Designating Target Components as Stalks

A Cylinder or Cone target component can be designated as a Stalk object.

The purpose of designating an object as a Stalk is to support the use of Target Mounts in the Target Positioning Viewer. This is needed in order to map the position of a target component used to represent a stalk in an experiment (set up in the Main Graphics Window) to the Target Positioner Rotation/Translation controls used in the Target Positioning Viewer. Without this mapping, when the user utilizes a stalk away from TCC (i.e., the axis of the stalk does not point at TCC), the determination of the location of the target mount axis is problematic.

A target component is designated to be a Stalk object by setting its Designation in the Object Parameters Dialog, and using a Target Mount as its Reference Coordinate System. When an object's designation as a Stalk is changed, or when its position changes, the Target Mount translation offsets in the Target Positioning Viewer are automatically updated to be consistent with the stalk's position.

An alternative method for adding a Stalk object at a particular point on a Target Component is to pick on a surface element in the target grid using the Picked Surface Node Positions tool button (). In the Picked Surface Node Positions Dialog, where the node positions, centroid, and unit normal for the surface are shown, select one of the surface element nodes or the centroid position, and click on the Add a Stalk at this Surface button. A dialog showing a list of available Target Mounts is shown, along with a few selected parameters. The new Stalk object is then added to the Target Components List, and can be later edited using the Object Parameters Dialog.

Below are comments on the use of Stalk objects. Note that if not using the Target Positioning Viewer, there is no need to be concerned with Stalk objects. (However, keep in mind that when VISRAD files are supplied to laser facilities, the personnel there may utilize the Target Positioning Viewer with that file.)

• Each Target Mount that is being used as the Reference Coordinate System for any target component must have one (and only one) object designated as a Stalk object.
• A Stalk must be either a Cylinder or a Cone. Its z-axis should be closely aligned with the Target Mount axis (i.e., its axis should point toward the center of the port).
• The position of the Stalk object is used to set default Translation values for the Target Mount in the Target Positioning Viewer.
• Any time there is a change in the position of a Stalk object that is attached to a Target Mount, the Translation values for that Target Mount in the Target Positioning Viewer are set to be consistent with the position of the Stalk object.
• In the Target Positioning Viewer, the Target Positioner "z" translation value defaults to zero and the rotation value is unaffected by the re-positioning of the Stalk object.

The use of support tools, such as the Orientation Angles Calculator, the Line-Target Intersection Points Tool, and the Coordinate Transformation Tool, can facilitate positioning a Stalk object with respect to other target components.

• For example, to attach a Stalk to a particular point on a Hohlraum (e.g., 200 microns from the end of the Hohlraum, and in the direction nearest the port for Target Mount TM-TIM3), a user could:
  • Using the Line-Target Intersection Points Tool, find the position of the intersection of the hohlraum surface and a line extending between the hohlraum center and the center of port H18. (Note that when using a Port as a reference coordinate system, the origin of that coordinate system is at TCC, and the center of the port is at z = R(chamber).)
  • In the Object Parameters Dialog, position the Top end of the stalk at the desired intersection point. One end of the stalk should now be at the correct position.
  • Compute the Orientation Angles, using the position of the top of the stalk for start point, and the port center for the end point. Copy the angles to the Object Parameters Dialog.
  • Check the "Automatically update position..." check box, and in the change the Reference Coordinate System to be that of the hohlraum. Use a cylindrical coordinate system to show the (r,z,φ) values. The r and φ values are now correct. Adjust the z value to be 200 microns from the end of the cylindrical hohlraum.

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