# Publications

## Large tangential electric fields in plasmas close to temperature screening

Plasma Physics and Controlled Fusion 60 (2018)

JL Velasco, I Calvo, JM García-Regana, FI Parra, S Satake, JA Alonso

© 2018 Laboratorio Nacional de Fusion, CIEMAT. Low collisionality stellarator plasmas usually display a large negative radial electric field that has been expected to cause accumulation of impurities due to their high charge number. In this paper, two combined effects that can potentially modify this scenario are discussed. First, it is shown that, in low collisionality plasmas, the kinetic contribution of the electrons to the radial electric field can make it negative but small, bringing the plasma close to impurity temperature screening (i.e., to a situation in which the ion temperature gradient is the main drive of impurity transport and causes outward flux); in plasmas of very low collisionality, such as those of the large helical device displaying impurity hole (Ida et al (The LHD Experimental Group) 2009 Phys. Plasmas 16 056111; Yoshinuma et al (The LHD Experimental Group) 2009 Nucl. Fusion 49 062002), screening may actually occur. Second, the component of the electric field that is tangent to the flux surface (in other words, the variation of the electrostatic potential on the flux surface), although smaller than the radial component, has recently been suggested to be an additional relevant drive for radial impurity transport. Here, it is explained that, especially when the radial electric field is small, the tangential magnetic drift has to be kept in order to correctly compute the tangential electric field, that can be larger than previously expected. This can have a strong impact on impurity transport, as we illustrate by means of simulations using the newly developed code kinetic orbit-averaging-solver for stellarators, although it is not enough to explain by itself the behavior of the fluxes in situations like the impurity hole.

## A theoretical explanation for the Central Molecular Zone asymmetry

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 475 (2018) 2383-2402

MC Sormani, RG Tress, M Ridley, SCO Glover, RS Klessen, J Binney, J Magorrian, R Smith

## A hybrid gyrokinetic ion and isothermal electron fluid code for astrophysical plasma

JOURNAL OF COMPUTATIONAL PHYSICS 360 (2018) 57-73

Y Kawazura, M Barnes

## Laboratory evidence of dynamo amplification of magnetic fields in a turbulent plasma.

Nature communications 9 (2018) 591-

P Tzeferacos, A Rigby, AFA Bott, AR Bell, R Bingham, A Casner, F Cattaneo, EM Churazov, J Emig, F Fiuza, CB Forest, J Foster, C Graziani, J Katz, M Koenig, C-K Li, J Meinecke, R Petrasso, H-S Park, BA Remington, JS Ross, D Ryu, D Ryutov, TG White, B Reville, F Miniati, AA Schekochihin, DQ Lamb, DH Froula, G Gregori

Magnetic fields are ubiquitous in the Universe. The energy density of these fields is typically comparable to the energy density of the fluid motions of the plasma in which they are embedded, making magnetic fields essential players in the dynamics of the luminous matter. The standard theoretical model for the origin of these strong magnetic fields is through the amplification of tiny seed fields via turbulent dynamo to the level consistent with current observations. However, experimental demonstration of the turbulent dynamo mechanism has remained elusive, since it requires plasma conditions that are extremely hard to re-create in terrestrial laboratories. Here we demonstrate, using laser-produced colliding plasma flows, that turbulence is indeed capable of rapidly amplifying seed fields to near equipartition with the turbulent fluid motions. These results support the notion that turbulent dynamo is a viable mechanism responsible for the observed present-day magnetization.

## Is the Milky Way still breathing? RAVE-Gaia streaming motions

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 475 (2018) 2679-2696

I Carrillo, I Minchev, G Kordopatis, M Steinmetz, J Binney, F Anders, O Bienayme, J Bland-Hawthorn, B Famaey, KC Freeman, G Gilmore, BK Gibson, EK Grebel, A Helmi, A Just, A Kunder, P McMillan, G Monari, U Munari, J Navarro, QA Parker, W Reid, G Seabroke, S Sharma, A Siebert, F Watson, J Wojno, RFG Wyse, T Zwitter

## Optimized up-down asymmetry to drive fast intrinsic rotation in tokamaks

NUCLEAR FUSION 58 (2018) ARTN 026003

J Ball, FI Parra, M Landreman, M Barnes

## Confirming chemical clocks: asteroseismic age dissection of the Milky Way disc(s)

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 475 (2018) 5487-5500

VS Aguirre, M Bojsen-Hansen, D Slumstrup, L Casagrande, D Kawata, I Ciuca, R Handberg, MN Lund, JR Mosumgaard, D Huber, JA Johnson, MH Pinsonneault, AM Serenelli, D Stello, J Tayar, JC Bird, S Cassisi, M Hon, M Martig, PE Nissen, HW Rix, R Schonrich, C Sahlholdt, WH Trick, J Yu

## Improved distances and ages for stars common to TGAS and RAVE

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 477 (2018) 5279-5300

PJ McMillan, G Kordopatis, A Kunder, J Binney, J Wojno, T Zwitter, M Steinmetz, J Bland-Hawthorn, BK Gibson, G Gilmore, EK Grebel, A Helmi, U Munari, JF Navarro, QA Parker, G Seabroke, F Watson, RFG Wyse

