Heavy-ion Clusters Research Articles

Quantification of ionic-liquid ion source beam composition from time-of-flight data

Ionic-liquid ion sources produce beams of charged particles through evaporation and acceleration of ions and charged droplets from the surface of an ionic liquid. The composition of the emitted beam can impact the performance of ion sources for various applications such as focused beams for microfabrication and space propulsion. Numerical inference is considered for quantification of the beam composition of an ionic-liquid ion source through determining the current fraction of different species along with providing uncertainty in inferred values. An analysis of previously presented data demonstrates the ability to quantify the presence of ion clusters, including the distinct presence of heavy ion clusters such as heptamers. Quantification of beam composition will be an important technique for quantitative comparison of different time-of-flight data.

Dissipative instability of charged aerosol flows in the mesosphere

We consider the possible mechanism of generation of charged-particle density irregularities and electric field in the middle atmosphere based on the development of the dissipative instability of a flow of large charged aerosols. A dispersion equation describing the properties of the spectral component of a quasi-static electric field with allowance for the aerosol charging inertia is obtained. This equation is used to study characteristics of the instability threshold. It is shown that the charging inertia and the presence of photoelectrons lead to an increase and a decrease in the threshold plasma frequency of the aerosols, respectively. It is found that there exist optimal combinations of such parameters as the radius of spherical aerosols and the mass of heavy ion clusters for which the instability threshold is minimum. It is also shown that the instability threshold is lower for the particles stretched along the motion direction. Quantitative estimates are given for medium parameters necessary for the excitation of instability in the region of existence of polar mesospheric summer echo as well as for spatial scales of unstable perturbations.

Au-marked RBS technique for measuring the energy loss of small heavy-ion clusters

The Au-marked Rutherford backscattering spectroscopy (Au-marked RBS) technique is used to measure the energy losses of energetic heavy ions. With this technique, an enhancement in energy losses of small cluster Si 2 + and Si 3 + in C films, in comparison with the atomic Si ions at the same velocities, has been experimentally observed.

Comment on “Stopping power of nonmonochromatic heavy-ion clusters with two-ion correlation effects”

We reconsider the results of Lontano and Raimondi [Phys. Rev. E {bold 51}, R2755 (1995)] within the full random-phase approximation. We show that the correlation and also velocity dispersion of the cluster ions enhance and reduce the stopping power, respectively. Nevertheless, the enhancement of energy losses due to ionic correlation is much stronger than that obtained by Lontano and Raimondi, and furthermore, the projectile velocity dependence of the stopping power is strictly monotonic, presenting no oscillations. We also did not obtain negative values for the cluster stopping power, as did Lontano and Raimondi. {copyright} {ital 1997} {ital The American Physical Society}

Reply to “Comment on ‘Stopping power of nonmonochromatic heavy-ion clusters with two-ion correlation effects’ ”

In this Reply it is claimed that, although in the Comment by Tkachenko, Mu{tilde n}oz-Cobo, and Mu{tilde n}oz, a full random-phase (RP) analysis of the problem of the stopping power of an expanding charged ion cluster is presented, the main conclusions drawn by these authors are substantially identical to those of our paper [Phys. Rev. E {bold 51}, R2755 (1995)], where only collective effects were considered. Indeed, the strong enhancement of the stopping power of the ion cluster with respect to that evaluated for the same number of uncorrelated projectiles at high velocity, and the decreasing two-ion correlation effect for increasing velocity spread and interaction time, are already predicted in our paper. The full RP approximation makes the behavior of the stopping power at slightly suprathermal velocities more regular. {copyright} {ital 1997} {ital The American Physical Society}

Inertial confinement fusion using hohlraum radiation generated by heavy-ion clusters

