The Stanford Linear Accelerator Center, in collaboration with Argonne National Laboratory, Brookhaven National Laboratory, Los Alamos National Laboratory, Lawrence Livermore National Laboratory, and the University of California at Los Angeles, have collaborated to create a conceptual design for a Free-Electron-Laser (FEL) R&D facility operating in the wavelength range 1.5-15 {angstrom}. This FEL, called the ''Linac Coherent Light Source'' (LCLS), utilizes the SLAC linac and produces sub-picosecond pulses of short wavelength x-rays with very high peak brightness and full transverse coherence. The first two-thirds of the SLAC linac are used for injection into the PEP-II storage rings. The last one-third will be converted to a source of electrons for the LCLS. The electrons will be transported to the SLAC Final Focus Test Beam (FFTB) Facility, which will be extended to house a 122-m undulator system. In passing through the undulators, the electrons will be bunched by the force of their own synchrotron radiation to produce an intense, spatially coherent beam of x-rays, tunable in energy from 0.8 keV to 8 keV. The LCLS will include two experiment halls as well as x-ray optics and infrastructure necessary to make use of this x-ray beam for research in a variety of disciplines suchmore » as atomic physics, materials science, plasma physics and biosciences. This Conceptual Design Report, the authors believe, confirms the feasibility of constructing an x-ray FEL based on the SLAC linac.« less

/pdf/linac-coherent-light-source-lcls-conceptual-design-report-3sis5uwe9k.pdf

Linac coherent light source (LCLS) conceptual design report

A generalized fast feedback system has been developed to stabilize beams at various locations in the SLC. The system is designed to perform measurements and change actuator settings to control beam states such as position, angle and energy on a pulse to pulse basis. The software design is based on the state space formalism of digital control theory. The system is database-driven, facilitating the addition of new loops without requiring additional software. A communications system, KISNet, provides fast communications links between microprocessors for feedback loops which involve multiple micros. Feedback loops have been installed in seventeen locations throughout the SLC and have proven to be invaluable in stabilizing the machine.

/pdf/generalized-fast-feedback-system-in-the-slc-3fdmutdxnf.pdf

Generalized fast feedback system in the SLC

We report direct observations of submicropulse beam centroid shifts (head-tail kicks) correlated with short-range wakefields generated by off-axis electron-beam steering in Tesla-type superconducting rf cavities. The experiments were performed at the Fermilab Accelerator Science and Technology (FAST) Facility using its unique configuration of a photocathode rf gun injecting beam into two separated nine-cell cavities. The cavities are in series with corrector magnets and beam position monitors (BPMs) located before, between, and after them. The off-axis steering in the cavity was guided by the rf BPM data and higher-order mode circuitry targeting the first and second dipole passbands. The centroid shifts of up to 300  μm from head to tail of the ∼10-ps-long micropulses at 500  pC/b in a 3-MHz pulse train were measured via optical transition radiation at a downstream screen with a Hamamatsu C5680 synchroscan streak camera. We also showed that we could compensate such kicks from the first cavity with the short-range wakefields (SRWs) in the second cavity, and we observed the dilution of the beam size in the tail of the pulses. A simple numerical model of the SRW effect in a single Tesla cavity is compared to the experiment successfully. In principle, these fundamental results may be scaled to cryomodule configurations of major free-electron laser (FEL) facilities such as the European XFEL, Linac Coherent Light Source or LCLS-II XFEL, and the conceptual international linear collider.

https://link.aps.org/pdf/10.1103/PhysRevAccelBeams.23.054401

Submicropulse electron-beam dynamics correlated with short-range wakefields in Tesla-type superconducting rf cavities

Transverse wakefields in the linac of the SLAC Linear Collider (SLC) have been observed to enlarge the effective emittance of beams which are not properly centered in the accelerating structure.‘12 A fast feedback system has been constructed to minimize the enlargement under changing conditions by controlling the beam launching parameters. Theoretical aspects of this transverse feedback system are reviewed as well as the design of the beam sensors, launch controllers, communication equipment and data processing micro-computer. A variety of beam observations have been made. They show that dispersion as well as wakefield effects are important. In the near future the fast transverse feedback system will be beam tested, and algorithms tailored to the noise environment of the SLC will be tried. System Overview The transverse feedback system of the linac has components for both slow and fast beam control. Trajectory correction over the entire linac2T3 involving 550 dipoles and 275 beam position monitors (BPM) is performed about every 30 minutes. In this way, trajectory errors are kept below 200 pm rms. Linac input and output launch parameters (z, z’, y, y’) are corrected3 about once per minute in order to maintain injection from the Ring-ToLinac transport line (RTL) into the linac and from the linac into the ARC system. Both of these controls rely on information from local beam position monitors with resolutions of order 50 pm and ignore current-dependent phenomena. At high beam intensities transverse wakefields make the beams very sensitive to small changes in launching position and angle. As a result, beam positions must be controlled to a few microns’ which is beyond the sensitivities of the local beam monitors. Furthermore, the parameters are expected to change sufficiently rapidly that the VAX control system cannot simultaneously handle the feedback load above all the other necessary control functions. Thus, a stand-alone micro-computer is needed as well as an independent feedback process. The fast transverse feedback system has sensors at the end of the linac where the transverse beam distortions are most pronounced. The control elements are located in the e+ and eRTL’s because the beams are most sensitive to errors (and to corrections) in the early part of the linac. As an illustration, in the absence of transverse wake fields a beam with a bunch length of 1 mm and 5 x 1O’O particles which is injected into the linac off axis by 10 pm at p = 10 m will oscillate with an amplitude that damps via acceleration to about 2 pm at 50 GeV. IIowever, with transverse wakefields a particle behind the bunch center by a,/2 will be driven to an amplitude of about 120 pm by the end of the linac. A particle 2a, behind the bunch center will have an amplitude over 1 mm. Integrating over the bunch, a 10 pm injection error will be manifested as a 100 pm centroid shift at the end of the linac plus tails which extend to 1 mm. The

