in the synchrotron community users from Mexico, in this work we studied the emission spectra from some hard X-ray sources which could be the best options for the parameters of the present Mexican synchrotron design. The calculations of the flux and the brightness for one Bending Magnet and four Insertion Devices are presented; specifically, for a Superconducting Bending Magnet (SBM), a Superconducting Wiggler (SCW), an In Vacuum Short Period Undulator (IV-SPU), a Superconducting Undulator (SCU) and for a Cryogenic Permanent Magnet Undulator (CPMU). Two commonly available synchrotron radiation programs were used for the computation (XOP and SRW). From the results, it can be concluded that the particle beam energy from the current design is enough to have one or more sources of hard X-rays. Furthermore, a wide range of hard X-ray region can be covered by the analyzed sources, and the choice of each type should be based on the specific characteristics of the X-ray beam to perform the experiments at the involved beamline. This work was done within the project Fomix Conacyt-Morelos ”Plan Estrategico para la construccion y operación de un Sincrotron en Morelos” (224392).