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

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Presentation on theme: "Magnetic Relaxation in MST S. Prager University of Wisconsin and CMSO."— Presentation transcript:

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

2 MST Reversed field pinch

3 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

4 Helicity conserving relaxation

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

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

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

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

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

10 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 Can investigate differences between spontaneous and forced reconnection; coupling leads to energy release radius

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

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

13 Rotation profile flattens Parallel Velocity (km/s)

14 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

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

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

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