A. Sayapin

Underwater electrical explosion of a Cu wire

Results and analysis of a microsecond time scale underwater electrical wire explosion are presented. Experiments were carried out with a Cu wire exploded by a current pulse ⩽100kA with microsecond time duration. The analysis is based on shadow and spectrally resolved streak photography which were used to monitor the evolution of the discharge channel and the shock wave. The obtained data were used for hydrodynamic calculation of the generated water flow parameters, such as pressure and flow velocity distribution between the discharge channel and the shock wave. In particular, the pressure at the discharge channel boundary and the energy transferred to the water were estimated. The results of the calculation have been verified by comparing the measured and calculated trajectories of the shock wave. Based on the results of the calculation the energy transferred to the water was estimated. In addition, the analysis shows that the energy initially deposited in the discharge channel continues to produce mechan...

Analysis of shock wave measurements in water by a piezoelectric pressure probe

Investigation of underwater electrical wire explosions occurring in the time scale of few microseconds requires a measurement of pressure waves with nanosecond rise time and microsecond fall time. Various types of pressure gauges are used for this purpose, however, none of them seems to be suitable for the task since the frequency range of the pressure waves lies between 107 and 109 Hz, whereas all types of mechanical gauges have a bandwidth below 107 Hz. Therefore, a mathematical processing of measurements is required for reconstruction of the actual pressure wave forms. In this article, a signal processing algorithm, based on energy conservation requirements and Fourier analysis, for reconstruction of the wave form of the pressure wave generated under water by electrical explosion of wires is proposed. The gauge used in the experiments is a PCB 119A12 type pressure gauge with a bandwidth below 1 MHz produced by Piezo-Electronics, Inc. Pressure waves were produced by underwater electrical explosion of a ...

Plasma dynamics during relativistic S-band magnetron operation

Results of a time- and space-resolved spectroscopic research studies of an S-band relativistic magnetron generating 1.5×108 W microwave power at f=2950 MHz, powered by a linear induction accelerator (450 kV, 4 kA, 150 ns), are presented. The cathode plasma electron density and temperature were obtained by analyzing Hα and Hβ hydrogen Ballmer series and carbon C II and C III ion spectral lines and the results of collision radiative modeling. It was shown that the microwave generation is accompanied by a significant increase in plasma density and ion temperature, up to ∼5×1016 cm−3 and ∼8 eV, respectively. The plasma electron temperature was found to be ∼8 eV. It was shown that the plasma expansion velocity in the axial direction reaches ∼107 cm/s and does not exceed ∼2×105 cm/s in the radial direction. In addition, it was shown that the plasma is not uniform and consists of separate plasma spots whose number increases during the accelerating pulse. Estimates of the plasma transport parameters and its inter...

Transient operation of the relativistic S-band magnetron with radial output

The influence of the time-varying accelerating voltage and electromagnetic waves reflected from the output window of the antenna on the operation of a relativistic S-band magnetron with radial output is analyzed. It is shown that within the range of radiation frequencies generated by the magnetron, the antenna with the dielectric window and feed waveguide can be considered as a resonant load. Depending on the phase relations between the reflected electromagnetic waves and those traveling in the magnetron, minimal coupling between the magnetron cavities adjacent to the place of microwave extraction can be realized. In this regime, the magnetron represents an open-end chain of coupled cavities and maintains the effective interaction of the electron flow and generated electromagnetic wave at a decreasing voltage. As the drift velocity of electrons decreases and its difference from the electromagnetic wave phase velocity increases, the microwave frequency changes. The changed frequencies do not necessarily belong to and are not limited by the discrete spectrum of closed resonant ring waveguide structures.

Underwater electrical wire explosion

The results of the investigation of the underwater electrical wire explosions using a high power sub-ns generator are reported. The spectroscopic analysis of the emitted radiation has unveiled no evidence for the formation of shunting plasma channel. The latter appears in vacuum and gas wire explosions and causes to the seizure of energy deposition into an exploding wire material. The combination of mechanism for the suppression of formation of shunting channel together with the increased energy deposition rate allows busting the efficiency of the energy deposition into the exploding wire. Estimated energy deposition into Cu and Al wire of up to 200 eV/atom was reported.

