10,302 research outputs found
Tevatron Beam Halo Collimation System: Design, Operational Experience and New Methods
Collimation of proton and antiproton beams in the Tevatron collider is
required to protect CDF and D0 detectors and minimize their background rates,
to keep irradiation of superconducting magnets under control, to maintain
long-term operational reliability, and to reduce the impact of beam-induced
radiation on the environment. In this article we briefly describe the design,
practical implementation and performance of the collider collimation system,
methods to control transverse and longitudinal beam halo and two novel
collimation techniques tested in the Tevatron.Comment: 25 p
The STAR MAPS-based PiXeL detector
The PiXeL detector (PXL) for the Heavy Flavor Tracker (HFT) of the STAR
experiment at RHIC is the first application of the state-of-the-art thin
Monolithic Active Pixel Sensors (MAPS) technology in a collider environment.
Custom built pixel sensors, their readout electronics and the detector
mechanical structure are described in detail. Selected detector design aspects
and production steps are presented. The detector operations during the three
years of data taking (2014-2016) and the overall performance exceeding the
design specifications are discussed in the conclusive sections of this paper
Energy of taut strings accompanying Wiener process
Let be a Wiener process. The function minmizing energy
among all functions satisfying on an interval is called taut string. This is a classical
object well known in Variational Calculus, Mathematical Statistics, etc. We
show that the energy of this taut string on large intervals is equivalent to
where is some finite positive constant. While the precise
value of remains unknown, we give various theoretical bounds for it as well
as rather precise results of computer simulation.
While the taut string clearly depends on entire trajectory of , we also
consider an adaptive version of the problem by giving a construction (Markovian
pursuit) of a random function based only on the past values of and having
minimal asymptotic energy. The solution, an optimal pursuit strategy, quite
surprisingly turns out to be related with a classical minimization problem for
Fisher information on the bounded interval
Historical overview of V/STOL aircraft technology
The requirements for satisfactory characteristics in several key technology areas are discussed and a review is made of various V/STOL aircraft for the purpose of assessing the success or failure of each design in meeting design requirements. Special operating techniques were developed to help circumvent deficiencies. For the most part performance and handling qualities limitations restricted operational evaluations. Flight operations emphasized the need for good STOL performance, good handling qualities, and stability and control augmentation. The majority of aircraft suffered adverse ground effects
A Formal Model for Trust in Dynamic Networks
We propose a formal model of trust informed by the Global Computing scenario and focusing on the aspects of trust formation, evolution, and propagation. The model is based on a novel notion of trust structures which, building on concepts from trust management and domain theory, feature at the same time a trust and an information partial order
Overview of the design of the ITER heating neutral beam injectors
The heating neutral beam injectors (HNBs) of ITER are designed to deliver 16.7MWof 1 MeVD0 or
0.87 MeVH0 to the ITER plasma for up to 3600 s. They will be the most powerful neutral beam\uf0a0(NB)
injectors ever, delivering higher energy NBs to the plasma in a tokamak for longer than any previous
systems have done. The design of the HNBs is based on the acceleration and neutralisation of negative
ions as the efficiency of conversion of accelerated positive ions is so low at the required energy that a
realistic design is not possible, whereas the neutralisation ofH 12 andD 12 remains acceptable ( 4856%).
The design of a long pulse negative ion based injector is inherently more complicated than that of
short pulse positive ion based injectors because:
\u2022 negative ions are harder to create so that they can be extracted and accelerated from the ion source;
\u2022 electrons can be co-extracted from the ion source along with the negative ions, and their
acceleration must be minimised to maintain an acceptable overall accelerator efficiency;
\u2022 negative ions are easily lost by collisions with the background gas in the accelerator;
\u2022 electrons created in the extractor and accelerator can impinge on the extraction and acceleration
grids, leading to high power loads on the grids;
\u2022 positive ions are created in the accelerator by ionisation of the background gas by the accelerated
negative ions and the positive ions are back-accelerated into the ion source creating a massive power
load to the ion source;
\u2022 electrons that are co-accelerated with the negative ions can exit the accelerator and deposit power on
various downstream beamline components.
The design of the ITER HNBs is further complicated because ITER is a nuclear installation which
will generate very large fluxes of neutrons and gamma rays. Consequently all the injector components
have to survive in that harsh environment. Additionally the beamline components and theNBcell,
where the beams are housed, will be activated and all maintenance will have to be performed remotely.
This paper describes the design of theHNBinjectors, but not the associated power supplies, cooling
system, cryogenic system etc, or the high voltage bushingwhich separates the vacuum of the beamline
fromthehighpressureSF6 of the high voltage (1MV) transmission line, through which the power, gas and
coolingwater are supplied to the beam source. Also themagnetic field reduction system is not described
Initial results from flight testing a large, remotely piloted airplane model
The first four flights of a remotely piloted airplane model showed that a flight envelope can be expanded rapidly and that hazardous flight tests can be conducted safely with good results. The flights also showed that aerodynamic data can be obtained quickly and effectively over a wide range of flight conditions, clear and useful impressions of handling and controllability of configurations can be obtained, and present computer and electronic technology provide the capability to close flight control loops on the ground, thus providing a new method of design and flight test for advanced aircraft
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