Publications


High-m kink/tearing modes in cylindrical geometry

PLASMA PHYSICS AND CONTROLLED FUSION 56 (2014) ARTN 125006

JW Connor, RJ Hastie, I Pusztai, PJ Catto, M Barnes


Observation of a new high- β and high-density state of a magnetospheric plasma in RT-1

Physics of Plasmas 21 (2014)

H Saitoh, Y Yano, Z Yoshida, M Nishiura, J Morikawa, Y Kawazura, T Nogami, M Yamasaki

A new high-β and high-density state is reported for a plasma confined in a laboratory magnetosphere. In order to expand the parameter regime of an electron cyclotron resonance heating experiment, the 8.2 GHz microwave power of the Ring Trap 1 device has been upgraded with the installation of a new waveguide system. The rated input power launched from a klystron was increased from 25 to 50 kW, which enabled the more stable formation of a hot-electron high-β plasma. The diamagnetic signal (the averaged value of four magnetic loops signals) of a plasma reached 5.2 mWb. According to a two-dimensional Grad-Shafranov analysis, the corresponding local β value is close to 100%. © 2014 AIP Publishing LLC.


THE RELATION BETWEEN GAS DENSITY AND VELOCITY POWER SPECTRA IN GALAXY CLUSTERS: QUALITATIVE TREATMENT AND COSMOLOGICAL SIMULATIONS

ASTROPHYSICAL JOURNAL LETTERS 788 (2014) ARTN L13

I Zhuravleva, EM Churazov, AA Schekochihin, ET Lau, D Nagai, M Gaspari, SW Allen, K Nelson, IJ Parrish


The formation of stellar nuclear discs in bar-induced gas inflows

Monthly Notices of the Royal Astronomical Society 445 (2014) 3352-3369

DR Cole, VP Debattista, P Erwin, SWF Earp, R Rôkar

The role of gas in themass assembly at the nuclei of galaxies is still subject to some uncertainty. Stellar nuclear discs bridge the gap between the large-scale galaxy and the central massive objects that reside there. Using a high-resolution simulation of a galaxy forming out of gas cooling and settling into a disc, we study the formation and properties of nuclear discs. Gas, driven to the centre by a bar, settles into a rotating star-forming nuclear disc (ND). This ND is thinner, younger, kinematically cooler and more metal rich than the surrounding bar. The ND is elliptical and orthogonal to the bar. The complex kinematics in the region of the ND are a result of the superposition of older stars streaming along the bar and younger stars circulating within the ND. The signature of the ND is therefore subtle in the kinematics. Instead the ND stands out clearly in metallicity and age maps. We compare the model to the density and kinematics of real galaxies with NDs finding qualitative similarities. Our results suggest that gas dissipation is very important for forming nuclear structures.


A current driven electromagnetic mode in sheared and toroidal configurations

ArXiv (0)

I Pusztai, PJ Catto, FI Parra, M Barnes

The induced electric field in a tokamak drives a parallel electron current flow. In an inhomogeneous, finite beta plasma, when this electron flow is comparable to the ion thermal speed, the Alfven mode wave solutions of the electromagnetic gyrokinetic equation can become nearly purely growing kink modes. Using the new "low-flow" version of the gyrokinetic code GS2 developed for momentum transport studies [Barnes et al 2013 Phys. Rev. Lett. 111, 055005], we are able to model the effect of the induced parallel electric field on the electron distribution to study the destabilizing influence of current on stability. We identify high mode number kink modes in GS2 simulations and make comparisons to analytical theory in sheared magnetic geometry. We demonstrate reassuring agreement with analytical results both in terms of parametric dependences of mode frequencies and growth rates, and regarding the radial mode structure.


Turbulent momentum pinch of diamagnetic flows in a tokamak

ArXiv (0)

J Lee, FI Parra, M Barnes

The ion toroidal rotation in a tokamak consists of an $E\times B$ flow due to the radial electric field and a diamagnetic flow due to the radial pressure gradient. The turbulent pinch of toroidal angular momentum due to the Coriolis force studied in previous work is only applicable to the $E\times B$ flow. In this Letter, the momentum pinch for the rotation generated by the radial pressure gradient is calculated and is compared with the Coriolis pinch. This distinction is important for subsonic flows or the flow in the pedestal where the two types of flows are similar in size and opposite in direction. In the edge, the different pinches due to the opposite rotations can result in intrinsic momentum transport that gives significant rotation peaking.


Actions, angles and frequencies for numerically integrated orbits

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 441 (2014) 3284-3295

JL Sanders, J Binney


Turbulent heating in galaxy clusters brightest in X-rays.

