subroutine which_ibms_fiber(ibmsNum, orb, fiber, thickness)

use bmad
implicit none
type (coord_struct) orb
 
 integer ibmsNum, fiber
 integer i

 real(rp) xfiber(1:16)/-0.0225,-0.0195,-0.0165,-0.0135,-0.0105,-0.0075,-0.0045,-0.0015,0.0015,0.0045,0.0075,0.0105,0.0135,0.0165,0.0195,0.0225/
 real(rp) yfiber(-3:3)/-0.039,-0.026,-0.013,0.,0.013,0.026,0.039/
 real(rp)  radius/0.00025/
 real(rp) delta
 real(rp) thickness

 ! initialize harp positions

 fiber = 0
 thickness = 0
  if(ibmsNum == 3)then
    do i=1,16
        delta = orb%vec(1) - xfiber(i)
         if(abs(delta) < radius)then
            fiber = i
            thickness = 2*sqrt(radius**2 - delta**2)
            exit
         endif
      end do
   endif
   
  return
 end subroutine