Study of a Twin-Helix Undulator Design for the NSRRC VUV Free Electron Laser

Cheng Ying Kuo^1*, Ting Yi Chung¹, Cheng Hsing Chang¹, Chia Hsiang Chen¹, Jui Che Huang¹, Ching Shiang Hwang¹, Cheng Hsiang Chang¹

¹Magnet Group, National Synchrotron Radiation Research Center, Hsinchu, Taiwan

* Presenter:Cheng Ying Kuo, email:cy.kuo@nsrrc.org.tw

A high polarization rate and peak strength value of a helical field are significant parameters in free electron lasers (FEL). A 1.5m long twin-helix undulator (THU) with a short period of 20mm and a round bore of 5mm has been designed for the NSRRC VUV Free Electron Laser. The structure of the helical shaped magnet and pole is optimized to produce a peak field of 1.25T from half type magnet arrays. The high field strength can not only enhance the peak power but can also reduce the saturation length for a compact free electron laser. Moreover, simulations for a cryogenic THU operating at a temperature of 77K have been performed to reach a helical field strength of up to 1.46T. The ends of the magnet structure is optimized to compensate the first and second field integrals. A 10 period THU prototype is under construction and field measurement results will presented in this paper.

Keywords: twin-helix undulator, undulator