Cryogenic Permanent Magnet Undulator Research Articles

Design, construction and testing of the prototype cryogenic circulation centrifugal pump for the high energy photon source

A cryogenic circulation pump (CCP) with the small flow rate and low heat leakage, which is thekeyequipment of the cooling system for the cryogenic permanent magnet undulator (CPMU)and synchrotron monochromator in High Energy Photon Source(HEPS), is developed according to the design parameters and operation experiences. The mechanic structure of the CCP including a motor at room temperature, an impeller and a volute in the cryogenic environment is designed, and numerical simulation on the rotating shaft and internal flows are performed to predict the mechanical and hydrodynamic performances of the pump. Meanwhile, the experimental investigation of the CCP is carried out in the liquid nitrogen (LN2) cryogenic system, and the hydrodynamic performances of the CCP are verified experimentally. The results are shown that the calculated performances of the CCP are in reasonable agreement with the experimental results, which indicates that the numerical calculation model of the CCP is more effective. Moreover, the deviations of pressure drop and efficiency between the calculation and measurement are analyzed in this paper.

Study on the influence of gap dependent error on the cryogenic permanent magnet undulator performance

The mass production of the first stage of HEPS (High Energy Photon Source) is approaching its final stage. 6 CPMUs (cryogenic permanent magnet undulators) have been manufactured, with four successfully finalizing the tuning of the magnetic field. To ensure radiation performance, HEPS's CPMUs enforce stringent phase error protocols. Moreover, the contraction properties at cryogenic temperature lead to a decrease in phase error after cooling. In the process of CPMU commissioning, a technique for forecasting the change of magnetic errors from room to cryogenic temperature was discovered and studied, as will be demonstrated in this paper.

Novel correction procedure for compensating thermal contraction errors in the measurement of the magnetic field of superconducting undulator coils in a liquid helium cryostat.

Superconducting undulators (SCUs) can offer a much higher on-axis undulator field than state-of-the-art cryogenic permanent-magnet undulators with the same period and vacuum gap. The development of shorter-period and high-field SCUs would allow the free-electron laser and synchrotron radiation source community to reduce both the length of undulators and the dimensions of the accelerator. Magnetic measurements are essential for characterizing the magnetic field quality of undulators for operation in a modern light source. Hall probe scanning is so far the most mature technique for local field characterization of undulators. This article focuses on the systematic error caused by thermal contraction that influences Hall probe measurements carried out in a liquid helium cryostat. A novel procedure, based on the redundant measurement of the magnetic field using multiple Hall probes at known relative distance, is introduced for the correction of such systematic error.

Performance investigation of conduction-cooled cryogenic permanent magnet undulator at high beam currents

Performance investigation of conduction-cooled cryogenic permanent magnet undulator at high beam currents

An in-vacuum measurement system for CPMUs at Diamond Light Source

An in-vacuum Hall probe measurement system was designed, built, and used to measure four Cryogenic Permanent Magnet Undulators (CPMUs) at Diamond Light Source. The devices were tuned to correct the phase error at cold temperatures based on the measurements from the in-vacuum system. The in-vacuum system consists of a stretched wire system supplied by Danfysik and an in-house built Hall probe system. The Hall probe system has gone through two iterations: the first beam was prone to deforming with temperature changes; the second was made thicker following design changes to the magnet holders and girders of the CPMUs which allowed more space for the beam inside the vacuum vessel. The design and commissioning of the measurement system will be presented, along with some measurements of the CPMUs at room temperature and at 77 K. Details such as triggering of the Hall probe measurements, height compensation, and temperature compensation will be covered.

CPMU Development at Diamond Light Source

Over the last three years (2020-2022) Diamond Light Source has installed four in-house designed, built, and measured Cryogenic Permanent Magnet Undulators (CPMUs). All four are 2 m long with a 17.6 mm period and have a minimum operating gap of 4 mm. These have replaced existing 2 m long in-vacuum Pure Permanent Magnet (PPM) devices to improve the flux to several of Diamond’s MX (Macromolecular Crystallography) beamlines by a factor of 2-4. In this paper we present the mechanical and cryogenic design considerations, and the shimming procedures and tools developed to produce these devices. The performance of the CPMUs compared to their PPM counterparts will also be reviewed.

