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WIP: handling of negative poloidal field #57

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WIP: handling of negative poloidal field #57

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bendudson
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@bendudson bendudson commented Dec 8, 2020 •
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Checking calculations for negative poloidal magnetic field (Jacobian < 0)
Following checking of the coordinate system in boutproject/BOUT-dev#2165

TODO

  • Metric components
    • Test with forward & reverse fields (Bpol, Btor)
  • zShift, TwistShift
    • Test with forward & reverse fields (Bpol, Btor)
  • Curvature components
    • Test with forward & reverse fields (Bpol, Btor)

@bendudson
Add Bp sign to g23, g_12 and g_23
dcc434b 
Were already present in the non-orthogonal metric, but not the
orthogonal case.

Still remaining to check:

- zShift, TwistShift
- Curvature components
@bendudson bendudson added the wip Work in progress label Dec 8, 2020
@bendudson bendudson changed the title WIP: WIP: handling of negative poloidal field Dec 8, 2020
@bendudson
Add sigma_Bθ factor to zShift
3e7e79b 
Because the direction of Z reverses when Bθ reverses,
zShift also needs to be reversed.
@bendudson
Line too long
7be8608 
flake8 upset by overly long line length
@bendudson
Black formatting
60797a1
@johnomotani
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Possible alternative to this PR that might be simpler to implement: modify hypnotoad/cases/tokamak.py so that if 'reversed current' is detected, the gridding starts from the outer, lower divertor and winds anti-clockwise. That would mean that the y-direction on the grid is always parallel to the magnetic field (not anti-parallel), which is probably less likely to suffer from sign errors than fully supporting 'negative Bp'.

@bendudson
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Hey @johnomotani That sounds like a good option to have, at least as an alternative to a negative-Jacobian coordinate system. Even having that capability would allow us to compare simulation results with and without a reversed (anticlockwise) grid to check that these coordinate system issues are handled correctly.

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@bendudson @johnomotani