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Y. I. Kim,
R. Ainsworth,
A. Aryshev,
S. T. Boogert,
G. Boorman, J. Frisch,
A. Heo,
Y. Honda,
W. H. Hwang,
J. Y. Huang, [......],
S. J. Park,
Y. J. Park,
M. Ross,
S. Shin,
C. Swinson,
T. Smith,
N. Terunuma,
T. Tauchi,
J. Urakawa,
G. R. White
[show abstract]
[hide abstract]
ABSTRACT: The Accelerator Test Facility 2 (ATF2) is a scaled demonstrator system for
final focus beam lines of linear high energy colliders. This paper describes
the high resolution cavity beam position monitor (BPM) system, which is a part
of the ATF2 diagnostics. Two types of cavity BPMs are used, C-band operating at
6.423 GHz, and S-band at 2.888 GHz with an increased beam aperture. The
cavities, electronics, and digital processing are described. The resolution of
the C-band system with attenuators was determined to be approximately 250 nm
and 1 m for the S-band system. Without attenuation the best recorded C-band
cavity resolution was 27 nm.
01/2013;
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Y Ding,
F-J Decker,
P Emma,
C Feng,
C Field, J Frisch,
Z Huang,
J Krzywinski,
H Loos,
J Welch,
J Wu,
F Zhou
[show abstract]
[hide abstract]
ABSTRACT: We report the first measurements of x-ray single-pulse duration and two-pulse separation at the Linac Coherent Light Source using a cross-correlation technique involving x rays and electrons. An emittance-spoiling foil is adopted as a very simple and effective method to control the output x-ray pulse. A minimum pulse duration of about 3 fs full width at half maximum has been measured together with a controllable pulse separation (delay) between two pulses. This technique provides critical temporal diagnostics for x-ray experiments such as x-ray pump-probe studies.
Physical Review Letters 12/2012; 109(25):254802. · 7.37 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Energy extraction efficiency of a free electron laser (FEL) can be greatly increased using a tapered undulator and self-seeding. However, the extraction rate is limited by various effects that eventually lead to saturation of the peak intensity and power. To better understand these effects, we develop a model extending the Kroll-Morton-Rosenbluth, one-dimensional theory to include the physics of diffraction, optical guiding, and radially resolved particle trapping. The predictions of the model agree well with that of the GENESIS single-frequency numerical simulations. In particular, we discuss the evolution of the electron-radiation interaction along the tapered undulator and show that the decreasing of refractive guiding is the major cause of the efficiency reduction, particle detrapping, and then saturation of the radiation power. With this understanding, we develop a multidimensional optimization scheme based on GENESIS simulations to increase the energy extraction efficiency via an improved taper profile and variation in electron beam radius. We present optimization results for hard x-ray tapered FELs, and the dependence of the maximum extractable radiation power on various parameters of the initial electron beam, radiation field, and the undulator system. We also study the effect of the sideband growth in a tapered FEL. Such growth induces increased particle detrapping and thus decreased refractive guiding that together strongly limit the overall energy extraction efficiency.
Physical Review Special Topics - Accelerators and Beams 05/2012; · 1.52 Impact Factor
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D Ratner,
A Brachmann,
F J Decker,
Y Ding,
D Dowell,
P Emma,
A Fisher, J Frisch,
S Gilevich,
Z Huang, [......],
R Iverson,
J Krzywinski,
H Loos,
M Messerschmidt,
H D Nuhn,
T Smith,
J Turner,
J Welch,
W White,
J Wu
[show abstract]
[hide abstract]
ABSTRACT: The linac coherent light source (LCLS) is a self-amplified spontaneous emission (SASE) free-electron laser (FEL) operating at fundamental photon energies from 0.5 to 10 keV. Characterization of the higher harmonics present in the FEL beam is important to users, for whom harder x rays can either extend the useful operating wavelength range or increase experimental backgrounds. We present measurements of the power in both the second and third harmonics, and compare the results to expectations from simulations. We also present studies of the transport of harmonics to the users, and the harmonic power as a function of electron beam quality.
