Our Facilities

Shock Loading Apparatus

We operate three main tools for launching projectiles and generating shock-loading:

a) 40 mm propellant gun

b) 90 mm/25 mm light gas gun

c) 20 mm propellant gun (mostly used for recovery experiments)

The 40 mm apparatus (a) is used for low-pressure (≤50 GPa) equation of state and sound velocity experiments. For most minerals shock pressures of ~30 to 40 GPa can be produced by the direct impact of Ta or W flyer plates; for metallic targets pressures can exceed 50 GPa. This gun launches ~90 g projectiles at speeds of 0.01 to 2.6 km/sec with a compressed gas or propellant breech. Projectile velocity is measured to ± 0.5% using timed laser beam obscuration and flash radiometry methods. Recent upgrades to this gun include a much more precise three-laser beam interrupt system and better flash illumination of reflective targets. The output of the laser signals is suitable for use with an up-down counter to provide a precise non-contact trigger for detectors in pre-heated shots. The 90 mm/25 mm two-stage light gas gun (b) launches 15-25 g projectiles to velocities of up to 7.6 km/sec. Impact of Ta-faced projectiles induces shock pressures of up to ~250 GPa in minerals and up to ~400 GPa in metals, much higher than the pressure range of interest for this work.

Both guns (a) and (b) have evacuated impact chambers where measurements of projectile velocity, shock velocity, particle velocity profiles, or shock (or postshock) temperatures are conducted. Both these guns share a new high-throughput vacuum pumping system that can bring them down to ~65 mTorr in a couple hours. These guns are serviced with a traveling 10-ton bridge crane. Instrumentation shared by the two large guns (a) and (b) include (1) a Hadland Imacon, Model 790, Image Converter Streak Camera with high-speed plug-in unit, which writes over a 75 mm streak length onto a custom-built large-format CCD for streak durations ranging from 200 ns to several us. (2) A new multi-channel Photonic Doppler Velocimeter (PDV) system for simultaneous velocity history measurements at up to 16 points (using time-domain multiplexing) by direct of interference tunable infrared lasers recorded on 25 GHz analog bandwidth digital scopes; (3) A six-channel optical pyrometer for measurement of shock and postshock temperatures, with neutral density filters for optimal tuning of dynamic range to achieve sensitivity from ~2000 to over 9000 K. The pyrometer can also be used in single-channel mode to record as many as six optical analyzer intensity records. Supporting instrumentation includes synchronized flash xenon illumination, at least 16 channels of 2.5 Gs/s and 8 channels of 80 Gs/s high-speed digitizing oscilloscopes.

For the purpose of carrying out equation of state experiments on preheated silicates, we use a Lepel 10 kW radiofrequency induction heating power supply. This apparatus allows heating targets to over 2000 °C in both the 40 mm and 2-stage light gas gun system, as well as in a small vacuum test tank for rapid pump-down and easy-access, monitored by two-color optical pyrometer.

All recovery operations are conducted on the 20-mm propellant gun or flat-plate accelerator. Flyer plates are mounted on 3D-printed plastic sabots and launched by a gunpowder charge. Calibration of gunpowder charge to projectile mass ratio vs. projectile velocity over a shot history extending to over 1500 shots enables accurate a priori estimation of impact velocity, which is also measured to ±1% by dual laser interrupt. Recovery chambers are attached to the muzzle with nylon screws that break off after impact. Chambers may be sealed or vented; vented chambers may be pumped to vacuum or back-filled with controlled atmosphere composition. Suitable precautions are taken to dissipate the kinetic energy of impact and eliminate the risk of fire. Recovered chambers are machined open by on-campus machine shops, using suitable precautions against sample heating during cutting. All the necessary cabling and scopes for recording signals from embedded piezoresistive gauges are available on this gun.

The shock wave lab employs two full time technicians and a staff scientist. Stable long-term employment and on-the-job learning and training of this technical staff have been and continue to be essential to the quality of operations and data that we generate. Many expendable parts (as well as several permanent accessories) are manufactured in-house by the Caltech Aeronautics machine shop, by nearby contract machine shops to specifications prepared by our senior technician, or 3D printed in-house.

Caltech Sample preparation and characterization facilities

The experimental petrology facilities used to synthesize and characterize sample materials include:

1) Three piston-cylinder devices (to 3.5 GPa), cubic multi-anvil device (to 6 GPa), octahedral multi-anvil device (to 25 GPa, 2300 °C). Two internally-heated pressure vessels (to 0.5 GPa). Two TZM rapid-quench cold-seal furnaces (to 200 MPa, 1300° C). Four 1-atm Deltech furnaces with gas-mixing and fO2 control. Numerous muffle furnaces. Diamond anvil cells with gas loading (to >100 GPa). One of the piston-cylinder devices will be used to prepare aggregate targets for this work. All necessary pressure vessels, pistons, O-rings, thermocouple wire stock, pressure media, insulators, etc. are stocked and available for this work.

2) Sample preparation facilities: rock saws, jaw-crushers, shatterbox, disc grinders, polishing equipment; Pellet pressures with dies of various sizes for consolidating powder and regolith targets; sieves, magnetic and heavy liquid separation, and binocular microscopes for mineral separation.

3) Numerous Leica and Nikon petrographic microscopes equipped with high-definition digital still and video cameras and image acquisition software.

3) Electron microprobe (JEOL field-emission JXA iHP200F): light element capabilities, high-intensity spectrometer crystals, SDD EDS detector, cathodoluminescence camera, X-ray mapping software. Probe for EPMA software for data reduction.

4) Field-emission LEO 1550VP Scanning Electron Microscope: thin-window Si-drift EDS X-ray analyzer, HKL electron backscatter diffraction detector. Aztec software for data visualization and reduction.

5) Panalytical Zetium Wavelength-dispersive XRF spectrometer with preparation equipment for fused beads (Claisse Eagon 2 fluxer), for pellet samples, and for Loss on Ignition. XRF spectrometer features automated sample handler and integrated software system for routine whole-rock analyses of major elements and a number of trace elements down to detection limits of ~1 ppm.

6) Bruker Tornado M4 mapping XRF spectrometer.

7) Transmission Electron Microscope (Caltech Engineering Division): Tecnai TF20 and TF30 TEMs, supported by ORION NanoFab Helium, Neon & Gallium and ThermoFisher NOVA 600 FIBs.

8) Nicolet Magna 860 FTIR system for 10000 to 50 cm-1; NICplan IR microscope and IR polarizers.

9) Renishaw M1000 Micro Raman Spectrometer: dual lasers (514.5 and 782 nm).

10) Two ion probes: Cameca NanoSIMS 50L for high spatial resolution (to 10 nm) elemental and isotopic analysis, Cameca IMS 7f-geo for high precision analysis (to ~30 um). Ultra low-blank volatile analysis (H, C, S, Cl, F) on both instruments.

11) Laser-ablation ICP-MS (Thermo X-series II with New Wave 193 nm laser and New Wave Super Cell sample compartment; helium purge) for routine trace element analyses. Spot sizes to ~5 um; NIST 610-616 standards on hand.

12) Laser-induced Breakdown Spectroscopy (LIBS) (Photon Machines Insight with frequency-quadrupled 1064 nm laser) for rapid semi-quantitative analysis of trace, minor, and major elements of spots down to 20 um.

13) High-resolution solution-source single-collector and multi-collector ICP-MS and conventional TIMS mass spectrometers for isotopic analysis.

14) Gas-source and noble-gas mass spectrometers for stable isotope analysis.