This paper discusses the feasibility of employing heavy-ion cluster beams to generate thermal radiation that can be used to drive inertial fusion capsules. The low charge-to-mass ratio of a cluster may allow the driver beam to be focused to a very small spot size with a radius of the order of 100 μm, while the low energy per nucleon (of the order of 10 keV) may lead to a very short range of the driver particles in the converter material. This would result in high specific power deposition that may lead to a very high conversion efficiency. The problem of cluster stopping in cold matter, as well as in hot dense plasmas has been thoroughly investigated. The conversion efficiency of cluster ions using a low-density gold converter has also been calculated over a wide range of parameters including converter density, converter geometry, and specific power deposition. These calculations have been carried out using a one-dimensional hydrodynamic computer code that includes a multigroup radiation transport scheme [Ramis et al., Comput. Phys. Commun. 49, 475 (1988)]. The problem of symmetrization of this radiation field in a hohlraum with solid gold walls has also been thoroughly investigated using a three-dimensional view factor code. The characteristics of the radiation field obtained by this study are used as input to capsule implosion calculations that are done with a three-temperature radiation-hydrodynamic computer code MEDUSA-KAT [Tahir et al., J. Appl. Phys. 60, 898 (1986)]. A reactor-size capsule which contains 5 mg deuterium–tritium (DT) fuel is used in these calculations. The problem of using a fuel mixture with a substantially reduced tritium content has also been discussed.

Simulation of heavy-ion cluster impact fusion

A computer simulation by the time-evolution Monte Carlo code DYACAT has been performed in order to investigate the possibility of heavy-ion cluster impact fusion due to heavy-ion cluster impacts on a TiD 2 target. As a heavy-ion cluster, (Al) N , (Ti) N and (Ag) N clusters are considered. These three cluster impacts can produce a well-defined, long-lived quasi-equilibrium state. It is found that Al clusters can transfer their energy to target deuterium atoms most efficiently among these three clusters. For the (Al) N cluster impacts, the temperature of target deuterium atoms in the impact region is well represented by kT = E 0 1.13/79.6 exp[− t/ τ], where E 0is the cluster energy per atom in eV, and τ is the cooling time constant which is given as τ = 2.1 × 10 2 N 0.10/ E 0 0.12 fs. The total fusion yield per cluster impact is of the order of 10 −11 for 50 keV/atom (Al) 200 cluster impacts.

Simulation of heavy-ion cluster impact fusion

A computer simulation by the time-evolution Monte Carlo code DYACAT has been performed in order to investigate the possibility of heavy-ion cluster impact fusion due to heavy-ion cluster impacts on a TiD2 target. As a heavy-ion cluster, (Al)N, (Ti)N and (Ag)N clusters are considered. These three cluster impacts can produce a well-defined, long-lived quasi-equilibrium state. It is found that Al clusters can transfer their energy to target deuterium atoms most efficiently among these three clusters. For the (Al)N cluster impacts, the temperature of target deuterium atoms in the impact region is well represented by kT = E01.13/79.6 exp[−t/τ], where E0is the cluster energy per atom in eV, and τ is the cooling time constant which is given as τ = 2.1 × 102N0.10/E00.12 fs. The total fusion yield per cluster impact is of the order of 10−11 for 50 keV/atom (Al)200 cluster impacts.

Stopping power of nonmonochromatic heavy-ion clusters with two-ion correlation effects.

The stopping power of an ensemble of a large number of fast heavy ions, moving in a plasma, with a distribution function which has small spreads both in the physical and in the velocity spaces, is computed on the basis of a classical dielectric theory, retaining two-ion correlation effects. Averaging procedures in the configuration space are used to determine the actual friction force acting on the whole system and to evaluate the vicinage effects when the ion beam is not strictly monochromatic, as it was considered previously. Approximate analytical scalings with the physical parameters of the considered system of the average vicinage function and of the decorrelation time are given.

Indirect drive inertial fusion using heavy ion cluster beams

Energetic heavy ion clusters may be used as an efficient driver for inertial confinement fusion. Such cluster beams may implode direct drive as well as indirect drive targets. This paper discusses the advantages of using a cluster driver as compared to a heavy ion driver from the point of view of a target designer. Numerical simulation results of implosion of a reactor-size, indirect drive target are also presented. This target is imploded by a homogeneous radiation field that may be generated by heavy ion beam or a cluster beam. About 5.4 MJ input radiation energy is needed to implode the target and the implosion yields 770 MJ output thermonuclear energy so that the overall target gain is of the order of 140.

