Using pulsed power machines to generate high energy density plasmas

Imagine the intensity of energy exuding from the sun. If the same kind of energy, or fusion power, is harnessed on Earth, we would be able to replace fossil fuels with clean “central station power.” Therefore, studying science that may one day enable fusion on Earth is important. The breakthroughs that researchers might experience during this process are absolutely invaluable. Dr. David Hammer, of Cornell University, studies the fundamental science underlying high energy density paths to fusion, a path that involves achieving energy density comparable to that at the center of the sun. Using an innovative pulsed power machine, his lab can achieve states of matter that don’t exist otherwise on Earth. By researching these states of matter, Dr. Hammer hopes to gain key insights about high energy density plasmas and how to manipulate them. The discoveries that Dr. Hammer finds in his lab may provide a basis for much larger laboratories and experiments to create practical means of producing power and energy on earth from the fusion of hydrogen into helium.

Dr. Hammer’s laboratory together with associated theoretical and computer simulation research is in "steady state" operation at present, producing new scientific results a few times a year that are reported at conferences and published in peer-reviewed journals. Because of the lab’s extraordinary method of turning normal matter into nothing like that on Earth, the students who have their Ph.D.'s from Dr. Hammer’s laboratory are much sought after by national laboratories and companies like Raytheon. Although not directly studying fusion, Dr. Hammer and his lab are contributing to fusion with their fundamental science research, learning everything they can about high density plasma so others can utilize this knowledge-base for further applications.

Current research focuses include:

  • Fundamental Science that Underlies Inertial Confinement Fusion: Making plasmas at high energy density allows Dr. Hammer and his lab to contribute to the development of inertial confinement fusion. Because these plasmas are so difficult to study, there are boundless possibilities for new discoveries. By testing new hypotheses with novel methods, Dr. Hammer is excited to learn more about the properties of these unique states of matter.

  • The Dynamics of High Energy Density Plasmas: Dr. Hammer and his team use locally designed and built pulsed power machines to generate states of matter at a very high temperature and density, or the high energy density plasmas. High energy density plasma is hot, dense, ionized gas. This is the form of matter at the center of the sun and all of the stars that we can see. The term “high energy density” referenced to matter at the density of common materials on earth, like the air near earth's surface or an ordinary solid, but at a temperature of millions to hundreds of millions of degrees. This high temperature is why the matter has become a plasma. Such matter is so hot and dense that special techniques must be used to study it, some of which researchers have to invent themselves; material probes simply melt or vaporize under such conditions. Dr. Hammer’s primary goal day-to-day is to measure the properties of different examples of high energy density plasmas and to understand how they respond to electric and magnetic fields. Ultimately, Dr. Hammer hopes to contribute scientific results that will enable fusion reactions in a controlled way to be used to produce practical power for the grid.

  • Pulsed Power Machines: Dr. Hammer and his team’s specialty is in producing high energy density plasmas using "pulsed power machines" rather than lasers, which are more commonly used. A pulsed power machine produces a very high voltage (e.g., 1 million volts) and current (e.g., 1 million amperes) pulse for less than a microsecond in order to generate the hot, dense matter. The facilities in Dr. Hammer’s lab are the most scientifically productive pulsed power machines in the country at the present time. When Dr. Hammer was a graduate student at Cornell University, he helped build, test and initiate experimental research on the first pulsed power generator at a university in the US in 1967. New, state-of-the-art pulsed power generators have been a unique signature for the experiments performed at Cornell ever since. The present state-of-the-art machine, called COBRA, produces a 1.1 million ampere current pulse that lasts about 0.2 microseconds is being used for many different high energy density experiments, and its usage will continue into the future as it is a very cost-effective experimental facility.


It was in junior high school that Dr. David Hammer was listening to and reading about all the breakthroughs in nuclear physics. His mother had wanted him to be a dentist, but this experience in junior high school gave birth to a dream to become a nuclear physicist. Thankfully, his mother saw as much value in physics as she saw in dentistry, and all of the teachers he encountered along the way helped shape who he is now.

In the summer of 1964, Dr. Hammer had a summer job at the Oak Ridge National Laboratory in Oak Ridge, Tennessee, in a division conducting research on plasma physics, the science that underlies controlled fusion. The idea that it was possible to produce power and energy on earth with the same mechanism as is used by the sun and the stars captivated Dr. Hammer, and he has been hooked for the last 50 years. Achieving practical fusion power is much closer now than it was 50 years ago, but nobody realized how difficult a science and engineering problem it would be in the 1960's. Dr. Hammer is continuing plasma physics research 50 years later because the idea of contributing to producing all of the electric power and energy everyone on the planet can possibly need for millions of years from an isotope of hydrogen that is readily available on Earth, while making helium as the "ash" of the process, is about as attractive a career goal as one can have!

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Study of gas-puff Z-pinches on COBRA

Describes research on one of the principal high energy density plasma configurations that the team now uses. It enables the study of a fundamental instability of plasmas called the Rayleigh-Taylor instability. Among the authors are 6 Cornell students, 2 Russian and 3 Israeli research collaborators, two Cornell staff scientists and four faculty members.


The impact of Hall physics on magnetized high energy density plasma jets

Describes how the team has determined that a piece of physics that most high-energy-density scientists ignore in their research, Hall physics, is in fact important in many experiments in which it is ignored.


Plasma density measurements in tungsten wire array z-pinches

The team invented an x-ray source called the X-pinch that can be used to make calibrated density measurements in high energy density plasmas. Graduate student Jonathan Douglass developed a way to make 5 measurements at different times in one test.


Measuring magnetic fields in single aluminum wire plasmas with time-resolved optical spectroscopy

Making magnetic field measurements in high energy density plasma experiments has proven to be very difficult. Therefore, together with Israeli collaborators, the team has attempted to develop a new method called Zeeman Broadening that will enable measurements in plasmas in which they cannot now make them.


Calibration and analysis of spatially resolved x-ray absorption spectra from a non-uniform plasma

In this paper, a student working with the team's two Russian collaborators and a Sandia National Laboratory staff scientist has demonstrated that the X-pinch mentioned above can be used for a diagnostic method called X-ray absorption spectroscopy, which is another way to determine density, temperature and even magnetic field.



Electrical and Computer Engineering Ruth and Joel Spira Excellence in Teaching Award, 2007

Cornell College of Engineering Teaching Award, 1998 and 2006

Cornell IEEE Professor of the Year Award, 2006

McCormack Award for Excellence as an undergraduate advisor, 2005

IEEE Plasma Science and Applications Committee Award, 2004


U.S. Patent No. 7,292,676: "System for Phase-Contrast X-ray Radiography Using X pinch Radiation and a Method Thereof.”

November 6, 2007, K.M. Chandler, Tatania Chelkovenko, David Hammer, Sergei Pikuz, Daniel Sinars and Byungmoo Song.