## Polarization of Sunyaev-Zel'dovich signal due to electron pressure anisotropy in galaxy clusters

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 474 (2018) 2389-2400

I Khabibullin, S Komarov, E Churazov, A Schekochihin

## Correlations between age, kinematics, and chemistry as seen by the RAVE survey

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 477 (2018) 5612-5624

J Wojno, G Kordopatis, M Steinmetz, P McMillan, J Binney, B Famaey, G Monari, I Minchev, RFG Wyse, T Antoja, A Siebert, I Carrillo, J Bland-Hawthorn, EK Grebel, T Zwitter, O Bienayme, B Gibson, A Kunder, U Munari, J Navarro, Q Parker, W Reid, G Seabroke

## On the maximum energy of non-thermal particles in the primary hotspot of Cygnus A

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 473 (2018) 3500-3506

AT Araudo, AR Bell, KM Blundell, JH Matthews

## Radiation-hydrodynamic simulations of thermally-driven disc winds in X-ray binaries: A direct comparison to GRO J1655-40

Monthly Notices of the Royal Astronomical Society (2018)

N Higginbottom, C Knigge, KS Long, JH Matthews, SA Sim, HA Hewitt

## Optimisation of confinement in a fusion reactor using a nonlinear turbulence model

JOURNAL OF PLASMA PHYSICS 84 (2018) ARTN 905840208

EG Highcock, NR Mandell, M Barnes, W Dorland

## Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk.

Nature 555 (2018) 334-337

M Bergemann, B Sesar, JG Cohen, AM Serenelli, A Sheffield, TS Li, L Casagrande, KV Johnston, CFP Laporte, AM Price-Whelan, R Schönrich, A Gould

Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo-the faint, roughly spherical component of the Galaxy-reveals rich 'fossil' evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane-locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

## Cosmic-ray acceleration by relativistic shocks: limits and estimates

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 473 (2018) 2364-2371

AR Bell, AT Araudo, JH Matthews, KM Blundell

## Generation of Internal Waves by Buoyant Bubbles in Galaxy Clusters and Heating of Intracluster Medium

Monthly Notices of the Royal Astronomical Society Blackwell Publishing Inc. (2018)

C Zhang, E Churazov, AA Schekochihin

Buoyant bubbles of relativistic plasma in cluster cores plausibly play a key role in conveying the energy from a supermassive black hole to the intracluster medium (ICM) - the process known as radio-mode AGN feedback. Energy conservation guarantees that a bubble loses most of its energy to the ICM after crossing several pressure scale heights. However, actual processes responsible for transferring the energy to the ICM are still being debated. One attractive possibility is the excitation of internal waves, which are trapped in the cluster's core and eventually dissipate. Here we show that a sufficient condition for efficient excitation of these waves in stratified cluster atmospheres is flattening of the bubbles in the radial direction. In our numerical simulations, we model the bubbles phenomenologically as rigid bodies buoyantly rising in the stratified cluster atmosphere. We find that the terminal velocities of the flattened bubbles are small enough so that the Froude number ${\rm Fr}\lesssim 1$. The effects of stratification make the dominant contribution to the total drag force balancing the buoyancy force. In particular, clear signs of internal waves are seen in the simulations. These waves propagate horizontally and downwards from the rising bubble, spreading their energy over large volumes of the ICM. If our findings are scaled to the conditions of the Perseus cluster, the expected terminal velocity is $\sim100-200{\,\rm km\,s^{-1}}$ near the cluster cores, which is in broad agreement with direct measurements by the Hitomi satellite.

## Semianalytical calculation of the zonal-flow oscillation frequency in stellarators

PLASMA PHYSICS AND CONTROLLED FUSION 59 (2017) ARTN 065005

P Monreal, E Sanchez, I Calvo, A Bustos, FI Parra, A Mishchenko, A Koenies, R Kleiber

## Ion cyclotron resonance heating system in the RT-1 magnetospheric plasma

NUCLEAR FUSION 57 (2017) ARTN 086038

M Nishiura, Y Kawazura, Z Yoshida, N Kenmochi, Y Yano, H Saitoh, M Yamasaki, T Mushiake, A Kashyap, N Takahashi, M Nakatsuka, A Fukuyama

## Disruption of Alfvenic turbulence by magnetic reconnection in a collisionless plasma

JOURNAL OF PLASMA PHYSICS 83 (2017) UNSP 905830609

A Mallet, AA Schekochihin, BDG Chandran

## Magneto-optic probe measurements in low density-supersonic jets

JOURNAL OF INSTRUMENTATION 12 (2017) ARTN P12001

M Oliver, T White, P Maybe, M Kuehn-Kauffeldt, L Dohl, R Bingham, R Clarke, P Graham, R Heathcote, M Koenig, Y Kuramitsu, DQ Lamb, J Meinecke, T Michel, F Miniati, M Notley, B Reville, S Sarkar, Y Sakawa, AA Schekochihin, P Tzeferacos, N Woolsey, H-S Park, G Gregori