Utilization of RADFET sensors for x-ray undulators: experiential considerations on magnetic field profile before commissioning

Abstract

Concerning accelerator-based light sources, electrons are accelerated in conformity with specific time structures (i.e. continuous wave, ‘cw’, or bunched), which arise out of accelerating frequencies of employed radiofrequency cavities. Thus, the concept of transverse emittance of electron bunches comes into prominence, simply defining the area of an ellipse in phase space where the electrons are occupied. In nonideal cases (i.e. in real life), when some fraction of these electrons sneak out of a bunch, the concept of ‘energy spread’ automatically arises. Since the energy spread resulting from off-axis relativistic electrons in an insertion device induces considerable radiation damage on magnetic structures of x-ray undulators, radiation-sensitive field effect transistors (RADFETs) are utilized for quantification of radiation intensity. Hence, it is crucial to bring out their influence on magnetic field profiles before commisioning in tunnels. In this respect, two different types of RADFET sensors were investigated over the magnetic poles of an undulator with 40 mm period length (shortened as an U40 undulator). The effects of the sensors on magnetic field were measured using transverse and longitudinal scans through 6.5 m-long magnetic measurement benches (MMBs). The results of two RADFET standard systems are presented, wherein one contains the magnetic material nickel. Finally, novel magnetic measurement techniques for x-ray undulators via unique MMBs are thoroughly explained as well.