T-CUP: A New High-Pressure Apparatus for X-ray Studies. M. T. Vaughan, D. J. Weidner, Y. B. Wang, J. H. Chen, C. C. Koleda, Center for High Pressure Research, SUNY, Stony Brook, NY, 11794, and I. C. Getting, University of Colorado, Boulder, CO, 80309

We have designed and tested a new apparatus for in-situ x-ray diffraction studies under high pressures and temperatures. The apparatus is a two-stage multi-anvil; the first stage is a steel cylinder split into six parts enclosing a cubic cavity (19.5 mm edge length with the [111] axis of the cube vertical) which contains the second stage anvil assembly. The second stage consists of eight 10 mm edge length WC or polycrystalline diamond cubes, separated by spacers. Each cube has one corner truncated into a triangular face; the eight truncations form an octahedral cavity in which the pressure medium is compressed.

The cell assembly is an octahedron made of semi-sintered MgO or boron-epoxy. The incident x-ray beam passes through the gaps between the WC cubes in the [110] direction of the eight-cube assembly and diffracts parallel to one of the (100) planes, through gaps between the WC anvils, with a diffraction vector 35.3deg. from the vertical plane. A special holder is built for a solid-state detector for energy dispersive measurements at several 2[theta] angles.

24 GPa can be routinely achieved in 6-8 high pressure systems such as the USSA-2000 at Stony Brook, using 36 mm edge length tungsten carbide second stage anvils. Typically, these pressure are obtained at 800 tons of loading force on a system with 2 mm truncations on the WC anvils. The challenge of the T-Cup system is to achieve comparable pressures with a limit of 200 tons of loading force. The system should be optimized to provide maximum pressurizing efficiency while minimizing anvil failure. We have conducted several tests of pressure generating capacity for three different anvil designs.