HR: 0800h
AN: NG21B-0528    [Abstracts]
TI: Characterisation of edge turbulence in relation to edge magnetic field configuration in L-mode plasmas in the Mega Amp Spherical Tokamak.
AU: Dewhurst, J
EM: J.M.Dewhurst@warwick.ac.uk
AF: University of Warwick, CFSA, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom
AU: * Hnat, B
EM: B.Hnat@warwick.ac.uk
AF: University of Warwick, CFSA, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom
AU: Dudson, B
EM: bd512@york.ac.uk
AF: University of York, Physics Department, York, YO10 5DD, United Kingdom
AU: Dendy, R O
EM: richard.dendy@ukaea.org.uk
AF: Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom
AU: Counsell, G F
EM: glenn.counsell@ukaea.org.uk
AF: Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom
AU: Kirk, A
EM: andrew.kirk@ukaea.org.uk
AF: Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom
AU: Team, M
EM: richard.dendy@ukaea.org.uk
AF: Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, United Kingdom
AB: Almost all astrophysical and magnetically confined fusion plasmas are turbulent. Here, we examine ion saturation current (I_sat) measurements of edge plasma turbulence for three MAST L-mode plasmas that differ primarily in their edge magnetic field configurations. First, absolute moments of the coarse grained data are examined to obtain accurate values of scaling exponents. The dual scaling behaviour is identified in all samples, with the temporal scale τ \! ≈ \!40\!-\!60 μs separating the two regimes. Strong universality is then identified in the functional form of the probability density function (PDF) for I_sat fluctuations, which is well approximated by the Fréchet distribution on temporal scales τ ≤ 40μs. For temporal scales τ > 40μs, the PDFs appear to converge to the Gumbel distribution, which has been previously identified as a universal feature of many other complex phenomena. The optimal fitting parameters k=1.15 for Fréchet and a=1.35 for Gumbel provide a simple quantitative characterisation of the full spectrum of fluctuations. We conclude that, to good approximation, the properties of the edge turbulence are independent of the edge magnetic field configuration.
DE: 4430 Complex systems
DE: 4475 Scaling: spatial and temporal (1872, 3270, 4277)
DE: 4490 Turbulence (3379, 4568, 7863)
DE: 7831 Laboratory studies and experimental techniques
DE: 7839 Nonlinear phenomena (4400, 6944)
SC: Nonlinear Geophysics [NG]
MN: 2007 Fall Meeting