In a z-pinch, a plasma is generated by passing a fast current pulse through many thin metal wires. These wires are usually initially arranged in a cylindrical shell geometry. After the current pulse ablates the wire material, the strong magnetic forces resulting from the current tend to crush the plasma toward the central z axis of the shell, hence the name “z-pinch.”
Sandia National Laboratories is currently investigating the z-pinch as a possible ignition source for inertial confinement fusion. On its “Z-machine,” Sandia can achieve dense, high temperature plasmas by firing fast, 100 nanosecond current pulses exceeding 20 million amps through hundreds of tungsten wires with diameters on the order of tens of microns. In cooperation with Sandia, the NERS Department at the University of Michigan is performing experimental research related to the z-pinch. Currently, there is work being done to study the explosions of single wires, and very soon a multi-wire experiment will be up and running.
For a short tutorial on the state-of-the-art in liner implosion physics, please see this recent MIPSE seminar by Prof. McBride.
Linear Transformer Driver Arrives at the University of Michigan from Russia:
The University of Michigan has taken delivery of the first 1-MA Linear Transformer Driver (LTD) in the USA. This unique, compact, 0.1- TW, 100 ns plasma generator will be used to implode wire-array z-pinches in the Plasma, Pulsed Power and Microwave Laboratory in the Nuclear Engineering and Radiological Sciences (NERS) Department. Lab Director Ron Gilgenbach describes the LTD as a 3-meter diameter-ring filled with 80 high voltage (100 kV) capacitors and 40 switches (see Figure 1 below). The current of the capacitors is inductively added by a magnetic core, hence the transformer designation. This z-pinch research project is part of an inertial confinement fusion (ICF) collaboration between UM and Sandia National Laboratories. Sandia ICF experiments transmit up to 20 MA current through imploding arrays of wire-plasmas to generate the world’s most powerful x-ray pulse for heating and compression of DT fusion fuel. The UM team involves NERS Professors Ron Gilgenbach and Y.Y Lau along with their graduate students, while the Sandia collaborators include Mike Mazarakis, Tom Mehlhorn, and Mike Cuneo. In August 2006, Gilgenbach and Mazarakis traveled to the Institute for High Current Electronics in Tomsk, Siberia to join Russian LTD developer Alexander Kim for testing of the Michigan LTD (see Figure 2 below). When the UM LTD module was stacked in an array with four such Sandia LTD modules the experiment successfully generated pulses of -0.5-MV and 1-MA, demonstrating inductive voltage adding. Sandia scientists are considering LTD technology for the next generation PW z-pinch driver (see Sandia’s page). The advantages of the revolutionary LTD circuit are its repetitive-pulsing capability, high current, fast-risetime, greatly improved reliability and approximately double energy efficiency compared to conventional Marx/water line technology, compactness and inductive voltage addition. The UM team is working intensively to develop a new experimental facility: MAIZE (Michigan Accelerator for Inductive Z-pinch Experiments). This UM facility will be utilized to investigate the plasma physics and engineering issues involved in generating intense x-ray pulses for ICF by LTD-driven, imploding, wire-array z-pinches. This work is supported by the U. S. Department of Energy through a Sandia National Laboratories contract; extensive cost-sharing has also been provided by the University of Michigan.
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Figure 1: Ron Gilgenbach with UM students and the 1-MA LTD machine, MAIZE, on its arrival at the University of Michigan. From left to right: Ed Cruz, Tim Rabin, Brad Hoff, David french, Jacob Zier, Ron Gilgenbach, Matt Gomez, Tyler Fowler-Guzzardo, and Nick Jordan.
Figure 2: September 2006 experiments with 5 LDT-modules at the Institute for High Current Electronics (IHCE) in Tomsk, Russia. From left to right: Ron Gilgenbach (UM), Alexander Kim (IHCE) and Mike Mazarakis (Sandia National Labs).
UM LTD:
Capacitors and switches for the LTD.
All 80 capacitors and 40 switches installed inside the LTD.
Radial magnetically insulated transmission line (MITL) installed.
A view of 20 carbon resistors set up for the resistive load test.
Vacuum resistive load.