Publications


Suppression of local heat flux in a turbulent magnetized intracluster medium

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 440 (2014) 1153-1164

SV Komarov, EM Churazov, AA Schekochihin, JA ZuHone


Resolving ultrafast heating of dense cryogenic hydrogen.

Physical review letters 112 (2014) 105002-

U Zastrau, P Sperling, M Harmand, A Becker, T Bornath, R Bredow, S Dziarzhytski, T Fennel, LB Fletcher, E Förster, S Göde, G Gregori, V Hilbert, D Hochhaus, B Holst, T Laarmann, HJ Lee, T Ma, JP Mithen, R Mitzner, CD Murphy, M Nakatsutsumi, P Neumayer, A Przystawik, S Roling, M Schulz, B Siemer, S Skruszewicz, J Tiggesbäumker, S Toleikis, T Tschentscher, T White, M Wöstmann, H Zacharias, T Döppner, SH Glenzer, R Redmer

We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ≲300  fs, 92 eV free electron laser x-ray burst. The rise of the x-ray scattering amplitude from a second x-ray pulse probes the transition from dense cryogenic molecular hydrogen to a nearly uncorrelated plasmalike structure, indicating an electron-ion equilibration time of ∼0.9  ps. The rise time agrees with radiation hydrodynamics simulations based on a conductivity model for partially ionized plasma that is validated by two-temperature density-functional theory.


Reduction of core turbulence in I-mode plasmas in Alcator C-Mod

NUCLEAR FUSION 54 (2014) ARTN 083019

AE White, M Barnes, A Dominguez, M Greenwald, NT Howard, AE Hubbard, JW Hughes, DR Mikkelsen, FI Parra, ML Reinke, C Sung, J Walk, DG Whyte


Fast electron energy transport in solid density and compressed plasma

NUCLEAR FUSION 54 (2014) ARTN 054004

P Norreys, D Batani, S Baton, FN Beg, R Kodama, PM Nilson, P Patel, F Perez, JJ Santos, RHH Scott, VT Tikhonchuk, M Wei, J Zhang


Synchrotron radiation, pair production, and longitudinal electron motion during 10-100 PW laser solid interactions

PHYSICS OF PLASMAS 21 (2014) ARTN 033108

CS Brady, CP Ridgers, TD Arber, AR Bell


Inboard and outboard radial electric field wells in the H- and I-mode pedestal of Alcator C-Mod and poloidal variations of impurity temperature

NUCLEAR FUSION 54 (2014) ARTN 083017

C Theiler, RM Churchill, B Lipschultz, M Landreman, DR Ernst, JW Hughes, PJ Catto, FI Parra, IH Hutchinson, ML Reinke, AE Hubbard, ES Marmar, JT Terry, JR Walk, AC-M Team


Intensity enhancement of O VI ultraviolet emission lines in solar spectra due to opacity

Astrophysical Journal Letters 784 (2014)

FP Keenan, JG Doyle, MS Madjarska, SJ Rose, LA Bowler, J Britton, L McCrink, M Mathioudakis

Opacity is a property of many plasmas. It is normally expected that if an emission line in a plasma becomes optically thick, then its intensity ratio to that of another transition that remains optically thin should decrease. However, radiative transfer calculations undertaken both by ourselves and others predict that under certain conditions the intensity ratio of an optically thick to an optically thin line can show an increase over the optically thin value, indicating an enhancement in the former. These conditions include the geometry of the emitting plasma and its orientation to the observer. A similar effect can take place between lines of differing optical depths. While previous observational studies have focused on stellar point sources, here we investigate the spatially resolved solar atmosphere using measurements of the I(1032 Å)/I(1038 Å) intensity ratio of O VI in several regions obtained with the Solar Ultraviolet Measurements of Emitted Radiation instrument on board the Solar and Heliospheric Observatory satellite. We find several I(1032 Å)/I(1038 Å) ratios observed on the disk to be significantly larger than the optically thin value of 2.0, providing the first detection (to our knowledge) of intensity enhancement in the ratio arising from opacity effects in the solar atmosphere. The agreement between observation and theory is excellent and confirms that the O VI emission originates from a slab-like geometry in the solar atmosphere, rather than from cylindrical structures. © 2014. The American Astronomical Society. All rights reserved.


