Sample Problem: Cylindrical Hohlraum at OMEGA

Setting Up the Grid

This sample problem includes several features and tools in VISRAD designed to facilitate target grid setup:

• Using a Stalk object with a TIM-based target mount
• Using clipping volumes to build a cylindrical hohlraum with a flat surface region
• Use of the Orientation Angles Calculator
• Use of the Coordinate Transformation Tool
• Use of the Line-Target Intersection Points Tool
• Use of the Port Positions Dialog
• Use of the Set Viewing Parameters Dialog

In this example, we set up a hohlraum for the OMEGA target chamber with the following characteristics:

• The hohlraum is aligned along the P6-P7 axis
• The hohlraum cylinder is mounted to a stalk originating from TIM #1
• A flat region is cut into the side of the hohlraum
• A backlighter is located above the flat region on the side opposite from TIM #5
• A hole is cut into the hohlraum to provide a line-of-sight that passes through TIM #5, the flat region, and the center of the backlighter.
• The hohlraum wall is viewed through one of the LEHs with Dante.

Step-by-step instructions for setting up a hohlraum target are:

• Set up the cylindrical hohlraum
• Attach the hohlraum to the TIM #1 target mount
• Add a flat rectangular surface on the side of the hohlraum
• Insert inner shields inside the hohlraum
• Attach a backlighter to TIM #2 target mount
• Cut a hole in the hohlraum along the TIM #5 / Backlighter axis

The images below shows the target after all of the steps is completed. Left: TIM #5 view. Center: Dante view. Right: X-TVS view.

Cylindrical Hohlraum Setup

The hohlraum cylinder will serve as the reference coordinate system for other target components. Doing this, all of the components will stay attached to the hohlraum if its Position or Orientation Angles change.

• Add a Cylinder object aligned along the the P6-P7 axis:
  • Set the name to "hohlraum_cylinder".
  • In the Position tab:
    • Set the Reference Coordinate System to the P6 Port Axis.
  • In the Size/Gridding tab:
    • Set the Radius to 0.08 cm, the Length to 0.16 cm, and R-Corner to 0.01 cm.¹
    • Set the number of grid points to 21 along the z-axis, 24 in the azimuthal direction.
    • Set the Surface Normals to In.²
• Add open disks at the top and bottom of the hohlraum.
  • Add a Disk object at the top of the hohlraum.
    • Set the name to "hohlraum_top"
  • In the Position tab:
    • Set the Reference Coordinate System to that of the Target Component "hohlraum_cylinder".
    • Set z = 0.08 cm (half the hohlraum length).
  • In the Size/Gridding tab:
    • Set the Outer Radius = 0.07 cm, Inner Radius = 0.06 cm.
    • Set the number of grid points to 3 in the radial and 24 in the azimuthal.
    • Set the Surface Normals to Down.
  • Add a Disk at the bottom of the hohlraum by duplicating the top disk.
    • Right-click on "hohlraum_top" in the Target Components List and select Duplicate. A new object called "hohlraum_top_2" appears in the list. Edit this object.
    • Set the name to "hohlraum_bottom".
    • In the Position tab:
      • Set z = -0.08 cm.
    • In the Size/Gridding tab:
      • Set the surface normals to Up.

Attach the Hohlraum to the TIM #3 Target Mount

Let's assume we want to mount the stalk to the hohlruam cylinder 300 microns from the bottom end of the cylinder. To do this, we first attached the bottom of the stalk to the hohlraum using the hohlraum's coordinate system, and then reverse the coordinate system referencing.

• Add a Cylinder object for the stalk, attached to the "hohlraum_cylinder", and pointed toward TIM #1.
  • Set the name to "stalk_TIM1"
  • In the Position tab:
    • Set the Reference Coordinate System to that of the Target Component "hohlraum_cylinder".
    • Set the Coordinate System to Cylindrical, and Set Position Of to Bottom.
    • Check the Port Positions Dialog to get the angles to TIM #1 (Diagnostic Port P3) in the Reference Coordinate System of the "hohlraum_cylinder". They are θ_port = 116.57,φ_port = 144.00.
    • Set r = 0.08 cm (the radius of the hohlraum), z = -0.05 (500 μm from midplane, 300 μm from bottom end), and φ = 144.00 (= φ_port).
    • Compute Orientation Angles: Get direction vector from Start point at position of stalk bottom (r = 0.08 cm, z = -0.05, φ = 144.00 in hohlraum_cylinder coord. system) to the End point at the center of port P3 (x = 0, y = 0, z = 164 cm in Port P3 coord. system. (Notes: OMEGA target chamber radius = 164 cm; 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).) The computed values are: Polar angle = 116.57, Azimuthal angle = 144.00.
  • In the Size/Gridding tab:
    • Set the Radius to 0.01 cm, the Length to 2 cm.
    • Set the number of grid points to 21 along the z-axis, 12 in the azimuthal direction.
    • Set the Surface Normals to Out.
• Reverse the coordinate system referencing so that the "stalk_TIM1" is mounted to TIM #1.
  • In the Object Parameters Dialog, check the box at the bottom of the Position tab ("Automatically update...").
  • For "stalk_TIM1", change the Reference Coordinate System to TM-TIM1 under the Target Chamber/Mount button. The Position and Orientation Angles are automatically updated such that "stalk_TIM1" maintains the same physical position. Hit the Apply or OK button (in the Main Graphics Frame, the stalk should not move).
  • For the "hohlraum_cylinder", change the Reference Coordinate System to "stalk_TIM1" under the Target Component button. Hit the Apply or OK button (again, the "hohlraum_cylinder" should not move).
  • The hohlraum is now mounted to TIM #1 Target Mount. The allows the target to be manipulated in the Target Positioning Viewer using the Target Positioner controls.
  • Designate "stalk_TIM1" to be a Stalk object (this provides stalk positioning parameters for the Target Positioning Viewer).

