J. Sielanko

The sputtering of light target material during implantation of heavy ions

Abstract In the paper we present the results of a computer simulation and measurements of heavy ions implantation into light target material (low atomic number). The calculations have been done using the SATVAL code, and the results are compared with the experimental data from the SIMS measurement. We used the W–Be, Cs–Be, and Cs–C ion–target combinations for computer modelling of the low energy ion implantation and sputtering processes. The experimental measurements for Be and C target material have been performed using the Cs + as a primary ion beam in the SIMS apparatus. The results of computer modelling show that the ballistic phenomena cannot satisfactorily explain the experimental data.

The freon flooding technique in SIMS analysis

Abstract The efficiency of the positive secondary ion emission when exposing Cu and stainless steel samples to a freon 12 (CF 2 CI 2 ) gas under Cs + ion bombardment has been investigated. The results show a significant enhancement of secondary positive ion yield in both cases. For the Cu sample a much greater enhancement was found under the freon gas flooding in comparison with that under oxygen.

Monte Carlo simulation of the concentration distribution of sputtered cathode material in glow discharge plasma

Abstract The Monte Carlo computer code for the determination of the spatial distribution of atoms sputtered from the cathode material is presented. The code calculates the trajectories of sputtered particles in the plasma region assuming their neutral charge status during the whole path, which means that only scattering by plasma gas particles is taken into account in this model. The Moliere approximation to the Thomas–Fermi interatomic model of potential is used in the collision integrals calculations. The calculations were made for the N–Ti combination of buffer gas-cathode material. Theoretical calculations are also compared with the experimental data based on light emission of sputtered particles.

Ti and Fe cathode sputtering by the glow discharge plasma

In the paper experimental, as well as theoretical studies of sputtering yield of the Ti and Fe cathode under irradiation by nitrogen and neon glow discharge plasma are presented. The experimentally measured efficiency of the metallic cathode sputtering by neon plasma is four times higher than that of the sputtering by nitrogen plasma, despite the similarity of energy-flux characteristic of both plasmas. We suggest that such results can be explained by the influence of some parameters like the ion flux energy distribution, the dynamic change of the composition of surface layers of the cathode, the choice of proper parameter characteristics for the complex structure of the cathode surface and the backdeposition of sputtered material on sputtering efficiency. The modelled sputtering yields are finally similar to those measured.

An alternative residual ion dump for the ITER neutral beam system

Abstract An alternative concept of the residual ion dump for the ITER NBI system is presented. The incentive is to avoid the inherent risk of the in-line electrostatic ion removal concept, which is presently foreseen in the NBI design: beam-blocking by enhanced reionization losses and potential amplification of electron currents by electrostatic acceleration. It is proposed to use instead a conventional magnetic ion removal system with remote ion dumps. This method of removing the residual ions has been proven in almost all injection systems world-wide over the last two decades. First calculations show that the maximum power load can be kept below 15 MW/m2, sufficiently low to use conventional dump plate designs.

In-line magnetic residual ion dump for the ITER neutral beam system

Abstract An alternative magnetic residual ion removal concept with in-line ion dumps for the ITER neutral beam system is presented. The target plates are hit from one side and form a 500 mm wide opening to the beam. First calculations show that for the most severe case of a 3 mrad beam the maximum power load (in hot spots) can be kept below 17 MW/m 2 . Although the magnet creates additional stray fields and the concept is more complicated than the present design of an electrostatic ion removal system, the overall beamline transmission increases by about 10% (i.e. additional 1.7 MW injected power for each beamline) due to the open structure of the magnet and the ion dumps. Furthermore, the concept offers a much larger operating window regarding beam alignment, divergence and steering and it avoids creating accelerated secondary electrons.

Low energy Cs+ and Cl− ion implantation into Si — SIMS investigations

The measurements of intensity of secondary caesium, as well as chlorine ion peaks, as a function of time of irradiation were made for the Si samples using a secondary ion mass spectrometer (SIMS). The results of such measurements enable us to study the effects of variation of secondary ion emission yield during the increasing dose of irradiation of the samples. The information about saturation effects during the implantation may also be obtained. The results of measurements were compared with the computer simulation data.

A magnetic residual ion removal system with in-line ion dumps for the iter neutral beam injection system

Abstract An alternative residual ion removal concept for the ITER neutral beam system is presented. It consists of magnetic deflection of the residual ions to in-line ion dumps. The target plates are hit from one side and form a 0.5-m-wide opening to the beam. First calculations show that for the most severe case of a 3-mrad beam, the maximum power load can be kept below 15 MW/m2, using a different horizontal focal length. However, this different beamlet optic increases the beam peak power density changing the plasma deposition profile and increasing the shine-through power during low-density operation. First calculations showed that using a passive screening, the additional stray field created by the magnet could be kept below the required 1 gauss within the neutralizer. The overall beamline transmission increases by ~10% (i.e., an additional 1.7-MW injected power for each beamline for a 3-mrad beam) due to the open structure of the magnet and the ion dumps. Furthermore, the concept offers a larger operating window regarding beam alignment, divergence, steering, and transmission, and it avoids creating accelerated secondary electrons.