/pdf/transverse-wakefield-control-and-feedback-in-the-slc-linac-452ss1zfkd.pdf

Transverse wakefield control and feedback in the slc linac

The algorithms used in the database-driven SLC fast-feedback system are based on the state-space formalism of digital control theory. These are implemented as a set of matrix equations which use a Kalman filter to estimate a vector of states from a vector of measurements and then apply a gain matrix to determine the actuator settings from the state vector. The matrices used in the calculation are derived offline using linear quadratic Gaussian minimization. For a given noise spectrum, this procedure minimizes the RMS of the states (e.g., the position or energy of the beam). The offline program also allows simulation of the loop's response to arbitrary inputs and calculates its frequency response. >

/pdf/use-of-digital-control-theory-state-space-formalism-for-18b183mbjg.pdf

Use of digital control theory state space formalism for feedback at SLC

The energies and energy spectra of the positron and electron beams emerging from the SLC Linac must be carefully maintained so that the beams can be transported through the Arcs to the Final Focus without phase space dilution and also to specify the collision energy. A fastback system has been designed and constructed to control these parameters. The energies and energy spectra are measured nondestructively using position monitors and synchrotron radiation width monitors. The controls consist of rf phases in the Damping Rings, SLED timing, and rf amplitude. Theoretical aspects of the feedback process, algorithms, and operational experience are discussed.

/pdf/fast-energy-and-energy-spectrum-feedback-in-the-slc-linac-1x1c3mvd80.pdf

Fast Energy and Energy Spectrum Feedback in the SLC Linac

1. Abstract The component installation for the upgrade of the threekilometer linac’ for the SLAC Linear Collider (SLC) was completed in late summer 1986. The system status and measurements of beam properties made during commissioning are described in this paper. Further linac measurements are reviewed in companion papers.213’4 In simmar;, a low-emittance electron beam from a damping rinrr has been accelerated through the linac and iniected into the-north SLC Arc with negligible loss. The maximum bunch intensity is 2.9 X 10 lo electrons/pulse. A peak particle energy of 53 GeV has been reached. Operation at 47 GeV is now routine. The energy and energy spectrum of the electron beam can be rapidly measured nondestructively at high energy . These signals will be used in a fast feedback system nearing completion. The electron beam can be centered in the accelerator to about 200 pm rms. Slow feedback of the injection position and angle into the linac and injection into the north Arc are operational.5 Longitudinal and transverse wakefields have been measured and appear to be near expectations. Transverse position measurements at the end of the linac show a 120 pm horizontal and a 30 pm vertical (rms) jitter from pulse to pulse. The spot shape, including the transverse tails, also shows some jitter. The transverse position and shape fluctuations have several sources involving launch instabilities, chromatic effects, RF deflections and lattice mismatches. Continued improvements are expected. These parameter jitters would not preclude collisions. The measured invariant transverse emittances of the beam at 47 GeV are 2 x lop5 rm vertically and 12 - 25 x low5 rm horizontally at 1 x 10” e-. The horizontal emittance increases with beam intensity. Damped positrons have been injected into the linac, and trajectory correction is underway.

https://epaper.kek.jp/p87/pdf/pac1987_0073.pdf

Experimental beam dynamics in the slc linac

The linac of the SLAC (Stanford Linear Accelerator Center) Linear Collider (SLC) must accelerate three high-intensity bunches on each linac pulse from 1.2 GeV to 50 GeV with minimal increase of small transverse emittance. The procedures and adjustments used to obtain this goal are outlined. Some of the accelerator parameters and components which interact are the beam energy, transverse position, component alignment, RF manipulation, feedback system, quadrupole lattice, BNS damping, energy spectra, phase space matching, collimation, instrumentation, and modeling. The method to bring these interdependent parameters collectively into specification has evolved over several years. The sequence which is sued to turn on the linac from a cold start and produce acceptable beams for the final focus and collisions is reviewed. Approximate time estimates for the various activities are given. >

/pdf/the-slac-linac-as-used-in-the-slc-collider-1otvn2e6w1.pdf

The SLAC linac as used in the SLC collider

Fast Energy Spectrum and Transverse Beam Profile Monitoring and Feedback Systems for the SLC Linac

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