At this point, the target, as viewed from the X-TVS (left) and Y-TVS (right) are shown below.

Add a Flat Rectangular Surface on the Side of the Hohlraum

Add a flat surface (of length 800 μm) on the side of the hohlraum, and position it such it can be backlight along the H7-H14 (TIM #5) axis. Put the flat on the H7 side.

• Check the Port Positions Dialog to get the angles to Diagnostic Port H7 in the Reference Coordinate System of the "hohlraum_cylinder". They are θ_port = 100.81, φ_port = 108.00.
• Clip the hohlraum at its middle (z = 0) and φ_port = φ_port.
  • Right-click on "hohlraum_cylinder" in the Target Components List and select Clip. Select a Box clipping volume.
  • In the clipping volume Positions tab, use the "hohlraum_cylinder" as the Reference Coordinate System.
  • Set the Coordinate System to Cylindrical, and set r = 0.09 cm,³ z = 0, and φ = 108 (= φ_port).
  • Set Polar angle = 0, Azimuthal angle = 108 (= φ_port).
  • Hit the Apply button, and display the clipping volume (menu item Show | Clipping Volumes).
  • In the Size tab, set x = 0.04 cm, y = 0.2 cm, z = 0.08 cm.
• Add a Rectangle where the surface has been removed.
• Set the name to "flat", and change the color to readily distinguish it from the hohlraum.
• In the Position tab:
  • Uncheck the box at the bottom ("Automatically update...")
  • Set the Reference Coordinate System to that of the Target Component "hohlraum_cylinder".
  • Set the Coordinate System to Cylindrical.
  • Set r = 0.07 cm, z = 0, and φ = 108 (= φ_port).
  • Set Polar angle = 90, Azimuthal angle = 108 (= φ_port).⁴
• In the Size/Gridding tab:
  • Set x = 0.08 cm and y = 0.07746 cm.⁵
  • Set the Surface Normals to Down.²

Insert Inner Shields Inside the Hohlraum

Add open disk shields on the inside of the hohlraum at the edges of the "flat".

• Add a Disk object and set the name to "inner_shield_top".
  • In the Position tab:
    • Set the Reference Coordinate System to that of the Target Component "hohlraum_cylinder".
    • Set z = 0.04 cm.
  • In the Size/Gridding tab:
    • Set the Outer Radius = 0.079 cm,⁶ Inner Radius = 0.05 cm.
    • Set the number of grid points to 6 in the radial and 24 in the azimuthal.
    • User a non-zero wall thickness of 0.001 cm.²
• Add a second shield by duplicating "inner_shield_top".
  • Right-click on "inner_shield_top" in the Target Components List and select Duplicate. A new object called "inner_shield_top_2" appears in the list. Edit this object.
  • Set the name to "inner_shield_bottom".
  • In the Position tab:
    • Set z = -0.04 cm.

Attach the Backlighter to Stalk from TIM #2

Place a disk backlighter foil a distance 3.8 mm from target chamber center (about 3 mm above the "flat") toward Port H7 (away from TIM #5).

• Add a Disk object for the backlighter.
  • Set the name to "backlighter foil".
  • In the Position tab:
    • Initially set the Reference Coordinate System to that of the Port Axis H7.
    • Set the Coordinate System to Spherical.
    • Set r = 0.38 cm.
  • In the Size/Gridding tab:
    • Set the Outer Radius to 0.08 cm.
    • Set the Surface Normals to Down.

Add a stalk object for Target Mount TIM #2 to support for the backlighter foil. Attach the stalk to a 1 mm-long wire that extends out of the back of the backlighter foil.