Search for non-relativistic magnetic monopoles with IceCube

EUROPEAN PHYSICAL JOURNAL C 74 (2014) ARTN 2938

MG Aartsen, R Abbasi, M Ackermann, J Adams, JA Aguilar, M Ahlers, D Altmann, C Arguelles, TC Arlen, J Auffenberg, X Bai, M Baker, SW Barwick, V Baum, R Bay, JJ Beatty, JB Tjus, K-H Becker, ML Benabderrahmane, S BenZvi, P Berghaus, D Berley, E Bernardini, A Bernhard, DZ Besson, G Binder, D Bindig, M Bissok, E Blaufuss, J Blumenthal, DJ Boersma, C Bohm, D Bose, S Boeser, O Botner, L Brayeur, H-P Bretz, AM Brown, R Bruijn, J Casey, M Casier, D Chirkin, A Christov, B Christy, K Clark, L Classen, F Clevermann, S Coenders, S Cohen, DF Cowen, AHC Silva, M Danninger, J Daughhetee, JC Davis, M Day, JPAM de Andre, C De Clercq, S De Ridder, P Desiati, KD de Vries, M de With, T DeYoung, JC Diaz-Velez, M Dunkman, R Eagan, B Eberhardt, B Eichmann, J Eisch, S Euler, PA Evenson, O Fadiran, AR Fazely, A Fedynitch, J Feintzeig, T Feusels, K Filimonov, C Finley, T Fischer-Wasels, S Flis, A Franckowiak, K Frantzen, T Fuchs, TK Gaisser, J Gallagher, L Gerhardt, L Gladstone, T Gluesenkamp, A Goldschmidt, G Golup, JG Gonzalez, JA Goodman, D Gora, DT Grandmont, D Grant, P Gretskov, JC Groh, A Gross, C Ha, C Haack, AH Ismail, P Hallen, A Hallgren, F Halzen, K Hanson, D Hebecker, D Heereman, D Heinen, K Helbing, R Hellauer, S Hickford, GC Hill, KD Hoffman, R Hoffmann, A Homeier, K Hoshina, F Huang, W Huelsnitz, PO Hulth, K Hultqvist, S Hussain, A Ishihara, E Jacobi, J Jacobsen, K Jagielski, GS Japaridze, K Jero, O Jlelati, B Kaminsky, A Kappes, T Karg, A Karle, M Kauer, JL Kelley, J Kiryluk, J Klaes, SR Klein, J-H Koehne, G Kohnen, H Kolanoski, L Koepke, C Kopper, S Kopper, DJ Koskinen, M Kowalski, M Krasberg, A Kriesten, K Krings, G Kroll, J Kunnen, N Kurahashi, T Kuwabara, M Labare, H Landsman, MJ Larson, M Lesiak-Bzdak, M Leuermann, J Leute, J Luenemann, O Macias, J Madsen, G Maggi, R Maruyama, K Mase, HS Matis, F McNally, K Meagher, A Meli, M Merck, T Meures, S Miarecki, E Middell, N Milke, J Miller, L Mohrmann, T Montaruli, R Morse, R Nahnhauer, U Naumann, H Niederhausen, SC Nowicki, DR Nygren, A Obertacke, S Odrowski, A Olivas, A Omairat, A O'Murchadha, T Palczewski, L Paul, JA Pepper, CP de los Heros, C Pfendner, D Pieloth, E Pinat, J Posselt, PB Price, GT Przybylski, M Quinnan, L Raedel, M Rameez, K Rawlins, P Redl, R Reimann, E Resconi, W Rhode, M Ribordy, M Richman, B Riedel, S Robertson, JP Rodrigues, C Rott, T Ruhe, B Ruzybayev, D Ryckbosch, SM Saba, H-G Sander, M Santander, S Sarkar, K Schatto, F Scheriau, T Schmidt, M Schmitz, S Schoenen, S Schoeneberg, A Schoenwald, A Schukraft, L Schulte, O Schulz, D Seckel, Y Sestayo, S Seunarine, R Shanidze, C Sheremata, MWE Smith, D Soldin, GM Spiczak, C Spiering, M Stamatikos, T Stanev, NA Stanisha, A Stasik, T Stezelberger, RG Stokstad, A Stoessl, EA Strahler, R Stroem, NL Strotjohann, GW Sullivan, H Taavola, I Taboada, A Tamburro, A Tepe, S Ter-Antonyan, G Tesic, S Tilav, PA Toale, MN Tobin, S Toscano, M Tselengidou, E Unger, M Usner, S Vallecorsa, N van Eijndhoven, J van Santen, M Vehring, M Voge, M Vraeghe, C Walck, M Wallraff, C Weaver, M Wellons, C Wendt, S Westerhoff, BJ Whelan, N Whitehorn, K Wiebe, CH Wiebusch, DR Williams, H Wissing, M Wolf, TR Wood, K Woschnagg, DL Xu, XW Xu, JP Yanez, G Yodh, S Yoshida, P Zarzhitsky, J Ziemann, S Zierke, M Zoll


