10489447
LEP OPERATION AND PERFORMANCE WITH 100 GEV COLLIDING BEAMS
Luminosity production in LEP was extended to 101 GeV beam energy in 1999 and 104.4 GeV in 2000. The performance was continually optimised, resulting in 1999 peak and integrated luminosities higher than in any previous year of LEP operation. In particular, the beambeam tune shift reached 0.083 per interaction point. This was achieved with the help of a faster luminosity monitoring, a new tune working point, a reduced design vertical dispersion and new dispersion and coupling optimisation tools. A higher beam rate from the injectors, a better injection efficiency, a faster ramp and a newly automated control of the horizontal damping partition number J x maximised the time available for physics and thus contributed to the higher integrated luminosity.
56290660
The Software for the CERN Detector Safety System
The CERN Detector Safety System (DSS) has been developed to monitor the state of the LHC detectors and protect their components against emer gency situations which other less reliable systems could possibly fail to handle, or which were not co vered by any other system. The DSS consists of two main components: a PLC-based Front-End and a supervisor Back-End. The two parts communicate via the OPC mechanism. The Front-End is the core of the DSS, to which all the runtime safety-critical actions are delegated. These are encoded in an "Alarm-Action Matrix", that can be seen as a set of user-defined rules relating the Input Channels (analogue and digital senso rs) to the Output Channels (actuators, typically on/off interlock switches). One of the user requireme nts is the possibility of modifying these rules at any time, without stopping the system. New Input and Output Channels can also be incrementally added to the system without perturbing the prev iously existing part. To fulfil these requirements without detriment to the safety-critical part, the PLC software has been designed in a completely datadriven way. This approach allowed the PLC code to be kept as simple as possible and independent from the user-defined rules. The rules, as well as the parameteri zation for the Input and Output Channels, are stored into PLC "datablocks", whose contents drive the execution of the PLC code. The supervisor Back-End, based on the CERN-chosen PVSS SCADA system, represents both the “Configuration Interface” and the “Operator Display” for the DSS. The User is able to define and parameterize Input and Output Channels and to modify the set of rules defining the Alarm-Action Matrix. These modifications, after passing some c onsistency checks, are accepted by the Back-End, permanently stored in PVSS "datapoints", and finally mirrored into the PLC datablocks via the OPC mechanism. In addition to this, the Back-End is constantly informed, again through OPC, of any changes in the status of the monitored system . The Back-End then displays all the relevant information to the User, both via an alarm screen and via an interactive synoptic system. This paper describes in greater details some of the ideas behind the design and the implementation of this system.
115464633
Do We Understand the Luminosity Imbalance
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.
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.
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.
120776511
The non-relativistic quark model
The classification scheme and decay properties of hadron states are investigated in the framework of the non relativistic quark model. The main successes and the unsolved difficulties of the model are presented indicating the future work which could be done to understand and exploit the non-relativistic quark ideas.РезюмеИсследованы схема классификации и распадные свойства адронов в рамках статической модели кварков. Изложены главные успехи и нерешенные проблемы модели, указывая задачи, которые должны быть решены для лучшего понимания и использования нерелятивистских идей.
12690675
The general QCD parametrization and the large Nc description: Some remarks
Stimulated by a recent paper of Buchmann and Lebed,a comparison is presented of the two methods mentioned in the title for treating hadron properties in QCD.Doubts arise on the equivalence of the large Nc description to real QCD. (PACS: 12.38.Aw; 11.15.Pg; 13.40.Dk)
120885277
Demodulation and detection of correlations in a beam by a scattering detector
Abstract The demodulation and the detection of correlations in a beam using a detector that scatters the beam is discussed employing a localized wave packet description of the beam. It is shown that a simple very general formula for the spectral excitation function of the detector can be given; by spectral excitation function we mean the rate of excitation of the detector to a given level. The formula is derived without making specific assumptions on the nature of the detector. The spectral excitation function is naturally decomposed as a sum of four terms: Two of these (the B terms in what follows) depend only on the wavefunction and stochastic distribution of the incident beam; they are proportional to the square (and higher powers) of the flux and contain all the information on the self-beat, Forrester-type effects and demodulation. More precisely, one of these B terms contains the information on the demodulation and the other on the beat effects. The remaining two terms (to be called the A terms) describe the conventional inelastic scattering (proportional to the flux) and some coherent corrections to it (proportional to higher powers of the flux): These A terms behave as noise if the signal of interest is that described by the B terms. The theory is illustrated with many examples to known situations; particular attention is given to some conceptual questions involved.
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