lcls_gun_solenoid: solenoid, 
  L = 0.45,
  tracking_method = time_runge_kutta,  mat6_calc_method = tracking, 
  field_calc = fieldmap, 
  grid_field = call::lcls_gun_solenoid.h5
 ! aperture_at = continuous, aperture_type=wall3d,
 ! wall = {section={s=0, v(1) = {0, 0, 0.012}}, section={s=0.45, v(1)={0, 0, 0.012}} }

lcls_gun_solenoid[grid_field(1)%master_parameter] = bs_field
lcls_gun_solenoid[grid_field(1)%ele_anchor_pt] = center