Electron-ion equilibration in ultrafast heated graphite.

Physical review letters 112 (2014) 145005-

TG White, NJ Hartley, B Borm, BJ Crowley, JW Harris, DC Hochhaus, T Kaempfer, K Li, P Neumayer, LK Pattison, F Pfeifer, S Richardson, AP Robinson, I Uschmann, G Gregori

We have employed fast electrons produced by intense laser illumination to isochorically heat thermal electrons in solid density carbon to temperatures of ∼10,000  K. Using time-resolved x-ray diffraction, the temperature evolution of the lattice ions is obtained through the Debye-Waller effect, and this directly relates to the electron-ion equilibration rate. This is shown to be considerably lower than predicted from ideal plasma models. We attribute this to strong ion coupling screening the electron-ion interaction.


Modelling gamma-ray photon emission and pair production in high-intensity laser-matter interactions

Journal of Computational Physics 260 (2014) 273-285

CP Ridgers, JG Kirk, R Duclous, TG Blackburn, CS Brady, K Bennett, TD Arber, AR Bell

In high-intensity (>1021 Wcm -2) laser-matter interactions gamma-ray photon emission by the electrons can strongly affect the electron's dynamics and copious numbers of electron-positron pairs can be produced by the emitted photons. We show how these processes can be included in simulations by coupling a Monte Carlo algorithm describing the emission to a particle-in-cell code. The Monte Carlo algorithm includes quantum corrections to the photon emission, which we show must be included if the pair production rate is to be correctly determined. The accuracy, convergence and energy conservation properties of the Monte Carlo algorithm are analysed in simple test problems. © 2013 Elsevier Inc.


Quantum radiation reaction in laser-electron-beam collisions.

Phys Rev Lett 112 (2014) 015001-

TG Blackburn, CP Ridgers, JG Kirk, AR Bell

It is possible using current high-intensity laser facilities to reach the quantum radiation reaction regime for energetic electrons. An experiment using a wakefield accelerator to drive GeV electrons into a counterpropagating laser pulse would demonstrate the increase in the yield of high-energy photons caused by the stochastic nature of quantum synchrotron emission: we show that a beam of 10(9) 1 GeV electrons colliding with a 30 fs laser pulse of intensity 10(22)  W cm(-2) will emit 6300 photons with energy greater than 700 MeV, 60× the number predicted by classical theory.