Physical Review Special Topics - Accelerators and Beams 06/2011; 14. · 1.52 Impact Factor
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James M Glownia,
J Cryan,
J Andreasson,
A Belkacem,
N Berrah,
C I Blaga,
C Bostedt,
J Bozek,
L F DiMauro,
L Fang, [......],
C Raman,
D Ray,
D A Reis,
M Trigo,
J L White,
W White,
R Wilcox,
L Young,
R N Coffee,
P H Bucksbaum
[show abstract]
[hide abstract]
ABSTRACT: The first time-resolved x-ray/optical pump-probe experiments at the SLAC Linac Coherent Light Source (LCLS) used a combination of feedback methods and post-analysis binning techniques to synchronize an ultrafast optical laser to the linac-based x-ray laser. Transient molecular nitrogen alignment revival features were resolved in time-dependent x-ray-induced fragmentation spectra. These alignment features were used to find the temporal overlap of the pump and probe pulses. The strong-field dissociation of x-ray generated quasi-bound molecular dications was used to establish the residual timing jitter. This analysis shows that the relative arrival time of the Ti:Sapphire laser and the x-ray pulses had a distribution with a standard deviation of approximately 120 fs. The largest contribution to the jitter noise spectrum was the locking of the laser oscillator to the reference RF of the accelerator, which suggests that simple technical improvements could reduce the jitter to better than 50 fs.
Optics Express 08/2010; 18(17):17620-30. · 3.59 Impact Factor
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P. Emma,
R. Akre,
J. Arthur,
R. Bionta,
C. Bostedt,
J. Bozek,
A. Brachmann,
P. Bucksbaum,
R. Coffee,
F.-J. Decker, [......],
D. Schultz,
T. Smith,
P. Stefan,
H. Tompkins,
J. Turner,
J. Welch,
W. White,
J. Wu,
G. Yocky,
J. Galayda
[show abstract]
[hide abstract]
ABSTRACT: The recently commissioned Linac Coherent Light Source is an X-ray free-electron laser at the SLAC National Accelerator Laboratory. It produces coherent soft and hard X-rays with peak brightness nearly ten orders of magnitude beyond conventional synchrotron sources and a range of pulse durations from 500 to <10 fs (10−15 s). With these beam characteristics this light source is capable of imaging the structure and dynamics of matter at atomic size and timescales. The facility is now operating at X-ray wavelengths from 22 to 1.2 Å and is presently delivering this high-brilliance beam to a growing array of scientific researchers. We describe the operation and performance of this new ‘fourth-generation light source’.
Nature Photonics 07/2010; 4(9):641-647. · 29.28 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Die Diffusion von In in reinen und In-dotierten AgCl-Einkristallen wurde bei kleinen In-Konzentrationen (cIn < 10−4 mol%) in Abhängigkeit von der Temperatur mit der Tracer-Methode (In114m) untersucht. Für die Messungen im Konzentrationsbereich bis zu 2mol° In erfolgte die Diffusion in nichtdotierte AgCl-Kristalle aus der Gasphase; die Konzentrationsverteilung der Indiumionen wurde dabei über eine Aktivierungsanalyse aufgenommen. Sämtliche experimentellen Ergebnisse lassen sich unter der Annahme der Zweiwertigkeit des Indiums und mit einem von Lidiard angegebenen Ansatz für einen Lückenkomplexmechanismus interpretieren; dabei wurden die Experimente bei den höheren Konzentrationen unter Berücksichtigung einer Debye-Hückel-Wechselwirkung ausgewertet.The diffusion of indium in pure and indium doted AgCl-single crystals has been measured as a function of temperature. In the region of low In-concentration (cIn < 10−4mol%) the tracer method (In114m) was used. At larger In-concentration up to 2 mol% In-diffusion in pure AgCl-single crystals was started from the gaseous In-phase. The In-diffusion profiles were determined by neutron activation analysis. On condition that indium ions are divalent impurities all experimental results agree well with Lidiards vacancy complex association model. At larger indium concentrations Debey-Hückel-interactions has been considered.
Berichte der Bunsengesellschaft für physikalische Chemie. 05/2010; 77(7):513 - 517.
