Clarification of units used in example parameters for plasma_source

[rworrall-ukaea]

The example values for the major and minor radius seem to be in cm, but the densities match the example values in the Fausser paper which quotes the units as m^-3.

Some clarification on the units and ensuring constency for the user could increase clarity for the user.

[RemDelaporteMathurin]

That's a good point! I would be in favour of using metres everywhere for consistency... !

[RemDelaporteMathurin]

@rworrall-ukaea checking the code for the ion density, it appears that as long as major, minor radii, and r have the same units (here cm) then everything is fine since the dimensions cancel out:

openmc-plasma-source/src/openmc_plasma_source/tokamak_source.py

Lines 237 to 256 in 3d17caa

	if mode == "L":
	density = (
	ion_density_centre
	* (1 - (r / major_radius) ** 2) ** ion_density_peaking_factor
	)
	elif mode in ["H", "A"]:
	density = np.where(
	r < pedestal_radius,
	(
	(ion_density_centre - ion_density_pedestal)
	* (1 - (r / pedestal_radius) ** 2) ** ion_density_peaking_factor
	+ ion_density_pedestal
	),
	(
	(ion_density_pedestal - ion_density_separatrix)
	* (major_radius - r)
	/ (major_radius - pedestal_radius)
	+ ion_density_separatrix
	),
	)

Same for ion temperature:

openmc-plasma-source/src/openmc_plasma_source/tokamak_source.py

Lines 297 to 317 in 3d17caa

	if mode == "L":
	temperature = (
	ion_temperature_centre
	* (1 - (r / major_radius) ** 2) ** ion_temperature_peaking_factor
	)
	elif mode in ["H", "A"]:
	temperature = np.where(
	r < pedestal_radius,
	(
	ion_temperature_pedestal
	+ (ion_temperature_centre - ion_temperature_pedestal)
	* (1 - (np.abs(r / pedestal_radius)) ** ion_temperature_beta)
	** ion_temperature_peaking_factor
	),
	(
	ion_temperature_separatrix
	+ (ion_temperature_pedestal - ion_temperature_separatrix)
	* (major_radius - r)
	/ (major_radius - pedestal_radius)
	),
	)

So everything should be fine. But still, I agree that for clarity everything should be in the same units.