hfact uses wrong loss power index

[timothy-nunn]

This will only work for the selected scaling if the loss power index is (1-0.31), so really just the IPB98 scalings in this case

PROCESS/process/models/physics/confinement_time.py

Lines 953 to 966 in c4a5893

	elif (
	self.data.physics.i_rad_loss == ConfinementRadiationLossModel.FULL_RADIATION
	):
	self.data.physics.hstar = (
	hfact
	* (
	p_plasma_loss_mw
	/ (
	p_plasma_loss_mw
	+ self.data.physics.pden_plasma_rad_mw * vol_plasma
	)
	)
	** 0.31
	)

Originally posted by @chris-ashe in #4396

@chris-ashe please feel free to update the title and issue body since you know what the actual issue is

[k31i]

Hi, this looks like a fun issue i can have a attempt at. Is this free for anyone to attempt and is there any additional information i need to know?

[chris-ashe]

Hi, this looks like a fun issue i can have a attempt at. Is this free for anyone to attempt and is there any additional information i need to know?

Hi @k31i , thanks for wanting to have a go at this problem.

We need the exponent value (currently 0.31) to be equal to the absolute value of 1 plus the exponent value for the chosen scaling. Currently the 0.31 values matches that for the IPB98(y,2) scaling done by the iter_ipb98y2_confinement_time() function. You will see there that the loss power exponent is -0.69. So the absolute value of 1 -0.69 is 0.31.