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.
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.
CERN, Geneva
A high resolution beam position monitor (BPM) electronics based on diode peak detectors has been developed at CERN. The circuit processes the BPM electrode signals independently, converting the short beam pulses into slowly varying signals which are digitized with high resolution ADCs operating in the kHz range. For large enough amplitudes the non-linear forward voltage of the diodes is compensated by a simple network using signals from single-diode and double-diode peak detectors. This contribution discusses the performance of the built prototype with beam in the CERN-SPS and comments on possible future applications of the technique.