The ATLAS level-1 central trigger system
The central part of the ATLAS Level-1 trigger system consists of the central trigger processor (CTP), the local trigger processors (LTPs), the timing, trigger, and control (TTC) system, and the read-out driver busy (ROD/spl I.bar/BUSY) modules. The CTP combines information from calorimeter and muon trigger processors, as well as from other sources, and makes the final Level-1 accept decision (L1A) on the basis of lists of selection criteria, implemented as trigger menus. Timing and trigger signals are fanned out to about 40 LTPs, which inject them into the subdetector TTC partitions. The LTPs also support stand-alone running and can generate all necessary signals from memory. The TTC partitions fan out the timing and trigger signals to the subdetector front-end electronics. The ROD/spl I.bar/BUSY modules receive busy signals from the front-end electronics, and send them to the CTP (via an LTP) to throttle the generation of L1As. An overview of the ATLAS Level-1 central trigger system will be presented, with emphasis on the design and tests of the CTP modules.
Timing Distribution at the LHC
This paper describes a unified approach to fast timing distribution at the LHC. The timing signals for each ring of the machine will be encoded and transmitted over optical links from the RF system to the PCR, where beam-synchronous messages will be added. High power laser transmitters will then broadcast the signals over singlemode optical fibres to the four LHC experiments, to the test beam areas, and to the beam instrumentation located around the LHC ring and on the SPS transfer lines. At the experiment areas, trigger information and local synchronous commands and data will be added. The regenerated signals will then be broadcast over multimode passive optical networks to several thousand destinations.
A new method of near field analysis
The problem of the accurate determination of the total electromagnetic field produced by a current distribution on a circular disc type aperture is examined. For comparison of the near and Fresnel region solutions, an exact Maxwellian integral is used as the starting point. Aperture and space coordinates are separated by the use of Bessel function addition theorems, allowing the field to be expressed as a sum of terms containing radial and angular integrals. The radial integrals involve only the disc (aperture) distribution and coordinates while the angular integrals involve only the elevation angle. The distance from origin appears implicitly in the series coefficients. These integrals are suitable for high speed computations and have been evaluated for a number of cases. The results are compared with the small angle and general Fresnel formula values for various observation angles, distances from the aperture, and aperture distributions.