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Published byMia MacLeod Modified over 3 years ago

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Magnetic Relaxation in MST S. Prager University of Wisconsin and CMSO

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MST Reversed field pinch

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Experimental topics relevant to today Helicity conservation and fluxes during relaxation Multiple, interacting reconnection layers Flow and extended-MHD relaxation Key features for strong alpha effect

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Helicity conserving relaxation

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Magnetic relaxation occurs in bursts Toroidal Magnetic Flux (Wb) MST time (ms)

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Relaxation is helicity-conserving magnetic energy (kJ) Helicity (Wb) Time (ms)

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current profile relaxes toward a Taylor state radius (m) before after Taylor state radius 01 But not all the way to a Taylor state,

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Multiple reconnection layers Reconnection occurs where Satisfied as multiple radii (for different wave numbers) Two radii with spontaneous reconnection nonlinearly generate a third reconnection

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reconnection occurs in bursts core m = 1, n = 6 m = 0, n = 1 edge (G)

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Spontaneous and forced reconnection, coupled Consider 3 modes, each corresponding to reconnection 1)m = 1, n = 6, linearly unstable, spontaneous reconn 2)m = 1, n = 7, linearly unstable, spontaneous 3)m = 0, n = 1, linearly stable, forced reconn by NL coupling 1 2 3 Can investigate differences between spontaneous and forced reconnection; coupling leads to energy release radius

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What drives reconnection? (linearly unstable or nonlinearly driven? From MHD, linear drive Measuring terms directly in MST edge plasma nonlinear coupling

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Flow and two-fluid relaxation Flow relaxation as part of process Show flow profile change Generalized helicities Couples to momentum transport problem

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Rotation profile flattens Parallel Velocity (km/s)

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Two - fluid relaxation Generalized helicity for each species ( A s B s dV) is conserved where A s = A + (m s /q s ) v s and B s = A s Relaxes to minimum magnetic + flow energy (via v B and J B) Constant j || /B and v || /B profiles

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Strong alpha effect in MST Why strong in experiment weak in some dynamo in a box calculations?

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in experiment E || j || radius Strong current generation mechanism (measuring alpha effect, Hall dynamo……)

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