geometry_mod.F90
283e9b4a2feahalf_kx_plane

geometry_mod.F90
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			module geometry
			! computes geometrical quantities
			! Adapted from B.J.Frei MOLIX code (2021)

			use prec_const
			use model
			use grid
			use array
			use fields
			use basic

			implicit none
			public

			contains

			subroutine eval_magnetic_geometry
			! evalute metrix, elements, jacobian and gradient
			implicit none
			!
			IF( my_id .eq. 0 ) WRITE(,) 's-alpha geometry'
			! circular model
			call eval_s_alpha_geometry
			!
			END SUBROUTINE eval_magnetic_geometry
			!
			!--------------------------------------------------------------------------------
			!
			subroutine eval_s_alpha_geometry
			! evaluate circular geometry model

			! Ref: Lapilonne et al., PoP, 2009
			implicit none
			REAL(dp) :: z, kx, ky

			zloop: DO iz = izs,ize
			z = zarray(iz)

			! Metric elements
			gxx(iz) = 1._dp
			gxy(iz) = shearz -epsSIN(z)
			gyy(iz) = 1._dp +(shearz)2 -2._dpepsCOS(z) -2._dpshearepsz*SIN(z)

			! Relative strengh of radius
			hatR(iz) = 1._dp + eps*cos(z)

			hatB(iz) = SQRT(gxx(iz)gyy(iz) - gxy(iz)*2)

			! Jacobian
			Jacobian(iz) = q0hatR(iz)*2

			! Derivative of the magnetic field strenght
			gradxB(iz) = -(COS(z) + epsSIN(z)*2)/hatB(iz)/hatB(iz)
			gradzB(iz) = eps*SIN(z)
			! coefficient in the front of parallel derivative
			gradz_coeff(iz) = 1._dp / Jacobian(iz) / hatB(iz)

			! Curvature operator
			DO iky = ikys, ikye
			ky = kyarray(iky)
			DO ikx= ikxs, ikxe
			kx = kxarray(ikx)
			Ckxky(ikx,iky,iz) = -SIN(z)kx -(COS(z)+shearzSIN(z))ky
			ENDDO
			ENDDO

			ENDDO zloop
			END SUBROUTINE eval_s_alpha_geometry

			end module geometry