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D Ratner,
A Brachmann,
F J Decker,
Y Ding,
D Dowell,
P Emma, J Frisch,
S Gilevich,
G Hays,
P Hering, [......],
R Iverson,
H Loos,
A Miahnahri,
H D Nuhn,
J Turner,
J Welch,
W White,
J Wu,
D Xiang,
G Yocky
[show abstract]
[hide abstract]
ABSTRACT: We present experimental studies of the gain length and saturation power level from 1.5 nm to 1.5 Angstroms at the Linac Coherent Light Source (LCLS). By disrupting the FEL process with an orbit kick, we are able to measure the X-ray intensity as a function of undulator length. This kick method is cross-checked with the method of removing undulator sections. We also study the FEL-induced electron energy loss after saturation to determine the optimal taper of the undulator K values. The experimental results are compared to theory and simulations. Abstract We present experimental studies of the gain length and saturation power level from 1.5 nm to 1.5 A at the Linac Coherent Light Source (LCLS). By disrupting the FEL pro-cess with an orbit kick, we are able to measure the X-ray in-tensity as a function of undulator length. This kick method is cross-checked with the method of removing undulator sections. We also study the FEL-induced electron energy loss after saturation to determine the optimal taper of the undulator K values. The experimental results are compared to theory and simulations.
09/2009;
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Y Ding,
A Brachmann,
F-J Decker,
D Dowell,
P Emma, J Frisch,
S Gilevich,
G Hays,
Ph Hering,
Z Huang,
R Iverson,
H Loos,
A Miahnahri,
H-D Nuhn,
D Ratner,
J Turner,
J Welch,
W White,
J Wu
[show abstract]
[hide abstract]
ABSTRACT: The Linac Coherent Light Source (LCLS) is an x-ray free-electron laser project presently in a commissioning phase at the SLAC National Accelerator Laboratory. We report here on very low-emittance measurements made at low bunch charge, and a few femtosecond bunch length produced by the LCLS bunch compressors. Start-to-end simulations associated with these beam parameters show the possibilities of generating hundreds of GW at 1.5 A x-ray wavelength and nearly a single longitudinally coherent spike at 1.5 nm with 2-fs duration.
Physical Review Letters 07/2009; 102(25):254801. · 7.37 Impact Factor
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Y Ding,
A Brachmann,
F.-J Decker,
D Dowell,
P Emma, J Frisch,
S Gilevich,
G Hays,
Ph Hering,
Z Huang,
R Iverson,
H Loos,
A Miahnahri,
H.-D Nuhn,
D Ratner,
J Turner,
J Welch,
W White,
J Wu,
C Pellegrini
[show abstract]
[hide abstract]
ABSTRACT: The Linac Coherent Light Source (LCLS) is an x-ray Free-electron Laser (FEL) being commissioned at SLAC. Recent beam measurements have shown that, us-ing the LCLS injector-linac-compressors, the beam emittance is very small at 20 pC. In this paper we perform start-to-end simulations of the entire accelerator including the FEL undulator and study the FEL performance versus the bunch charge. At 20 pC charge, these calculations associated with the measured beam parameters suggest the possibility of generating a longitudinally coherent single x-ray spike with 2-femtosecond (fs) duration at a wavelength of 1.5 nm. At 100 pC charge level, our simulations show an x-ray pulse with 10 femtosecond dura-tion and up to 10 12 photons at a wavelength of 1. A. These results open exciting possibilities for ultrafast science and single shot molecular imaging. Abstract The Linac Coherent Light Source (LCLS) is an x-ray Free-electron Laser (FEL) being commissioned at SLAC. Recent beam measurements have shown that, using the LCLS injector-linac-compressors, the beam emittance is very small at 20 pC. In this paper we perform start-to-end simulations of the entire accelerator including the FEL un-dulator and study the FEL performance versus the bunch charge. At 20 pC charge, these calculations associated with the measured beam parameters suggest the possibility of generating a longitudinally coherent single x-ray spike with 2-femtosecond (fs) duration at a wavelength of 1.5 nm. At 100 pC charge level, our simulations show an x-ray pulse with 10 femtosecond duration and up to 10 12 photons at a wavelength of 1. A. These results open exciting possibili-ties for ultrafast science and single shot molecular imaging.