Characterization of Different Wire Configurations in Underwater Electrical Explosion

The results of a study of shock wave (SW) generation by means of underwater electrical wire explosion with different exploding wire configurations and two high-current microsecond and submicrosecond timescale generators are presented. By using aperiodical generator discharge, a ~85% and ~15% of the stored electrical energy was transferred to the exploding wire and energy of the generated water flow, respectively. The energy of the water flow is distributed between its internal (~25%) and kinetic (~75%) energies. It was shown that the exploding wire zigzag configuration, confinement of the SW propagation region, and an increase in the rate of the energy deposition into the exploding wire allow one to increase the SW pressure ges10 times that attained with microsecond timescale straight wire explosion. The averaged thermophysical properties of nonideal and weakly degenerated plasma formed as a result of the wire explosion were obtained and summarized.

Drastic improvement in the S-band relativistic magnetron operation

The superior operation of a S-band relativistic magnetron powered by a Linear Induction Accelerator with ≤400 kV, ≤4 kA, and ∼150 ns output pulses was revealed when the magnetron was coupled with a resonance load and a part of the generated microwave power stored in the resonator was reflected back to the magnetron. It is shown that, under optimal conditions, the efficiency of the magnetron operation increases by ∼40% and the generated microwave power reaches the power of the electron beam.

S-band relativistic magnetron operation with an active plasma cathode

Results of experimental research on a relativistic S-band magnetron with a ferroelectric plasma source as a cathode are presented. The cathode plasma was generated using a driving pulse (∼3 kV, 200 ns) applied to the ferroelectric cathode electrodes via inductive decoupling prior to the beginning of an accelerating pulse (200 kV, 150 ns) delivered by a linear induction accelerator. The magnetron and generated microwave radiation parameters obtained for the ferroelectric plasma cathode and the explosive emission plasma were compared. It was shown that the application of the ferroelectric plasma cathode allows one to avoid a time delay in the appearance of the electron emission to achieve a better matching between the magnetron and linear induction accelerator impedances and to increase significantly (∼30%) the duration of the microwave pulse with an ∼10% increase in the microwave power. The latter results in the microwave radiation generation being 30% more efficient than when the explosive emission cathod...

Numerical simulation of the magnetron operation with resonance load

The results of numerical simulations and a comparison with experimental data obtained in recent experiments with the relativistic S-band magnetron by Sayapin et al. [Appl. Phys. Lett. 95, 074101 (2009)], having a resonance load and without special measures being taken to suppress the microwaves reflected from the load, are presented. The numerical simulations were based on the model which considers a magnetron as a traveling wave resonator coupled with external resonator. In these simulations, experimentally determined parameters of the magnetron and resonator and their coupling coefficient were used. It was found that, under certain conditions, the electromagnetic wave reflected from the resonator leads to an increase in the efficiency of the magnetron operation. Taking into account microwave energy compression in the resonator, one obtains a microwave power comparable with the power of the electron beam in the magnetron. Also, it was shown that the magnetron traveling wave acquires a phase shift due to ...

Plasma parameters of an active cathode during relativistic magnetron operation

The results of time- and space-resolved spectroscopic studies of the plasma produced at the surface of the ferroelectric cathode during the operation of an S-band relativistic magnetron generating ∼50 MW microwave power at f=3005 MHz and powered by a linear induction accelerator (LIA) (150 kV, 1.5 kA, 250 ns) are presented. The surface plasma was produced by a driving pulse (3 kV, 150 ns) prior to the application of the LIA accelerating high-voltage pulse. The cathode plasma electron density and temperature were obtained by analyzing hydrogen Hα and Hβ, and carbon ions CII and CIII spectral lines, and using the results of nonstationary collision radiative modeling. It was shown that the microwave generation causes an increase in plasma ion and electron temperature up to ∼4 and ∼7 eV, respectively, and the plasma density increases up to ∼7×1014 cm−3. Estimates of the plasma transport parameters and its interaction with microwave radiation are also discussed.