Development of a 12 mm period cryogenic permanent magnet undulator for time-resolved X-ray beamline on HEPS

In order to obtain hard x-rays with the fundamental harmonic energy over 20 keV, a Pr2Fe14B based cryogenic permanent magnet undulator (CPMU) with the period length of 12 mm has been developed on High Energy Photon Source (HEPS) for time-resolved beamline. Several technical difficulties arise with the further shortening of the CPMU period length such as magnets and poles clamping, constitutionally stable pole height shimming, multipoles shimming within the small horizontal area according to the dynamic apertures of ultra-low emittance storage ring. Some specific treatments are adopted in response to these difficulties and proved to be effective. Details of development process including design, assembling, methods of optimization, measurement and shimming are presented.

Application of force-compensating spring modules on mechanical frame of undulators

A small RMS phase error and long-term stability of the gap-drive system are important criteria for realizing high performance undulators. The use of force compensating spring modules of self-contained type move toward the goals. Since magnetic forces from girders are vanished entirely at the spring module, so not only the small systematic phase error derived from deformation of the girders but also the small dynamic loadings on the mechanical frame and gap-drive system. Moreover, spring modules provide a supplemental mechanism to correct magnetic field errors at varied gaps. Such mechanism is particular benefit for the cryogenic permanent magnet undulators because the field errors of undulator shall correct in both cryogenic mode and room temperature mode.

A Temperature-Dependent Calibration of Hall Probes for CPMU

A cryogenic permanent-magnet undulator (CPMU) with period 18 mm and magnetic length 2 m is being constructed for Taiwan Photon Source. The CPMU (gap 5.5 mm) can generate effective magnetic field 1.18 T at magnetic arrays temperature of 170K. When the field is measured under long time, the temperature of a Hall probe decreases at a cryogenic temperature; a calibration of the field strength and a thermostatic control system for the tem-perature is hence necessary. The calibration range of the field strength of a dipole electromagnet is from 0.00055 to 1.5T. A two-axis compact Hall probe (SENIS) is mounted on a copper plate in a vacuum chamber. The system to control temperature consists of a cryocooler, a sensor (PT100) and a heater to control temperature of the Hall probe. A higher-order polynomial sur-face fit is applied to analyze the data measured from the calibra-tion system. The maximum error of field strength is less than 0.02 % at the fitted surface. Details of the temperature-dependent cal-ibration system are presented in this paper.

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.

Effect Analyses of Thermal Deformation on Magnetic Performance of the CPMU Prototype in SSRF

A cryogenic permanent magnet undulator (CPMU) prototype cooled by sub-cooled liquid nitrogen was developed in Shanghai Synchrotron Radiation Facility (SSRF) in 2016. The CPMU prototype mainly consist of NdFeB based hybrid magnet arrays with a period of 20 mm and a magnetic length of 1.6 m, a pair of girders to support the magnetic arrays, parallel SLN2 cooling loops attached to the girders, thermal spacers connecting the girders and the copper LN2 tubes, electric heaters to heat the girders and regulate the magnet working temperature at around 120 K, and stems made of stainless steel to support the girders. During the first magnetic field measurement, the RMS phase error of the CPMU prototype changed from 3.2 degree at room temperature to 4.5 degree at 135 K. By shimming the magnetic field, its RMS phase error is reduced to 3.5 at low temperature finally. This paper presents detailed analyses of temperature distribution and thermal deformation along the CPMU girder during cool down process. By comparison with test results, the deterioration of the RMS phase error is well explained. The analyses can provide guidance for magnetic field shimming and avoid or reduce the deterioration of the RMS phase error at low temperature.