Nature 515 (2014) 85-87

I Zhuravleva, E Churazov, AA Schekochihin, SW Allen, P Arévalo, AC Fabian, WR Forman, JS Sanders, A Simionescu, R Sunyaev, A Vikhlinin, N Werner

The hot (10(7) to 10(8) kelvin), X-ray-emitting intracluster medium (ICM) is the dominant baryonic constituent of clusters of galaxies. In the cores of many clusters, radiative energy losses from the ICM occur on timescales much shorter than the age of the system. Unchecked, this cooling would lead to massive accumulations of cold gas and vigorous star formation, in contradiction to observations. Various sources of energy capable of compensating for these cooling losses have been proposed, the most promising being heating by the supermassive black holes in the central galaxies, through inflation of bubbles of relativistic plasma. Regardless of the original source of energy, the question of how this energy is transferred to the ICM remains open. Here we present a plausible solution to this question based on deep X-ray data and a new data analysis method that enable us to evaluate directly the ICM heating rate from the dissipation of turbulence. We find that turbulent heating is sufficient to offset radiative cooling and indeed appears to balance it locally at each radius-it may therefore be the key element in resolving the gas cooling problem in cluster cores and, more universally, in the atmospheres of X-ray-emitting, gas-rich systems on scales from galaxy clusters to groups and elliptical galaxies.


Analytical model of eddy currents in a reaction sphere actuator

IEEE Transactions on Magnetics 50 (2014)

M Strumik, R Wawrzaszek, M Banaszkiewicz, K Seweryn, M Sidz, E Onillon, L Rossini

A recently proposed technique to control the satellite attitude using a magnetically levitated sphere requires the development of suitable models of its dynamics. One of the phenomena that can affect motion of the system are eddy currents induced in the stator of the actuator due to time variable magnetic field generated by rotational motion of a permanent magnet rotor. We present an analytical model of the eddy currents for the actuator with eight-pole rotor. The model is derived using a second-order vector potential-based approach, and the solution is obtained in terms of spherical harmonic functions. This model allows us to study rotor rotations with constant angular frequency around an axis arbitrarily oriented with respect to both rotor and stator of the reaction sphere actuator. © 1965-2012 IEEE.


Hyperchaotic intermittent convection in a magnetized viscous fluid.

Physical review letters 112 (2014) 074502-

WM Macek, M Strumik

We consider a low-dimensional model of convection in a horizontally magnetized layer of a viscous fluid heated from below. We analyze in detail the stability of hydrodynamic convection for a wide range of two control parameters. Namely, when changing the initially applied temperature difference or magnetic field strength, one can see transitions from regular to irregular long-term behavior of the system, switching between chaotic, periodic, and equilibrium asymptotic solutions. It is worth noting that owing to the induced magnetic field a transition to hyperchaotic dynamics is possible for some parameters of the model. We also reveal new features of the generalized Lorenz model, including both type I and III intermittency.


Advective transport of interstellar plasma into the heliosphere across the reconnecting heliopause

Astrophysical Journal Letters 782 (2014)

M Strumik, S Grzedzielski, A Czechowski, WM Macek, R Ratkiewicz

We discuss results of magnetohydrodynamical model simulations of plasma dynamics in the proximity of the heliopause (HP). The model is shown to fit details of the magnetic field variations observed by the Voyager 1 spacecraft during the transition from the heliosphere to the local interstellar medium (LISM). We propose an interpretation of magnetic field structures observed by Voyager 1 in terms of fine-scale physical processes. Our simulations reveal an effective transport mechanism of relatively dense LISM plasma across the reconnecting HP into the heliosphere. The mechanism is associated with annihilation of magnetic sectors in the heliospheric plasma near the HP. © 2014. The American Astronomical Society. All rights reserved..


Home energy efficiency and radon related risk of lung cancer: modelling study.

BMJ (Clinical research ed.) 348 (2014) f7493-

J Milner, C Shrubsole, P Das, B Jones, I Ridley, Z Chalabi, I Hamilton, B Armstrong, M Davies, P Wilkinson

