solar magnetic fields 2

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IAC Winter School 2013 Solar magnetic fields 2 Philip Judge Solar magnetic fields 2 1 Philip Judge, High Altitude Observatory, NCAR 1.Magnetised plasmas 2.How we measure solar (plasmas and) magnetic fields

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Solar magnetic fields 2. Philip Judge, High Altitude Observatory, NCAR. Magnetised plasmas How we measure solar (plasmas and) magnetic fields . What is a plasma?. m =E/c 2. Universe = dark energy + dark matter + plasma + gas + solid + liquid. Plasma:. - PowerPoint PPT Presentation

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Page 1: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge 1

Solar magnetic fields 2

Philip Judge, High Altitude Observatory, NCAR

1. Magnetised plasmas

2. How we measure solar (plasmas and) magnetic fields

Phillip Judge
Page 2: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

What is a plasma?

Universe = dark energy +dark matter +plasma +gas + solid + liquid

• free ions and e- (hot and/or energized), yet quasi-neutral• many interacting particles (Coulomb force, plasma no >> 1)• collective effects• complex nonlinear behavior, especially when magnetized

Plasma:

m=E/c2

Page 3: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge 3

Newtonian momentum equations and O(u/c) relativistic transformations

Maxwell

σ huge

Bulk fluid momentum equation

Nonlinear coupling

“This is supposed to be about magnetic fields: Why do we have to talk about plasmas...?”

0

…Where do r, u, j, s, T, p… come from?

Page 4: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge 4

Simple plasma, Boltzmann transport: Braginskii 1965

Page 5: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge 5

Plasma b,

equipartition

Bulk equation of motion (e+p)

Page 6: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge 6

Currents (npvpe-nev e): Ohm’s law in collisional plasmas

problem

Page 7: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

some plasmas

Page 8: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

why is plasma so prevelant? Range of plasma characteristics

…wow

Page 9: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

Allen 1973 compilation

Page 10: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

plasma characteristics

…wow

Page 11: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

plasmas vs gases

Page 12: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge 12

The Sun as a laboratory for plasmaphysics in space and astrophysical regimes where

Rm >>1, b >>1, b <<1,b=ratio plasma/magnetic pressure

Large Rm regimes exist outside of laboratory plasmas,

-> MHD regime (frozen fields)

Page 13: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge 13

Induction equation and Large magnetic Reynolds number RM

Induction diffusion (non-linear)

timescale L/u L2/h

RM = diffusion/induction times = Lu/h

h 0, Frozen flux condition (Alfven theorem)

Page 14: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge 14

RM = ∞ dynamics:

Lagrangian model (no diffusion)

C. de ForestL. Rachmeler

Page 15: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

Gold (1964)

Page 16: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

High and low b in the photosphere, quiet b >1, sunspot b <1,

b = plasma/magnetic pressure

Solar magnetic fields seen at the “surface”are intermittent-

Spots on large scales

tubes, sheets, ribbonson convective scales

Page 17: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

High and low b regimes, photosphere b >1, corona b <<1, b = plasma/magnetic pressure

dense, turbulent solar plasma patches (b >1) with tenuous field-aligned coronal plasma loops (b <<1)

Page 18: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge 18

signatures of solar magnetism

Slides from R. Casini

Page 19: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge 19

SPINOR- a real spectropolarimeter

Page 20: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

The “right stuff”: Navarro 2005a,bInversions of Fe I and Ca II lines in a sunspot, hydrostatic, DST 76cm, SPINOR, sensitivity 1.5x10-4

Current density

Temperature

“bandwidth limited”

Page 21: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

Instrument fringeremoval using2D PCA

Casini, Judge, Schad2012 in press ApJSi I/ He I 1083 nm regionFIRS/DST, noise ~ 3x10-4

Measuring magnetic fields in solarlow beta plasma is hard

Page 22: Solar magnetic fields  2

IAC Winter School 2013Solar magnetic fields 2Philip Judge

Measuring magnetic fields in solarlow beta plasma is hard

22

Uitenbroek 2011Ca II 854 nm

200-2000G

200-2000G