Resistive Heating in Radial Geometry Diamond Anvil Cell

High temperature and pressure experiments are important for understanding deep Earth geodynamics. Radial x-ray diffraction from samples under high pressure within a diamond anvil cell(DAC) provide information on lattice strain and crystallite preferred orientation. Understanding the development of crystallographic preferred orientation is essential for identifying deformation mechanisms as well as assessing anisotropy of bulk physical properties. Many high pressure radial diffraction experiments in the diamond anvil cell are performed at room temperature. For high temperatures, laser heating can be used but this technique produces large temperature gradients. Resistive heating provides a more homogeneous temperature distribution and covers the inaccessible low temperature range (<~1400K) of laser heating. Another advantage of this technique is stability, allowing long time period in-situ temperature experiments to be possible. Applying both heating techniques simultaneously covers a wider temperature range while minimizing temperature gradients. We are developing a resistive heating system for diamond anvil cells in radial geometry (rDAC) at beamline 12.2.2 of the Advanced Light Source (ALS) of Lawrence Berkeley Laboratory to recreate deep Earth deformation conditions. The design is based on a previous one by Due et al., in revision. The heater is laser-milled from high-purity solid graphite, and designed to fit slightly displaced from the diamond culets. Due to the low inherent resistivity and small size of the graphite heater, 6x3x0.5mm, we can achieve temperatures at the cullet of 300 to >1300 K at relatively low power loads of ~ 200 watts. The laser machining produces very uniform heater geometry which allows us to obtain reproducible temperatures in the rDAC. The assembly is modular and self supporting which allows for ease of assembly a requirement if users are to install the heater in a cell themselves. We are currently applying this technique to study lattice preferred orientation changes during phase transformations. We study the transformation of coesite and stishovite that occurs in the deep crust, and olivine transforming to ringwoodite and then to magnesiowuestite and perovskite in the lower mantle.