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Homework Help: Theta-pinch, plasma physics

  1. Aug 21, 2009 #1
    1. The problem statement, all variables and given/known data
    An idealized theta-pinch geometry is an infinitely long, cylindrically symmetric (d-by-d theta = 0), translationally-invariant (d-by-d z = 0) plasma column with an externally applied axial magnetic field B_z_ext. This induced a large diamagnetic azimuthal current which produces its own magnetic field which opposes the external magnetic field. Assume the plasma column is in MHD equilibrium with velocity v = 0 and with mag field B_z(r) and gas pressure p(r).
    I'm stuck on the first part of the question which is find the differential relationwhich the field B_z and the gas pressure must satisfy.

    2. Relevant equations
    gradp = j cross B
    maxwell's equations to replace the current with the curl of B

    3. The attempt at a solution
    grad p = (del cross B_z z-hat) cross B_z z-hat
    del cros B_x z-hat = - d-bydr B_z theta-hat
    grad p = d-by-dr p
    (1/mu_0)(- d-by-dr B_z)theta-hat cross B_z z-hat = (1/mu_0)(- d-by-dr B_z) = d-by-dr p

    Is that the correct answer? Do I need to go further?
    Next I need to integrate to find an expression for the externally applied mag field as a function of B_z and p and I just don't see how i can integrate the expression i found above.
  2. jcsd
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