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Inverse Free Electron Laser Heater for the LCLS

Description: The Linac Coherent Light Source (LCLS) free electron laser employs an RF photocathode gun that yields a 1nC bunch a few picoseconds long, which must be further compressed to yield the high current required for Self Amplified Spontaneous Emission (SASE) gain. The electron beam from the RF photocathode gun is quite sensitive to microbunching instabilities such as coherent synchrotron radiation (CSR) in the compressor chicanes and longitudinal space charge (LSC) in the linac. These effects can be Landau damped by adding energy spread to the electron bunch prior to compression. They propose to do this by co-propagating an infrared laser beam with the electron bunch in an undulator in the LCLS injector beamline. The undulator is placed in a four bend magnet chicane to allow the Ir laser beam to propagate colinearly with the e-beam while it oscillates in the undulator. The IR laser beam is derived from the photocathode gun drive laser, so the two beams are synchronized. Simulations presented elsewhere in these proceedings show that the laser interaction damps the microbunching instabilities to a very great extent. This paper is a description of the design of the laser heater.
Date: May 11, 2005
Creator: Bentson, L.D.; Bolton, P.; Carr, R.; Dowell, D.; Emma, P.; Gilevich, S. et al.
Partner: UNT Libraries Government Documents Department

Optimization of the LCLS X-Ray FEL Output Performance in the Presence of Strong Undulator Wakefields

Description: The Linac Coherent Light Source (LCLS) Free-Electron Laser will operate in the wavelength range of 1.5 to 15 Angstroms. Energy loss due to wakefields within the long undulator can degrade the FEL process by detuning the resonant FEL frequency. The wakefields arise from the vacuum chamber wall resistivity, its surface roughness, and abrupt changes in its aperture. For LCLS parameters, the resistive component is the most critical and depends upon the chamber material (e.g. Cu) and its radius. To study the expected performance in the presence of these wakefields, we make a series of start-to-end simulations with tracking codes PARMELA and ELEGANT and time-dependent FEL simulation codes Genesis 1.3 and Ginger. We discuss the impact of the wakefield on output energy, spectral bandwidth, and temporal envelope of the output FEL pulse, as well as the benefits of a partial compensation obtained with a slight z dependent taper in the undulator field. We compare these results to those obtained by decreasing the bunch charge or increasing the vacuum chamber radius. We also compare our results to those predicted in concurrent analytical work.
Date: March 17, 2006
Creator: Reiche, S.; /UCLA; Bane, K.L.F.; Emma, P.; Huang, Z.; Nuhn, H.D. et al.
Partner: UNT Libraries Government Documents Department

Optimization and Modeling of the Accelerator for the FERMI @ Elettra FEL

Description: Design studies are in progress to use the existing FERMI{at}Elettra linear accelerator for a seeded harmonic cascade free-electron laser (FEL) facility [1]. This accelerator will be upgraded to 1.2 GeV and equipped with a low-emittance RF photocathode gun, laser heater, two bunch compressors, and a beam delivery system. We present an optimization study of all the components downstream of the gun, aimed at achieving the high peak current, low energy spread and low emittance electron beam necessary for the FEL. Various operational scenarios are discussed. Results of accelerator simulations including effects of space charge, coherent synchrotron radiation and wakefields are reported.
Date: September 30, 2005
Creator: Di Mitri, S.; Cornacchia, M.; Craievich, P.; Trieste, /Sincrotrone; Emma, P.; Huang, Z. et al.
Partner: UNT Libraries Government Documents Department

LCLS X-Ray FEL Output Performance in the Presence of Highly Time-Dependent Undulator Wakefields

Description: Energy loss due to wakefields within a long undulator, if not compensated by an appropriate tapering of the magnetic field strength, can degrade the FEL process by detuning the resonant FEL frequency. The wakefields arise from the vacuum chamber wall resistivity, its surface roughness, and abrupt changes in its aperture. For LCLS parameters, the resistive-wall component is the most critical and depends upon the chamber material (e.g., Cu) and its radius. Of recent interest[1] is the so-called ''AC'' component of the resistive-wall wake which can lead to strong variations on very short timescales (e.g., {approx} 20 fs). To study the expected performance of the LCLS in the presence of these wakefields, we have made an extensive series of start-to-end SASE simulations with tracking codes PARMELA and ELEGANT, and time-dependent FEL simulation codes GENESIS1.3 and GINGER. We discuss the impact of the wakefield losses upon output energy, spectral bandwidth, and temporal envelope of the output FEL pulse, as well as the benefits of a partial compensation of the time-dependent wake losses obtained with a slight z-dependent taper in the undulator field. We compare the taper results to those predicted analytically[2].
Date: September 30, 2005
Creator: Fawley, W.M.; /LBL, Berkeley; Bane, K.L.F.; Emma, P.; Huang, Z.; Nuhn, H.-D. et al.
Partner: UNT Libraries Government Documents Department

