Studying matter at conditions found nowhere else on Earth
Z provides the fastest, most accurate, and most affordable method to determine how materials will react under high pressures and temperatures, characteristics that can then be expressed in formulas called equations of state. Combining theoretical simulations with laboratory work, Sandia researchers are able to perform more precisely than ever before. Exposing targets to the high power levels of Z also allows scientists to study extreme states of matter, such as plasmas, and it may produce unexpected reactions and generate responses of great interest to many areas of science.
Fusion research on Z contributes to broad scientific insight. Since near-perfect symmetry in a target capsules’ implosion is necessary to ignite fusion (so the particles implode evenly and are evenly balanced), a persistent challenge in fusion science has been to heat the target correctly. Both the capsule and container holding the target work together to produce the desired outcome, and their configurations and interactions have been the focus of intense theory and experimentation.
Diamond, for example, has been the object of much study as a potential capsule material. Z has so much energy that it can melt diamond, and in melting diamond to a puddle, Z scientists have been able to understand the material’s various states – from solid to liquid, with a mixed state in-between. Thanks to Z, researchers now have a better understanding of the mixed state, which is not ideal to ignite a fusion reaction.
Beyond the fabrication and careful design of fusion targets, achieving fusion requires work on many other interdependent elements, which include the mechanisms for delivering power to a target, detailed diagnostics for experiments, and computer codes to understand and then predict what the diagnostics revealed. Tests conducted on the Z machine are very useful for testing and refining those codes. Fusion is conducted in extremely complicated systems that involve radiation dynamics and high densities and temperatures that are only seen in the center of stars.
How does the Z machine work?
The Z machine uses electricity to create radiation and high magnetic pressure, which are both applied to a variety of scientific purposes ranging from weapons research to the pursuit of fusion energy.
The process starts with wall-current electricity, which Z uses to charge large capacitors — structures designed to store an electric charge and release it instantaneously. In every shot the machine consumes only about as much energy as it would take to light 100 homes for a few minutes. Metal cables arranged like the spokes of a wheel connect the capacitors to a central vacuum chamber, 10 feet in diameter and 20-feet high. The cables, some insulated by water and some by oil, are each as big around as a Volkswagen Beetle and 30-feet long.
When the accelerator fires, powerful electrical pulses strike a target at the center of the machine. Each shot from Z carries more than 1,000 times the electricity of a lightning bolt, and is 20,000 times faster. The target is about the size of a spool of thread, and it consists of hundreds of tungsten wires, each thinner than a human hair, enclosed in a small metal container known as a hohlraum (German for hollow space). The hohlraum serves to maintain a uniform temperature.
The flow of energy through the tungsten wires dissolves them into plasma and creates a strong magnetic field that forces the exploded particles inward. The speed at which the particles move is equivalent to traveling from Los Angeles to New York – about 3,000 miles – in slightly less than one second. The particles then collide with one another along the z axis (hence the name Z machine), and the collisions produce intense radiation (2 million joules of X-ray energy) that heats the walls of the hohlraum to approximately 1.8 million degrees Celsius.
Instruments that measure these implosions must be even faster in order to record the details of the process. This is an added challenge for researchers who rely on the accuracy of these measurements to understand Z's results and nuclear events in general. Accurate measurements allow scientists to experiment with a variety of target arrangements to create conditions useful for many different purposes.