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2D Field Loop Advection

Problem Background

For Background and problem setup see ​http://www.astro.virginia.edu/VITA/ATHENA/field-loop.html

And for a movie of what the solution should look like see ​http://www.youtube.com/watch?v=ztaoT1yPloc

Reason for Test

This test is run in order to verify that the ConstrainedTransport method to evolve magnetic fields is working correctly.

Since this problem should evolve in a well-defined way, any major deviations from this evolution signal a possible bug somewhere in one or more of the integration schemes.

This problem includes a restart test to make sure that the restarted magnetic loop is still divergenceless.

Results

Original Test

The new chombo can be verified by looking at the magnitude of the magnetic field in the x-direction. In this test, the field loop advects to the right for 1.0 seconds. Due to the periodic boundary conditions, the loop should come back to its original position which is in the middle of the domain.

Restart Test

The test is restarted from 0.5 seconds (halfway) into the original test and run to 1.0 seconds. Therefore, the loop should again be back at its original position. Both reference chombos should look the same.

Test	Reference Chombo	New Chombo
Original	TestRef(FieldLoopAdvection, 500px)	TestSim(FieldLoopAdvection, 500px)
Restart	TestRef(FieldLoopRestart, 500px)	TestSim(FieldLoopRestart, 500px)

TestLog(FieldLoopAdvection) TestLog(FieldLoopRestart)