We report the results of preliminary studies of a 2 to 4 nm SASE FEL, using a photoinjector to produce the electron beam, and the SLAC linac to accelerate it to an energy up to 10 GeV. Longitudinal bunch compression is used to increase ten fold the peak current to 2.5 kA, while reducing the bunch length to the subpicosecond range. The saturated output power is in the multi-gigawatt range, producing about 1014 coherent photons within a bandwidth of about 0.2% rms, in a pulse of several millijoules. At 120 Hz repetition rate the average power is about 1 W. The system is optimized for X-ray microscopy in the water window around 2 to 4 nm, and will permit imaging a biological sample in a single subpicosecond pulse.

/pdf/a-2-to-4-nm-high-power-fel-on-the-slac-linac-5frzrpp3o0.pdf

A 2 to 4 nm high power FEL on the SLAC linac

The authors describe the design, construction, commissioning and ultimate uses of wire scanners in the SLC (SLAC Linear Collider), focusing on the linear accelerator and upstream systems scanners. Of particular interest is the interaction between the wire and the scattered radiation from the wire with the extreme electric field of the beam. As this field reaches the level of several volts/angstrom, as it does easily at the SLC interaction point (and may in upstream parts of SLC), field emission from the wire may occur. A key feature of SLC operation is the degree of high level active control required to keep it optimized. Advanced high level control software allows the use of wire scanner data in feedback and beam optimization procedures. Non-invasive scans are performed almost continually and the results are logged so that long term trends in emittance can be examined. >

/pdf/wire-scanners-for-beam-size-and-emittance-measurements-at-48mkfpqzat.pdf

Wire scanners for beam size and emittance measurements at the SLC

This introductory course aims at a reasonably complete coverage of beam diagnostic devices used in linear and circular accelerators and in primary beam lines. The weight is on the concepts and the indication of variants, while for technical details the reader is referred to the literature. The present updated version replaces those from previous General Accelerator Physics Courses.

/pdf/beam-diagnostics-for-accelerators-mm89xf1thr.pdf

Beam diagnostics for accelerators

Beam size estimates made using beam-beam deflections are used for optimization of the Stanford Linear Collider (SLC) electron-positron beam sizes. Typical beam sizes and intensities expected for 1996 operations are 2.1 × 0.6 μm (x, y) at 4.0 × 1010 particles per pulse. Conventional profile monitors, such as scanning wires, fail at charge densities well below this. The laser-based profile monitor uses a finely-focused 350-nm wavelength tripled YLF laser pulse that traverses the particle beam path about 29 cm away from the e+/e− IP. Compton scattered photons and degraded e+/e− are detected as the beam is steered across the laser pulse. The laser pulse has a transverse size of 380 nm and a Rayleigh range of about 5 μm.

A laser-based beam profile monitor for the SLC/SLD interaction region

The Stanford Linear Collider (SLC) is the first and only high-energy e/sup +/e/sup -/ linear collider in the world. Its most remarkable features are high intensity, submicron sized, polarized (e/sup -/) beams at a single interaction point. The main challenges posed by these unique characteristics include machine-wide emittance preservation, consistent high intensity operation, polarized electron production and transport, and the achievement of a high degree of beam stability on all time scales. In addition to serving as an important machine for the study of Z/sup 0/ boson production and decay using polarized beams, the SLC is also an indispensable source of hands-on experience for future linear colliders. Each new year of operation has been highlighted with a marked improvement in performance. The most significant improvements for the 1994-95 run include new low impedance vacuum chambers for the damping rings, an upgrade to the optics and diagnostics of the final focus systems, and a higher degree of polarization from the electron source. As a result, the average luminosity has nearly doubled over the previous year with peaks approaching 10/sup 30/ cm/sup -2/ s/sup -1/ and an 80% electron polarization at the interaction point. These developments as well as the remaining identifiable performance limitations will be discussed.

/pdf/the-stanford-linear-collider-equvnbqxsi.pdf

The Stanford Linear Collider

The correlation plot facility is a powerful interactive tool for data acquisition and analysis throughout the SLC (Stanford Linear Collider). A generalized interface allows the user to perform a wide variety of machine physics experiments. The user may step one or two independent parameters such as magnet or feedback setpoints while measuring or calculating up to 160 others. Measured variables include all analog signals available to the control system as well as a variety of derived parameters such as beam size or emittance. Various fitting algorithms and display options are provided for data analysis. A software-callable interface is also provided. Applications based on this facility are used to phase klystrons, measure emittance and dispersion, minimize beam size at the interaction point and maintain beam collisions. >

/pdf/correlation-plot-facility-in-the-slc-control-system-21omuncoxf.pdf

Correlation plot facility in the SLC control system

Operational experience with model-driven steering in the linac of the Stanford Linear Collider (SLC) is discussed. Important issues include two-beam steering, sensitivity of algorithms to fault components, sources of disagreement with the model, and the effects of the finite resolution of beam position monitors. Methods developed to make the steering algorithms more robust in the presence of such complications are also presented. >

/pdf/operational-experience-with-model-based-steering-in-the-slc-17egd5jbij.pdf

Operational experience with model-based steering in the SLC Linac

Online computer models of first order beam optics have been developed for the commissioning, control and operation of the entire SLC including Damping Rings, Linac, Positron Return Line and Collider Arcs. A generalized online environment utilizing these models provides the capability for interactive selection of a desired optics configuration and for the study of its properties. Automated procedures have been developed which calculate and load beamline component set-points and which can scale magnet strengths to achieve desired beam properties for any Linac energy profile. Graphic displays facilitate comparison of design, desired and actual optical characteristics of the beamlines. Measured beam properties, such as beam emittance and dispersion, can be incorporated interactively into the models and used for beamline matching and optimization of injection and extraction efficiencies and beam transmission. The online optics modeling facility also serves as the foundation for many model-driven applications such as autosteering, calculation of beam launch parameters, emittance measurement and dispersion correction.

/pdf/application-of-online-modeling-to-the-operation-of-slc-2tnyxx8aks.pdf

Application of online modeling to the operation of SLC

Beam orbits in the SLC are monitored in real time, and the data are stored for future trend and correlation analysis. Software has been developed that permits both real-time and offline continuous monitoring and analysis of the beam orbits in all parts of the machine. A background process acquires beam position monitor (BPM) and toroid data on a periodic basis and saves the general quantities such as orbit RMS and beam intensity in addition to the individual readings. Some of this data is archived by the SLC history buffer facility and the rest is saved in files for later analysis. This has permitted the tracing of interaction point instabilities to specific devices as far away as the damping rings. In addition, the data are displayed for the operators both in summary and in full form. The different displays can be configured from the control consoles. >

https://epaper.kek.jp/p91/pdf/pac1991_1284.pdf

L. Sanchez-Chopitea

Papers

Wire scanners for beam size and emittance measurements at the SLC

Correlation plot facility in the SLC control system

Operational experience with model-based steering in the SLC Linac

Application of online modeling to the operation of SLC

Orbit monitoring in the SLC