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These devices cover a more limited pressure and temperature range than the DAC (Figure 2.1) but have the advantage of allowing larger volume samples (on the order of a few mm³), longer and more stable heating (via resistive heating), measurement of strain and strain rate, greater variation of grain size, and better control of the stress state (Karato & Weidner, 2008). The D−DIA is a six‐ram cubic type multianvil press. In this configuration, the top and bottom rams are differential, meaning that they can be moved independently of the other four rams (Y. Wang et al., 2003). This allows the user to advance all six rams simultaneously to increase pressure quasi‐hydrostatically. Additionally, by cycling the differential rams, the user can impose differential stress to shorten or lengthen the sample at a near fixed confining pressure. This allows better control of stress state and to some degree allows the user to decouple hydrostatic and deviatoric stresses. The D‐DIA generally operates up to ~10 GPa at 1600 K, but recent efforts using a D‐DIA with a multianvil 6‐6 assembly (a second stage of six anvils in a cubic geometry) has reached conditions as high as 20 GPa and 2000 K (Kawazoe et al., 2010). Tsujino et al. (2016) used a cubic press with a 6‐8 (a second stage of 8 anvils in octahedral geometry) assembly to deform a Brg sample to 25 GPa and 1873 K, by using pistons cut at 45° to induce shear strain. Another approach using the multianvil type apparatus that has proven successful is a 6–8 Kawai type multianvil assembly that has been modified with a pair of differential rams and is called the differential T‐CUP or DT‐CUP (Hunt et al., 2014). The 6‐8 multianvil design compresses an octahedral sample assembly and due to better support of the anvils can reach significantly higher pressures than a cubic (DIA) type press. Using a so‐called broken anvil design, the DT‐CUP has been used to successfully perform deformation experiments to 24 GPa and ~1800 K (Hunt & Dobson, 2017).

The Rotational Drickamer Apparatus (RDA) is an opposed anvil device, where one anvil has the capability to rotate. Pressure and compressive stress are increased by advancing the anvils. When the desired pressure is reached, large shear strain can be induced by rotation of the anvil (Yamazaki & Karato, 2001a). The RDA can reach P‐T conditions of the upper lower mantle ~27 GPa at ~2100 K (Girard et al., 2016). The main advantages of the RDA are that it can reach higher pressures than other large‐volume techniques and can reach high shear strains. However, the RDA is limited to smaller samples than the above multianvil techniques and also has larger temperature and pressure gradients. Due to the fact that deformation is induced by rotation of the anvils, the RDA also has large strain gradients across the sample, though this is somewhat alleviated by using a doughnut‐shaped sample. Generally speaking, the large volume apparatuses are far superior to the DAC in terms of measuring rheological properties but lack the pressure range available in the DAC, and thus, currently these two types of techniques are complementary for understanding deformation of lower mantle phases.