Considerations on Beam Quality Control in MIT X-Ray FEL

Description: The x-ray FEL at MIT is one example of a design for a new generation linac-based light source. Such a new machine requires very high quality electron beams. Besides the usual requirements on beam parameters such as emittance, energy spread, peak current, there are new challenges emerging in the design studies, e.g., the arrival timing of electron beam must reach precision below tens of femtoseconds level to ensure the laser seed overlaps the desired sections of electron bunch in the multiple-stage HGHG process. In this paper we report the progress on design optimization towards high quality and low sensitivity beams.
Date: March 15, 2006
Creator: Wang, D.; Graves, W.; Wang, D.; Zwart, T.; /MIT, Bates Linear Accelerator; Emma, P. et al.
Partner: UNT Libraries Government Documents Department

Electron Bunch Length Measurement for LCLS at SLAC

Description: At Stanford Linear Accelerator Center (SLAC) a Bunch Length Measurement system has been developed to measure the length of the electron bunch for its new Linac Coherent Light Source (LCLS). This destructive measurement uses a transverse-mounted RF deflector (TCAV) to vertically streak the electron beam and an image taken with an insertable screen and a camera. The device control software was implemented with the Experimental Physics and Industrial Control System (EPICS) toolkit. The analysis software was implemented in Matlab{trademark} using the EPICS/Channel Access Interface for Scilab{trademark} and Matlab{trademark} (labCA). This architecture allowed engineers and physicists to develop and integrate their control and analysis without duplication of effort.
Date: October 4, 2007
Creator: Zelazny, M.; Allison, S.; Chevtsov, Sergei; Emma, P.; Kotturi, K.d.; Loos, H. et al.
Partner: UNT Libraries Government Documents Department

LCLS LLRF Upgrades to the SLAC Linac

Description: 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.
Date: October 4, 2007
Creator: Akre, R.; Dowell, D.; Emma, P.; Frisch, J.; Hong, B.; Kotturi, K. et al.
Partner: UNT Libraries Government Documents Department

Interplay of the Chirps and Chirped Pulse Compression in a High-gain Seeded Free-electron Laser

Description: In a seeded high-gain Free-electron Laser (FEL), where a coherent laser pulse interacts with an ultra-relativistic electron beam, the seed laser pulse can be frequency chirped, and the electron beam can be energy chirped. Besides these two chirps, the FEL interaction introduces an intrinsic frequency chirp in the FEL even if the above mentioned two chirps are absent. In this paper we examine the interplay of these three chirps. The problem is formulated as an initial value problem, and solved via a Green function approach. Besides the chirp evolution, we also give analytical expressions for the pulse duration and bandwidth of the FEL, which remains fully longitudinally coherent in the high gain exponential growth regime. Because the chirps are normally introduced for a final compression of the FEL pulse, some conceptual issues are discussed. We show that in order to get a short pulse duration, an energy chirp in the electron beam is necessary.
Date: January 3, 2007
Creator: Wu, Juhao; /SLAC; Murphy, J.B.; /LBNL, ALS; Emma, P.J.; /SLAC et al.
Partner: UNT Libraries Government Documents Department

Design Optimizations of X-Ray FEL Facility at MIT

Description: In recent years, a number of short wavelength FEL experiments have demonstrated key technologies and obtained good agreement between experiment and theory. The x-ray FEL at MIT[1] is one example of a design for a new generation linac-based light source. Such a new machine requires very high quality electron beams. Besides the usual requirements on beam quality such as emittance, energy spread, peak current, etc., there are new challenges emerging in the design studies, e.g., the precise arrival timing of electron beam at lower tens of femtoseconds level to ensure the laser seed overlap the desired sections of electron bunch in the multiple-stage HGHG process. In this paper we report the progress on design optimization towards high quality and low sensitivity beams.
Date: May 9, 2005
Creator: Farkhondeh, M.; Graves, W.; Van der Laan, J.; Wang, D.; Wang, F.; Zwart, T. et al.
Partner: UNT Libraries Government Documents Department

Using a Fast-Gated Camera for Measurements of Transverse Beam Distributions and Damping Times

Description: With a fast-gated camera, synchrotron light was used for studying the transverse beam distributions and damping times in the Stanford Linear Collider (SLC) damping rings. By digitizing the image in the camera signal, the turn-by-turn time evolution of the transverse beam distribution was monitored and analyzed. The projections of the digitized image were fit with Gaussian functions to determine the moments of the distribution. Practical applications include the determination of injection matching parameters and the transverse damping times. In this report we describe a synchrotron light monitor and present experimental data obtained in the SLC damping rings.
Date: November 1, 1992
Creator: Minty, M.; Brown, R.; Decker, F. J.; Emma, P.; Krejcik, P.; Limberg, T. et al.
Partner: UNT Libraries Government Documents Department

