A Structure for a Wide Band Wall Current Monitor

In the framework of the EuroTeV programme a new wall current monitor for application in linear accelerators is currently being developed. A bandwidth of 20 GHz is aimed for in the new design. This note proposes an improved structure with very high bandwidth

Incoherent High-Frequency Schottky Signals in LHC

A detector for high-frequency Schottky signals in the LHC is currently being designed in the framework of the US-LARP collaboration. The detector will work at 4.8 GHz, where coherent beam signals should be rather low and the incoherent Schottky bands should not yet overlap. This note discusses the expected properties of the incoherent Schottky signals in this frequency range for various types of proton and ion beams in the LHC. The use of gating to increase the signal-to-noise ratio for the pilot beam is also discussed

Design of a spin-flip cavity for the measurement of the antihydrogen hyperfine structure

In the framework of the ASACUSA collaboration at the CERN Antiproton Decelerator an experiment for precisely testing the CPT invariance of the hydrogen hyperfine structure is currently being designed. An integral part of the set-up is the 1.42 GHz spin-flipping cavity, which should have a good field homogeneity over the large aperture of the antihydrogen beam. After the evaluation of various approaches a structure based on a resonant stripline is proposed as a concrete cavity design. For this structure the field homogeneity, undesired modes, coupling and power issues are discussed in detail

Simulation of wire scanner heating by the electromagnetic field of a particle beam

It was found in several machines that wire scanners may break due to beam-induced heating. In this paper the losses in the wire due to the fields of a passing particle beam are calculated using numerical simulation tools. Special care was taken when modeling the small diameter wire. The heating of carbon wires with LHC beam is calculated and the different regimes at low and high frequency are discussed

Simulation of the low-frequency collimator impedance

The low-frequency transverse collimator impedance constitutes a major part of the LHC impedance budget. In this paper numerical simulations for frequencies below 1 MHz using a commercial package are presented. From the 3D field solution of the two-wire simulations the transverse impedance is directly calculated. After a cross-check with theory for rotationally symmetric structures a geometry with two jaws and an LHC graphite collimator is examined. Furthermore, a simple physics picture that explains the principal characteristics of the impedance at high and low frequencies is given

Longitudinal and Transverse Wire Measurements for the Evaluation of Impedance Reduction Measures on the MKE Extraction Kickers

In 2003 significant heating of the MKE Extraction kicker magnets in CERN's SPS was confirmed by measurements with beam. The dissipated power was so high that it would seriously jeopardize the good functioning of the kicker by warming the ferrite above the Curie temperature. In an impedance reduction campaign the beam coupling impedance of the present kickers was assessed with wire measurements and possible cures were evaluated. For a reliable impedance determination refined measurement methods had to be used. Any kicker modification should not deteriorate kick field quality and high voltage capability. Shielding the ferrites with printed metallic strips turned out to be a promising solution. Technological issues of the metallic coatings are also discussed

The CERN SPL Chopper Structure. A Status Report

In the framework of HIPPI, a study for a Superconducting Proton Linac is being carried out at CERN. An integral part of the medium energy line is the chopper, which has to establish the required time structure of the beam by cutting out selected bunches from the continuous bunch train coming out of the RFQ. Due to the bunch spacing of 2.84 ns a system rise and fall time of 2 ns is required. A slow wave structure matched to the beam speed of 0.08c was chosen as the most promising candidate. This structure was implemented as a meander line printed on a ceramic substrate. The mechanical design as well as technological issues are discussed. Furthermore, the results of comprehensive tests on the prototype are reported

Experimental Electron Cloud Studies in the CERN Proton Synchrotron

Indications for a beam-induced electron cloud build-up are observed since 2000 for the nominal LHC beam in the PS to SPS transfer line and during the last turns before ejection from the PS. A new electron cloud setup was designed, built, and installed in the PS. It contains shielded button-type pickups, a dipole magnet, a vacuum gauge, and a dedicated stripline electrode to experimentally verify the beneficial effect of electron cloud clearing electrodes. During the 2007 run, the electron cloud effect was also clearly observed in the PS and efficient electron cloud suppression has been obtained for negative and positive bias voltages on the clearing electrode. Here, we present electron cloud measurements with different filling patterns and bunch spacings in the PS

The Beam Screen for the LHC Injection Kicker Magnets

The two LHC injection kicker magnet systems must each produce a kick of 1.2 T.m with a flattop duration variable up to 7.86 ìs, and rise and fall times of less than 0.9 ìs and 3 ìs, respectively. Each system is composed of four 5 Ù transmission line kicker magnets with matched terminating resistors and pulse forming networks (PFN). The LHC beam has a high intensity, hence a beam screen is required in the aperture of the magnets This screen consists of a ceramic tube with conducting ?stripes? on the inner wall. The stripes provide a path for the image current of the beam and screen the magnet ferrites against Wake fields. The stripes initially used gave adequately low beam impedance however stripe discharges occured during pulsing of the magnet: hence further development of the beam screen was undertaken. This paper presents options considered to meet the often conflicting needs for low beam impedance, shielding of the ferrite, fast field rise time and good electrical and vacuum behaviour