The dense plasma focus (DPF) is a Z-pinch that has been studied for 50 years. Within ten years of its discovery by Fillipov and Fillipova in Russia and Mather in the USA, this dense pinch was scaled up to 2-MA currents and neutron outputs of ~ 1012/pulse. More remarkable is the fact that most of the relevant physics and scaling laws were elucidated within this first decade. The subsequent period has seen this type of pinch used as a teaching tool, developed as a portable neutron source for security applications, as a soft X-ray source for lithography, and as an energetic ion source for nanofabrication applications. This review builds upon several prior reviews. From the plasma physics standpoint, DPF physics is examined in light of fast Z-pinches to examine the similarities. More cross-fertilization between the two communities is suggested as a means to improve both types of pinches. From the applications standpoint, the many uses of DPFs are summarized to demonstrate the versatility of these pinches. Their ease of assembly and relatively low voltage operation have allowed DPFs to be disseminated worldwide as fusion testbeds (unlike their fast Z-pinch counterparts). Smaller or less economically developed nations have made valuable contributions to our understanding of the physics, as evidenced by the rich lode of publications that have advanced the field.

The Dense Plasma Focus: A Versatile Dense Pinch for Diverse Applications

The paper presents a comparison of the main characteristics and experimental results obtained in plasma focus (PF) experiments in the POSEIDON 500 kJ facility in Stuttgart and the PF-360 kJ device in Świerk. Parameters of various electrodes and insulators are given, and studies on the evolution of the discharges are summarized. Selected data on X-ray, ion and neutron emission are given. Also presented are recent experimental results — a maximum neutron yield of up to 2.5 × 1011 for 500 kJ/80 kV runs with a new ceramic insulator in POSEIDON and an average neutron yield of 1.2 × 1011 for operation at 171 kJ/36 kV in PF-360. Particular attention is paid to the neutron scaling and the saturation effects observed at higher energy and current levels. Proposals are made for new experimental studies which can facilitate further progress in PF research.

http://iopscience.iop.org/article/10.1088/0029-5515/29/8/002/pdf

Comparative analysis of large plasma focus experiments performed at IPF, Stuttgart, and IPJ, Świerk

Computation of MHD equilibrium of Tokamak Plasma

Measurements on plasma focusion beams include various advanced techniques producing a variety of data which has yet to produce benchmark numbers [A Bernard et al., J. Mosc. Phys. Soc. 8, 93-170 (1998)]. This present paper uses the Lee Model code [S Lee, http://www.plasmafocus.net (2012)], integrated with experimental measurements to provide the basis for reference numbers and the scaling of deuteron beams versus stored energy E0. The ion number fluence (ions m−2) and energy fluence (J m−2) computed as 2.4−7.8 × 1020 and 2.2−33 × 106, respectively, are found to be independent of E0 from 0.4 to 486 kJ. Typical inductance machines (33–55 nH) produce 1.2−2 × 1015 ions per kJ carrying 1.3%–4% E0 at mean ion energy 50–205 keV, dropping to 0.6 × 1015 ions per kJ carrying 0.7% E0 for the high inductance INTI PF.

Plasma focus ion beam fluence and flux—Scaling with stored energy

The total current Itotal waveform in a plasma focus discharge is the most commonly measured quantity, contrasting with the difficult measurement of Ipinch. However, yield laws should be scaled to focus pinch current Ipinch rather than the peak Itotal. This paper describes how Ipinch may be computed from the Itotal trace by fitting a computed current trace to the measured current trace using the Lee model. The method is applied to an experiment in which both the Itotal trace and the plasma sheath current trace were measured. The result shows good agreement between the values of computed and measured Ipinch.

/pdf/computing-plasma-focus-pinch-current-from-total-current-2x29unlv48.pdf

Computing plasma focus pinch current from total current measurement

Numerical and experimental studies have been made concerning an increase of the effective discharge current for the plasma focus from a bank of constant energy. From the higher discharge current an increased neutron yield is expected. Experimentally an 85 kV/12 kJ device with a current rise time of 600 ns was investigated. The obtained neutron yield was larger by a factor of 3 compared to devices of equal energy but low voltage. The geometrical and pressure variations necessary for optimization, are discussed. Using MHD-calculations and impedance considerations, various banks, including those with high voltage and low inductance, are compared with respect to plasma data and discharge current.

https://iopscience.iop.org/article/10.1088/0032-1028/22/3/003/pdf

H. J. Kaeppeler

Papers

Current and neutron yield scaling of fast high voltage plasma focus