Pulsed Wire Method for Field Integral Measurement at SSRF

The performance of synchrotron radiation facilities and free electron lasers facilities relies not only on the quality of the electron beam but also on that of the undulator. To shim field errors stemming from the undulator's manufacturing process, precise magnetic field measurements are imperative. The traditional measurement approach involves point-by-point assessments using Hall probes. However, deploying Hall probes for magnetic measurements becomes significantly more challenging when confronted with circumstances such as small gaps, closed gaps, or mechanical constraints, as is the case with superconducting undulators. In the pulsed wire method, an extremely thin wire is employed, allowing for direct measurement of the first and second integrals of the magnetic field, even within confined spaces. This method comes with several drawbacks, including wire sagging due to its weight, dispersion effects, attenuation of transverse waves in the wire, and the potential for stray signals resulting from wire irregularities or impurities. Nevertheless, after years of refinement, this method's accuracy has markedly improved. This paper introduces the development of the pulsed wire method at the Shanghai Synchrotron Radiation Facility.