Clamped accelerating structures for the generation of high brightness electron beams.

This dissertation will illustrate the design, theory and fabrication of a newgeneration of radiofrequency (RF) photoinjector aimed at obtaining signicantimprovements in beam brightness, through an innovative accelerating cavity design,with minimized RF breakdown rates and a novel fabrication technique. TheUCLA 1.4 cell RF photoinjector has been inspired by the SPARC (LNF-INFN,Italy) 1.6 cell RF electron gun currently operating in the Pegasus beamline. Usingthe clamping technique with the INFN proprietary-design gaskets, the fabricationfor the 1.4 cell photoinjector the INFN can be completed without any brazingprocess. Careful rounding of all the inside surfaces allows better management ofthe pulsed heating temperature rise that largely contributes to the rf breakdownlimits of older generations of high gradient electron guns. Finally, the clampingtechnique and innovative gasket design offers a lower risk assembly and lowerfabrication costs.The UCLA 1.4 cell rf electron gun has been designed to operate at a 120MV/mgradient and an optimal injection phase of 70 degrees in order to increase the extractionfield experienced by the electrons at photo-emission by a factor of 1.9 comparedto the one in the standard 1.6 cell design running at the same peak eld. Themaximum achievable beam brightness in a RF photogun depends on the extractioneld with a scaling which diers for the various regimes of operation (cigar,pancake, blowout). Nevertheless, for all cases, improving the extraction fieldimproves the beam brightness at least linearly regardless of operating regime.From the electromagnetic point of view the gun presents a large mode separation,an extra pumping port for dipole moment compensation, a racetrack fullcell geometry for quadrupole moment compensation, strongly rounded ellipticaliris and coupler for minimal pulsed heating. The electron gun has also been designedto be compatible with several cutting edge experiments. The inclusion ofoblique incidence laser ports allows for short focal length laser illumination onthe cathode to generate ultra-low emittance bunches as demonstrated in recentexperiments. The new photoinjector is also compatible with a load-lock chamberto test advanced photocathodes, such as alkali antimonide cathodes. Thesepromising materials have yet to be tested in high gradient accelerating cavitiesdue to the lack of an ultra-high vacuum (UHV) storage system that is capable ofloading cathodes into the injector without breaking vacuum.The clamping technique has proven useful in the assembly of accelerating cavities.In the last chapter of this thesis, we will also discuss the design and use of theclamping method in the realization of an X-band deflecting cavity that will playa role in the future ultrafast electron diffraction (UED) experiments at UCLA.The goal of the new deflecting cavity is to develop an innovative, inexpensive andlow energy UED system that provides short bunches and others improvements inthe temporal resolution of ultrafast electron diffraction measurements

New technology based on clamping for high gradient radio frequency photogun

High gradient rf photoguns have been a key development to enable several applications of high quality electron beams. They allow the generation of beams with very high peak current and low transverse emittance, satisfying the tight demands for free-electron lasers, energy recovery linacs, Compton/Thomson sources and high-energy linear colliders. In the present paper we present the design of a new rf photogun recently developed in the framework of the SPARC_LAB photoinjector activities at the laboratories of the National Institute of Nuclear Physics in Frascati (LNF-INFN, Italy). This design implements several new features from the electromagnetic point of view and, more important, a novel technology for its realization that does not involve any brazing process. From the electromagnetic point of view the gun presents high mode separation, low peak surface electric field at the iris and minimized pulsed heating on the coupler. For the realization, we have implemented a novel fabrication design that, avoiding brazing, strongly reduces the cost, the realization time and the risk of failure. Details on the electromagnetic design, low power rf measurements and high power radiofrequency and beam tests performed at the University of California in Los Angeles (UCLA) are discussed in the paper

Clamped accelerating structures for the generation of high brightness electron beams.

This dissertation will illustrate the design, theory and fabrication of a newgeneration of radiofrequency (RF) photoinjector aimed at obtaining signicantimprovements in beam brightness, through an innovative accelerating cavity design,with minimized RF breakdown rates and a novel fabrication technique. TheUCLA 1.4 cell RF photoinjector has been inspired by the SPARC (LNF-INFN,Italy) 1.6 cell RF electron gun currently operating in the Pegasus beamline. Usingthe clamping technique with the INFN proprietary-design gaskets, the fabricationfor the 1.4 cell photoinjector the INFN can be completed without any brazingprocess. Careful rounding of all the inside surfaces allows better management ofthe pulsed heating temperature rise that largely contributes to the rf breakdownlimits of older generations of high gradient electron guns. Finally, the clampingtechnique and innovative gasket design offers a lower risk assembly and lowerfabrication costs.The UCLA 1.4 cell rf electron gun has been designed to operate at a 120MV/mgradient and an optimal injection phase of 70 degrees in order to increase the extractionfield experienced by the electrons at photo-emission by a factor of 1.9 comparedto the one in the standard 1.6 cell design running at the same peak eld. Themaximum achievable beam brightness in a RF photogun depends on the extractioneld with a scaling which diers for the various regimes of operation (cigar,pancake, blowout). Nevertheless, for all cases, improving the extraction fieldimproves the beam brightness at least linearly regardless of operating regime.From the electromagnetic point of view the gun presents a large mode separation,an extra pumping port for dipole moment compensation, a racetrack fullcell geometry for quadrupole moment compensation, strongly rounded ellipticaliris and coupler for minimal pulsed heating. The electron gun has also been designedto be compatible with several cutting edge experiments. The inclusion ofoblique incidence laser ports allows for short focal length laser illumination onthe cathode to generate ultra-low emittance bunches as demonstrated in recentexperiments. The new photoinjector is also compatible with a load-lock chamberto test advanced photocathodes, such as alkali antimonide cathodes. Thesepromising materials have yet to be tested in high gradient accelerating cavitiesdue to the lack of an ultra-high vacuum (UHV) storage system that is capable ofloading cathodes into the injector without breaking vacuum.The clamping technique has proven useful in the assembly of accelerating cavities.In the last chapter of this thesis, we will also discuss the design and use of theclamping method in the realization of an X-band deflecting cavity that will playa role in the future ultrafast electron diffraction (UED) experiments at UCLA.The goal of the new deflecting cavity is to develop an innovative, inexpensive andlow energy UED system that provides short bunches and others improvements inthe temporal resolution of ultrafast electron diffraction measurements