After 2001, the upgraded ep collider HERA will provide an about five times higher luminosity for the two experiments H1 and ZEUS. To cope with the expected higher event rates, the H1 collaboration is ...building a track-based trigger system, the Fast Track Trigger (FTT). It will be integrated in the first three levels (L1-L3) of the H1 trigger scheme to provide higher selectivity for events with charged particles. The FTT will allow reconstruction of three-dimensional tracks in the central drift chamber down to 100 MeV/c within the L2 latency of /spl sim/23 /spl mu/s. To reach the necessary momentum resolution of /spl sim/5% (at 1 GeV/c), sophisticated reconstruction algorithms have to be implemented using high-density field-programmable gate arrays and their embedded content addressable memories. The final track parameter optimization will be done using noniterative fits implemented in digital signal processors. While at the first trigger level rough track information will be provided, at L2 tracks with high resolution are available to form trigger decisions on topological and other track-based criteria like multiplicities and momenta. At the third trigger level, a farm of commercial processor boards will be used to compute physics quantities such as invariant masses.
Backscattering of electrons in depressed collectors has a significant effect on the collector efficiency and other performance parameters. We have studied these phenomena using our code BSCAT. It ...allows for tracking of multiple generations of backscatter by a representative set of trajectories without going to an excessively large number of them. By examining the trajectories and the impact angles of incoming rays, it is possible to modify the geometry of the electrodes, such that the effects of backscatter are minimized. In particular, we have studied the effects of using an undulating surface of the collector, and analyzed its effects taking into account the effect on angles of incidence of impacting rays. Using as a test vehicle a two-stage depressed collector for a 1.5-MW 110-GHz gyrotron, we have thus been able to increase the estimated collector efficiency from 62% to 65%. We present these results along with data on other performance parameters such as the heat-dissipation profile. We discuss the potential for application of the approach to other devices operating at different frequencies and power levels.
One of the main goals of the HERA-B experiment at DESY in Hamburg, Germany, is to study the properties of B-mesons with the emphasis on CP violation. B-mesons are produced in hadronic interactions of ...a 920-GeV proton beam with an internal wire target. An effective bunch crossing rate of about 8.5 MHz leads to about 200 charged tracks per event. Therefore, a highly selective and efficient trigger system providing high suppression of background events is required. The HERA-B trigger system consists of four levels. A rate reduction factor of 200 is aimed at by the first-level trigger (FLT). The muon pretrigger system, as a part of the FLT, is a modular system consisting of about 100 large-size VME modules of three different types: the pretrigger link board (PLB), the pretrigger coincidence unit (PCU), and the pretrigger message generator (PMG). The data rate processed by the pretrigger system is about 19.5 GByte/s. The PLBs process digitized hit information in eight independent electronic channels in parallel. Every electronic channel handles 32 bits of hit information received from the front-end driver buffer system. Optical links operating at 800 Mb/s transmit the data after serialization to PCUs, which calculate coincidences using complex programmable logic devices. The PMGs transform this coincidence information into messages for the FLT processors. The concept and design as well as results of the muon pretrigger running at HERA-B are presented.
The BSCAT computer code being developed by us for the design of depressed collectors for gyrotrons employs a special algorithm for tracing the trajectories of backscattered electrons. Monte Carlo ...techniques are used on a large ensemble of rays to ensure accurate representation of the stochastic process. Recent work has focused on improvement of the modeling of the electron backscatter phenomenon itself. We have introduced more accurate models for the backscatter coefficients for true secondaries, as well as elastically and inelastically backscattered primaries. These models are adapted to the energy ranges and the angles of incidence of the primaries. They are linked with experimental data as available in current literature or with Monte Carlo simulations. Analytical representations have been used where they closely approximate the experimental or simulation data, in an effort to make the computation as versatile and computationally inexpensive as feasible. The same has been done for angular and energy distributions of the emitted electrons.
Since 1996 the H1 experiment is fully equipped with two independent fast pattern recognition systems operating as second level triggers (L2). The decision time is 20 μs. One of the two is the neural ...network trigger. It runs an array of presently ten VME-boards with CNAPS 1064 chips (20 MHz, 128 Mcps) by Adaptive Solutions. The input trigger data from the detector components arrive in various formats on a 8 × 16 bit wide 10 MHz bus. Before usable as 8-bit input values to the CNAPS they are preprocessed by several bit-manipulating algorithms and arithmetic functions implemented on XILINX 4008 field programmable gate arrays (FPGA). The startup strategy for the new system is to concentrate on photoproduction channels or low multiplicity final states which so far could only be efficiently triggered with unacceptable high rates.
We have added some features to our library of computer-aided design codes for design of depressed collectors and to the code for tracing the trajectories of backscattered electrons. In the former ...case, the process of optimization of depressed potentials is facilitated. The computer code changes the combinations of potentials by controllable amounts. The trajectory tracing code runs the modified input files sequentially and feeds data to post processors. This generates charts of important parameters in the performance of the collectors. The parameter space can, thus, be explored quickly for optimum operation. In the second case, we have automated the iterative simulation of trajectories of primary and secondary electrons, which interact by virtue of their space charge. This is with a view to obtaining enhanced mutual consistency between them. Furthermore, a specified number of orders of backscattered electrons can be traced. These codes have been used for exploring the dependence of depressed collector performance on various geometrical and electrical parameters for megawatt continuous wave power gyrotrons.
This paper describes the muon pretrigger system of the HERA-B experiment. The muon pretrigger is designed to detect track candidates for muons in order to generate seeds for the first level trigger ...(FLT) search algorithm. Muons provide the cleanest event signature in the large amount of hadronic background. In order to achieve the required precision the muon pretrigger system has to cope with an interaction rate of about 40 MHz at the HERA bunch crossing rate of 10.4 MHz. This results in a total input data rate of about 10 Gbyte/s. A total rate reduction by a factor of 200 is aimed at by the complete FLT, including the pretrigger systems (electromagnetic calorimeter, muon and high-p/sub T/), within at most 12 /spl mu/s.
The ARGUS vertex trigger Koch, N.; Kolander, M.; Kolanoski, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/1996, Letnik:
373, Številka:
3
Journal Article
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A fast second level trigger has been developed for the ARGUS experiment which recognizes tracks originating from the interaction region. The processor compares the hits in the ARGUS micro vertex ...drift chamber to 245 760 masks stored in random access memories. The masks which are fully defined in three dimensions are able to reject tracks originating in the wall of the narrow beampipe of 10.5 mm radius.
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