Muons, Inc, Batavia, USA
Old Dominion University, Norfolk, Virginia, USA
LBNL, Berkeley, California, USA
ANL, Argonne, USA
Fermilab, Batavia, USA
Voss Scientific, Albuquerque, New Mexico, USA
Many present and future particle accelerators are limited by the maximum electric gradient and peak surface fields that can be realized in RF cavities. Despite considerable effort, a comprehensive theory of RF breakdown has not been achieved, and mitigation techniques to improve practical maximum accelerating gradients have had only limited success. Recent studies have shown that high gradients can be achieved quickly in 805 MHz RF cavities pressurized with dense hydrogen gas without the need for long conditioning times, because the dense gas can dramatically reduce dark currents and multipacting. In this project we use this high pressure technique to suppress effects of residual gas and geometry found in evacuated cavities to isolate and study the role of the metallic surfaces in RF cavity breakdown as a function of radiofrequency and surface preparation. A 1.3-GHz RF test cell with replaceable electrodes (e.g. Mo, Cu, Be, W, and Nb) has been built, and a series of detailed experiments is planned at the Argonne Wakefield Accelerator. These experiments will be followed by additional experiments using a second test cell operating at 402.5 MHz.
LBNL, Berkeley, California, USA
CLASSE, Ithaca, New York, USA
Harvard University, Cambridge, Massachusetts, USA
The TE wave propagation method has become a widely used technique for measuring electron cloud density in an accelerator beampipe. In most instances the wave very low power is not capable of affecting the low-energy electrons distribution. During experiments in the CESR Damping Ring Test Accelerator (Cesr-TA), we have observed a particular situation where a resonance between the wave and a dipole magnetic field produces a large modification in the electron cloud distribution that can be measured by other detectors. We believe this resonance is strongly dependent on the geometry of standing waves pattern that discontinuities in the beampipe generate. We present measurements in Cesr-TA, which describe the effect and are in support of our hypothesis.
TUB, Beijing, People's Republic of China
LBNL, Berkeley, California, USA
LBNL, Berkeley, California, USA
UCB, Berkeley, California, USA
ANL, Argonne, USA
The Next Generation Light Source (NGLS) is a design concept, under development at LBNL, for a multi‐beamline soft x‐ray FEL array powered by a 2 GeV superconducting linear accelerator, operating with a 1 MHz bunch repetition rate. The CW superconducting linear accelerator is supplied by a high-brightness, high-repetition-rate photocathode electron gun. Electron bunches are distributed from the linac to the array of independently configurable FEL beamlines with nominal bunch rates up to 100 kHz in each FEL, and with even pulse spacing. Individual FELs may be configured for EEHG, HGHG, SASE, or oscillator mode of operation, and will produce high peak and average brightness x-rays with a flexible pulse format, and with pulse durations ranging from sub-femtoseconds to hundreds of femtoseconds.
WEOBS2
LBNL, Berkeley, California, USA
The scientific potential of femtosecond x-ray pulses at Linac-driven FELs is tremendous. Time-resolved pump-probe experiments require a measure of the relative arrival time of each x-ray pulse with respect to the experimental pump laser. To achieve this, precise synchronization is required between the arrival time diagnostic and the laser, which are often separated by hundreds of meters. The speaker will report on the present state of an effort to reach femtosecond level synchronization as well as discuss future directions.
ANL, Argonne, USA
LBNL, Berkeley, California, USA
JLAB, Newport News, Virginia, USA
The Advanced Photon Source Upgrade project (APS-U) at Argonne includes implementation of Zholents’* deflecting cavity scheme for production of short x-ray pulses. This is a joint project between Argonne National Laboratory, Thomas Jefferson National Laboratory, and Lawrence Berkeley National Laboratory. This paper describes performance characteristics of the proposed source and technical issues related to its realization. Ensuring stable APS storage ring operation requires reducing quality factors of these modes by many orders of magnitude. These challenges reduce to those of the design of a single-cell SC cavity that can achieve the desired operating deflecting fields while providing needed damping of all these modes. The project team is currently prototyping and testing several promising designs for single-cell cavities with the goal of deciding on a winning design in the near future.
*A. Zholents et al., NIM A 425, 385 (1999).
LBNL, Berkeley, California, USA
A high-repetition rate (MHz-class), high-brightness electron beam photo-gun is under construction at Lawrence Berkeley National Laboratory in the framework of the Advanced Photo-injector EXperiment (APEX). The injector gun is based on a normal conducting 187 MHz RF cavity operating in CW mode. In its first operational phase it will deliver short bunches (~ 1 to tens of picoseconds) with energy of 750keV, and bunch charges ranging from 1pC to 1nC. Different high efficiency cathode materials will be tested, and the beam quality will be studied as a function of parameters as charge, initial bunch length and transverse size, focusing strength. Both the laser and electron beam diagnostics have been designed to assure the needed flexibility. In particular a high-resolution electron diagnostic section after the photo-gun provides the necessary dynamical range for scanned beam parameters: energy and energy spread, charge and current, transverse and longitudinal phase spaces, slice properties. The photo-gun electron beam diagnostic layout is presented, and the hardware choices, resolution and achievable dynamical ranges are also discussed.