Simulations of magnetic reconnection during merging start-up in the MAST Spherical Tokamak. Adam Stanier 1 , P. Browning 1 , M. Gordovskyy 1 , K. McClements 2 , M. Gryaznevich 2,3 , V.S. Lukin 4. 1 Jodrell Bank Centre for Astrophysics, University of Manchester, UK
Simulations of magnetic reconnection during merging start-up in the MAST Spherical Tokamak
Adam Stanier1, P. Browning1, M. Gordovskyy1,
K. McClements2, M. Gryaznevich2,3, V.S. Lukin4
1Jodrell Bank Centre for Astrophysics, University of Manchester, UK
2EURATOM/CCFE Fusion Association, Culham Science Centre, UK
3Present affiliation:Imperial College of Science and Technology, London, UK
4Space Science Division, Naval Research Laboratory, DC, USA
EPS Conference, Espoo, July 2013
Why study reconnection in MAST?
Understanding of reconnection in parameter regime relevant to tokamak disruptions.
Solar flare: lifetime of active region ~ 1 week, release ~ 1025 J over 100 sec.
Tokamak Sawtooth crash: Build up (sawtooth period) ~ 100 ms, crash ~ 100 μs.
Thomson Scattering lasers
Pick-up Coil (CCMV20)
Typical start-up parameters:
Magnetic:Bp = 0.1 T, BT = 0.5 T, IT = 0.2 - 0.5 MA
Thermal:Te = Ti = 10 eV, n = 5x1018 m-3, Deuterium
Time resolution: 0.1 ms. Total time: ~ 7ms.
βT = 4x10-5
βp = 10-3
Anisotropic heat conduction:
Hyper-resistivity (anomalous electron viscosity).
Code and initial conditions
(Glasser and Tang 2004, Lukin 2008).
∆Rmin = 0.5mm
∆Zmin = 0.3mm
Hall-MHD simulation in toroidal geometry
(CS) width: δ = 2.4 cm
∆Zmin = 0.03cm
X-point at t = 0
Density profiles: Comparison with experiment
Experiment: Nd:Yag ne
Nd:YAG TS laser
Hall-MHD Simulation: Density
What causes the double peak in density?
Toroidal resistive MHD simulation
(see also Kleva et al. 1995).
Cartesian Hall-MHD simulation
di = 0.145 m
ηH = 10-8
MHD di = 0
High density seperator
Cartesian Hall-MHD: Effect of collisions
Scan in hyper-resistivity (collisions)
Grid: ∆Rmin = 4x10-4 m, ∆Zmin = 2x10-4 m
δ = 4.5 mm
ρis= 2.9 cm
Grid: ∆Rmin = 1x10-4 m, ∆Zmin = 4x10-5 m
Future work: Simulations and M9 Campaign (with H. Tanabe and the MAST team)
We have also simulated separate ion and electron temperature profiles.
(Stanier et al. 2013).
Additional: Reconnection rates
(eg. Kleva et al. 1995., Simakov et al. 2010)
Additional: Numerical grid and convergence
25 cells across CS width
NR=360, NZ=540, NP=4
NR=180, NZ=270, NP=4
Direction of island ejection depends upon radial positions of O-points and X-point
Additional slide: q-profile
Additional: Resistive MHD sloshing
(Biskamp & Welter 1980, Knoll and Chacon 2005)
S = 105, mu = 10-3, BT= 0.5 T, a=0.6, Iplasma = 268 kA