Fragmentation and stopping of heavy cluster ions in a lithium target−Application to target implosion

Heavy-ion clusters are considered for driving directly a pellet for inertial confinement fusion. They are shown to be effective at much lower energy than requested for heavy atomic ions. Multifragmentation, arising from a Coulomb explosion, in the target, is discussed with a maximum entropy hypothesis. Direct driving pressure imparted to a deuterium–tritium (DT) pellet is estimated through the ion debris range in the target. The correlated stopping of N ions flowing close to the initial projectile trajectory is seen to be much larger than the uncorrelated one. Specific attention is paid to a few regular geometrics of cluster ion debris stopped in a lithium pusher. The calculations elaborate on the very high driving pressure obtained, for the case of a solid-state density of cluster ion projectiles around the pellet (moving tamper). A target containing 4 mg of deuterium and tritium fuel is demonstrated to be thus imploded in 5 nsec. A driving pressure of 500 Mbars yields an energy output of 630 MJ. This result can be obtained with an initial cluster kinetic energy smaller than 20 keV/amu.

Ion cluster interaction with cold targets for ICF: Fragmentation and stopping

Heavy ion clusters are considered for driving an inertial confinement fusion (ICF) pellet. They are shown to be effective at much lower energy than required for atomic ions. Multifragmentation is discussed with a maximum entropy hypothesis. Direct pressure imparted to a DT pellet is estimated. The stopping of strongly correlated ion cluster debris flowing in a degenerate electron jellium target is calculated for polarized and unpolarized (with respect to velocity) projectiles. A reduced stopping occur for elongated configurations at low velocities (υ ⋍ 1 a.u.) and very dense targets. Transverse geometries experience a very large and enhanced stopping. Systematic trends are stressed out. Largest stopping is achieved when debris correlation lengths are smaller than the target jellium screening length.

Ion Cluster Stopping in Cold Targets for Icf

Heavy ion clusters are considered for driving an ICF pellet. They are shown to be effective at much lower energy and intensity than required for atomic ions. Direct pressure imparted to a DT pellet is estimated.The stopping of strongly correlated ion cluster debris flowing in a degenerate electron jellium target is considered for polarized (with respect to velocity) projectiles. Chains and rectangle geometries are considered. Systematic trends are stressed out.

252Cf plasma desorption in ion implanted mica

252Cf plasma-desorption mass spectrometry was first used1 to determine the masses of heavy molecules of biological interest2,3. In this technique 252Cf fission fragments penetrate a thin deposit of material (105 cm−2) inducing the desorption of neutral and ionized species. The ionized species are accelerated by an external electrical field and their mass analysed using a time-of-flight (TOF) mass spectrometer run in the coincidence mode with each fission fragment. We have tried to assess the analytical and/or simulation potential of heavy-ion stimulated desorption of ions (HISD) in other fields ranging from the so-called ‘gas–grain’ interactions in astrophysics to the complex ageing of surfaces exposed to strongly ionizing environments in fast neutron fission reactors and fusion reactors. We outline here the potential of HISD for investigating ion implantation effects in insulators, and report a very strong enhancement in the HISD of ionized species from ion implanted mica. This enhancement, which generates heavy-ion clusters up to mass ∼500 AMU, grows around a critical fluence of implanted ions, and originates from two distinct types of radiation damage defects.

Realistic heavy-ion adiabatic potentials

The K-matrix model of Cusson, Trivedi, Meldner and Weiss has been used to compute static adiabatic heavy-ion cluster potentials in a constrained self-consistent Brueckner-Hartree-Fock scheme. Heavy-ion potentials are found which can simultaneously reproduce the experimentally deduced heavy-ion potentials in the asymptotic region and the total energy versus quadrupole moment in the fused, compound nucleus region. Potentials for α-α, α- 12C, α- 16O, 12C- 12C, 16O- 16O are shown and compared with other work. The total energy of 12C and 24Mg versus deformation is also given.