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A Brief Introduction to Space Plasma Physics.pdf - Institute of ...

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• Magne<strong>to</strong>hydrodynamics (MHD)<br />

– The average properties are governed by the basic<br />

conservation laws for mass, momentum and energy in a<br />

fluid.<br />

– Continuity equation<br />

∂n<br />

∂t<br />

s<br />

+ ∇ ⋅ n<br />

– S s and L s represent sources and losses. S s -L s is the net rate<br />

at which particles are added or lost per unit volume.<br />

– The number <strong>of</strong> particles changes only if there are sources<br />

and losses.<br />

s<br />

r<br />

u<br />

– S s ,L s ,n s , and u s can be functions <strong>of</strong> time and position.<br />

– Assume S s =0 and L s =0, ρ s= m<br />

sn<br />

, s ∫ ρ sdr<br />

= M<br />

s where M s is<br />

the <strong>to</strong>tal mass <strong>of</strong> s and dr is a volume element (e.g. dxdydz)<br />

∂M<br />

s<br />

r ∂M<br />

s<br />

r r<br />

+ ∇ ⋅<br />

sus<br />

dr = +<br />

sus<br />

⋅ds<br />

∂t<br />

∫ (ρ )<br />

∂t<br />

∫ ρ<br />

where ds<br />

r is a surface element bounding the volume.<br />

s<br />

=<br />

S<br />

s<br />

−<br />

L<br />

s

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