4.7 define_solenoid

• description: Define solenoid coils, from which static magnetic fields will be computed and imposed on the particle motion. The define_solenoid command permits defining a solenoid with a specified length, radius, symmetry, and current/field.
• example:
  &define_solenoid  
     radius = 0.05,  
     z_start = 0.01, z_end = 0.02,  
     current = 1,  
     Bz_peak = 1,  
     turns = 100  
  &end

  This command defines a 100-turn solenoid extending longitudinally between coordinates 1cm and 2cm, at a radius of 5cm. The current, initial 1A, is adjusted to obtain a peak on-axis longitudinal B field of 1Tesla.

• synopsis and defaults:
  #namelist define_solenoid  
          double radius = 0;  
          double evaluation_radius_limit = 0;  
          double z_start = 0;  
          double z_end = 0;  
          double current = 0;  
          double Bz_peak = 0;  
          long turns = 1;  
          long symmetry = 0;  
          STRING field_output = NULL;  
          long bucking = 0;  
          double z_buck = 0;  
  #end

• details:
  • radius: The radius of the coils in meters.
  • evaluation_radius_limit: The maximum radius in meters at which the solenoidal fields should be computed. This can save considerable CPU time if you are not interested in particles that go beyond a certain radius (e.g., you know they’ll be lost).
  • z_start, z_end: The starting and ending longitudinal coordinate of the coils, in meters.
  • current: The current in each coil in Amperes (not Ampere-turns).
  • Bz_peak: The peak on-axis longitudinal magnetic field in Tesla desired from this solenoid. The current is scaled to achieve this value. Even if you give this value, you must give an initial value for current.
  • turns: The number of turns (or coils) in the solenoid.
  • symmetry: Either 0, 1, or -1 for no symmetry, even symmetry, or odd symmetry. For codes of ±1, the resulting fields are those produced by the combination of the specified solenoid and another identical solenoid extending from -z_start to -z_end. If symmetry is 1 (-1), the field from the mirror solenoid adds to (subtracts from) the field due to the specified solenoid.
  • field_output: Requests output of the solenoid field to an SDDS file. This output is accumulated field from all solenoids defined up to this point, including the solenoid presently being defined.
  • bucking: If nonzero, indicates that this is a bucking solenoid. The solenoid current is adjusted to zero the on-axis value of B_z at z_buck.
  • z_buck: If bucking is nonzero, the location at which the field is bucked.

Here is an example of using three define_solenoid commands to make a solenoid field with a peak on-axis B_z value of 0.3T that is bucked to zero at z = 0. The main solenoid field is produced by two sets of windings with a ratio of 10:1 between the current: