Emittance of single-gate field emitter arrays

Emittance is a key cathode parameter for the high brightness applications. However, experimental study is rare in literature, even for single-gate FEAs. We therefore measured array size dependence [1] and the uniformity dependence [2] of the single-gate FEA emittance for the first time. These measurements were done in part using the combined dioide-RF cavity accelerator, as well as in the dc gun teststand [3] previously established in the SwissFEL project. We observed that the single-gate FEA normalized emittance is ~2 mm-mrad per 1 mm-diameter. Combined with the double-gate result (an order of magnitude reduction of the rms transverse electron velocity), the normalized emittance in the order of ~0.2 mm-mrad per 1 mm-diameter cathode is foreseen. The number is compatible with the previous PIC calculation [4,5]. The in-situ uniformity control [2] of the field emission beam was achieved by using the noble gas conditioning method reported in Ref. [6].



References

[1] S. Tsujino, M. Paraliev, E. Kirk, T. Vogel, F. Le Pimpec, C. Gough, S. Ivkovic, and H.-H. Braun, Nanosecond pulsed field emission from single-gate metallic field emitter arrays fabricated by molding, J. Vac. Sci. Technol. B29, 02B117 (2011).

[2] S. Tsujino, M. Paraliev, P. Helfenstein, and H.-H. Braun, Transverse emittance of single-gate FEAs ~ influence of the beam uniformity, C6, 25st International Vacuum Nanoelectronics Conference (IVNC2012), (Jeju, Korea, 9-13, July, 2012).

[3] S. C. Leemann, A. Straudel, A. Wrulich, Beam characterization for the field-emitter-array cathode-based low-emittance gun, Phys. Rev. ST Accel. Beams 10, 071302 (2007).

[4] M. Dehler, A. Candel, E. Gjonaj, Full scale simulation of a field-emitter arrays based electron source for free-electron lasers, J. Vac. Sci. Tech. B24,892-897 (2006).

[5] M. Dehler, Design and modeling of field emitter arrays for a high brilliance electron source, Proceedings of the 9th International Computational Accelerator Physics Conference (ICAP2006), (Chamonix, France, 2-6, Oct. 2006).

[6] S. Tsujino, M. Paraliev, E. Kirk, and H.-H. Braun, Homogeneity improvement of field emission beam from metallic nano-tip array by noble-gas conditioning, Appl. Phys. Lett. 99, 073101 (2011).