12798237
Overview of LEP operation in 1998
After the installation of 32 additional RF cavities in the 1997-1998 shutdown LEP was operated at a beam energy of 94.5 GeV. The total integrated luminosity for the year 1998 clearly surpassed its target and reached 198 pb/sup -1/. Vertical beam-beam tuneshifts of more than 0.07 were obtained. The performance did not seem to be beam-beam limited, but the total beam current was limited by power dissipation problems to around 6 mA. A high phase advance optics (102/spl deg/, 90/spl deg/), with a smaller natural emittance, was used for regular operation in 1998. This contributed to the excellent performance of LEP, together with the further reduction of both the horizontal and vertical beta function at the interaction points. No dynamic aperture problems were encountered.
36021315
The detector safety system for LHC experiments
The Detector Safety System (DSS), currently being developed at CERN under the auspices of the Joint Controls Project (JCOP), will be responsible for assuring the protection of equipment for the four Large Hadron Collider (LHC) experiments. Thus, the DSS will require a high degree of both availability and reliability. After evaluation of various possible solutions, a prototype is being built based on a redundant Siemens PLC front-end, to which the safety-critical part of the DSS task is delegated. This is then supervised by a PVSS SCADA system via an OPC server. The PLC front-end is capable of running autonomously and of automatically taking predefined protective actions whenever required. The supervisory layer provides the operator with a status display and with limited online reconfiguration capabilities. Configuration of the code running in the PLCs will be completely data driven via the contents of a "configuration database." Thus, the DSS can easily adapt to the different and constantly evolving requirements of the LHC experiments during their construction, commissioning, and exploitation phases.
62825805
THE CLIC MACHINE PROTECTION
INTRODUCTION The proposed Compact Linear Collider (CLIC) [1, 2] is based on a two-beam acceleration scheme. The energy of two high-intensity, low-energy drive beams is extracted and transferred to the two low-intensity, high-energy main beams. The machine protection has to cope with a wide variety of failures, from real-time failures (RF breakdowns, kicker misfiring), to slow equipment failures, to beam instabilities (caused by e.g. temperature drifts, slow ground motions). Due to the many different types of accelerator components and the beams of various characteristics throughout the entire complex, the CLIC machine protection is an extensive subject. The machine protection has the mission to protect the various machine components from damage caused by ill controlled beams. The severity of the damage is given by the financial impact of the damage and the reduction in the operational availability of the facility. The risk equivalent is given by the product of the fault rate and the impact of the fault (i.e. in statistical terms: risk is the expectation value of the fault impact). This concept is illustrated by some examples for downtime in Table 1.
17683309
Parasitic energy loss in the LEP superconducting cavities
The energy loss of bunches in the LEP superconducting (SC) cavities has been determined by measuring the closed orbit as a function of current with the beam position monitors located at finite dispersion. This method has already been used in earlier experiments to determine the distribution of the longitudinal impedance of different parts of LEP. In the present experiment the energy loss in two straight sections, containing only SC cavities, was compared with that in sections having both copper cavities and SC cavities. The results confirm the impedance calculations for the two types of cavities. The accuracy of the measurements was considerably improved by determining simultaneously the orbits of bunches with different currents. At the same time with these beam-based impedance measurements, the power dissipation was observed directly by local temperature monitors in different elements: the inter-cavity bellows inside the cryostat, the warm intermodule bellows, and ferrite absorbers which were installed in two places to reduce the energy leaking out of cavities. These observations were correlated with the change of cryogenics power consumption, and showed an unexpected dependence of energy loss on beam energy.
55988463
Dynamic beam based calibration of orbit monitors at LEP
The properties of an electron positron storage ring are mainly determined by the quadrupole magnets. Highest luminosity and best performance are obtained when the beam is well centered in the quadrupole magnets. The quadrupole magnets are accurately aligned to form a reference system. Beam position monitors (BPM) are installed with tight mechanical tolerances with respect to to the magnets to measure the closed orbit relative to this reference. Despite careful alignment and electrical calibration of the monitors, there can still be a residual offset between the monitor and the magnetic centre of the quadrupole. The system described measures this offset by a beam-based method [ 1, 2, 3].
115611632
Turn by turn observation of the vertical size of LEP bunches with an x-ray detector
125470398
The Nonrelativistic quark model from QCD and related topics
119968526
SEARCHES OF FRACTIONALLY CHARGED PARTICLES IN MATTER WITH THE MAGNETIC LEVITATION TECHNIQUE
Abstract A survey is given of the experiments performed with the magnetic levitation electrometer to search for stable fractional charges in matter. After a general introduction, illustrating the principle of the method, an analysis is presented of the electric forces acting on the levitating object (who se knowledge is essential to determine the residual charge). This is followed by a short account of the historical evolution of the subject, after which we proceed to a detailed description of the ferromagnetic levitation electrometer used in our laboratory and of the results obtained. The main differences with the Stanford diamagnetic (superconducting) instrument are also illustrated. The final section contains a concise summary of the other experiments of search of quarks in matter, in particular of the Millikan automated ones.
123242166
The magnetic levitation electrometer and its use in the search for fractionally charged particles
Abstract The operation of the magnetic levitation electrometer both in the static and in the resonance version is described in detail. The sensitivity of the instrument in the resonance version allows measurements of charge to a precision often better than 1 20 e in grains of matter (graphite) having a mass of the order of 5×10 −7 g. On a total amount of 3.4 × 10 −6 g of pyrolitic graphite explored, corresponding to ≈2 × 10 18 nucleons, no fractionally charged quark has been found.
123073842
QCD with pion exchange, double counting and the baryon magnetic moments
118367014
The General QCD parametrization and the hierarchy of its parameters: Why some simple models of hadrons work so well
After summarizing the basic points of the general QCD parametrization (GP) we discuss systematically its applications to the properties of the lowest families of baryons and mesons. We show how the hierarchy of the parameters in the GP emerges clearly in the properties of hadrons. Among other things, it explains why simple models can work reasonably well and clarifies the relationship between current and constituent quarks. More details on the hadron properties discussed with the GP appear from the list of secrions at the beginning of the paper.