Neutral Beam Armor for NSTX Upgrade

The National Spherical Torus Experiment (NSTX) is a low aspect ratio, spherical torus (ST) configuration device which is located at Princeton Plasma Physics Laboratory (PPPL). This device is presently being upgraded to enhance its operations by adding a second Neutral Beamline (NBL). This change will nearly double the power available to the plasma but necessitate improvements to other design aspects of NSTX. Included in these upgrades are the relocation and upgrade of the NSTX Neutral Beam Armor to capture both sets of beamline source profiles while maintaining the same level of vacuum vessel wall protection.

In order to minimize the space required to accomplish this, it has been proposed to relocate and reuse the existing armor array, improving the design so that two overlapping sets of beam profiles both fit completely. This beamline overlap could possibly cause the armor tiles to experience higher heat fluxes which translate into higher internal mechanical stresses. This would be mitigated by changing the isotropic graphite (ATJ) tiles in the overlap areas to a rugged 3D carbon-fiber composite (CFC) material, capable of handling thermally-induced stresses. Additional benefits to this recycling design proposal include opportunities to reduce project cost, increase diagnostic port access, and improve an awkward and difficult mounting scheme.