X-ray Free Electron Laser concept of the PSI-FEL project.
 

Schematic cross-section of a double-gated field-emitter array (FEA) device. When a sufficient positive bias is applied to the gate-1 (extraction gate) relative to the emitter-tips, electron beams with low-thermal emittance are emitted by Fowler-Nordheim tunneling. A bias with an opposite polarity to the gate-2 (focusing gate) collimate each electron beam individually. Consequently, an ultimately low emittance beam can be extracted from such an electron source.

 
Field emitter array (FEA) devices equipped with double-gate electrodes have been considered as candidates for the cathode of PSI XFEL. Combining highly coherent field emission from a point-like source with a built-in focusing element, the performance of FEAs can potentially surmount that of the photocathode.[1-4] The specification of the device performance requiring emittance of ~nm rad, emission charges of 0.2 nC from an area with a diameter below 1 millimeter and switching speed below (10-40) ps, or brightness above ~1 kAcm-2, which has been specified from the accelerator design, is however beyond the state-of-the-art. The goal of the R&D at LMN, as a part of the PSI XFEL project, is to clarify physical obstacles and to go beyond the state-of-the art based on novel device design, fabrication methods, and experimental methods. [4-9]

	/\   <	Schematic cross-section of a single-gate field-emitter SEM images of a fabricated single-gate field-emitter array device

References
[1] Cha-Mei Tang, Antonio C. Ting and Thomas Swyden, “Field-emission arrays – a potentially bright source”, Nuclear Inst. Meth. A 318 (1992) 353-357.

[2] 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. B 24 (2006) 892-897.

[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 (2007) 071302 .

[4] S. Tsujino, P. Beaud, E. Kirk, T. Vogel, H. Sehr, J. Gobrecht, A. Wrulich, Ultrafast electron emission from metallic nanotip arrays induced by near infrared femtosecond laser pulses , Applied Physics Letters 92, 193501 (2008).

[6] E. Kirk, S. Tsujino, T. Vogel, H. Sehr, J. Gobrecht,  A. Wrulich, “Development of metallic field emitter arrays with individual focusing electrodes for high-brightness, low-emittance cathode", the 21st international vacuum nanoelectronics conference (July 13-17, 2008, Wroclaw, Poland) AT14.

[7] S. Tsujino, P. Beaud, E. Kirk, T. Vogel, H. Sehr, J. Gobrecht, A. Wrulich, "Ultrafast single-photon photoemission from metallic field-emitter arrays excited by near infrared femtosecond laser pulses", the 21st international vacuum nanoelectronics conference (July 13-17, 2008, Wroclaw, Poland) F-CH2.

[8] S. Tsujino, E. Kirk, T. Vogel, J. Gobrecht, P. Beaud, C. Escher, H.-W. Fink, K. Jefimovs, A. Wrulich, "Development of metallic field-emitter arrays by molding for high-current and low-emittance applications", the seventh international vacuum electron sources conference (Aug 3-6, 2008, London, UK).

[9] R. Bakker et al., “PSI-XFEL: the challenge for ultra-bright X-rays(135kB)”, Paul Scherrer Institut, Annual report 2006 (16MB), pp.114.

Collaborations
FIRST lab., ETH Zürich
C. Escher, Dr. and H.-W. Fink, Prof. Dr. (University Zürich)
Paul Beaud, Dr. (SYN-FEMTO, femtosecond spectroscopy)
S. C. Leemann, Dr. (Max-lab, Lund University, High-gradient experiment)
T. Feurer (University of Bern)
Roger Bischofberger (Applied MicroSWISS GmbH)
Konstantins Jefimovs, Dr., (EMPA Dübendorf, Focused Ion Beam)
Oliver Gröning, Dr. (EMPA Thun, Scanning anode field-emission microscopy)
Jörg Raabe, Dr. (SYN, Photoelectron emission microscopy)
Christian David, Dr., (LMN, Electron-beam lithography)

Contact Information (PSI-XFEL Field-Emitter Group)
Dr. Eugenie Kirk
Patrick Helfenstein
Thomas Vogel
Prof. Jens Gobrecht
Dr. Soichiro Tsujino, (Group Leader) : soichiro.tsujino psi.ch