H.R. Yousefi

Simulation of high-energy proton production by fast magnetosonic shock waves in pinched plasma discharges

High-energy particles of a few hundred keV for electrons and up to MeV for ions were observed in a plasma focus device. Haruki et al. [Phys. Plasmas 13, 082106–1 (2006)] studied the mechanism of high-energy particle production in pinched plasma discharges by use of a 3D relativistic and fully electromagnetic particle-in-cell code. It was found that the pinched current is unstable against a sausage instability, and then becomes unstable against a kink instability. As a result high-energy electrons were observed, but protons with MeV energies were not observed. In this paper the same pinch dynamics as Haruki and co-workers is investigated, focusing on the shock formation and the shock acceleration during the pinched current. It is found that a fast magnetosonic shock wave is produced during the pinching phase which, after the maximum pinch occurs, is strongly enhanced and propagates outwards. Some protons trapped in the electrostatic potential produced near the shock front can be accelerated to a few MeV by...

Compression and neutron and ion beams emission mechanisms within a plasma focus device

This paper reports some results of investigations of the neutron emission from middle energy Mather-type plasma focus. Multiple compressions were observed, and it seems that multiple compression regimes can occur at low pressure, while single compression appeared at higher pressure, which is favorable for neutron production. The multiple compression mechanism can be attributed to the (m=0 type) instability. The m=0 type instability is a necessary condition for fusion activity and x-ray production, but is not sufficient by itself. Accompanying the multiple compressions, multiple deuteron and neutron pulses were detected, which implies that there are different kinds of acceleration mechanisms.

Simulation of high-energy particle production through sausage and kink instabilities in pinched plasma discharges

In an experimental plasma, high-energy particles were observed by using a plasma focus device, to obtain energies of a few hundred keV for electrons, up to MeV for ions. In order to study the mechanism of high-energy particle production in pinched plasma discharges, a numerical simulation was introduced. By use of a three-dimensional relativistic and fully electromagnetic particle-in-cell code, the dynamics of a Z-pinch plasma, thought to be unstable against sausage and kink instabilities, are investigated. In this work, the development of sausage and kink instabilities and subsequent high-energy particle production are shown. In the model used here, cylindrically distributed electrons and ions are driven by an external electric field. The driven particles spontaneously produce a current, which begins to pinch by the Lorentz force. Initially the pinched current is unstable against a sausage instability, and then becomes unstable against a kink instability. As a result high-energy particles are observed.

Runaway electrons as a source of impurity and reduced fusion yield in the dense plasma focus

Impurities produced by the vaporization of metals in the electrodes may be a major cause of reduced fusion yields in high-current dense plasma focus devices. We propose here that a major, but hitherto-overlooked, cause of such impurities is vaporization by runaway electrons during the breakdown process at the beginning of the current pulse. This process is sufficient to account for the large amount of erosion observed in many dense plasma focus devices on the anode very near to the insulator. The erosion is expected to become worse with lower pressures, typical of machines with large electrode radii, and would explain the plateauing of fusion yield observed in such machines at higher peak currents. Such runaway electron vaporization can be eliminated by the proper choice of electrode material, by reducing electrode radii and thus increasing fill gas pressure, or by using pre-ionization to eliminate the large fields that create runaway electrons. If these steps are combined with monolithic electrodes to el...

Simulations of plasma heating caused by the coalescence of multiple current loops in a proton-boron fusion plasma

Two dimensional particle-in-cell simulations of a dense plasma focus were performed to investigate a plasma heating process caused by the coalescence of multiple current loops in a proton-boron-electron plasma. Recently, it was reported that the electric field produced during the coalescence of two current loops in a proton-boron-electron plasma heats up all plasma species; proton-boron nuclear fusion may therefore be achievable using a dense plasma focus device. Based on this work, the coalescence process for four and eight current loops was investigated. It was found that the return current plays an important role in both the current pinch and the plasma heating. The coalescence of four current loops led to the breakup of the return current from the pinched plasma, resulting in plasma heating. For the coalescence of eight current loops, the plasma was confined by the pinch but the plasma heating was smaller than the two and four loop cases. Therefore the heating associated with current loop coalescence depends on the number of initial current loops. These results are useful for understanding the coalescence of multiple current loops in a proton-boron-electron plasma.

Multiple Compressions in the Middle Energy Plasma Focus Device

This paper reports some of the results that are aimed to investigate the neutron emission from the middle energy Mather‐type plasma focus. These results indicated that with increase the pressure, compression time is increase but there is not any direct relation between the compression time and neutron yield. Also it seems that multiple compression regimes is occurred in low pressure and single compression is appeared at higher pressure where is the favorable to neutron production.

New Mechanism for Ion Emission in Plasma Focus Device

A new mechanism for the acceleration and production of ions in Z-pinch discharges, especially plasma focus is presented. Previously, Yousefi et al. [Phys.Plasma 13, 114506 (2006)] studied the multiple compression and pinch mechanism; they reported that this event can be attributed to the (m=0) type instability, while the subsequent ion and neutron acceleration mechanism was not reported. Continuing from previous work, Mizuguchi et al. [Phys.Plasma 14, 032704 (2007)] studied the simulation of high-energy proton production, generated by shock waves in pinch plasma discharge, by use of a 2D relativistic and fully electromagnetic particle-in-cell code. It was found that protons trapped in the electrostatic potential produced near the shock front, can be accelerated to a few Mev by the surfatron acceleration mechanism. On the other hand, the ring-shape of ion bunches, which is in good agreement with the experimental results, were shown. Now we report another acceleration mechanism for subsequent ion production, which differs from the m=0 instabilities caused by the surfatron acceleration mechanism.