Anatoli S. Shlapakovski

Materials modification using intense ion beams

Pulsed intense ion beams have been developed for applications including surface modification and alloying, and thin-film and nanopowder synthesis. Rapid thermal processing with ions is quite promising for large-scale commercial use, due to the high specific ion energy deposition (joules per cubic centimeter) without reflection, and to the relative efficiency and low cost of the pulsed power ion-beam drivers compared to other high-kinetic energy alternatives. We discuss in this paper the basis for the use of ions in materials processing and the methods of beam formation and impingement on material to be treated, and give examples of recent and ongoing work in materials processing.

Formation of protective coatings on metals by intense pulsed ion beam

Abstract The results of the development of a combined method for protective coating deposition by plasma-generated ablation under the action of an intense pulsed ion beam (IPIB) on the surface of ablated materials are reported. This method deals with: cleaning of a substrate surface and thin Ti film deposition by the IPIB; radiation-induced mass transfer of elements of both the film and substrate to increase adhesion; deposition of thin Ti and C films by IPIB; and mixing of elements of this heterogeneous binary system by IPIB to create TiC coatings. The Ti film was deposited onto both Al and Fe, and then mixing was performed by IPIB using current density of 35 A/cm 2 with various numbers of pulses. The substrate temperature was 20–300 °C. Analysis of the elemental composition of the coating–substrate system was performed by the Rutherford backscattering method. After deposition of the main TiC coating at a substrate temperature of 300 °C, analysis of the elemental composition of the coating–substrate interface was performed using the Auger electron spectroscopy method. The microhardness was measured using the Vickers method.

Development of an X-band Antenna-Amplifier: Numerical Simulations and Plasma-Related Investigations

In this work, new results obtained in the course of antenna-amplifier development are reported. These are the results of PIC simulations using the 3-D version of the MAGIC code and studies concerning the possibility of plasma formation at the dielectric rod surface located within the annular beam. The latter studies include theoretical consideration of the device slow-wave structure with a plasma layer near the rod surface and model experiments on beam transport in the guide magnetic field with the rod inside, aimed at estimating the plasma density

Combining different modes of high-power ion beam application for creation of metallic and diamond-like coatings

Some results of the experiments on thin film deposition using pulsed high-power ion beam (HPIB) are reported. Ti, Nb, Pt, and C films were produced from ablation plasma generated under the action of pulsed HPIB on a surface of ablated materials. We are developing the combined technology that deals with cleaning a substrate surface by HPIB, thin film deposition by HPIB, and the radiation-induced mass transfer of elements of both film and substrate to increase the adhesion. The deposition of the diamond-like titanium carbide has been realized on the basis of the scheme including Ti film deposition, C film deposition, and the ion beam mixing to form TiC carbide. The main parameters of the Ti-substrate transition layers have been determined for different regimes of their creation by Rutherford backscattering (RBS). Ti, Nb, and Pt coatings were deposited on silicon cantilevers used in high-resolution scanning probe microscopes. The analysis of the composition of TiC coatings at a substrate was performed using the Auger electron spectroscopy (AES) method.

Numerical simulations of output pulse extraction from a high-power microwave compressor with a plasma switch

Numerical simulations of the process of electromagnetic energy release from a high-power microwave pulse compressor comprising a gas-filled cavity and interference switch were carried out. A microwave plasma discharge in a rectangular waveguide H-plane tee was modeled with the use of the fully electromagnetic particle-in-cell code MAGIC. The gas ionization, plasma evolution, and interaction with RF fields accumulated within the compressor were simulated using different approaches provided by the MAGIC code: particle-in-cell approach accounting for electron-neutral collisions, gas conductivity model based on the concept of mobility, and hybrid modeling. The dependences of the microwave output pulse peak power and waveform on parameters that can be controlled in experiments, such as an external ionization rate, RF field amplitude, and background gas pressure, were investigated.

Status of the development of X-band antenna-amplifier: design, simulations, and prototype experiments

Summary form only given. An antenna-amplifier, Cherenkov maser with a rod slow-wave structure operating in the non-axisymmetric HE11 mode (fundamental mode of a dielectric rod antenna), can be a compact, controllable, high-power microwave source. In this work, new results obtained in the course of the development of the X-band antenna-amplifier are reported. The design of the proof-of-principle experiments on gain demonstration in the device assumes employing a microwave pulse compressor as a source of external signal, so that the RF drive pulse duration would be less than that of the operating voltage of the linear induction accelerator (LIA), a compact source of electron beam. Also, this allows one to increase the input microwave power up to ~1 MW. The results of numerical simulations using the 3-D version of the PIC code MAGIC show that the output power of ~30 MW is achievable with the operating voltage of ~290 kV and beam current of ~1.17 kA at the frequency of ~9.3 GHz. The prototype experiments included the annular beam transport with a dielectric rod inside (in the absence of input microwave signal) and the low-power microwave transmission (in the absence of the beam). The experiments on beam transport were aimed at estimating the density of plasma that can appear at the rod surface, since too dense plasma could prevent amplification in the device. It has been shown that one can avoid plasma formation to the degree inadmissible for an X-band device, when the density much exceeds 1012 cm-3; thus, the concept of the antenna-amplifier can be considered realizable. The dielectric rod antenna excitation has been studied using the microwave transmission system placed inside the LIA module (so that the antenna feed waveguide can serve also as a cathode holder). The antenna matching and radiation pattern have been measured, and it has been shown that the real geometry of the antenna-amplifier practically does not change the angular distribution of radiated power and its dependence on frequency in comparison with the case of isolated antenna

