Time behavior of an electron beam current pulse in the axial and peripheral zones of an anode in vacuum and gas-filled diodes

The study of the time behavior of a current pulse of an electron beam generated during a high-voltage nanosecond discharge in gas-filled and vacuum diodes has been carried out. As follows from the experimental results, in both cases, the distribution of the beam current density in the plane of a grounded anode is non-uniform. The highest beam current density is recorded in the axial part of the anode. It was established that in the case of a gas-filled diode, ~ 2 ns after the onset of the beam current pulse, its shape in the axial anode zone changes relative to that in the peripheral one. It is assumed that the most probable reason for this is the effect of compensation of the charge of the beam electrons by the positive charge of ions arising in the ionization process in the paraxial zone.

Toward Next Generation Plasmonic Nanopore Slit Platform with a ~10 nm Slit-Width

We fabricated various nanoaperture plasmonic platforms for single-molecule detection. We fabricated nanoapertures like nanopores on a pyramid and nanoslits on an Au flat membrane using a Ga ion focused ion beam drilling technique, followed by irradiating with a high energy electron beam, dependent on the electron beam current density to obtain nanoapertures with a few nanometer sizes (circular nanopore, nanoslit pores). We examined their optical characteristics with varying aperture sizes and sample thicknesses. We obtained broad emission spectra in the visible and infrared region from the (7 x 7) slit array and a sharp, strong infrared emission peak from the Au nanoparticle on the substrate. The fabricated Au platform with ~10 nm nanometer opening can be employed as a single-molecule sensor and an infrared thermal emission device.

The ordering effects of an n-Si defect structure, induced by high fluences of ions with MeV energies

The results of studies of the structural and optical properties of silicon irradiated with light ions of MeV energies with fluences exceeding 1016 cm–2 are generalized. The structure of silicon irradiated with ions is con ventionally divided into several regions (ion path, braking, and outside the braking region), the kind of which is determined by the type of ions, their mass, energy, and temperature during irradiation. It is established that the irradiation with high fluences of light ions of MeV energies causes the formation of ordered layers in the bulk of silicon at depths up to several hundred microns, associated with defects whose properties differ from those of the matrix. It is shown that, under such irradiation conditions, the nature of the defect formation (the number and width of the revealed ordered linear structures and their location relative to the braking region of ions) depends on the mass and energy of ions, the ion beam intensity, the irradiation temperature, and the crystal properties. The effect of the ordering of defects in the form of stress lines and their propagation outside the braking region was discovered, when silicon was irradiated with ions of both hydrogen and helium. It is found that this effect depends on the irradiation intensity and occurs, only when the beam current density is less than 0.45 μA/cm2. It is established that, for silicon irradiated with helium ions in the region of ion path, characteristic is not the monocrystalline, but fragmentary structure, which has an aggregate of ordered stress lines (associated with defects) located in parallel to the braking band of helium ions, and the braking band consists of voids etched as a continuous layer and in the form of separate clusters. It is revealed that the irradiation of dis location silicon with deuterium ions leads to the movement of dislocations during the irradiation and to their crossing of the deuteron braking line due to the formation of stacking faults.

Improving beam simulations as well as machine and target protection in the SINQ beam line at PSI-HIPA

With a nominal beam power of nearly 1.4 MW, the PSI High Intensity Proton Accelerator (HIPA) is currently at the forefront of the high intensity frontier of particle accelerators. Key issues of this facility are minimization of beam losses as well as safe operation of the SINQ spallation source. Particular attention is being recently paid towards an improved understanding of the properties of the SINQ beam line by both enhancing the beam transport simulations and developing new diagnostic elements which can also, in some cases, preserve the target integrity by preventing too large beam current density, inaccurate beam steering or improper beam delivery. Moreover, part of the SINQ beam diagnostic concept is being rethought in order to include important missing devices like BPMs. On the simulation side, newly developed composite calculations involving general purpose particle transport programs like MCNPX and BDSIM will deliver insights about beam losses and transmission through collimators. All recent and planned developments of the SINQ beam line will be discussed in this contribution.

Fabrication of Various Plasmonic Nano-aperture Platforms with a ~10 nm Width

We fabricated the nano-aperture plasmonic platforms for single molecule detection and other various applications such as infrared thermal emission device. The nano-apertures including the nanopores on the pyramid, and the nano-slits on the Au flat membrane were fabricated using a Ga ion focused ion beam drilling technique, followed by high energy electron beam irradiations dependent upon the electron beam current density. The nanopores with a few nanometer size and the nanoslit array with order of ~ 100 nm width were fabricated. Optical characteristics for the various nanoslits were examined dependent upon the slit opening width and sample thickness. The broad emission spectra from the (7x 7) slit array are obtained from spp-mediated emission in the visible and infrared region. A sharp strong infrared emission peak is also obtained due to Au nanoparticle. The fabricated Au platform can be utilized as single molecule sensor and infrared thermal emission device.

Nanostructures on Sapphire Surfaces Induced by Metal Impurity Assisted Ion Beam

The metal impurity assisted ion beam technology has shown its uniqueness and effectiveness in the formation and precise control of nanostructures on the surface of materials. Hence, the investigation in this area is vital. The morphology evolution of self-organized nanostructures induced by Fe co-deposition assisted Ar+ ion beam sputtering at a different distance from the impurity target was investigated on sapphire, using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). We also investigated the role of metal impurities on sapphire ripple formation. Experiments were carried out at an oblique angle of incidence 65° with constant ion beam current density 487 μA/cm2 and the erosion duration of 60 min at room temperature (20 °C). The introduction of Fe impurity increased the longitudinal height and roughness of the surface nanostructures. Moreover, the amounts of Fe deposited on the surface decreased with increasing distance, and the morphology of the smooth sapphire surface demonstrated a strong distance dependence. Differences in surface morphology were attributed to changes in metal impurity concentration. With an increase of impurity target distance, island-like structures gradually evolved into continuous ripples. At the same time, the orderliness of nanostructures was enhanced, the longitudinal height gradually decreased, while the spatial frequency was unchanged. In addition, there were very few metal impurities on the etched sample. During the ion beam sputtering process, island-like structures promoted the growth of ripples but destroyed their orderliness.

Филаментация и самофокусировка электронных пучков в вакуумных и газовых диодах

In this paper, we experimentally studied pulsed electron beams with a high local density. The conditions in which the energy density cumulation is observed during the interaction of electrons with the anode are shown to develop in vacuum and gas diodes at nanosecond and subnanosecond durations of a beam current pulse and a decrease in the interelectrode gap. The average electron energy in filamentation and self-focusing of an electron beam in a vacuum diode of an accelerator at a current of ~2 kA and a no-load voltage of ~400 kV was established to be 50–100 keV while the energy density was 10^9–10^10 J/cm^3. It is confirmed that the beam current density in a gas diode can exceed 1 kA/cm^2. It is hypothesized that superdense electron beams in vacuum and gas diodes are formed as a result of avalanche multiplication of runaway electrons in the cathode–anode gap plasma.