1,645 research outputs found
Beam losses from ultra-peripheral nuclear collisions between Pb ions in the Large Hadron Collider and their alleviation
Electromagnetic interactions between colliding heavy ions at the Large Hadron
Collider (LHC) at CERN will give rise to localized beam losses that may quench
superconducting magnets, apart from contributing significantly to the
luminosity decay. To quantify their impact on the operation of the collider, we
have used a three-step simulation approach, which consists of optical tracking,
a Monte-Carlo shower simulation and a thermal network model of the heat flow
inside a magnet. We present simulation results for the case of Pb ion operation
in the LHC, with focus on the ALICE interaction region, and show that the
expected heat load during nominal Pb operation is 40% above the quench level.
This limits the maximum achievable luminosity. Furthermore, we discuss methods
of monitoring the losses and possible ways to alleviate their effect.Comment: 17 pages, 20 figure
Beam Loss Monitors for Heavy Ion Operation
The performance of the LHC as a heavy-ion collider is expected to be limited by a variety of beam loss mechanisms that are non-existent, or substantially different, in the case of protons. Among these are ultra-peripheral interactions of the colliding beams and the collimation inefficiency. Loss patterns are different and require additional installations of beam loss monitors. Further, the relation between energy deposition in superconducting magnet coils and the loss monitor signals has to be reassessed for heavy ions in order to determine the thresholds for dumping beams
Monitoring heavy-ion beam losses in the LHC
The LHC beam loss monitor (BLM) system, primarily designed for proton operation, will survey particle losses and dump the beam if the loss rate exceeds a threshold expected to induce magnet quenches. Simulations of beam losses in the full magnet geometry allow us to compare the response of the BLMs to ion and proton losses and establish preliminary loss thresholds for quenches. Further simulations of beam losses caused by collimation and electromagnetic interactions peculiar to heavy ion collisions determine the positions of extra BLMs needed for ion operation in the LHC
Kinetic model for multidimensional opinion formation
In this paper, we deal with a kinetic model to describe the evolution of the opinion in a closed group with respect to a choice between multiple options, e.g. political parties, which takes into account two main mechanisms of opinion formation, namely, the interaction between individuals and the effect of the mass media. We numerically test the model in some relevant cases and eventually provide an existence and a uniqueness result for i
Communicating Carabids: Engaging farmers to encourage uptake of Integrated Pest Management.
BACKGROUND: Natural enemy pest control (NPC) is becoming more desirable as restrictions increase on pesticide use. Carabid beetles are proven agents of NPC, controlling pests and weeds in crop areas. Agro-ecological measures can be effective for boosting carabid abundance and associated NPC, however the benefits of specific interventions to production are seldom communicated to farmers. We explore pathways to improved NPC by engaging farmers and increasing knowledge about Farm Management Practices (FMPs) beneficial to carabids using engagement materials. We used a questionnaire to measure awareness, beliefs, and attitudes to carabids and analysed these within a framework of the Theory of Planned Behaviour (TPB), relative to a control group.
RESULTS: We found awareness of carabid predation to be associated with beliefs of pest and weed control efficacy. Within the framework of TPB, we found that current implementation of FMPs was higher if farmers perceived them to be both important for carabids, and easy to implement. This was also true for future intention to implement, yet the perceived importance was influenced by engagement materials. Field margins/buffer strips and beetle banks (16% and 13% of responses) were the most favoured by farmers as interventions for carabids.
CONCLUSION: The TPB is a valuable tool with which to examine internal elements of farmer behaviour. In this study self-selected participants were influenced by online engagement in a single intervention, proving this approach has the potential to change behaviour. Our results are evidence for the effectiveness of raising awareness of NPC to change attitudes and increase uptake of sustainable practices
Physics Opportunities with the FCC-hh Injectors
In this chapter we explore a few examples of physics opportunities using the
existing chain of accelerators at CERN, including potential upgrades. In this
context the LHC ring is also considered as a part of the injector system. The
objective is to find examples that constitute sensitive probes of New Physics
that ideally cannot be done elsewhere or can be done significantly better at
theCERN accelerator complex. Some of these physics opportunities may require a
more flexible injector complex with additional functionality than that just
needed to inject protons into the FCC-hh at the right energy, intensity and
bunch structure. Therefore it is timely to discuss these options concurrently
with the conceptual design of the FCC-hh injector system.Comment: 13 pages, chapter 5 in Physics at the FCC-hh, a 100 TeV pp collide
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Aboveâ and belowâground assessment of carabid community responses to crop type and tillage
Carabid beetles are major predators in agroâecosystems. The composition of their communities within crop environments governs the pest control services they provide. An understudied aspect is the distribution of predacious carabid larvae in the soil.
We used novel subterranean trapping with standard pitfall trapping, within a multiâcrop rotation experiment, to assess the responses of aboveâ and belowâground carabid communities to management practices.
Crop and trap type significantly affected pooled carabid abundance with an interaction of the two, the highest numbers of carabids were caught in subterranean traps in barley under sown with grass.
Trap type accounted for the most variance observed in carabid community composition, followed by crop.
Tillage responses were only apparent at the species level for three of the eight species modelled.
Responses to crop type varied by species. Most species had higher abundance in underâsown barley, than grass, wheat and barley. Crop differences were greater in the subterranean trap data. For predaceous larvae, standard pitfalls showed lowest abundances in underâsown barley, yet subterranean traps revealed abundances to be highest in this crop.
Comprehensive estimation of ecosystem services should incorporate both aboveâ and belowâground community appraisal, to inform appropriate management
Accelerator physics concept for upgraded LHC collimation performance
The LHC collimation system is implemented in phases, in view of the required extrapolation by 2-3 orders of magnitude beyond Tevatron and HERA experience in stored energy. All available simulations predict that the LHC proton beam intensity with the "Phase I" collimation system may be limited by the impedance of the collimators or cleaning efficiency. Maximum efficiency requires collimator materials very close to the beam, generating the dominant resistive wall impedance in the LHC. Above a certain intensity the beam is unstable. On the other hand, even if collimators are set very close to the beam, the achievable cleaning efficiency is predicted to be inadequate, requiring either beam stability beyond specifications or reduced intensity. The accelerator physics concept for upgrading cleaning efficiency, for both proton and heavy ion beams, and reducing collimator-related impedance is described. Besides the "Phase II" secondary collimators, new collimators are required in a few super-conducting regions
The Diversity of Core Halo Structure in the Fuzzy Dark Matter Model
In the fuzzy dark matter (FDM) model, gravitationally collapsed objects
always consist of a solitonic core located within a virialised halo. Although
various numerical simulations have confirmed that the collapsed structure can
be described by a cored NFW like density profile, there is still disagreement
about the relation between the core mass and the halo mass. To fully understand
this relation, we have assembled a large sample of cored haloes based on both
idealised soliton mergers and cosmological simulations with various box sizes.
We find that there exists a sizeable dispersion in the core-halo mass relation
that increases with halo mass, indicating that the FDM model allows cores and
haloes to coexist in diverse configurations. We provide a new empirical
equation for a core halo mass relation with uncertainties that can encompass
all previously found relations in the dispersion, and emphasise that any
observational constraints on the particle mass using a tight one-to-one
core-halo mass relation should suffer from an additional uncertainty on the
order of 50 % for halo masses . We suggest that tidal stripping may be one of the effects
contributing to the scatter in the relation
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