CERN, Geneva
CLASSE, Ithaca, New York
PSI, Villigen
In the CLIC project, highest luminosity will be achieved by generation and preservation of ultra low beam emittances. It will require a mechanical stability of the quadrupoles down to 1 nm rms above 1 Hz through up to 24 km of linac structures. Studies are being undertaken to stabilize each quadrupole by an active feedback system based on motion sensors and piezoelectrical actuators. Since it will be very difficult to prove the stability of the magnetic field down to that level of precision, an attempt was made to use a synchrotron electron beam as a sensor and the beam motion was observed with a standard button BPM equipped with high resolution electronics. Hence in two consecutive experiments at CESR-TA (Cornell University, Wilson Lab) and at SLS (PSI-Villingen) the residual eigenmotion of the electron beam circulating in these two machines was measured in the frequency range 5700 Hz. This paper describes in detail the achieved results alongside with purpose of the measurement, the equipment used for observation of the beam rest-motion, and the vibration measurements of mechanical machine elements.
Fermilab, Batavia
Optical transition radiation (OTR) imaging for transverse beam-size characterization is a well-established technique at many accelerators including the Fermilab A0 photoinjector (A0PI) facility. However, there is empirical evidence for gamma greater than 1000 beams that the utilization of the polarization component orthogonal to the dimension of interest resulted in a smaller projected image profile. Generally, at the A0PI low beam energies of 14-15 MeV and emittances of 3 mm mrad, one encounters beam sizes of 0.8 to 1.5 mm (σ). However, the use of 50-micron wide slits to sample the beam’s transverse phase spaces significantly alters the required resolution of the converter screen and imaging system. In this case, we dealt with slit-image sizes of about σ 100 microns and less, depending on drift distance and beam divergence. In the course of our study of the slit images, we have found that the OTR polarized component orthogonal to the narrow beam dimension of interest systematically gave us ~20-micron smaller projected image sizes than with the total OTR intensity. This is one of the first reports of this polarization effect at such a low-gamma regime (~30).
Diamond, Oxfordshire
JAI, Egham, Surrey
UCL, London
Royal Holloway, University of London, Surrey
This paper describes the design of a cavity BPM for use in single pass machines. The design was modelled using a number of different EM codes to allow cross comparison of the simulation results. Furthermore, in addition to existing designs, the geometry has been modified to introduce a frequency separation between the horizontal and vertical dipole signals, as well as a reduction of the sensitivity of the position monitor to the monopole sum signal. The next stage of this project will be the manufacture of a prototype for tests in the transfer path at Diamond Light Source.
SLAC, Menlo Park, California
A new stripline beam position monitoring (BPM) readout and processing system was installed and successfully tested over a two-week period at the Accelerator Test Facility 2 (ATF2), in KEK, Japan during February 2010. The core analog processing board used in the system is a duplicate of that developed for, and in use at, the Linac Coherent Light Source (LCLS) at SLAC. The digitization, processing and control front-end were custom designed for ATF2 using a 14-bit 100-MHz VME digitizer and an EPICS Input/Output Controller (IOC) running on the VME controller. Control of the analog boards is via EPICS, which controls a serial-over-TCP/IP port server. Hardware for the readout of up to 14 BPMs with 3 spare analog boards was delivered. The goal of this installation was to provide ~<10 micron resolution, non-charge-dependent readout of the ATF2 electron beam with long-term gain stability compensation. These criteria were tested and successfully met. This design was found to be highly effective and to have many advantages, especially that it required minimal installation effort at ATF2.
CERN, Geneva
The BBQ tune (Q) and chromaticity (Q') diagnostic systems played a crucial role during LHC commissioning, both in establishing circulating beam and for the first ramps. Early on, they allowed identification of issues such as the residual tune stability, beam spectrum interferences and beam-beam effects – all of which may impact beam life times and are therefore being addressed in view of nominal LHC operation. This contribution discusses the initial beam stability in relation to the achieved instrumentation sensitivity, corresponding tune frequency and chromaticity resolution.
