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 The ACTT (Active Control of Turbulent Transport) Experiment

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A new plasma experiment, the ACTT (Active Control of Turbulent Transport) device, has recently begun operation in the Electrical and Computer Engineering Department at the University of New Mexico. The ACTT device produces a relatively large-scale laboratory plasma, which will be used to study fundamental processes relevant to the goal of realizing fusion energy - a potentially much safer, cleaner form of nuclear energy than currently exists.

Looking into the end of the ACTT device: Plasma column, with heater, cathode, anode assembly [photo album]

Fusion is the type of nuclear reaction that powers stars, including our own sun. One scheme - perhaps the most promising - to "bring a star to earth" and realize a practical energy-producing fusion reactor, is to confine a hot plasma of two isotopes of hydrogen in a magnetic field, so that enough fusion reactions can occur to produce a net energy gain. While magnetic fusion has been realized in large experiments, such as those in the United States at Princeton University, MIT, and General Atomics in San Diego, more energy is now required to operate the experiment than is produced. One current problem is that heat and plasma particles escape from the "magnetic bottle" faster than expected. It is believed that this transport of heat and particles is due to turbulence in the plasma.

It has been found that spatially-varying (sheared) flows can reduce or suppress the turbulent transport. The goal of the ACTT experiment is to investigate the active feedback control of turbulent transport in a controlled laboratory environment, through control of plasma flows. Fundamental physics of turbulence and transport in plasmas will also be studied.

The ACTT device uses a hot cathode in a vacuum chamber to create a plasma whose temperature is about 100,000 degrees Kelvin. The cathode consists of a Nickel plate coated with Barium Oxide, which is heated to about 900 degrees centigrade from the back by tungsten filaments. A mesh anode resides about 20 cm in front of the cathode. When a voltage is pulsed between the cathode and anode, electrons are emitted from the cathode, which stream through the anode mesh and ionize gas in the chamber (typically helium or argon) by collision. Coils surround the vacuum chamber, producing an axial magnetic field than confines the plasma in the radial direction. Plasma properties such as density and temperature are measured with small metal probes inserted into the plasma from the side.

The ACTT group, headed by Prof. Mark Gilmore, is collaborating on the project with Prof. Chaouki Abdallah, an expert in nonlinear control systems. The project is supported by a 3 year grant from the US Department of Energy, Office of Fusion Energy Sciences.