ABSTRACT The surface flashover ion source is a possible development direction of micro/nano ion source technology. In this paper, a two‐electrode surface flashover ion source was fabricated by deposition of titanium film on a ceramic substrate by magnetron sputtering. The evolution of luminescence image, temperature distribution and erosion characteristics of this ion source during discharge were analyzed by using a high‐speed camera, a multispectral temperature measurement method and a microscope. A simplified simulation model of the initial discharge of this ion source is established by using a two‐dimensional particle‐in‐cell coupled with Direct Simulation Monte Carlo method. The evolution characteristics of plasma distribution, electric field distribution and potential distribution during the discharge process were obtained. It is shown that the electric field at the metal‐ceramic‐vacuum “triple junction” is suppressed during the discharge process, and field‐induced electron emission is formed at the edge of the cathode, which leads to the discharge. In addition, it is revealed that the high density plasma accumulated near the cathode will form a sheath, which enlarges the strong electric field region and makes the cathode spot develop along the cathode surface. This is the reason why the discharge process of this ion source is different from that of the usual surface flashover. These findings provide support for further understanding of the physical mechanism of surface flashover ion sources.
Measurements of ion acceleration in laser-generated plasma obtained at intensities from 1010 up to 1015 W/cm2 using IR laser ablation of aluminum, copper, silver, and tantalum in high vacuum are presented. At low intensity, data were acquired from the MIFT Department of Messina University (Italy) using a Q-switched Nd:YAG laser operating at 1064 nm, and at high intensity from the PALS Laboratory (Czech Republic) using the Asterix Iodine laser operating at 1315 nm. In both cases, ions were detected using a Faraday cup as an ion collector to measure their energy via time-of-flight, and an ion energy analyzer with electrostatic deflection to evaluate the ion charge state. The ablation yield, in terms of the mass removed per laser pulse, was acquired. Measurements demonstrated that the ion acceleration depends strongly on the laser intensity. Moreover, at low intensity, the maximum ion energy is not very dependent on the focal position with respect to the target surface. In contrast, at high intensity, it is strongly dependent on this parameter. The Coulomb-Boltzmann-shifted theory is applicable in both cases. Applications of produced ions to the deposition of thin films and to substrate ion implantation have been reported and discussed.
At the Laser Plasma Physics laboratories of the University of Messina, an experimental platform for generating and accelerating low-energy ions (keV) using pulsed lasers and for their potential applications has been put into operation. A Q-switched Nd:YAG laser produces the beam for the system, operating at 1064 nm. It is pulsed with a 3 ns duration, pulse energy adjustable from 10 mJ to 1 J, and repetition frequency adjustable from single-pulse operation to 10 Hz. It enables the stable production of high-current ion beams of all species in the periodic table, especially heavy elements with high boiling points and high latent heat of evaporation. The laser-plasma ion sources, produced in vacuum, were characterised as a function of the laser intensity on the target by varying the laser parameters and providing evidence of the important role of the latent heat of evaporation of the heavy irradiated targets for the production of ions. The versatility and tunability of such laser-plasma ion sources are of potential interest for many applications in research, industry, medicine, nuclear physics, analysis and processing of innovative materials and more.
ABSTRACT High quality grids are a crucial ingredient to obtain trustworthy results from any plasma edge simulation code, especially those that employ low order discretization schemes such as SOLPS‐ITER. We present a grid generation algorithm that is able to generate 2D unstructured aligned grids for arbitrary toroidally‐symmetric magnetic field topologies and quasi‐arbitrary wall geometry. Since the algorithm requires only a relatively small set of user inputs that is mainly dependent on machine parameters, it is capable of generating grids for different magnetic topologies automatically. Furthermore, grids extending up to the vessel wall can be generated without additional user intervention. This makes it ideal for remeshing purposes for shape and magnetic field optimization in the future, contrary to existing grid generators. The algorithm consists of two main steps: a magnetic topology mesh generation step and a grid generation step. The first step partitions the domain into topologically rectangular regions, which are used in the second step to apply a block‐structured mesh approach. Several useful features, such as local refinement and boundary layers, are implemented to arrive at high quality grids. The grid generator is currently implemented in the Grid Optimization and Adaptation Toolbox (GOAT) and the resulting grids have been used for plasma edge simulation with SOLPS‐ITER.
ABSTRACT In this work, we investigate the electrical conductivity of weakly coupled hydrogen plasma using the electric field autocorrelation function (EACF). The EACF is evaluated from an effective interaction potential that includes electron‐ion, electron–electron, and electron‐background interactions. For weakly coupled plasmas, the electron‐ion interaction is described by the Debye‐screened potential. The velocity autocorrelation function (VACF) is also calculated. The electrical conductivity investigated using the EACF and VACF, respectively, in the electron‐density range from 10 22 to 10 25 m −3 , is compared with the Lorentz model, the Spitzer theory, and a quantum‐statistical approach. Good agreement is obtained with the Lorentz model. Results indicate that the EACF provides a reliable alternative to the VACF for calculating the electrical conductivity of weakly coupled hydrogen plasmas due to its faster relaxation time.
