A. V. Dubrovsky

Plasma dynamics in the PF-1000 device under full-scale energy storage: II. Fast electron and ion characteristics versus neutron emission parameters and gun optimization perspectives

Electron and ion beam dynamics of the PF-1000 facility were investigated for the first time at its upper energy limit (≈1 MJ) in relation to neutron emission, the pinch’s plasma (‘target’) characteristics and some other parameters with the help of a number of diagnostics with ns temporal resolution. Special attention was paid to the temporal and the spatial cross correlations of different phenomena. Results of these experiments are in favour of a neutron emission model based on ion beam–plasma interaction with three important features: (1) the plasma target is hot and confined during a few ‘inertial confinement times’; (2) the ions of the main part of the beam are magnetized and entrapped around the pinch plasma target for a period longer than the characteristic time of the plasma inductive storage system and (3) ion–ion collisions (both fusion collisions, due to head-on impacts and Coulomb collisions) are responsible for neutron emission. Analysis has shown that one of the ways for achieving a future improvement in the neutron yield of the PF-1000 facility may by changing the geometry of the device. It may ensure an increase in both the discharge current and the initial working gas pressure, eventually resulting in the neutron yield boost.

Plasma dynamics in PF-1000 device under full-scale energy storage: I. Pinch dynamics, shock-wave diffraction, and inertial electrode

This paper (paper I) presents the first part of results obtained with the PF-1000 facility for the first time at its upper energy limit (≈ 1 MJ). Special attention is paid here to plasma (‘pinch’) dynamics, which was investigated in relation to its electro-technical and radiation (especially neutron) characteristics with the help of a number of diagnostics, both time-integrated and with nanosecond temporal resolution. In these methods we utilized a Rogowski coil for the routine electro-technical measurements, visual multi-frame and streak cameras, soft x-ray pin-hole multi-frame cameras, PIN-diode assembly and PM tubes with scintillators for soft and hard x-rays as well as for neutron investigations together with a set of activation counters. In particular, the temporal cross correlation of different phenomena taking place during the discharge was investigated. The pinch’s longevity appears to be 10–15 times larger than the ideal magnetohydrodynamic growth time (ratio of the pinch radius to the ion thermal velocity). It is demonstrated how the ‘target’ dynamics (pinch plasma of the dense plasma focus (DPF)) depends on and may be controlled by the electrode’s size and the geometry of the chamber in this large-scale device. Diffraction of a shock wave together with a current sheath on an obstacle made at the DPF anode cap opens an opportunity for an inertial electrode to be used in future at larger DPF devices.

Damage of structural materials for fusion devices under pulsed ion and high temperature plasma beams

Results of experiments are presented on the influence of high-energy pulses on austenitic and ferritic steels carried out using dense plasma foci devices PF-1000 and PF-60 with hydrogen and deuterium as working gas, respectively. Pulsed irradiation of specimens was performed in two regimes: (1) under microsecond hydrogen plasma pulses with power density q=107–109 W/cm2, and (2) under 100-ns deuterium plasma pulses with q=109–1011 W/cm2. Features of damage, phase-structural transformations and compositional changes in these materials under these conditions were investigated.

Pseudosparks in the nanosecond range of operation: firing, jitter, and current disruption

The operation of pseudosparks (thyratrons with cold cathodes) of the TDI1-150k/25 type was investigated in the nanosecond time range of control and switching. Their most important characteristics are their reliability of firing—practically in 100% of cases, a jitter time—less than 4 ns, and the possibility of them switching off (interruption of a current) at a particular moment (after the first half of a discharge cycle). Investigations have shown that the TDI1-150k/25 device has all the above characteristics (which meet the current industrial demands) if the proper operational regimes are chosen. We have proven its parameters with a set of four switches working in parallel at the current level of a few hundred kiloamperes at our installations of the Dense Plasma Focus type, having an energy of several kilojoules.