Using a fast-gated camera for measurements of transverse beam distributions and damping times

Description: With a fast-gated camera, synchrotron light was used for studying the transverse beam distributions and damping times in the Stanford Linear Collider (SLC) damping rings. By digitizing the image in the camera signal, the turn-by-turn time evolution of the transverse beam distribution was monitored and analyzed. The projections of the digitized image were fit with Gaussian functions to determine the moments of the distribution. Practical applications include the determination of injection matching parameters and the transverse damping times. In this report we describe a synchrotron light monitor and present experimental data obtained in the SLC damping rings.
Date: November 1, 1992
Creator: Minty, M.; Brown, R.; Decker, F. J.; Emma, P.; Krejcik, P.; Limberg, T. et al.
Partner: UNT Libraries Government Documents Department

THE VISA FEL UNDULATOR

Description: The Visible-Infrared SASE Amplifier (VISA) FEL is an experimental device designed to show Self Amplified Spontaneous Emission (SASE) to saturation in the visible light energy range. It will generate a resonant wavelength output from 800--600 nm, so that silicon detectors may be used to characterize the optical properties of the FEL radiation. VISA is the first SASE FEL designed to reach saturation, and its diagnostics will provide important checks of theory. This paper includes a description of the VISA undulator, the magnet measuring and shimming system, and the alignment strategy. VISA will have a 4 m pure permanent magnet undulator comprising four 99 cm segments, each with 55 periods of 18 mm length. The undulator has distributed focusing built into it, to reduce the average beta function of the 70--85 MeV electron beam to about 30 cm. There are four FODO cells per segment. The permanent magnet focusing lattice consists of blocks mounted on either side of the electron beam, in the undulator gap. The most important undulator error parameter for a free electron laser is the trajectory walkoff or lack of overlap of the photon and electron beams. Using pulsed wire magnet measurements and magnet shimming, the authors expect to be able to control trajectory walkoff to less than {+-}50 pm per field gain length.
Date: August 16, 1998
Creator: CARR,R.; CORNACCHIA,M.; EMMA,P.; NUHN,H.D.; FULAND,R.; JOHNSON,E. et al.
Partner: UNT Libraries Government Documents Department

Recent improvements in the SLC positron system performance

Description: The positron system is very specific to the SLC in that the positrons are accelerated in the same linac as the electrons that produce them and the electrons with which they collide. Some of the difficulties in tuning this system to peak performance are thus unlikely to be encountered in future linear colliders, but many of the lessons learned in beam matching are useful for future machines. The design and commissioning of this system has been previously reported so we only briefly describe the major subsystems before detailing the tuning and diagnostics involved in optimizing the performance of the overall system.
Date: March 1, 1992
Creator: Krejcik, P.; Corbett, J.; Ecklund, S.; Emma, P.; Fieguth, T.; Helm, R. et al.
Partner: UNT Libraries Government Documents Department

Measured emittance versus store time in the SLC damping ring

Description: Emittance studies at the SLC North Damping Ring led to precise measurements of the damping time using three independent methods. These measurements were done at three different locations: (1) in the ring using a fast gated video camera which allows the acquisition of the image of the synchrotron light from a single turn, (2) using the extracted beam and a single wire scanner in the ring-to-linac transport line, and (3) in the linac using four wire scanners. In addition the extracted beam emittance was studied as a function of various parameters. A significant dependence on the tune was observed.
Date: March 1, 1992
Creator: Decker, F.J.; Emma, P.; Krejcik, P.; Limberg, T.; Minty, M.; Moshammer, H. et al.
Partner: UNT Libraries Government Documents Department

Commissioning the LCLS Injector

Description: The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project presently under construction at SLAC. 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 was completed in August 2007, with the goal of a 1.2-micron emittance in a 1-nC bunch clearly demonstrated. The second phase of commissioning, including second bunch compressor and full linac, is planned for 2008, with FEL commissioning in 2009. We report experimental results and experience gained in the first phase of commissioning, including the photo-cathode drive laser, RF gun, photocathode, S-band and X-band RF systems, first bunch compressor, and the various beam diagnostics.
Date: November 28, 2007
Creator: Akre, R.; Dowell, D.; Emma, P.; Frisch, J.; Gilevich, S.; Hays, G. et al.
Partner: UNT Libraries Government Documents Department

LCLS Injector Drive Laser

Description: 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.
Date: November 2, 2007
Creator: Dowell, D.H.; Castro, J.; Emma, P.; Frisch, J.; Gilevich, A.; Hays, G. et al.
Partner: UNT Libraries Government Documents Department

