The Shock Compression Laboratory at Harvard: a New Facility for Planetary

Introduction: The Shock Compression Laboratory in the Department of Earth and Planetary Sciences at Harvard is a new facility for the study of impact and collisional phenomena. The following describes the experimental capabilities of the laboratory (Fig. 1). Shockwave experiments. The laboratory contains a 40-mm single stage launch system, manufactured by Physics Applications Inc., capable of accelerating hundred gram projectiles to velocities between 10's m/s to over 2600 m/s and generating shock pressures over 40 GPa. High accuracy over the large range of launch velocities is achieved by using both a 10,000 psi compressed gas (He) breech (10's m/s to ~1.5 km/s) and a powder breech system (~1 km/s to >2.5 km/s). The 40-mm smooth bore barrel (6-m length) is designed for high precision, near-muzzle, planar shock-wave experiments that are required to measure shock Hugoniot states, shock and post-shock temperatures, release isentropes, and dynamic compressive and tensile strength. Shockwave profiles are measured directly with embedded gauges (e.g., PVDF piezoelectric stress gauges or electromagnetic particle velocity gauges). Tektronix 2-GHz digital oscilloscopes resolve the shock loading and unloading profiles to record dynamic strength and phase transformation features within the shock front, as well as the final shock state. The target chamber is evacuated to <100 mtorr to achieve the highest impact velocities, and the projectile velocity is measured to within ±1% by the timing of extinction between cross barrel lasers and shorting pins. Future instrumental capabilities will include shock and post-shock temperature pyrometry and the latest generation multi-beam VALYN Velocity Interferome-ter System for Any Reflector (VISAR). The system will utilize a Coherent solid state laser to provide a high power (5 watts), single frequency (532 nm) source for high fidelity interferometry on low reflectiv-ity rocks and minerals. The VISAR system is expand-able to 7 beams to allow for faithful characterization of heterogeneous samples. Impact cratering and shockwave decay experiments. The launch system also contains a 40-mm rifled barrel (4-m length), which is interchangeable with the smooth bore barrel and capable of generating launch velocities between ~100 m/s to >2.2 km/s. The primary use of the rifled barrel will be downrange impact experiments in a large enclosed range (6 m from the muzzle), where a diverse range of projectile sizes and shapes (up to about 25 mm diameter) are possible using spin separation of the sabot. In this manner, the shock pulse or impact crater from a spherical (or arbitrary shape) projectile may …