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IPAC 2016

Name: IPAC 2016

Location: Busan, Korea

Date: 2016-01-01

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Created at: Thu Sep 01 11:36:46 -0700 2016

Updated at: Thu Sep 01 11:36:46 -0700 2016

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4 papers from the conference:

title: Measurements of Copper RF Surface Resistance at Cryogenic Temperatures for Applications to X-Band and S-Band Accelerators
format: conference proceeding
conference: IPAC 2016
year: 2016
11 authors: A. Cahill | A. Fukasawa | J.B. Rosenzweig | Y. Higashi | G.B. Bowden | V.A. Dolgashev | J. Guo | M. Franzi | S. Tantawi | P.B. Welander | C. Yoneda
abstract: Recent SLAC experiments with cryogenically cooled X- band standing wave copper accelerating cavities have shown that these structures can operate with accelerating gradi- ents of 250 MV/m and low breakdown rates. These results prompted us to perform systematic studies of copper rf prop- erties at cryogenic temperatures at low rf power. We placed copper cavities into a cryostat with a cryocooler, so the cavities could be reduced to 4K. We used different shapes of cavities for the X-band and S-band measurements. RF properties of the cavities were measured using a network analyzer. We calculated rf surface resistance from measured Q 0 at temperatures from 4 K to room temperature. The re- sults were then compared to the theory proposed by Reuter and Sondheimer. These measurements are part of studies with the goal of reaching very high operating accelerating gradients in normal conducting rf structures.
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title: HIGH EFFICIENCY, HIGH BRIGHTNESS X-RAY FREE ELECTRON LASERS VIA FRESH BUNCH SELF-SEEDING
format: conference proceeding
conference: IPAC 2016
year: 2016
6 authors: C. Emma | C. Pellegrini | A. Lutman | M. Guetg | A. Marinelli | J. Wu
abstract: High efficiency, terawatt peak power X-ray Free Electron Lasers (XFELs) are a promising tool for enabling 3D atomic resolution single molecule imaging and nonlinear science using X-ray beams. Increasing the efficiency of XFELs while maintaining good longitudinal coherence can be achieved via self-seeding and tapering the undulator magnetic field. The efficiency of tapered self seeded XFELs is limited by two factors: the ratio of seed power to beam energy spread and the ratio of seed power to electron beam shot noise. We present a method to overcome these limitations by producing a strong X-ray seed and amplifying it with a small energy spread electron bunch. This can be achieved by selectively suppressing lasing for part of the electron beam in the SASE section and using the rest of the bunch to generate the seed radiation. In this manner one can reach saturation with the seeding electrons and the strong seed pulse can be overlapped with the “fresh" electrons downstream of the self-seeding monochromator. Simulations of this scenario demonstrating an increased efficiency are presented for two systems, an optimal superconducting undulator design and the Linac Coherent Light Source. In the case of the LCLS we examine how the betatron oscillations leading to selective suppression can be induced by using the transverse wakefield of a parallel plate corrugated structure, a dechirper.
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title: TM01 Mode Launcher for use in High Brightness Photoguns
format: conference proceeding
conference: IPAC 2016
year: 2016
3 authors: A. Cahill | M. Dal Forno | V.A. Dolgashev
abstract: Photo rf guns are a source of electron beams for X-ray FELs such as LCLS and European XFEL. In existing photo-guns power is coupled into the cavity by rectangular waveguides through the cell walls, [1], or use coaxial coupling, [2]. We are considering feeding a gun using a circular waveguide with the TM01 mode. To do that we need a mode launcher, a matched device that couples the rectangular TE01 mode waveguide to a TM01 mode in a circular waveguide. Use of the mode launcher reduces complexity of the gun cavity and increases flexibility of positioning the input waveguide relative to the gun body. Mode launchers have been successfully used at SLAC and elsewhere for X-band high gradient tests. Because the existing mode launchers were not built for high brightness rf guns, they have a significant quadrupole field component. High brightness rf guns have tight requirements on output beam properties. The quadrupole component of the mode launcher adversely affects the beam quality. We have designed a mode launcher free of this disadvantage. We present an example S-band mode launcher with minimized quardupole field component.
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title: Automated Design for Standing Wave Electron Photoguns: TOPGUN RF Design
format: conference proceeding
conference: IPAC 2016
year: 2016
3 authors: A. Cahill | M. Dal Forno | V.A. Dolgashev
abstract: Systematic design of RF photoguns involves multiple RF simulations in conjunction with beam dynamic simulations. RF simulations include tuning gun frequency, matching the gun to the feeding RF circuit, balancing the on axis electric fields between gun cells, minimizing surface electric and magnetic fields and power consumption, and optimizing separation of resonant mode frequencies. We created a tool that allows this multiple parameter optimization to be done automatically. We used SUPERFISH to accomplish the RF simulations. We present an example of the rf photogun TOPGUN design using these tools.
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