module sim_decay_mod

  use bmad
  use sim_bpm_mod
  
  implicit none


  type meas_beam_struct
     real(rp) :: current = 7500
     real(rp) :: I0 = 7500
     real(rp) :: tau = -1 ! lifetime of beam; -1 = infinite
  end type meas_beam_struct
  

contains

!++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
! Subroutine sim_decay(beam, time)
!
! Simulate a simple exponential beam decay; for coarse beam current 
! dependence studies.
!
! Input:
!   beam    -- meas_beam_struct
!       %tau -- Lifetime, in seconds
!       % I0 -- Initial current
!   time    -- Total time elapsed
!
! Output:
!   beam
!       %current -- Present current of the beam
!--------------------------------------------------------------------------

  subroutine sim_decay(beam, time)
    use bmad
    !use sim_meas_mod

    implicit none


    
    type(meas_beam_struct) :: beam
    real(rp), intent(in) :: time

    if (beam%tau .ne. -1) then
       beam%current = beam%I0 * exp(-time/beam%tau)
    endif

  end subroutine sim_decay





end module sim_decay_mod