subroutine time_dep_quad_field (start_orb, ele, quad_number, err_flag)

use bmad 
use quad_scrape_parameters
use parameters_bmad
use muon_mod
use muon_interface, except_dummy => time_dep_quad_field
implicit none

type (coord_struct) :: start_orb, orb
type (ele_struct), target :: ele
type (ele_struct), pointer :: ele_init
type (ele_struct), pointer :: lord

logical err_flag, err
logical grid
logical local_ref_frame/.true./

!real(rp) scrape_scale, omega, init_scrape/0.70937/, quad_ramp_start_time/7.e-6/, quad_ramp_end_time/30.e-6/
real(rp) focus_scrape_scale, omega, steer_scrape_scale, tau
real(rp) scale
real(rp) t
real(rp) voltage
real(rp) q1ltop, q1lbottom
real(rp) f_index, v_value
real(rp) rf_v_field_scale, rf_h_field_scale
real(rp) t0/1.e-6/ 

real(rp) temp
real(rp) dx/0.001/

integer i, igrid/1/
integer state
integer quad_number
integer,  save ::  lun
integer, save :: save_number

logical first/.true./

   rf_v_field_scale=0
   rf_h_field_scale=0


if((associated(ele%grid_field)))then
   grid = .true.
   lord => ele 
elseif(ele%field_calc == refer_to_lords$)then
   do i=1,ele%n_lord
     lord => pointer_to_lord(ele,i)
     if(associated(lord%grid_field))exit
    end do
 endif

   igrid = size(lord%grid_field)-6
   
   if(allocated(ele_ref))then
     do i=1,size(ele_ref)  !find reference
        if(ele_ref(i)%name == ele%name)then
           ele_init => ele_ref(i)
           exit
        endif
     end do
  else
     print '(a,a)','time_dep_quad_field: ele_ref(i)%name /= ele%name = ', ele%name
  endif
  
   t = start_orb%t  + t0   !start time is ~1us earlier than the beam injection (IBMS3 trigger)
   if(.not. fixed_quad_time)quad_time = start_orb%t !if positive, then use the orbit time. If negative use abs quad_time
   i=abs(quad_number)
   save_number = quad_number

   rf_v_field_scale = rf_quad(i)%amp_v * (0.3/0.2)/27.2   * 100 * sin(twopi*rf_quad(i)% freq_v* (t - t0_v_min(i)))    !see below for scaling rule
   if(quad_number < 0 .or. t < t0_v_min(i) .or. t > t0_v_max(i)) rf_v_field_scale=0

   if(t > t0_h_min(i) .and. t < t0_h_max(i))then
      rf_h_field_scale =  rf_quad(i)%amp_h * (1.0/0.2)/27.2   * 100 * sin(twopi*rf_quad(i)% freq_h * (t-t0_h_min(i)))
   else
      rf_h_field_scale=0
   endif
   
!   if(t < t0_h_min(i) .or. t > t0_h_max(i)) rf_h_field_scale = 0 
 
   if(scraping_on)then
      if(quad_time < quad_ramp_start_time)then
        focus_scrape_scale = init_quad_focus
        steer_scrape_scale = init_quad_steer
!        elseif(quad_time > quad_ramp_start_time .and. quad_time < quad_ramp_end_time)then
     elseif(quad_time > quad_ramp_start_time)then
!         omega = twopi/4./(quad_ramp_end_time - quad_ramp_start_time)
!         focus_scrape_scale = init_quad_focus * (1 - sin(omega * (quad_time-quad_ramp_start_time)))
!         steer_scrape_scale = init_quad_steer * (1 - sin(omega * (quad_time-quad_ramp_start_time)))
        tau= 7.e-6
        focus_scrape_scale = init_quad_focus * exp(- (quad_time-quad_ramp_start_time)/tau)
        steer_scrape_scale = init_quad_steer * exp(- (quad_time-quad_ramp_start_time)/tau)
     else
       focus_scrape_scale = 0
       steer_scrape_scale = 0
    endif
    scale = value_of_attribute(lord, 'QUAD_VOLTAGE', err) * value_of_attribute(lord, 'FIELD_INDEX', err) / 0.185
!    v_value = value_of_attribute(lord, 'QUAD_VOLTAGE', err)
    !    f_index= value_of_attribute(lord, 'FIELD_INDEX', err)