The effect of diamagnetic flows on turbulent driven ion toroidal rotation

PHYSICS OF PLASMAS 21 (2014) ARTN 056106

JP Lee, M Barnes, FI Parra, EA Belli, J Candy


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


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


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


Observations of continuum depression in warm dense matter with x-ray Thomson scattering.

Physical review letters 112 (2014) 145004-

LB Fletcher, AL Kritcher, A Pak, T Ma, T Döppner, C Fortmann, L Divol, OS Jones, OL Landen, HA Scott, J Vorberger, DA Chapman, DO Gericke, BA Mattern, GT Seidler, G Gregori, RW Falcone, SH Glenzer

Detailed measurements of the electron densities, temperatures, and ionization states of compressed CH shells approaching pressures of 50 Mbar are achieved with spectrally resolved x-ray scattering. Laser-produced 9 keV x-rays probe the plasma during the transient state of three-shock coalescence. High signal-to-noise x-ray scattering spectra show direct evidence of continuum depression in highly degenerate warm dense matter states with electron densities ne>1024  cm-3. The measured densities and temperatures agree well with radiation-hydrodynamic modeling when accounting for continuum lowering in calculations that employ detailed configuration accounting.


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

ArXiv (0)

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

Experimental data from the Mega Amp Spherical Tokamak (MAST) is used to show that the inverse gradient scale length of the ion temperature R/LTi (normalized to the major radius R) has its strongest local correlation with the rotational shear and the pitch angle of the magnetic field (or, equivalently, an inverse correlation with q/{\epsilon}, the safety factor/the inverse aspect ratio). Furthermore, R/LTi is found to be inversely correlated with the gyro-Bohm-normalized local turbulent heat flux estimated from the density fluctuation level measured using a 2D Beam Emission Spectroscopy (BES) diagnostic. These results can be explained in terms of the conjecture that the turbulent system adjusts to keep R/LTi close to a certain critical value (marginal for the excitation of turbulence) determined by local equilibrium parameters (although not necessarily by linear stability).


Effect on plasma rotation of lower hybrid (LH) waves in Alcator C-Mod

AIP Conference Proceedings 1580 (2014) 398-401

JP Lee, M Barnes, RR Parker, JE Rice, FI Parra, PT Bonoli, ML Reinke

The injection of LH waves for current drive into a tokamak changes the ion toroidal rotation. In Alcator C-Mod, the direction of the steady state rotation change due to LH waves depends on the plasma current and the density. The change in rotation can be estimated by balancing the external torque of lower hybrid waves with the turbulent radial transport of the momentum. For high plasma current, the turbulent pinch and diffusion of the injected counter-current momentum are sufficient to explain the rotation change. However, for low plasma current, the change in the the intrinsic momentum transport (residual stress) for a non-rotating state is required to explain the co-current rotation change. Accordingly, we investigate the intrinsic momentum transport for the non-rotating state when diamagnetic flow and ExB flow cancel each other. The change in the intrinsic momentum transport due to lower hybrid waves is significant when the plasma current is low, which may explain the rotation reversal for low plasma current. The effect of changed q (safety factor) profile by lower hybrid on the intrinsic momentum transport is estimated by gyrokinetics. © 2014 AIP Publishing LLC.


Erratum: "Correlations at large scales and the onset of turbulence in the fast solar wind" (2013, ApJ, 778, 177)

Astrophysical Journal 782 (2014)

RT Wicks, DA Roberts, A Mallet, AA Schekochihin, TS Horbury, CHK Chen


Alternative ignition schemes in inertial confinement fusion

Nuclear Fusion 54 (2014)

M Tabak, P Norreys, VT Tikhonchuk, KA Tanaka

This paper presents a short overview of a series of review articles describing alternative approaches to ignition of fusion reactions in inertially confined plasmas. © 2014 IAEA, Vienna.