Control system for cryogenic permanent magnet undulator (CPMU) of high energy photon source (HEPS)

Control system for cryogenic permanent magnet undulator (CPMU) of high energy photon source (HEPS)

Single-block measurement for the cryogenic permanent magnet undulator sorting

The magnet sorting is a standard step in the undulator fabrication procedure. The shortest undulators period used in the High Energy Photon Source (HEPS) is only 12 mm. To the short period undulator, the sorting may be more important than the long-period undulator. Normally, the Helmholtz measurement is used as the input for the work. It is the averaged orthogonal magnetization of each block. In order to investigate whether the Helmholtz coil measurement is enough for the sorting, a careful study has been made. Firstly, a magnetic camera was used to scan the 3D surface field of a magnet. Afterward, its field integral is measured by the stretched wire. In the measurement, the magnet was placed at different statuses. The results were checked to see whether they are consistent with expected features supposing a homogeneous magnetized block. Finally, the results measured by the Helmholtz coil and the stretched wire were compared. The surface field scan demonstrates that the field over a magnet block is inhomogeneous. Moreover, the field integral measurement by the stretched wire also shows big difference when the different magnet sides toward the wire. The comparison between the stretched wire and the Helmholtz coil measurement shows no correlation. The study presented in this paper reveals that the homogeneity of the magnetization is imperfect. Therefore, the Helmholtz coil data are insufficient to the short-period undulators sorting.

High-accuracy stretched-wire measurement system for cryogenic permanent magnet undulator (CPMU) in High Energy Photon Source (HEPS)

A new stretched-wire system is built for a cryogenic permanent magnet undulator in High Energy Photon Source Testing Facility. The system has two functions: integral field measurement and magnet gap measurement. Integral field measurement and gap measurement are important for evaluation and optimization of the magnetic performance of the undulator in cryogenic–vacuum environment. Two high-precision, high-load motion stages are used for accurate positioning. A special fix structure of stretched wire is adopted for vacuum environment. To reduce the deflection of the 3-meter-long wire, constant tension is maintained along the wire. The measurement repeatability of field integral and magnetic gap is the key performance which depends on the stability of wire and suppression of the electric noise. Strategy of improving the measurement accuracy and stability is presented.

Control System for a Cryogenic Permanent Magnet Undulator at the Taiwan Photon Source

A hybrid cryogenic permanent-magnet undulator (CPMU) with a 15-mm period length is being constructed for a TPS Phase-II beamline. A control system for this CPMU (CU15) is under development since 2018 and is based on the Experimental Physics and Industrial Control System (EPICS) architecture and Ethernet Control Automation Technology (EtherCAT) framework. The main control components include a motor with encoder for gap adjustment, corrector magnet power supplies, ion pumps and BA gauges for the vacuum system, resistance temperature detectors (RTD) and heaters for temperature control of the cryogenic environment and magnet arrays, motion safety interlock, cryogenic system and vibration monitor system. The design and implementation of the CU15 control system will be summarized in this paper.

Field Measurements of a Cryogenic Permanent Magnet Undulator at the TPS

A PrFeB-based cryogenic permanent-magnet undulator (CPMU) with a period length of 15 mm (CU15) is being constructed to provide high brilliant X-rays for the Taiwan Photon Source (TPS) nano-probe beamline. Field measurements of this undulator will be performed with a Hall probe in a vacuum environment. The in-situ Hall probe measurement system (Yang et al. , 2014) was improved (Yang et al. , 2016) to allow measurement and tuning of the CU15 magnetic field. A field strength and temperature dependent calibration of the Hall probe was done to obtain realistic field distributions. By tuning the differential adjusters and spring modules, we can correct magnetic field errors caused by assembly tolerances and temperature gradients along the magnetic arrays, thus lowering phase errors to reach our design goals. This paper describes details of improvements in the measurement system, field tuning methods, and measurement results at cryogenic temperatures.