Precision Measurement of the Undulator K Parameter using Spontaneous Radiation

Description: Obtaining precise values of the undulator parameter, K, is critical for producing high-gain FEL radiation. At the LCLS [1], where the FEL wavelength reaches down to 1.5 {angstrom}, the relative precision of K must satisfy ({Delta}K/K){sub rms} {approx}< 0.015% over the full length of the undulator. Transverse misalignments, construction errors, radiation damage, and temperature variations all contribute to errors in the mean K values among the undulator segments. It is therefore important to develop some means to measure relative K values, after installation and alignment. We propose a method using the angle-integrated spontaneous radiation spectrum of two nearby undulator segments, and the natural shot-to-shot energy jitter of the electron beam. Simulation of this scheme is presented using both ideal and measured undulator fields. By ''leap-frogging'' to different pairs of segments with extended separations we hope to confirm or correct the values of K, including proper tapering, over the entire 130-m long LCLS undulator.
Date: April 17, 2007
Creator: Welch, J.J.; Arthur, J.; Emma, P.; Hastings, J.B.; Huang, Z.; Nuhn, H.D. et al.
Partner: UNT Libraries Government Documents Department

Picosecond Bunch length and Energy-z correlation measurements at SLAC's A-Line and End Station A

Description: 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. Modeling 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 FEL at SLAC. The LCLS also plans precise bunch length and energy-z correlation measurements using transverse RF deflecting cavities.
Date: June 27, 2007
Creator: Molloy, Stephen; Emma, P.; Frisch, J.C.; Iverson, R.H.; Ross, M.; McCormick, D.J. et al.
Partner: UNT Libraries Government Documents Department

Longitudinal Bunch Shape Diagnostics With Coherent Radiation And a Transverse Deflecting Cavity at TTF2

Description: At the DESY TTF2 linear accelerator three special techniques to characterize the longitudinal charge distribution of the electron bunches that drive the free-electron laser are currently under study: electro-optical sampling, far-infrared spectral analysis of coherent radiation and the use of a transverse deflecting cavity to streak the bunch. The principles and implementations of the latter two are described in this paper. Details on electro-optical sampling can be found in [1].
Date: August 4, 2005
Creator: Grimm, O.; Frohlich, L.; Klose, K.; Nagl, M.; Peters, O.; Rossbach, J. et al.
Partner: UNT Libraries Government Documents Department

Database Applications to Integrate Beam Line Optics Changes with the Engineering Databases

Description: The LCLS project databases provide key nomenclature information while integrating many engineering and physics processes in the building of an accelerator. Starting with the elements existing in the beam line optics files, the engineers add non-beam-line elements, and controls engineers assign ''Formal Device Names'' to these elements. Inventory, power supplies, racks, crates and cable plants are databases that are being integrated into the project database. This approach replaces individual spreadsheets and/or integrates standalone existing institutional databases.
Date: July 6, 2007
Creator: Chan, A.; Bellomo, P.; Crane, G.R.; Emma, P.; Grunhaus, E.; Luchini, K. et al.
Partner: UNT Libraries Government Documents Department

Measurements of Compression and Emittance Growth after the First LCLS Bunch Compressor Chicane

Description: The Linac Coherent Light Source (LCLS) is a SASE xray free-electron laser project presently under construction at SLAC. 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.
Date: November 2, 2007
Creator: Bane, K.; Ding, Y.; Emma, P.; Frisch, J.; Huang, Z.; Loos, H. et al.
Partner: UNT Libraries Government Documents Department

Recent improvements in the SLC positron system performance

Description: The positron system is very specific to the SLC in that the positrons are accelerated in the same linac as the electrons that produce them and the electrons with which they collide. Some of the difficulties in tuning this system to peak performance are thus unlikely to be encountered in future linear colliders, but many of the lessons learned in beam matching are useful for future machines. The design and commissioning of this system has been previously reported so we only briefly describe the major subsystems before detailing the tuning and diagnostics involved in optimizing the performance of the overall system.
Date: March 1, 1992
Creator: Krejcik, P.; Corbett, J.; Ecklund, S.; Emma, P.; Fieguth, T.; Helm, R. et al.
Partner: UNT Libraries Government Documents Department

Measured emittance versus store time in the SLC damping ring

Description: Emittance studies at the SLC North Damping Ring led to precise measurements of the damping time using three independent methods. These measurements were done at three different locations: (1) in the ring using a fast gated video camera which allows the acquisition of the image of the synchrotron light from a single turn, (2) using the extracted beam and a single wire scanner in the ring-to-linac transport line, and (3) in the linac using four wire scanners. In addition the extracted beam emittance was studied as a function of various parameters. A significant dependence on the tune was observed.
Date: March 1, 1992
Creator: Decker, F. J.; Emma, P.; Krejcik, P.; Limberg, T.; Minty, M.; Moshammer, H. et al.
Partner: UNT Libraries Government Documents Department