Study of three-dimensional structure in wire-array z pinches by controlled seeding of axial modulations in wire radius

Three-dimensional perturbations have been seeded in wire-array z pinches by etching 15 microm diameter aluminum wires to introduce 20% modulations in radius with a controlled axial wavelength. These perturbations seed additional three-dimensional imploding structures that are studied experimentally and with magnetohydrodynamics calculations, highlighting the role of current path nonuniformity in perturbation-induced magnetic bubble formation.     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.     

An understanding of the properties of the dineutron and the deuteron in terms of quantum wave function interference

The recently reported evidence for the existence of an unstable state of the dineutron has raised again the issues associated with this particle and with the related deuteron. For the dineutron there is the question of why it has no stable ground state, while for the deuteron the magnetic and electric properties are unusual. In this Letter we show how it is possible to explain these effects in a simple way, using only considerations of interference between the wave functions of two spin 1/2 particles in the same energy state.     

Ion temperature and hydrodynamic-energy measurements in a Z-pinch plasma at stagnation

The time history of the local ion kinetic energy in a stagnating plasma was determined from Doppler-dominated line shapes. Using independent determination of the plasma properties for the same plasma region, the data allowed for inferring the time-dependent ion temperature, and for discriminating the temperature from the total ion kinetic energy. It is found that throughout most of the stagnation period the ion thermal energy constitutes a small fraction of the total ion kinetic energy; the latter is dominated by hydrodynamic motion. Both the ion hydrodynamic and thermal energies are observed to decrease to the electron thermal energy by the end of the stagnation period. It is confirmed that the total ion kinetic energy available at the stagnating plasma and the total radiation emitted are in balance, as obtained in our previous experiment. The dissipation time of the hydrodynamic energy thus appears to determine the duration (and power) of the K emission.     

Spectroscopic diagnosis of the temperature profile of an Al:MgZ-pinch

We consider the question of how the temperature profile of a Z-pinch plasma can be determined and/or constrained by the requirement that its observed K-shell spectrum be replicated. As a case study we employ spatially integrated, time-resolved K-shell data obtained from the implosion of 30-wire Al:Mg alloy arrays on the Saturn driver at Sandia National Laboratories. Given the measured pinch size, its K-shell power and line intensities are compared with the predictions of a collisional-radiative-equilibrium plasma model whose temperature profile is varied in seeking agreement with the data. The Al data rules out a large range of possible temperature profiles, but two quite different temperature distributions can both match the measurements. These are: a uniform temperature, or, one with a sharply dropping temperature near the pinch outer edge. However, the measured ratio of the Mg α resonance lines to those of Al, even though time-integrated, excludes the possibility of a uniform temperature distribution     

Ion-kinetic-energy measurements and energy balance in a Z-pinch plasma at stagnation

The ion-kinetic energy throughout K emission in a stagnating plasma was determined from the Doppler contribution to the shapes of optically thin lines. X-ray spectroscopy with a remarkably high spectral resolution, together with simultaneous imaging along the pinch, was employed. Over the emission period, a drop of the ion-kinetic energy down to the electron thermal energy was seen. Axially resolved time-dependent electron-density measurements and absolute intensities of line and continuum allowed for investigating, for the first time, each segment of the pinch, the balance between the ion-kinetic energy at the stagnating plasma, and the total radiation emitted. Within the experimental uncertainties, the ion-kinetic energy is shown to account for the total radiation.     

Transition metal derivatives of arene diazonium ions : X. Four-coordinate arenediazo derivatives of iron(−II) and cobalt(−)

The first arenediazo derivatives of iron(?II), Fe(N₂Ar)(NO)(CO)(PPh₃), have been synthesised and their properties are described. A linear relationship has been found between v(CO) in these complexes and η^? for the para substituent in the arenediazo aryl ring. The ⁵⁷Fe Mössbauer spectra of the complexes indicate that [ArN₂]⁺ is a stronger σ-donor and weaker π-acceptor than [NO]⁺. The relationship between ΔE_q and σ_p^? suggests that changes in ΔE_q with aryl substitution involve both substituent-specific and substituent-independent effects. The unstable cobalt(?I) compound Co(N₂C₆H₅)(CO)₂(PPh₃), the first arenediazo derivative of cobalt, is also described.     

On the issue of zero point energy in Bose–Einstein condensates

Following on our earlier work in this area, here we examine in some detail the physical mechanism involved in the Bose–Einstein condensation process. In particular we emphasise the significance of the zero value of the chemical potential at and below the critical temperature. The molar zero-point energy (ZPE) for an ideal gas of He⁴ atoms in our new analysis is estimated and found to be very close to that calculated for an ideal Fermi gas of He³ atoms under the same conditions. This gives numerical support to our theory. We also show how the theory is consistent with the presence of a density maximum in liquid He⁴.     

Relaxation effects in the mössbauer spectra of some seven-coordinate iron(III) complexes

Mössbauer studies have been carried out on a series of high-spin seven-coordinate complexes of iron(III). The group show interesting temperature-dependent properties which may be interpreted in terms of paramagnetic relaxation effects. A detailed analysis of these properties allows a direct correlation to be drawn between the spectroscopic zero-field splitting and the quadrupole splitting for high-spin iron(III) complexes