Research on the comprehensive performance of PrFeB magnets for synchrotron radiation and free electron laser

PrFeB magnets, which possess excellent magnetic properties at low temperatures, have important application value as cryogenic permanent magnet undulators for synchrotron radiation sources and free electron lasers. In this research study, several high-performance PrFeB magnets (P42H, P48SH, and P48UH) were prepared, and their performance was comprehensively examined, including evaluations of their magnetic properties, microstructures, uniformity, and stability. Next, their application prospects were analyzed and discussed. In China, the first cryogenic permanent magnet undulators (CPMUs) with P48SH magnets with 18 mm cycle lengths have been developed. When the temperature is 80 K and the gap is 6.0 mm, the magnetic field measurement results of the CPMU showed that the effective magnetic field peak was approximately 0.92 T, yielding an increase of 11.76% relative to operation at 300 K, with an RMS phase error of about 4.99°.

The Magnetic Field Measurement Systems for a Cryogenic Undulator and a Superconducting Undulator at SSRF

Two cryogenic permanent magnet undulators (CPMU) have been developed and assembled into storage ring at Shanghai Synchrotron Radiation Facility (SSRF) in order to produce higher brilliance in the hard X rays domain. At low temperatures, permanent magnet materials can provide both higher magnetic field and higher resistance to radiation-induced demagnetization of the magnet compared to room temperature operation. Test results indicate that lowering the temperature of permanent magnets (Nd2Fe14B) increases the magnetic field strength about by 11%. The magnetic field distribution of the CPMU must be measured after the magnetic arrays are installed into the vacuum chamber and cooled to cryogenic temperature. We have finished a magnetic measurement bench based on a Hall probe to perform cryogenic temperature measurement. In this papers, the details of the magnetic field measurement system and some test results of a CPMU20 with 20mm period and Nd2Fe14B type are described. In addition, two superconducting planar undulator (SCU) prototypes with period 16mm are also under development at SSRF to research some key technologies.

Influence of cryogenic permanent magnet undulator motion error on magnetic field error and radiation intensity loss

A cryogenic permanent magnet undulator prototype designed for Chinese High Energy Photon Source Test Facility (HEPS-TF) at Institute of High Energy Physics is constructed and now commissioning. Motion precision of girders is a significant parameter to guarantee gap error so as to avoid phase error and radiation intensity loss. In order to study and minimize girder parallelism errors, RADIA and SPECTRA are used to calculate qualified motion precision. Spring Modules and single motor closed-loop feedback are designed to compensate the errors. Magnetic field is finally tuned to reach specifications. Details of the study and analysis will be presented in this paper.

Magnetic field strength and temperature-dependent calibration system of Hall probe for the HEPS-TF cryogenic permanent magnet undulator

High energy photon source test facility (HEPS-TF) has manufactured a three-dimensional Hall probe to measure the cryogenic permanent magnet undulator (CPMU). Since the operating environment of the CPMU is the subcooled liquid nitrogen (85K), the temperature of the Hall probe will have a decrease of several degrees while carrying out the local magnetic measurement. We established a magnetic field strength and temperature-dependent calibration system to calibrate the Hall probe. The magnetic field strength of the Hall probe was calibrated by a standard dipole electromagnet and a nuclear magnetic resonance Tesla meter (NMR). The temperature of Hall probe was controlled by a control system which can modulate temperature from $$0^{\circ }$$ C to $$30^{\circ }$$ C. A new homemade Hall probe has finished the temperature-dependent ( $$0^{\circ }$$ C to $$30^{\circ }$$ C), magnetic field strength (-1.2 to 1.2 T) and angle error calibration at this new calibration system. The temperature correction error is less than 0.045%. The calibration error of magnetic field strength is less than 1.5 Gs. The RMS calibration error of Hall sensors angle matrix is less than 5.1E-5. The magnetic field strength and temperature-dependent calibration system including a standard dipole electromagnet, a temperature regulation system, an NMR and a five-dimensional Hall bench was established. The detailed magnetic field strength and temperature-dependent calibration system is introduced and the results of the calibrations are presented.