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

Background High energy photon source(HEPS)is the fourth-generation light source,which uses a large number of highperformance insertion devices to generate synchrotron radiation.The control system is an important part of the insertion device(ID).Purpose Cryogenic permanent magnet undulator(CPMU)is one kind of IDs that works in liquid nitrogen temperature and ultra-high vacuum environment,and its control system is more difficult and complex than in-air ID.The design of the control system for CPMU will be introduced in detail.Method The sub-systems include high-precision magnetic gap control,safety protection,measurement and compensation of magnetic gap at cryogenic temperature and cryogenic temperature monitoring.Mature,reliable,stable technical schemes are designed to meet the technical specifications of sub-systems.Results The experiment results show that the magnetic gap motion accuracy can be controlled within 0.2–0.3μm under the step size of 1μm.The safety protection system has been tested in turn,and the predetermined protection can be achieved.The average value of magnetic gap cold contraction is 1.512 mm measured by optical micrometer,and the compensation is realized by software.The average temperature of the main magnet structure measured by the temperature sensors is 81.0 K,and the temperature gradient is 0.7 K/m.The temperature monitoring is reliable and stable.Conclusion The CPMU control system which is based on EPICS has been successfully applied to the CPMU prototype,and the test results have met the design specifications.

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.

Hall sensor angle error and relative position calibrations for cryogenic permanent magnet undulator of high energy photon source test facility(HEPS-TF)

Purpose A new in-vacuum three-dimensional Hall probe magnetic measurement system is under fabrication for characterizing the magnetic performance of the Cryogenic Permanent Magnet Undulator(CPMU).In order to fit the small gap(5 mm)of magnetic structure and vacuum environment,a small three-dimensional Hall probe has been manufactured.The angular and positional misalignment errors of the Hall sensors play an important role in the measurement accuracy of the CPMU.In order to minimize the misalignment errors,a method of calibrating angle error and relative assembly displacements of a three-dimensional Hall probe is carried out.Methods The angle error of Hall sensors will be calibrated by a standard dipole magnet and a five-dimensional Hall bench.The standard dipole magnet will generate a single direction and uniform magnetic field.And the fivedimensional Hall bench is used to rotate the Hall probe which is put in the center of magnet.Based on the relationship between angle and magnetic field strength,the angle error of each Hall sensor will be obtained.The relative position between the sensitive areas of the Hall sensors will be calibrated by a two-dimensional magnetic field undulator section.Based on Maxwell’s equations,through the calculation of measurement magnetic field strength,the relative assembly displacements of the three Hall sensors can be derived.Results The details of the calibration methods and the data processing of angle error and relative assembly displacements of a three-dimensional Hall probe are presented.The three-dimensional magnetic fields of a cryogenic permanent magnet undulator can be received accurately by correcting these angle errors and position errors of Hall sensors.Conclusions This paper illustrates the relative position and angle calibration procedures and the data processing of a three-dimensional Hall probe.Now the design of a smaller Hall probe is in process.The calibration of the angle errors and position errors will be carried out after the fabrication of the standard dipole magnet.

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(HEPSTF)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

Purpose 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.Methods 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℃ to 30℃.Results A new homemade Hall probe has finished the temperature-dependent(0℃ to 30℃),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.Conclusion 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.