MODULE ExB_shear_flow
! This module contains the necessary tools to implement ExB shearing flow effects.
! The algorithm is taken from the presentation of Hammett et al. 2006 (APS) and
! it the one used in GS2.
USE prec_const, ONLY: xp, imagu
IMPLICIT NONE
! Variables
REAL(xp), PUBLIC, PROTECTED :: gamma_E = 0._xp ! ExB background shearing rate \gamma_E
REAL(xp), PUBLIC, PROTECTED :: t0, inv_t0 = 0._xp ! charact. shear time
REAL(xp), DIMENSION(:), ALLOCATABLE, PUBLIC, PROTECTED :: sky_ExB ! shift of the kx modes, kx* = kx + s(ky)
INTEGER, DIMENSION(:), ALLOCATABLE, PUBLIC, PROTECTED :: jump_ExB ! jump to do to shift the kx grids
LOGICAL, DIMENSION(:), ALLOCATABLE, PUBLIC, PROTECTED :: shiftnow_ExB ! Indicates if there is a line to shift
COMPLEX(xp),DIMENSION(:,:), ALLOCATABLE, PUBLIC, PROTECTED :: ExB_NL_factor! factor for nonlinear term
COMPLEX(xp),DIMENSION(:,:), ALLOCATABLE, PUBLIC, PROTECTED :: inv_ExB_NL_factor
! Routines
PUBLIC :: Setup_ExB_shear_flow, Apply_ExB_shear_flow, Update_ExB_shear_flow
CONTAINS
! Setup the variables for the ExB shear
SUBROUTINE Setup_ExB_shear_flow
USE grid, ONLY : Nx, local_nky, local_nx, Ny, deltakx, deltaky
USE model, ONLY : ExBrate
IMPLICIT NONE
! Setup the ExB shift
ALLOCATE(sky_ExB(local_nky))
sky_ExB = 0._xp
! Setup the jump array and shifting flag
ALLOCATE(jump_ExB(local_nky))
jump_ExB = 0
ALLOCATE(shiftnow_ExB(local_nky))
shiftnow_ExB = .FALSE.
! Setup nonlinear factor
ALLOCATE( ExB_NL_factor(Nx,local_nky))
ALLOCATE(inv_ExB_NL_factor(Ny/2+1,local_nx))
ExB_NL_factor = 1._xp
inv_ExB_NL_factor = 1._xp
IF(ExBrate .NE. 0) THEN
t0 = deltakx/deltaky/ExBrate
inv_t0 = 1._xp/t0
ELSE ! avoid 1/0 division (t0 is killed anyway in this case)
t0 = 0._xp
inv_t0 = 0._xp
ENDIF
END SUBROUTINE Setup_ExB_shear_flow
! Update according to the current ExB shear value
! -the grids
! -the spatial operators
! -the fields by imposing a shift on kx
SUBROUTINE Apply_ExB_shear_flow
USE basic, ONLY: chrono_ExBs, start_chrono, stop_chrono
USE grid, ONLY: local_nky, kxarray, update_grids, &
total_nkx, deltakx, kx_min, kx_max
USE prec_const, ONLY: PI
USE geometry, ONLY: gxx,gxy,inv_hatB2, evaluate_magn_curv
USE numerics, ONLY: evaluate_EM_op, evaluate_kernels
USE fields, ONLY: moments, phi, psi
IMPLICIT NONE
! local var
INTEGER :: iky, ikx, ikx_s, i_, loopstart, loopend, increment
CALL start_chrono(chrono_ExBs)
! shift all fields and correct the shift value
DO iky = 1,local_Nky
IF(shiftnow_ExB(iky)) THEN
! We shift the array from left to right or right to left according to the jump
! This avoids to make copy
IF(jump_ExB(iky) .GT. 0) THEN
loopstart = 1
loopend = total_nkx
increment = 1
ELSE
loopstart = total_nkx
loopend = 1
increment = -1
ENDIF
!loop to go through the array in a monotonic kx order
! Recall: the kx array is organized as
! 6 7 8 1 2 3 4 5 (indices ikx)
! -3 -2 -1 0 1 2 3 4 (values in dkx)
! so to go along the array in a monotonic way one must travel as
! 67812345 or 54321678
DO i_ = loopstart, loopend, increment
