Patrik U. Andersson

Efficient source for the production of ultradense deuterium D(-1) for laser-induced fusion (ICF)

A novel source which simplifies the study of ultradense deuterium D(-1) is now described. This means one step further toward deuterium fusion energy production. The source uses internal gas feed and D(-1) can now be studied without time-of-flight spectral overlap from the related dense phase D(1). The main aim here is to understand the material production parameters, and thus a relatively weak laser with focused intensity ≤10(12) W cm(-2) is employed for analyzing the D(-1) material. The properties of the D(-1) material at the source are studied as a function of laser focus position outside the emitter, deuterium gas feed, laser pulse repetition frequency and laser power, and temperature of the source. These parameters influence the D(-1) cluster size, the ionization mode, and the laser fragmentation patterns.

Laser-induced variable pulse-power TOF-MS and neutral time-of-flight studies of ultradense deuterium

The ultradense atomic deuterium material named D(−1) is conveniently studied by laser-induced Coulomb explosion methods. A well-defined high kinetic energy release (KER) from this material was first reported in Badiei et al (2009 Int. J. Hydrog. Energy 34 487) and a two-detector setup was used to prove the high KER and the complex fragmentation patterns in Badiei et al (2009 Int. J. Mass Spectrom. 282 70). The common KER is 630 ±30 eV, which corresponds to an interatomic distance D–D of 2.3 ±0.1 pm. In both ion and neutral time-of-flight (TOF) measurement, two similar detectors at widely different flight distances prove that atomic particles are observed. New results on neutral TOF spectra are now reported for the material D(−1). It is shown that density changes of D(−1) are coupled to similar changes in ordinary dense D(1), and it is proposed that these two forms of dense deuterium are rapidly transformed into each other. The TOF-MS signal dependence on the intensity of the laser is studied in detail. The fast deuteron intensity is independent of the laser power over a large range, which suggests that D(−1) is a superfluid with long-range efficient transport of excitation energy or particles.

Production of ultradense deuterium: A compact future fusion fuel

Ultradense deuterium as a nuclear fuel in laser-ignited inertial confinement fusion appears to have many advantages. The density of ultradense deuterium D(−1) is as high as 140 kg cm−3 or 1029 cm−3. This means that D(−1) will be very useful as a target fuel, circumventing the complex and unstable laser compression stage. We show that the material is stable apart from the oscillation between two forms, and can exist for days in the laboratory environment. We also demonstrate that an amount of D(−1) corresponding to tens of kilojoules is produced in each experiment. This may be sufficient for break-even.

Dissociative recombination of NH4+ and ND4+ ions: storage ring experiments and ab initio molecular dynamics.

The dissociative recombination (DR) process of NH4+ and ND4+ molecular ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for DR of NH4+ and ND4+ in the collision energy range 0.001-1 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 2000 K are calculated from the experimental data. The absolute cross section for NH4+ agrees well with earlier work and is about a factor of 2 larger than the cross section for ND4+. The dissociative recombination of NH4+ is dominated by the product channels NH3+H (0.85+/-0.04) and NH2+2H (0.13+/-0.01), while the DR of ND4+ mainly results in ND3+D (0.94+/-0.03). Ab initio direct dynamics simulations, based on the assumption that the dissociation dynamics is governed by the neutral ground-state potential energy surface, suggest that the primary product formed in the DR process is NH3+H. The ejection of the H atom is direct and leaves the NH3 molecule highly vibrationally excited. A fraction of the excited ammonia molecules may subsequently undergo secondary fragmentation forming NH2+H. It is concluded that the model results are consistent with gross features of the experimental results, including the sensitivity of the branching ratio for the three-body channel NH2+2H to isotopic exchange.

Scattering of water from graphite: simulations and experiments

Abstract The scattering of water molecules from a graphite (0001) surface has been studied experimentally and using molecular dynamics simulations. Model potentials for the gas–solid interaction have been developed and tested by comparing experimental and simulated angular distributions for different translational energies (0.09–0.8 eV), incident angles (30–75°) and surface temperatures (300–1200 K). Good agreement is found for both scattering intensities and angular resolved average velocities, supporting the main features of the model potentials. The importance of trapping at low incident energy is discussed as well as the possibility of vibrational excitation at high collision energy. The latter phenomenon is investigated using purely classical trajectory calculations, a forced oscillator model and a wavepacket propagation scheme. The results indicate that meaningful estimates of the vibrational excitation can be obtained using classical simulations, supporting previously reported results on the CF 3 Br/graphite system [M.B. Nagard, N. Markovic, J.B.C. Pettersson, J. Chem. Phys. 109 (1998) 10350].

