title: Experimental signatures of critically balanced turbulence in MAST.
abstract: Beam emission spectroscopy (BES) measurements of ion-scale density fluctuations in the MAST tokamak are used to show that the turbulence correlation time, the drift time associated with ion temperature or density gradients, the particle (ion) streaming time along the magnetic field, and the magnetic drift time are consistently comparable, suggesting a "critically balanced" turbulence determined by the local equilibrium. The resulting scalings of the poloidal and radial correlation lengths are derived and tested. The nonlinear time inferred from the density fluctuations is longer than the other times; its ratio to the correlation time scales as ν(*i)(-0.8 ± 0.1), where ν(*i) = ion  collision rate/streaming rate. This is consistent with turbulent decorrelation being controlled by a zonal component, invisible to the BES, with an amplitude exceeding those of the drift waves by ∼ ν(*i)(-0.8).
authors.affiliation: Rudolf Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, United Kingdom and EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB, United Kingdom and Department of Nuclear and Quantum Engineering, KAIST, Daejeon 305-701, Republic of Korea.
authors.forename: Y-C
authors.initials: YC
authors.lastname: Ghim
authors.affiliation: Rudolf Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, United Kingdom and Merton College, Oxford OX1 4JD, United Kingdom.
authors.forename: A A
authors.initials: AA
authors.lastname: Schekochihin
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB, United Kingdom.
authors.forename: A R
authors.initials: AR
authors.lastname: Field
authors.affiliation: Rudolf Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, United Kingdom and Merton College, Oxford OX1 4JD, United Kingdom.
authors.forename: I G
authors.initials: IG
authors.lastname: Abel
authors.affiliation: Plasma Science and Fusion Center, MIT, Cambridge, Massachusetts 02139, USA and Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 37831, USA.
authors.forename: M
authors.initials: M
authors.lastname: Barnes
authors.affiliation: Rudolf Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, United Kingdom and EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Colyer
authors.affiliation: EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB, United Kingdom and Blackett Laboratory, Imperial College, London SW7 2AZ, United Kingdom.
authors.forename: S C
authors.initials: SC
authors.lastname: Cowley
authors.affiliation: Plasma Science and Fusion Center, MIT, Cambridge, Massachusetts 02139, USA.
authors.forename: F I
authors.initials: FI
authors.lastname: Parra
authors.affiliation: Wigner Research Centre for Physics, Association EURATOM/HAS, P.O. Box 49, H-1525 Budapest, Hungary.
authors.forename: D
authors.initials: D
authors.lastname: Dunai
authors.affiliation: Wigner Research Centre for Physics, Association EURATOM/HAS, P.O. Box 49, H-1525 Budapest, Hungary.
authors.forename: S
authors.initials: S
authors.lastname: Zoletnik