OBJECTIVE: To investigate the effect of reducing home ventilation as part of household energy efficiency measures on deaths from radon related lung cancer. DESIGN: Modelling study. SETTING: England. INTERVENTION: Home energy efficiency interventions, motivated in part by targets for reducing greenhouse gases, which entail reduction in uncontrolled ventilation in keeping with good practice guidance. MAIN OUTCOME MEASURES: Modelled current and future distributions of indoor radon levels for the English housing stock and associated changes in life years due to lung cancer mortality, estimated using life tables. RESULTS: Increasing the air tightness of dwellings (without compensatory purpose-provided ventilation) increased mean indoor radon concentrations by an estimated 56.6%, from 21.2 becquerels per cubic metre (Bq/m(3)) to 33.2 Bq/m(3). After the lag in lung cancer onset, this would result in an additional annual burden of 4700 life years lost and (at peak) 278 deaths. The increases in radon levels for the millions of homes that would contribute most of the additional burden are below the threshold at which radon remediation measures are cost effective. Fitting extraction fans and trickle ventilators to restore ventilation will help offset the additional burden but only if the ventilation related energy efficiency gains are lost. Mechanical ventilation systems with heat recovery may lower radon levels and the risk of cancer while maintaining the advantage of energy efficiency for the most airtight dwellings but there is potential for a major adverse impact on health if such systems fail. CONCLUSION: Unless specific remediation is used, reducing the ventilation of dwellings will improve energy efficiency only at the expense of population wide adverse impact on indoor exposure to radon and risk of lung cancer. The implications of this and other consequences of changes to ventilation need to be carefully evaluated to ensure that the desirable health and environmental benefits of home energy efficiency are not compromised by avoidable negative impacts on indoor air quality.


Firehose and Mirror Instabilities in a Collisionless Shearing Plasma

PHYSICAL REVIEW LETTERS 112 (2014) ARTN 205003

MW Kunz, AA Schekochihin, JM Stone


A NEW STELLAR CHEMO-KINEMATIC RELATION REVEALS THE MERGER HISTORY OF THE MILKY WAY DISK

ASTROPHYSICAL JOURNAL LETTERS 781 (2014) ARTN L20

I Minchev, C Chiappini, M Martig, M Steinmetz, RS de Jong, C Boeche, C Scannapieco, T Zwitter, RFG Wyse, JJ Binney, J Bland-Hawthorn, O Bienayme, B Famaey, KC Freeman, BK Gibson, EK Grebel, G Gilmore, A Helmi, G Kordopatis, YS Lee, U Munari, JF Navarro, QA Parker, AC Quillen, WA Reid, A Siebert, A Siviero, G Seabroke, F Watson, M Williams


Galactic kinematics and dynamics from Radial Velocity Experiment stars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 439 (2014) 1231-1244

J Binney, B Burnett, G Kordopatis, M Steinmetz, G Gilmore, O Bienayme, J Bland-Hawthorn, B Famaey, EK Grebel, A Helmi, J Navarro, Q Parker, WA Reid, G Seabroke, A Siebert, F Watson, MEK Williams, RFG Wyse, T Zwitter


Rates of capture of stars by supermassive black holes in non-spherical galactic nuclei

Classical and Quantum Gravity 31 (2014)

E Vasiliev

© 2014 IOP Publishing Ltd.We consider the problem of star consumption by supermassive black holes in non-spherical (axisymmetric, triaxial) galactic nuclei. We review the previous studies of the loss-cone problem and present a novel simulation method that allows us to separate out the collisional (relaxation-related) and collisionless (related to non-conservation of angular momentum) processes and determine their relative importance for the capture rates in different geometries. We show that for black holes more massive than 107 M⊙, the enhancement of the capture rate in non-spherical galaxies is substantial, with even modest triaxiality being capable of keeping the capture rate at the level of a few percent of black hole mass per Hubble time.


Erratum: Long-wavelength limit of gyrokinetics in a turbulent tokamak and its intrinsic ambipolarity (Plasma Phys. Control. Fusion (2012) 54 (115007))

Plasma Physics and Controlled Fusion 56 (2014)

I Calvo, FI Parra


Phase-space Lagrangian derivation of electrostatic gyrokinetics in general geometry (vol 53, 045001, 2011)

PLASMA PHYSICS AND CONTROLLED FUSION 56 (2014) ARTN 099501

FI Parra, I Calvo


Local dependence of ion temperature gradient on magnetic configuration, rotational shear and turbulent heat flux in MAST

NUCLEAR FUSION 54 (2014) ARTN 042003

Y-C Ghim, AR Field, AA Schekochihin, EG Highcock, C Michael, MAST Team


The RAVE survey: the Galactic escape speed and the mass of the Milky Way

ASTRONOMY & ASTROPHYSICS 562 (2014) ARTN A91

T Piffl, C Scannapieco, J Binney, M Steinmetz, R-D Scholz, MEK Williams, RS de Jong, G Kordopatis, G Matijevic, O Bienayme, J Bland-Hawthorn, C Boeche, K Freeman, B Gibson, G Gilmore, EK Grebel, A Helmi, U Munari, JF Navarro, Q Parker, WA Reid, G Seabroke, F Watson, RFG Wyse, T Zwitter

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