04/2009;
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J Frisch,
R Akre,
F.-J Decker,
Y Ding,
D Dowell,
P Emma,
S Gilevich,
G Hays,
Ph Hering,
Z Huang, [......],
H Loos,
E Medvedko,
A Miahnahri,
H.-D Nuhn,
D Ratner,
S Smith,
J Turner,
J Welch,
W White,
J Wu
04/2008;
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[show abstract]
[hide abstract]
ABSTRACT: We report on measurements of picosecond bunch lengths and the energy-z correlation of the bunch with a high energy electron test beam to the A-line and end station A (ESA) facilities at SLAC. The bunch length and the energy-Z correlation of the bunch are measured at the end of the linac using a synchrotron light monitor diagnostic at a high dispersion point in the A-line and a transverse RF deflecting cavity at the end of the linac. Measurements of the bunch length in ESA were made using high frequency diodes (up to 100 GHz) and pyroelectric detectors at a ceramic gap in the beamline. Modelling of the beam's longitudinal phase space through the linac and A-line to ESA is done using the 2-dimensional tracking program LiTrack, and LiTrack simulation results are compared with data. High frequency diode and pyroelectric detectors are planned to be used as part of a bunch length feedback system for the LCLS EEL at SLAC. The LCLS also plans precise bunch length and energy-Z correlation measurements using transverse RF deflecting cavities.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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[show abstract]
[hide abstract]
ABSTRACT: The ultra-short bunches of the electron beam for LCLS are generated in two 4-dipole bunch compressors located at energies of 250 MeV and 4.3 GeV. Although an absolute measurement of the bunch length can be done by using a transverse deflecting cavity in an interceptive mode, a non-interceptive single shot method is needed as a relative measurement of the bunch length used in the continuous feedback for beam energy and peak current. We report on the design and implementation of two monitors measuring the integrated power of coherent edge radiation from the last dipole in each chicane.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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K. Bane,
Y. Ding,
P. Emma, J. Frisch,
Z. Huang,
H. Loos,
F. Sannibale,
K. Sonnad,
G. Stupakov,
J. Wu,
M. Zolotorev,
E. Prat
[show abstract]
[hide abstract]
ABSTRACT: The Linac Coherent Light Source (LCLS) is a SASE X-ray free-electron laser project presently under construction at SLAC [1]. The injector section from RF photocathode gun through first bunch compressor chicane was installed during the fall of 2006. The first bunch compressor is located at 250 MeV and nominally compresses a 1-nC electron bunch from an rms length of about 1 mm to 0.2 mm. Transverse phase space and bunch length diagnostics are located immediately after the chicane. We present preliminary measurements and simulations of the longitudinal and transverse phase space after the chicane in various beam conditions, including extreme compression with micron-scale current spikes.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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S. Molloy,
C. Adolphsen,
K. Bane, J. Frisch,
Z. Li,
J. May,
D. McCormick,
T. Smith,
N. Baboi,
N. Eddy,
L. Piccoli,
R. Rechenmacher,
R. Jones
[show abstract]
[hide abstract]
ABSTRACT: Higher Order Modes (HOMs) excited by the passage of the beam through an accelerating cavity depend on the properties of both the cavity and the beam. It is possible, therefore, to draw conclusions on the inner geometry of the cavities based on observations of the properties of the HOM spectrum. A data acquisition system based on two 20 GS/s, 6 GHz scopes has been set up at the FLASH facility, DESY, in order to measure a significant fraction of the HOM spectrum predicted to be generated by the TESLA cavities used for the acceleration of its beam. The HOMs from a particular cavity at FLASH were measured under a range of known beam conditions. The dipole modes have been identified in the data. 3D simulations of different manufacturing errors have been made, and it has been shown that these simulations can predict the measured modes.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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[show abstract]
[hide abstract]
ABSTRACT: The Linac Coherent Light Source (LCLS) at SLAC will be the brightest X-ray laser in the world when it comes on line. In order to achieve the brightness a 200fS length electron bunch is passed through an undulator. To create the 200fS, 3kA bunch, a 10pS electron bunch, created from a photo cathode in an RF gun, is run off crest on the RF to set up a position to energy correlation. The bunch is then compressed by chicanes. The stability of the RF system is critical in setting up the position to energy correlation. Specifications derived from simulations require the RF system to be stable to below 200fS in several critical injector stations and the last kilometer of linac. The SLAC linac RF system is being upgraded to meet these requirements.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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D.H. Dowell,