IF (i_ .LT. total_nkx/2) THEN ! go to the negative kx region
ikx = i_ + total_nkx/2 + 1
ELSE ! positive
ikx = i_ - total_nkx/2 + 1
ENDIF
ikx_s = ikx + jump_ExB(iky)
! We test if the shifted modes are still in contained in our resolution
! IF( (kxarray(iky,ikx)-sky_ExB(iky) .GE. kx_min) .AND. (kxarray(iky,ikx)-sky_ExB(iky) .LE. kx_max) ) THEN
IF ( ((ikx_s .GT. 0 ) .AND. (ikx_s .LE. total_nkx )) .AND. &
(((ikx .LE. (total_nkx/2+1)) .AND. (ikx_s .LE. (total_nkx/2+1))) .OR. &
((ikx .GT. (total_nkx/2+1)) .AND. (ikx_s .GT. (total_nkx/2+1)))) ) THEN
moments(:,:,:,iky,ikx,:,:) = moments(:,:,:,iky,ikx_s,:,:)
phi(iky,ikx,:) = phi(iky,ikx_s,:)
psi(iky,ikx,:) = psi(iky,ikx_s,:)
ELSE ! if it is not, it is lost (~dissipation for high modes)
moments(:,:,:,iky,ikx,:,:) = 0._xp
phi(iky,ikx,:) = 0._xp
psi(iky,ikx,:) = 0._xp
ENDIF
ENDDO
! correct the shift value s(ky) for this row
sky_ExB(iky) = sky_ExB(iky) - jump_ExB(iky)*deltakx
ENDIF
ENDDO
! After shifting and correction, we update the operators and grids
! update the grids
CALL update_grids(sky_ExB,gxx,gxy,inv_hatB2)
! update the EM op., the kernels and the curvature op.
CALL evaluate_kernels
CALL evaluate_EM_op
CALL evaluate_magn_curv
CALL stop_chrono(chrono_ExBs)
END SUBROUTINE Apply_ExB_shear_flow
! update the ExB shear value for the next time step
SUBROUTINE Update_ExB_shear_flow
USE basic, ONLY: dt, time, chrono_ExBs, start_chrono, stop_chrono
USE grid, ONLY: local_nky, local_nky_offset, kyarray, kyarray_full, inv_dkx, xarray, Nx, Ny, &
local_nx, local_nx_offset, deltax, &
ikyarray, inv_ikyarray, deltakx, deltaky
USE model, ONLY: ExBrate
IMPLICIT NONE
! local var
INTEGER :: iky, ix
REAL(xp):: dtExBshear, ky, kx, J_dp, inv_J, x
CALL start_chrono(chrono_ExBs)
! update the ExB shift, jumps and flags
shiftnow_ExB = .FALSE.
DO iky = 1,local_Nky
sky_ExB(iky) = sky_ExB(iky) - kyarray(iky)*ExBrate*dt
jump_ExB(iky) = NINT(sky_ExB(iky)*inv_dkx)
! If the jump is 1 or more for a given ky, we flag the index
! in shiftnow_ExB and will use it in Shift_fields to avoid
! zero-shiftings that may be majoritary.
shiftnow_ExB(iky) = (abs(jump_ExB(iky)) .GT. 0)
ENDDO
! Update the ExB nonlinear factor...
DO iky = 1,local_Nky
! for readability
ky = kyarray_full(iky+local_nky_offset)
J_dp = ikyarray(iky+local_nky_offset)
inv_J = inv_ikyarray(iky+local_nky_offset)
! compute dt factor
dtExBshear = time - t0*inv_J*ANINT(J_dp*time*inv_t0,xp)
DO ix = 1,Nx
x = xarray(ix)
! assemble the ExB nonlin factor
ExB_NL_factor(ix,iky) = EXP(-imagu*x*ExBrate*ky*dtExBshear)
ENDDO
ENDDO
! ... and the inverse
DO iky = 1,Ny/2+1
! for readability
ky = kyarray_full(iky)
J_dp = ikyarray(iky)
inv_J = inv_ikyarray(iky)
! compute dt factor
dtExBshear = time - t0*inv_J*ANINT(J_dp*time*inv_t0,xp)
ky = REAL(iky-1,xp)*deltaky
DO ix = 1,local_nx
x = xarray(ix+local_nx_offset)
! assemble the inverse ExB nonlin factor
inv_ExB_NL_factor(iky,ix) = EXP(imagu*x*ExBrate*ky*dtExBshear)
ENDDO
ENDDO
CALL stop_chrono(chrono_ExBs)
END SUBROUTINE Update_ExB_shear_flow
END MODULE ExB_shear_flow