! initialize lord%grid_field()%field_scale
       lord%grid_field(igrid+3)%field_scale = ele_init%grid_field(igrid+3)%field_scale !inner
       lord%grid_field(igrid+4)%field_scale = ele_init%grid_field(igrid+4)%field_scale !bottom
       lord%grid_field(igrid+5)%field_scale = ele_init%grid_field(igrid+5)%field_scale !outer
       lord%grid_field(igrid+6)%field_scale = ele_init%grid_field(igrid+6)%field_scale !top

    
    if(index(lord%name,'QUAD1') /= 0)then     
       if(bad_resistors.and. index(lord%name,'QUAD1_LONG')/=0)then! field_scale * 27.2 = plate voltage, -> field_scale = plate_voltage/27.2
          call bad_resistor_voltages(quad_time, q1lbottom, q1ltop)  !seconds, kV
          lord%grid_field(igrid+6)%field_scale = q1ltop/27.2 * 100
          lord%grid_field(igrid+4)%field_scale = q1lbottom/27.2 * 100
       else
          lord%grid_field(igrid+6)%field_scale = (1 + focus_scrape_scale - steer_scrape_scale) * ele_init%grid_field(igrid+6)%field_scale  !top   - in 821, focus_scrape_scale +steer_scrape_scale = 0.
          lord%grid_field(igrid+4)%field_scale = (1 + focus_scrape_scale + steer_scrape_scale) * ele_init%grid_field(igrid+4)%field_scale  !bottom - 821,   focus_scrape_scale - steer_scrape_ scale = 22.7/32. (at t=0)
       endif
       

    elseif(index(lord%name,'QUAD2') /= 0)then
     lord%grid_field(igrid+6)%field_scale = (1 + focus_scrape_scale - steer_scrape_scale) * ele_init%grid_field(igrid+6)%field_scale  !top
     lord%grid_field(igrid+4)%field_scale = (1 + focus_scrape_scale + steer_scrape_scale) * ele_init%grid_field(igrid+4)%field_scale !bottom
     if(horizontal_scrape)then
        lord%grid_field(igrid+3)%field_scale = (1 + focus_scrape_scale + steer_scrape_scale) * ele_init%grid_field(igrid+3)%field_scale !inner
        lord%grid_field(igrid+5)%field_scale = (1 + focus_scrape_scale - steer_scrape_scale) * ele_init%grid_field(igrid+5)%field_scale !outer
     else
        lord%grid_field(igrid+3)%field_scale = ele_init%grid_field(igrid+3)%field_scale !inner
        lord%grid_field(igrid+5)%field_scale = ele_init%grid_field(igrid+5)%field_scale !outer
     endif       
    elseif(index(lord%name,'QUAD3') /= 0)then
     lord%grid_field(igrid+6)%field_scale = (1 + focus_scrape_scale - steer_scrape_scale) * ele_init%grid_field(igrid+6)%field_scale ! top
     lord%grid_field(igrid+4)%field_scale = (1 + focus_scrape_scale + steer_scrape_scale) * ele_init%grid_field(igrid+4)%field_scale ! bottom
    elseif(index(lord%name,'QUAD4') /= 0)then
     lord%grid_field(igrid+6)%field_scale = (1 + focus_scrape_scale - steer_scrape_scale) * ele_init%grid_field(igrid+6)%field_scale !top
     lord%grid_field(igrid+4)%field_scale = (1 + focus_scrape_scale + steer_scrape_scale) * ele_init%grid_field(igrid+4)%field_scale !bottom
     if(horizontal_scrape)then
        lord%grid_field(igrid+5)%field_scale = (1 + focus_scrape_scale + steer_scrape_scale) * ele_init%grid_field(igrid+5)%field_scale !outer
        lord%grid_field(igrid+3)%field_scale = (1 + focus_scrape_scale - steer_scrape_scale) * ele_init%grid_field(igrid+3)%field_scale !inner
     else
        lord%grid_field(igrid+5)%field_scale =  ele_init%grid_field(igrid+5)%field_scale !outer
        lord%grid_field(igrid+3)%field_scale =  ele_init%grid_field(igrid+3)%field_scale !inner
     endif
    endif
  endif  ! scraping on, set quad voltages

  if(rf_h_field_scale /= 0)then
       lord%grid_field(igrid+5)%field_scale = lord%grid_field(igrid+5)%field_scale + rf_h_field_scale
       lord%grid_field(igrid+3)%field_scale =lord%grid_field(igrid+3)%field_scale - rf_h_field_scale
   endif
   if(rf_v_field_scale /= 0 )then
      lord%grid_field(igrid+6)%field_scale = lord%grid_field(igrid+6)%field_scale + rf_v_field_scale
      lord%grid_field(igrid+4)%field_scale =  lord%grid_field(igrid+4)%field_scale  - rf_v_field_scale
   endif
  
   return
 end subroutine time_dep_quad_field