1. Moving Solid Walls Type of Moving Walls: 1- Solid pebbles falling down under gravity for intercepting ion and X-ray radiation. 2- Moving metallic surfaces.

2. Moving Solid Pebble Beds History: There have not been any previous IFE designs employing moving solid pebble beds exposed to the target emanations. Method: Solid pebbles are allowed to fall under gravity intercepting ema- nations from the target such as ions and x-rays. After going through the chamber the particles are taken through a heat exchanger for energy extraction and then returned to the chamber for more passes. Issues:Concave surfaces in the chamber would be difficult to protect since particles cannot follow concave geometry such as the chamber roof Accommodating beam ports would be difficult. Electro-statically levitated dust particles could deposit on optics, intercept beams and deposit on targets during injection. Ensuring uniform coverage would be difficult. A separate system is needed for the blanket for breeding and energy recovery which adds to cost and complexity

3. Moving Solid Metallic Surfaces History: There have not been any previous designs that have proposed moving metallic surfaces as first wall armor. Method: The first wall is covered with vertically moving flexible belts supported on rotating drums which absorb the target emanations from several shots then radiate the energy to a cooled surface in the back. A series of vertical cylinders covering the first wall which rotate, being exposed to the target on one side then rotating to radiate the energy to a cooled surface in the back.

4. Solid Moving Belt Required Geometry: The chamber must consist of a cylindrical mid-section with conical ends. Three system of belts are required, one covering the mid-section, and two covering each conical section How they operate. The belts must be flexible, made of links, and must be not trans- parent to visible radiation.They move vertically up or down, are exposed to radiation facing the target then dissipate the energy in the back to cooled surfaces. Issues: Long survival of such a belt in these conditions is doubtful. Covering the conical ends of the chamber is difficult. Having motors in close proximity to the chamber is a problem Many moving surfaces and crevices from the belts would provide problems of friction and make evacuation of the chamber very difficult if at all possible Large metallic surfaces in front of the first wall will impede breeding.

5. Rotating Cylinders Required Geometry: The same as in the case of moving belts. How they operate: Vertical solid metallic cylinders surround the chamber at mid-section and at the conical ends. At the conical ends the cylinders must be interweaved with each other to accommodate the restricting geometry. Cylinder rotation exposes one side to the target emanations, then radiates the energy to a cooled surface in the back. Issues: As in the case of moving belts problems of friction and evacuation exist, although survivability is considerably better than in moving belts. Motors are also needed for driving the cylinders. Large metallic surfaces in front of the first wall will impede breeding.

6. Liquid Walls History: There have been several IFE reactor designs utilizing liquid walls: 1- HYLIFE: Thick liquid walls of about a meter, oscillating to provide protection for the roof. 2- HIBALL: Flexible woven metallic tubes covering the cylindrical portion of the chamber with liquid flowing in the tubes providing a wetted surface on the tubes. Coverage of the roof is a difficult problem.

7. Wetted Walls A wetted wall chamber can be designed with a porous surface which oozes a coolant such as LiPb at a rate con- sistent with the evaporation rate. With the proper design, the roof can be made to condense a thin layer of evaporated material, which is vaporized on the next shot, thus providing roof protection. As in any other liquid wall design there are issues: Preventing condensation on optics. Evacuating the chamber between shots Splashing, or dripping. Protection of beam ports.

8. Wetted Walls contd Assuming a 10 m radius chamber using a wetted wall of LiPb. A 350 MJ target, of which 90 MJ are in ions and x-rays. Using the whole surface area, about 29 kg of material is evaporated per shot, a depth of 2.5 microns, raising the pressure in the chamber by 10 -6 torr. Assuming issues of wetted walls listed in the previous view-graph can be resolved, this may be a viable solution.