Surface properties of water ice at 150–191K studied by elastic helium scattering

A highly surface sensitive technique based on elastic scattering of low-energy helium atoms has been used to probe the conditions in the topmost molecular layer on ice in the temperature range of 150-191 K. The elastically scattered intensity decreased slowly as the temperature was increased to about 180 K, followed by a rapid decrease at higher temperatures. An effective surface Debye temperature of 185+/-10 K was calculated from the data below 180 K. The changes in the ice surface above 180 K are interpreted as the onset of an anomalous enhancement of the mean square vibrational amplitude for the surface molecules and/or the onset of a limited amount of disorder in the ice surface. The interpretation is consistent with earlier experimental studies and molecular dynamics simulations. The observed changes above 180 K can be considered as the first sign of increased mobility of water molecules in the ice surface, which ultimately leads to the formation of a quasiliquid layer at higher temperatures. A small shift and broadening of the specular peak was also observed in the range of 150-180 K and the effect is explained by the inherent corrugation of the crystalline ice surface. The peak shift became more pronounced with increasing temperature, which indicates that surface corrugation increases as the temperature approaches 180 K. The results have implications for the properties and surface chemistry of atmospheric ice particles, and may contribute to the understanding of solvent effects on the internal molecular motion of hydrated proteins and other organic structures such as DNA.

Activation energies for evaporation from protonated and deprotonated water clusters from mass spectra

Experimental mass abundance spectra are used to extract evaporative activation energies (dissociation energies) for protonated water clusters, (H(2)O)(N)H(+), and deprotonated water clusters, (H(2)O)(N)OH(-), in the size range up to hundred molecules. The inversion is achieved by application of the shell correction method adapted from nuclear physics to the abundance spectra. The well known abundance anomaly for protonated clusters which occurs for N=20-22 is found to have the characteristic behavior of a shell closing, whereas other apparent magic numbers are only prominent peaks in the abundance spectra because of the instability of the evaporative precursor. For the deprotonated clusters, we find a similar shell closing for N=55-56.

Emission of small fragments during water cluster collisions with a graphite surface

Abstract The emission of small fragments during collisions of ( H 2 O ) n ( n ≤ 4000) with graphite surfaces is studied to characterize the cluster decomposition dynamics. Angular distributions for the emitted flux are measured for non-normal cluster incidence with 1375 ± 20 m/s. In the surface temperature range 800–1400 K, the distributions are well described by a model where fragments thermally evaporate from parent clusters gliding along the surface plane. When the surface temperature is decreased, clusters are slowed down by friction forces before complete evaporation takes place, and the decomposition is instead dominated by evaporation of monomers following a cosine law dependence.

Scattering and trapping dynamics of gas-surface interactions: Theory and experiments for the Xe-graphite system

We report on molecular beam experiments and molecular dynamics simulations of xenon scattering with incident energies E=0.06−5.65 eV from graphite. The corrugation felt by an atom interacting with the surface is found to be influenced by both surface temperature, Ts, and E. Angular distributions are significantly broadened when Ts is increased, clearly indicating corrugation induced by thermal motion of the surface also at the highest E employed. Direct scattering dominates for high E, while trapping becomes important for kinetic energies below 1 eV. The coupling between atom translation and surface modes in the normal direction is very effective, while trapped atoms only slowly accommodate their momentum parallel to the surface plane. The very different coupling normal and parallel to the surface plane makes transient (incomplete) trapping-desorption unusually pronounced for the Xe/graphite system, and atoms may travel up to 50 nm on the surface before desorption takes place. The nonlocal and soft charac...

Structural Rearrangements and Magic Numbers in Reactions between Pyridine-Containing Water Clusters and Ammonia

Molecular cluster ions H(+)(H(2)O)(n), H(+)(pyridine)(H(2)O)(n), H(+)(pyridine)(2)(H(2)O)(n), and H(+)(NH(3))(pyridine)(H(2)O)(n) (n = 16-27) and their reactions with ammonia have been studied experimentally using a quadrupole-time-of-flight mass spectrometer. Abundance spectra, evaporation spectra, and reaction branching ratios display magic numbers for H(+)(NH(3))(pyridine)(H(2)O)(n) and H(+)(NH(3))(pyridine)(2)(H(2)O)(n) at n = 18, 20, and 27. The reactions between H(+)(pyridine)(m)(H(2)O)(n) and ammonia all seem to involve intracluster proton transfer to ammonia, thus giving clusters of high stability as evident from the loss of several water molecules from the reacting cluster. The pattern of the observed magic numbers suggest that H(+)(NH(3))(pyridine)(H(2)O)(n) have structures consisting of a NH(4)(+)(H(2)O)(n) core with the pyridine molecule hydrogen-bonded to the surface of the core. This is consistent with the results of high-level ab initio calculations of small protonated pyridine/ammonia/water clusters.