Magnetic characterization of the undulator for infra red free-electron laser at RRCAT

An Infra-Red Free Electron Laser (IR-FEL) designed to operate in the 12.5-50 μm wavelength band is presently in an advanced stage of commissioning at the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore. One of the crucial components of an FEL is the undulator, which produces static, sinusoidal vertical magnetic field along the axis through which an electron beam is propagated to generate coherent radiation. A 2.5 m long, pure permanent magnet based undulator with a period of 50 mm has been procured, installed and commissioned at its designated location inside the radiation shielded area built to house the IRFEL. For the successful operation of an FEL, the magnetic field profile of the undulator has to satisfy stringent criterion on parameters such as rms error in the peak field, optical phase error, trajectory errors etc. Detailed magnetic characterization of the undulator installed inside the shielded area has been performed using in-house developed measurement benches to measure the magnetic field profile as well as magnetic field integrals. This paper describes the details of magnetic characterization performed to ensure that all the required criteria on the field quality are satisfied by the undulator. (author)