YerPhI, Yerevan
Thermal sensors based on the vibrating wire principle are distinguished by high accuracy and stability. An important advantage of these sensors is that they produce a frequency signal that can be transferred large distances without disturbance. Original vibrating wire sensors and monitors for the measurement of beam transversal characteristics of charged-particle and photon beams are described. By means of these devices, measurements of an electron beam in the Yerevan synchrotron, a proton beam at PETRA (DESY), and a hard x-ray undulator beam at the APS (ANL) have been performed.
LBNL, Berkeley, California
CERN, Geneva
SLAC, Menlo Park, California
Clouds of low energy electrons in the vacuum beam pipes of accelerators of positively charged particle beams present a serious limitation for operation of these machines at high currents. Because of the size of these accelerators, it is difficult to probe the low energy electron clouds over substantial lengths of the beam pipe. We have developed a novel technique to directly measure the electron cloud density via the phase shift induced in a TE wave which is independently excited and transmitted over a section of the accelerator. We infer the absolute phase shift with relatively high accuracy from the phase modulation of the transmission due to the modulation of the electron cloud density from a gap in the positively charged beam. We have used this technique for the first time to measure the average electron cloud density over a 50 m straight section in the positron ring of the PEP-II collider at the Stanford Linear Accelerator Center. We have also measured the variation of the density by using low field solenoid magnets to control the electrons.
ORNL, Oak Ridge, Tennessee
Taking Advantage of recent successes with the Laser Profile monitor, a new protottype is being built to use the laser wire as both a profile monitor and a slit for an emittance measuring device. This improved system takes advantage of the steering dipole magnet prior to ring injection of SNS such that only the recently stripped H0 protons continue forward to the emmitance device. In this way we hope to make an emittance device that is both parasitic to neutron production, and capable of accurate measurements during full power applications.
ELETTRA, Basovizza
FERMI@Elettra is a seeded FEL source, currently under construction at the Elettra Synchrotron Light Laboratory. On-line single shot and non destructive longitudinal bunch profile and bunch arrival time measurements are of great importance for this type of FEL source. These measurements will be performed by means of two Electro Optic Station (EOS) to be installed just upstream each of the two undulator chains. The paper describes the EOS stations design based on the spatial conversion scheme tested at SPPS and FLASH, and proposed for LCLS. The EOS will make use of two laser sources: a fiber laser at 780nm and the seed laser oscillator. A set of ZnTe and GaP crystal of different thicknesses will allow for flexibility in choosing high signal or high resolution configurations. The maximum resolution is expected to be of about100 fsec. The time profile mapped in a spatial laser profile will be acquired by a gated Intensified CCD. Calculations are presented for the expected EO signal and THz pulse broadening and distortion during propagation in the crystals.
KEK, Ibaraki
Button electrodes with good time response are essential for the bunch-by-bunch feedback / diagnostic systems needed for future short-bunch-spacing accelerators, such as energy recovery linacs (ERL) or a super B-factory. The impedance matching and time-domain response of electrodes, particularly around the vacuum seal, have been studied using 3-D electromagnetic codes (HFSS, MAFIA and GdfidL). Several candidates have been fabricated to examine the tolerance for mechanical pressures and heat stress due to the welding process. The real beam response from a short bunch has also been studied using a test-beam line at the KEK-PF injector beam transport section.
Fermilab, Batavia
This paper presents a condensed, simplified, and practical discussion of the principles, procedures, and operating parameters of particle accelerator vacuum systems as practiced at Fermilab. It is intended to provide a basis for designers, builders, and operators of accelerator systems to communicate with each other about the needs and impact of the vacuum system. Rigorous analytical development of the equations and concepts are not given. It is assumed that the reader has some limited understanding of the subject. Practical examples of real world experiences are used to illustrate the concepts outlined.
SOLEIL, Gif-sur-Yvette
The Soleil Fast Orbit Feedback System has been integrated in the BPM electronics, using the FPGA resources of the Libera modules. On top of their position measurement, the FPGAs compute the orbit correction and drive the power-supplies of the 48 dedicated air coil correctors. Position data are distributed all over the ring by a dedicated network connecting the 120 BPMs modules together. The correction rate is 10 kHz and is applied with low latency. At almost all the source points, the high frequency stability specifications have already been achieved thanks to great care in the design of the machine. Remaining vibrations are still observed in the 46-54 Hz band and during the change in gap and phase of some insertion devices. Those perturbations are efficiently damped by the fast orbit feedback system. The BPM system has been operational for some time. The fast orbit feedback system is in its commissioning phase. The design and first results of the latter are reported.