• Add a Cylinder object extending from the back of the "backlighter_foil".
  • Set the name to "BL_wire"
  • In the Position tab:
    • Set the Reference Coordinate System to "backlighter_foil".
    • Set Set Position Of to Bottom.
  • In the Size/Gridding tab:
    • Set the Radius = 0.006 cm and Length = 2 cm.
    • Set the Surface Normals to Out.
• Add a Cylinder object (a stalk) extending from the top of "BL_wire" toward the center of TIM #2 (Port H3).
  • Set the name to "stalk_TIM2"
  • In the Position tab:
    • Set the Reference Coordinate System to "BL_wire".
    • Set the Coordinate System to Cylindrical and Set Position Of to Bottom.
    • Compute Orientation Angles: Get direction vector from Start point at position of stalk bottom (r = 0 cm, z = 0.05, φ = 0 in BL_wire coord. system) to the End point at the center of port H3 (x = 0, y = 0, z = 164 cm in Port H3 coord. system. The computed values are: Polar angle = 70.69, Azimuthal angle = 142.24.
  • In the Size/Gridding tab:
    • Set the Radius = 0.01 cm and Length = 2 cm.
    • Set the Surface Normals to Out.
• Reverse the coordinate system referencing so that the "stalk_TIM2" is mounted to TIM #2.
  • In the Object Parameters Dialog, check the box at the bottom of the Position tab ("Automatically update...").
  • For "stalk_TIM2", change the Reference Coordinate System to TM-TIM2 under the Target Chamber/Mount button. The Position and Orientation Angles are automatically updated such that "stalk_TIM2" maintains the same physical position. Hit the Apply or OK button (in the Main Graphics Frame, the stalk should not move).
  • For the "backlighter_foil", change the Reference Coordinate System to "stalk_TIM2" under the Target Component button. Hit the Apply or OK button (again, the "backlighter_foil" should not move).
  • The backlighter foil and its attached BL_wire are now mounted to TIM #2 Target Mount. The allows the target to be manipulated in the Target Positioning Viewer using the Target Positioner controls.
  • Designate the "stalk_TIM2" to be a Stalk object (this provides stalk positioning parameters for the Target Positioning Viewer).

Cut a Hole in the Hohlraum Along the TIM #5 / Backlighter Axis

Clip the "hohlraum_cylinder" such that there is a clear line-of-sight that extends from TIM #5 (i.e., a point located, say, 30 cm from target chamber center in the direction of TIM #5), through the "flat" on the hohlraum, to the center of the "backlighter_foil".

• Right-click on the "hohlraum_cylinder" in the Target Components List, and select Clip.
• Select a Cylinder clipping volume.
• Use the Line-Target Intersection Points Tool to find the point on the cylindrical hohlraum that is intersected by the TIM #5 / Backlighter line.
  • In the tool, for the Start point, select Port Axis "H14", use a Spherical geometry, and set r = 30 cm (θ = φ = 0).
  • For the End point, select Target Component "backlighter_foil", and use the origin (x = y = z = 0).
  • Press the Update button to generate a list of the intersection points (positions are given in the Target Chamber coordinate system).
  • Select the "hohlraum_cylinder" intersection point and press the Coordinate Transform () button, to bring up the Coordinate Transformation Tool with the "hohlraum_cylinder" intersection point pre-loaded for the Base point position.
  • In the Coordinate Transformation Tool, for the Reference Coordinate System of the New point, select the Target Component "hohlraum_cylinder" and select Cylindrical geometry.
  • Pressing the Update button gives the intersection point position in the coordinate system of the "hohlraum_cylinder" (It is r = 0.0796 cm, z = 0.0152 cm, φ = 288.0 deg).
• In the Clipping Parameters Dialog:
  • In the Position tab:
    • Use the "hohlraum_cylinder" as the Reference Coordinate System, and use a Cylindrical geometry.
    • Enter the position: r = 0.0796 cm, z = 0.0152 cm, φ = 288.0 deg.
    • For the Orientation Angles, enter θ = 90 and φ = 288.0 deg.
  • In the Size tab:
    • Set the Radius to 0.015 cm, the Length to 0.1 cm and Number of Grid Points to 24.
• Select Show | Clipping Volumes menu item to view the cylindrical clipping volume.
• Set the Viewing Parameters to view the target from TIM #5 to check the line-of-sight.
  • In the Set Viewing Parameters Dialog, set the Viewing position to Port H14 (TIM #5).
  • Set the Scene position to the origin of the Target Component "backlighter_foil".

Images of the final target build, as viewed from TIM #5 (wireframe (left) and filled surfaces (right)) are shown below.

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¹ Setting R-Corner to 0.01 cm provides a rounded edge to the cylinder.

² It is important to set the surface normals appropriately for radiation calculations. Surfaces have a preferred orientation, emitting/reflecting light on one side only. To emit/reflect light on both sides, either an object with non-zero thickness must be used (see Size/Grid tab of Object Parameters Dialog), or a second, nearly identical object must be set up which has surface normals facing in the opposite direction.

³ This is the centroid position of the clipping volume box. Since we will use a clipping box with a height of 0.4 cm and place the flat (rectangle) a r = 0.07 cm, the centroid of the clipping box is at r = 0.07 + 0.5*0.4 = 0.09 cm.

⁴ For information on setting the Polar and Azimuthal values, see Specifying Orientation Angles.

⁵ The value of 0.07746 = 2*sqrt( R_hohlraum ² - R_flat ²) = 2*sqrt( 0.08² - 0.07²).

⁶ Using an outer radius slightly less that the hohlraum radius avoids "bleedthrough" in the graphics.