J. Castro,
P. Emma, J. Frisch,
S. Gilevich,
G. Hays,
P. Hering,
C. Limborg-Deprey,
H. Loos,
A. Miahnahri,
W. White
[show abstract]
[hide abstract]
ABSTRACT: Requirements for the LCLS injector drive laser present significant challenges to the design of the system. While progress has been demonstrated in spatial shape, temporal shape,UV generation and rep-rate, a laser that meets all of the LCLS specifications simultaneously has yet to be demonstrated. These challenges are compounded by the stability and reliability requirements. The drive laser and transport system has been installed and tested. We will report on the current operational state of the laser and plans for future improvements.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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R. Akre,
J. Castro,
Y. Ding,
D. Dowell,
P. Emma, J. Frisch,
S. Gilevich,
G. Hays,
Z. Hering,
R.I. Huang, [......],
M. Saleski,
J. Schmerge,
D. Schultz,
J. Turner,
J. Welch,
W. White,
J. Wu,
L. Froelich,
T. Limberg,
E. Prat
[show abstract]
[hide abstract]
ABSTRACT: The linac coherent light source (LCLS) is a SASE X- ray free-electron laser (FEL) project presently under construction at SLAC [1]. The injector section, from drive-laser and RF photocathode gun through first bunch compressor chicane, was installed in fall 2006. Initial system commissioning with an electron beam is taking place during the spring and summer of 2007. The second phase of construction, including second bunch compressor and full linac, will begin later, in the fall of 2007. We report here on experience gained during the first phase of machine commissioning, including RF photocathode gun, linac booster section, S-band and X-band RF systems, first bunch compressor, and the various beam diagnostics.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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S. Walston,
C. Chung,
P. Fitsos,
J. Gronberg,
M. Ross,
O. Khainovski,
Y. Kolomensky,
P. Loscutoff,
M. Slater,
M. Thomson, [......],
J. May,
D. McCormick,
S. Smith,
T. Smith,
G. White,
T. Orimoto,
H. Hayano,
Y. Honda,
N. Terunuma,
J. Urakawa
[show abstract]
[hide abstract]
ABSTRACT: International Linear Collider (ILC) interaction region beam sizes and component position stability requirements will be as small as a few nanometers. It is important to the ILC design effort to demonstrate that these tolerances can be achieved - ideally using beam-based stability measurements. It has been estimated that RF cavity beam position monitors (BPMs) could provide position measurement resolutions of less than one nanometer and could form the basis of the desired beam-based stability measurement. We have developed a high resolution RF cavity BPM system. A triplet of these BPMs has been installed in the extraction line of the KEK Accelerator Test Facility (ATF) for testing with its ultra-low emittance beam. A metrology system for the three BPMs was recently installed. This system employed optical encoders to measure each BPM's position and orientation relative to a zero-coefficient of thermal expansion carbon fiber frame and has demonstrated that the three BPMs behave as a rigid-body to less than 5 nm. To date, we have demonstrated a BPM resolution of less than 20 nm over a dynamic range of +/- 20 microns.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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S. Molloy, J. Frisch,
J. May,
D. McCormick,
T. Smith,
N. Baboi,
O. Hensler,
L. Petrosyan,
N. Eddy,
L. Piccoli,
R. Rechenmacher,
M. Ross,
M. Wendt,
O. Napoly,
R.C. Paparella,
C. Simon
[show abstract]
[hide abstract]
ABSTRACT: It is well known that an electron beam excites higher order modes (HOMs) as it passes through an accelerating cavity. The properties of the excited signal depend not only on the cavity geometry, but on the charge and trajectory of the beam. It is, therefore, possible to use these signals as a monitor of the beam's position. Electronics were installed on all forty cavities present in the FLASH linac in DESY. These electronics filter out a mode known to have a strong dependence on the beam's position, and mix this down to a frequency suitable for digitisation. An analysis technique based on singular value decomposition (SVD) was developed to calculate the beam's trajectory from the output of the electronics. The entire system has been integrated into the FLASH control system.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
