The generation of energetic ions and DD neutrons from microfusion at the interelectrode space of a low-energy nanosecond vacuum discharge has been demonstrated recently [1, 2]. However, the physics of fusion processes and some results regarding the neutron yield from the database accumulated were poorly understood. The present work presents a detailed particle-in-cell (PIC) simulation of the discharge experimental conditions using a fully electrodynamic code. The dynamics of all charge particles was reconstructed in time and anode–cathode (AC) space. The principal role of a virtual cathode (VC) and the corresponding single and double potential wells formed in the interelectrode space are recognized. The calculated depth of the quasistationary potential well (PW) of the VC is about 50–60 keV, and the D+ ions being trapped by this well accelerate up to energy values needed to provide collisional DD nuclear synthesis. The correlation between the calculated potential well structures (and dynamics) and the neutron yield observed is discussed. In particular, ions in the potential well undergo high-frequency (∼80 MHz) harmonic oscillations accompanied by a corresponding regime of oscillatory neutron yield. Both experiment and PIC simulations illustrate favorable scaling of the fusion power density for the chosen IECF scheme based on nanosecond vacuum discharge.

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Experimental results of the observation of coherent stimulated radiation from subnanosecond electron bunches moving through a periodic waveguide and interacting with a backward propagating wave are presented. The subnanosecond microwave pulses in Ka and W bands were generated with repetition frequencies of up to 25 Hz. The mechanism of microwave pulse generation was associated with self-bunching, and the mutual influence of different parts of the electron pulse due to slippage of the wave with respect to the electrons; this can be interpreted as superradiance. The illumination of a panel of neon bulbs resulted in a finely structured pattern corresponding to the excitation of the TM01 mode. Observation of rf breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, leads to an estimate of the absolute peak power as high as 60 MW for the 300-ps pulses at 38 GHz. These results are compared with numerical simulations. The initial observation of 75-GHz, 10-15-MW radiation pulses with a duration of less than 150 ps is also reported.

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The energetic ions and DD neutrons from microfusion at the interelectrode space of a low energy nanosecond vacuum discharge with deuterium-loaded Pd anode has been demonstrated recently. To understand better the physics of fusion processes the detailed PIC simulation of the discharge experimental conditions have been developed using a fully electrodynamic code KARAT. The dynamics of main charge particle species was reconstructed in time and interelectrode space. The principal role of a virtual cathode (VC) and the corresponding single and double potential well formed in the interelectrode space are recognised. The calculated depth ϕ of the quasistationary potential well (PW) of the VC is about 50-60 kV, and the D + ions being trapped by this well accelerate up to energy values needed to provide collisional DD nuclear synthesis. Both experiment and PIC simulations illustrate very favourable scaling of the fusion power density at decreasing of VC radius ( ∼ ϕ 2 /r 4 V C ) for the chosen inertial electrostatic confinement fusion scheme based on miniature nanosecond vacuum discharge. Meanwhile, the initial stage of discharge is understood still poorly. When voltage is applied, the electron beam extracted from cathode starts to interact with the surface of deuterium-loaded Pd anode. This early stage of discharge manifests sometime the peaks registered by photomultipliers which are similar to neutron ones from time-of-flight measure under the study of collisional DD synthesis at the further stages of discharge. The detailed study of Pd anode surface morphology have been performed and recognized, in particular, the number of various pores and craters of different sizes. We remark that besides of rather usual craters (due to electron beams -anode interaction) some of the craters on the Pd anode surface may correspond to anode ectons (explosive centres) and consider their possible nature. Specifics of warm dense matter (WDM) generated at different stage of discharge is discussed. The data obtained are compared with recent results on initiation of DD reactions by electron beams at deuterium -loaded Pd foils and correspondent data on their surface morphology.

Within the framework of the average approach and direct 3D PIC (particle-in-cell) Many physical systems exhibit behavior associated with the emergence of the so-called rogue waves which represent dramatically high-amplitude events that occur with low probability but much more frequently than expected in ordinary (e.g., Gaussian or Rayleigh) wave statistics. can be suggested that, similar to lasers [5][6][7], the rogue waves can also occur in microwave oscillators representing active systems which are based on the interaction of electromagnetic waves with non-equilibrium electron beams.One of the widely studied microwave oscillators is a gyrotron in which a helical electron beam excites a waveguide mode near its cutoff frequency [10]. In this paper, we demonstrate that rogue waves can appear in gyrotrons operating in the regime of developed turbulence. It is well known that in electronic oscillators, including gyrotrons, an increase of the excess over the starting conditions leads to a complication of the radiation spectrum caused by the appearance of periodic self-modulation and then chaotic turbulent generation regimes [11][12][13][14][15][16][17]. Typically, realization of self-modulation regimes is a result of combination of a nonlinearity and delay effects [12].

The microwave breakdown in air is simulated numerically within a simple 1D model taking into account a perturbation of electromagnetic field by plasma. The simulations were performed using two qualitatively different codes. One of these codes is based on computation of Maxwell equations, whereas the other one utilizes an approximation of quasi-monochromatic electromagnetic field. There is a good agreement between simulation results obtained by using both codes. Calculations have been carried out in a wide range of air pressures and field frequencies; also varied were initial spatial distributions of plasma density. The results reveal strong dependence of the breakdown evolution on the relation between the field frequency and the gas pressure as well as on the presence of extended rarefied background plasma. At relatively low gas pressures (or high field frequencies), the breakdown process is accompanied by the stationary ionization wave propagating towards the incident electromagnetic wave. In the case of a high gas pressure (or a relatively low field frequency), the peculiarities of the breakdown are associated with a formation of plasma filament array. The extended background plasma can suppress formation of the plasma filament array completely even at high pressures (or low frequencies).