Influence of near-surface plasma layer on the wide-bandwidth dielectric Cherenkov maser operation

The results of experimental tests of the wide-bandwidth relativistic microwave amplifier,--dielectric Cherenkov maser,--are reported that revealed plasma presence in its interaction space, and the analysis of electromagnetic properties of a hybrid system,--dielectric-lined waveguide loaded with a plasma layer,--is presented. Experiments with the high-current electron beam showed the effect of strong enhancement of output microwave power by means of an external driver signal at different X-band frequencies, however, the said enhancement was poorly reproducible. Circumstantial evidences were obtained indicating that plasma could be produced at the dielectric surface from electron bombardment of the liner as well as from an rf breakdown caused by a microwave drive signal. The dispersion relation of the system with magnetized near-surface hollow plasma have been derived, and the spectra and electromagnetic field radial distributions for both waveguide and plasma modes have been analyzed depending on the plasma density and layer thickness. It has been found that for dense plasma, even a very thin layer gives a strong frequency upshift of a waveguide mode and reduces its coupling impedance at a given frequency whereas plasma of modest density improves the coupling impedance. Features of usual and hybrid waveguide and plasma modes are discussed in detail. It has been shown that for the hollow plasma configuration, a hybrid plasma mode is characterized with the longitudinal electric field component sign change across the layer.

Pulse-Shortening in a Relativistic Magnetron: The Role of Anode Block Axial Endcaps

A six-vane relativistic magnetron with a single radial output slot is studied by 3-D particle in cell simulations without the presence of plasma. We find that when the six radial slots in the anode block are closed at their axial ends by conducting endcaps, the power flow behaves in a way different from that when they are not. When there are no endcaps, microwave power pulse-shortening is the result of the magnetron impedance being undermatched to the pulsed-power generator, and it cancels when the magnetron impedance is increased sufficiently. The axial electron current flowing in the downstream cavity reduces to negligible values and plays no part in the power flow. When anode block endcaps are added, this axial leakage current is significant and the downstream cavity acts as a second load attached in parallel to the magnetron. For pulse-shortening to cancel, the magnetron impedance needs to increase, which can be achieved by reducing the downstream axial section impedance. We demonstrate this by increasing the axial current. Between the parameter regions where pulse-shortening exists and where it does not, there is a metastable transition region where there is mode competition resulting in a beating pattern separating two regions each characterized by a single mode.

Non-Axisymmetric Slowed Structure and Plasma Modes in a Waveguide with a Dielectric Rod and Magnetized Plasma

Electrodynamics of a circular waveguide with a dielectric rod and plasma layer adjoining the rod surface is considered. The dispersion relation has been derived in the general case of non-axisymmetric perturbations, and its numerical solutions corresponding to slowed structure and plasma modes have been studied, mostly for hybrid waves combining properties of structure and plasma modes. For the structure fundamental HE11 mode, plasma parameters have been identified that prevent a Cherenkov interaction of this mode with a relativistic electron beam at a given frequency. For both structure and plasma modes, coupling impedances and percentages of RF power transmitted through the dielectric, plasma, and vacuum regions were calculated depending on plasma density. Mutual transformation of the field structure in hybrid waves has been shown. Results of the phase velocity and coupling impedance calculations are analyzed from the standpoint of operation of an antenna-amplifier device, a relativistic traveling wave tube in the HE11 mode of a dielectric rod: the concept realizability with plasma presence is proved and the role of non-axisymmetric and symmetric plasma modes is discussed.

Effect of the External Coupling of Cavities on the Stability and Output Power of a Relativistic Magnetron

Thus, the results of our investigations show that the external coupling of cavities in a relativistic magnetron significantly influences on the spectral and energetic characteristics of the oscillations. The original configuration of the coupling circuit is proposed, based on the scheme with common dissipative elements. This significantly improves the output microwave radiation signal parameters. One can expect that using a coupling channel with many radiators will make possible to create stable, ultrahigh-power, high-directivity radiation sources