Field Integral Measurements Research Articles

Pulsed Wire Method for Field Integral Measurement at SSRF

Pulsed Wire Method for Field Integral Measurement at SSRF

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.

Magnetic Field Integral Measurements With Stretched Wire and Hall Probe Methods

In this article, we analyze magnetic measurements on the U50-II undulator. The U50-II undulator is a 50 mm period length NdFeB-based pure permanent-magnet undulator prototype. It is designed with 20 periods and delivers 0.88–0.17 T in the gap from 10 to 35 mm. The field integrals are measured on a Hall probe bench, and the measurements are compared with the stretched wire result. In the stretched wire setup, the field integral is measured with an accuracy of 2 mTmm. The details of the stretch wire probe setup, measurement procedure, and accuracy with Hall probe results are discussed.

Field quality of 1.5 m long conduction cooled superconducting undulator coils with 20 mm period length

The Institute for Beam Physics and Technology (IBPT) at the Karlsruhe Institute of Technology (KIT) and the industrial partner Babcock Noell GmbH (BNG) are collaborating since 2007 on the development of superconducting undulators both for ANKA and low emittance light sources. The first full length device with 15 mm period length has been successfully tested in the ANKA storage ring for one year. The next superconducting undulator has 20 mm period length (SCU20) and is also planned to be installed in the accelerator test facility and synchrotron light source ANKA. The SCU20 1.5 m long coils have been characterized in a conduction cooled horizontal test facility developed at KIT IBPT. Here we present the local magnetic field and field integral measurements, as well as their analysis including the expected photon spectrum.

Some aspects of achieving an ultimate accuracy during insertion device magnetic measurements by a Hall probe

An extensive test of a new Senis 2-axis Hall probe was done at the Advanced Photon Source using the Undulator A device and calibration system. This new probe has clear advantages compared with previously used Bell and Sentron Hall probes: very stable zero offset (less than the noise of 0.026 G) and compensated planar Hall effect. It can be used with proper calibration even for first and second field integral measurements. A comparison with reference measurements by long stretched coil shows that the difference in the first field integral measurement results for a 2.4-m-long Undulator A device is between 17 G cm for the best of four Hall probes used for the test and 51 G cm for the worst of them for all gap ranges from 10.5 mm to 150 mm.

Stretched wire measurement of multipole accelerator magnets

Theoretical aspects of stretched wire field integral measurements are investigated. A least square approach is used for the processing of the measured signal; it can be applied to any wire trajectory and it allows numerical correction of the wire position errors. Moreover, the signal from some multipoles can be compensated for in a way comparable to the ``bucked'' rotating coil method. This can be used for accurate measurements of field multipole errors. A stretched wire bench has been built at the European Synchrotron Radiation Facility. This bench has been used for measuring dipole, quadrupole, and sextupole magnets. The results obtained with various wire trajectories are compared. It is demonstrated that an accuracy of a few ${10}^{\ensuremath{-}4}$ of the main multipole can be obtained.

Pulse requirements for field integral measurements in pulsed wire method

The pulse requirements in pulsed wire measurements are verified for undulators with and without end field corrections. For a perfect undulator, the second field integral is uniform along the length of the undulator and the required pulse size is calculated by the distance of the sensor divided by the wave velocity. The undulator without end field correction or with improper end field configuration requires longer pulse sizes than the shimmed undulator for both first and second field integral results.

Field integral measurement of a six period undulator in a pulsed wire set up

A pulsed wire method is described for undulator field measurement. The results of the second field integral are compared with Hall probe results. The pulsed wire data are taken at different locations of the sensor along the length of the wire and with different gap of the undulator. A planar undulator with six periods is used in the pulsed wire set up. The total length of the undulator is 30 cm. The pulsed wire result shows good agreement with the Hall probe data.

Analysis of pulsed wire method for field integral measurements in undulators

Pulsed wire technique is a fast and accurate method for the measurement of first and second field integrals of undulators used in free-electron lasers and synchrotron light sources. In this paper, we present a theoretical analysis of this technique by finding out the analytic solution of the differential equation for the forced vibration of the wire taking dispersion due to stiffness into account. Method of images is used to extend these solutions to include reflections at the ends. For long undulators, the effect of dispersion of the acoustic wave in the wire could be significant and our analysis provides a method for the evaluation of the magnetic field profile even in such cases taking the effect due to dispersion into account in an exact way.

脉冲线积分场测量系统的研制

脉冲线积分场测量系统的研制

High accuracy field integral measurement for TJNAF beam energy determination

The determination of the beam energy in the experimental hall A of TJNAF (previously CEBAF) accelerator is done through a very accurate measurement of the field integral of a reference dipole magnet, electrically connected in series with the bending magnets transporting the beam from the accelerator to the experimental area. A new method is used to determine the field integral; this method is described, as well as the calibrations done in the laboratory. Finally, the goal to reach an accuracy of the field integral on the order of 10/sup -5/ has been reached, as it is shown by comparing the results of the beam energy determination obtained on the accelerator with this method to results obtained by other independant methods.

Precise integration of undulator Hall probe scans

Procedures are described for obtaining precise magnetic field integral values for Hall probe scans of undulators. A technique is discussed for scaling the even portion of a nonlinear Hall probe calibration based upon sets of scans with the Hall probe installed in opposing orientations. An example is discussed where a 293 G-cm error is corrected by scaling which corresponds to an average adjustment of 0.7 G over a 3.0 T range. An analysis of measurement uncertainty is presented. A quantitative example is presented which shows that the expected level of uncertainty is of the order of 20 G-cm for undulator field integrals using the Advanced Light Source (ALS) magnet measurement facility. Sets of duplicate field integral measurements of ALS undulators demonstrate an accuracy and variation of results of better than 20 G-cm. A comparison of integrated Hall probe scans with integral coil measurements shows good agreement. >