Lab of Plasma Studies
The XP pulse-powered generator delivers a half-million amperes of current in very short pulses for the study of high energy density plasma research. The delivered pulses are around 100 nanoseconds in length, or a 10th of a microsecond pulse. When the pulse is discharged, the power is between 100,000 million and 1,000,000 million watts. Compare that to energy used in a home—a light bulb with a 100-watt power rating uses 100 watts of power for an hour, while XP produces 100,000 million watts for a 10th of a microsecond.
XP’s power comes from charged energy-storage capacitors that are filled with insulating oil and stored in a tank on the generator. A switch causes this power to be delivered into a material or gas located in a small area in the middle of the generator’s experiment chamber. The power causes the material or gas to turn into a plasma, which disappears quickly after a pulse. Researchers use diagnostic devices, such as spectrometers, XUV (eXtreme-UltraViolet) cameras, lasers, and interferometers to collect data on the plasma.
The COBRA (Cornell Beam Research Accelerator) pulse-powered generator is like four XP machines in parallel. It delivers one million amperes of current in short bursts that last around 100 nanoseconds in length. Like the XP, the power generated by the short pulse is between 100,000 million, and 1,000,000 million watts. COBRA has two tanks filled with insulating oil that hold energy-storage capacitors to deliver the pulsed-power. Researchers use several diagnostic devices to study the plasma, including 2 spectrometers, a streak camera, several recording instruments, x-ray sources, and lasers. Data from these devices are sent to a computer that researchers can easily review.
Plasmas include atoms and ions (charged particles) in excited electronic states that emit light. Spectrometers are used by researchers to discover what atoms and charged particles are present in a plasma. Researchers in the lab use spectrometers to split the wavelengths of the emitted light. The wavelengths are unique to each atom or ion present in the plasma. Plasma spectroscopy is one of the most established and oldest tools in astrophysics and plasma physics.
All plasmas have a corona, an aura that surrounds the matter. The most commonly known corona is the sun’s, which reaches millions of kilometers into space. The plasmas created and studied in the lab are much smaller and last for a short period of time. XUV (extreme-ultraviolet) cameras take images of coronal plasma in the lab using high energy ultraviolet light.
The laser backlighter is used on COBRA to produce 150 picoseconds (one picosecond is one trillionth of a second) laser shadowgraph images. These images provide a valuable picture of what is happening in the bulk mass of the plasma.
The Lab of Plasma studies uses Mach-Zender and shearing interferometers. Interferometry is a family of techniques in which waves, usually electromagnetic, are superimposed causing the phenomenon of interference to help extract information. Researchers in the lab use their laser interferometer to measure pressure, density, and temperature changes in the gases they turn to plasma.
Plasma is one of the four fundamental states of matter, but it does not exist freely on the Earth’s surface. It must be artificially generated by heating or subjecting a neutral gas to a strong electromagnetic field. Located in the basement of Grumman Hall are two large pulse-power generators that create plasma by delivering extremely high currents to ordinary matter for short periods. These generators are part of the Lab of Plasma Studies at Cornell University.
The lab has studied different aspects of plasma since its inception in 1967, including electron beams, microwave generation, ion beams, and Z-pinches (in which an electric current produces a magnetic field that compresses the plasma). High-energy dense plasma research is commonly associated with nuclear weapons, as well as space and astrophysics, controlled fusion, accelerator physics, and beam storage. The mission of the lab is to understand the fundamental physics underlying plasma. The ultimate research goal is to discover a means to generate a new form of energy: a controlled fusion system that produces nuclear reactions similar to those happening at the center of the sun, but safe to harness for energy production on earth.
The work carried out in the Lab of Plasma Studies is supported by the United States Department of Energy and the National Nuclear Security Administration’s Stewardship Sciences Academic Programs. An important endeavor of the lab is to train new generations of plasma research scientists. Undergraduate and graduate students, postdoctoral associates, visiting scientists, and visiting professors are active contributors. The lab’s stewardship efforts have been successful, with many scientists in pulse-power programs around the country, hailing from Cornell.
“In the College of Engineering things have been getting very small, think nanoscale. Our lab is the opposite of that. We have very large machines that enable students to handle large-scale equipment that produce large powers. It is a different scale of operation, and it provides a category of projects that are mostly not provided within the academic programs at Cornell,” says David Hammer, Electrical and Computer Engineering, and a faculty member in the lab. “It’s a big operation,” says Bruce Kusse, Applied and Engineering Physics, another faculty member in the lab. “Cornell has invested a great deal into the lab over the last 50 years, and it’s paid off. The national labs that study plasma, like the Sandia National Laboratories in Albuquerque, New Mexico, often come to us when they need something studied quickly and efficiently.”