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In bubble-assisted Liquid HoleMultipliers(LHM), developed for noble-liquid radiation detectors, the stability of the bubble and the electro-mechanical properties of the liquid-to-gas interface play a dominant role in the detector performance. A model is proposed to evaluate the static equilibrium configurations of a bubble sustained underneath a perforated electrode immersed in a liquid. For the first time bubbles were optically observed in LAr; their properties were studied in contact with different material surfaces. This permitted investigating the bubble-electrodynamics via numerical simulations; it was shown that the electric field acts as an additional pressure term on the bubble meniscus. The predictions for the liquid-to-gas interface were successfully validated using X-ray micro-CT in water and in silicone oil at STP. The proposed model and the results of this study are an important milestone towards understanding and optimizing the parameters of LHM-based noble-liquid detectors., 25 pages, 15 figures

The recently developed variational cellular method (VCM) is used to investigate the ground and excited electronic structures of F2 and Ne2 molecules. This work reports our first attempt to apply the VCM to the study of molecular excited states. It is concluded that VCM yields potential energy curves for these molecules with a good degree of physical realism.

A method is presented to determine all the elements of the plasma Mueller matrix with high time-resolution (about 1 µs) using only measurements of phase. This knowledge allows one to derive the pure Cotton–Mouton and Faraday effects even when polarimetric effects are large.

A simple exact method is described for the analysis of mode purity produced inside magnetized plasma as a function of input polarization of the injected electromagnetic wave. The method is applied to experimental results obtained for RF heating on the large helical device (Notake T et al 2005 Plasma Phys. Control. Fusion 47 531).

Two new methods are proposed for the simultaneous determination of the Cotton–Mouton and the Faraday effects in a magnetized plasma from direct measurements of phase only, which are preferable to amplitude measurements since they do not require detector calibrations and allow better signal-to-noise ratios. The present methods can achieve frequencies up to hundreds of kHz, much higher than with a previously proposed method. The choice between the two alternative methods is dictated by practical considerations and is briefly discussed.

A formalism is developed for treating the evolution of polarization in a magnetized plasma with dissipation (which is a birefringent and dichroic medium). An expression for the differential Mueller matrix describing the evolution in a weakly nonuniform plasma is found, directly in terms of the dielectric tensor of the plasma. The formalism is illustrated by applying it to the case where dissipation is due to particle collisions, when simple analytic expressions can be obtained. The formalism will be useful in more complicated situations, such as a plasma with Landau damping, where a numerical analysis becomes necessary.

The effects of a finite electron temperature on the refractive index N and on the evolution of polarization for radiation propagating in a magnetized plasma are considered. Analytic expressions for N and for the Stokes vector evolution equation are found to lowest order in Te/mec2. For interferometric and polarimetric measurements on typical plasma confinement configurations, the thermal effects are found to be significant. Neglecting them can lead to systematic errors in polarimetry greater than 10% for a temperature of 5 keV and to a systematic (positive) error on electron density from interferometry of 3% for Te=15 keV.

High density plasmas (n0 ≈ 8 × 1020m-3) featuring steady improved core confinement have been obtained in FTU up to the maximum nominal toroidal field (8 T) by deep multiple pellet injection. These plasmas also feature high purity efficient electron-ion coupling and peaked density profiles sustained for several confinement times. Neutron yields in excess of 1 × 1013 n/s are measured, consistent with the reduction of the ion transport to neoclassical levels.

First the complete change of polarization is obtained for radiation crossing a layer of quasi-transverse propagation in a plasma where the longitudinal component of the magnetic field changes signs along the propagation direction, while the transverse component is different from zero. The analysis is made for arbitrary input polarization. The results are then used for the interpretation of previously published measurements of radio emission from solar active regions. It is found that if a sufficiently narrow detection bandwidth is used, more information can be obtained from measurements than has been considered up to now. The present analysis is also of interest for other astrophysics problems.

The state of polarization of radiation scattered from hot plasma for any given input polarization is obtained by a relativistic derivation. Approximate analytical expressions are obtained for electron temperatures below about 10 keV. The characteristics of the scattered polarization are presented in detail for fully and linearly polarized incident radiation and their implications for the design of experiments are discussed.

The evolution equation describing the change of polarization for radiation propagating in a magnetized plasma, derived previously for negligible absorption, is extended here to the case where collisions are significant and the plasma is dichroic, namely it has anisotropic absorption.

Electron temperatures in excess of 8 keV have been obtained by electron-cyclotron-resonance heating on FTU plasmas at peak densities up to $8\ifmmode\times\else\texttimes\fi{}{10}^{19}\mathrm{m}{}^{\ensuremath{-}3}$. The magnetic shear in the plasma core is low or negative, and the electron heat diffusivity remains at, or below, the Ohmic level $(0.2\mathrm{m}{}^{2}/\mathrm{s})$, in spite of the very large heating power density $(10--20\mathrm{MW}/\mathrm{m}{}^{3})$ which produces extremely high temperature gradients (up to 120 keV/m). The ion heat transport remains at the neoclassical level.

In this review of plasma polarimetry, first the theory is discussed in general, then exact analytic solutions of the evolution equation for polarization are presented, as well as approximate analytic solutions. Numerical integration of the evolution equation is also discussed. The design of experiments is then considered taking into account the maximum amount of information which can be obtained from polarimetric measurements. Special attention is devoted to the techniques of polarization modulation (including both progressive and alternating modulation). Different alternative configurations are described which are of special interest because they can be realized in the far infrared and because they allow a measurement of phases rather than amplitudes. The effects of refraction are then briefly considered. Finally, the combination of polarimetry and interferometry on the same instrument is discussed, including the effects of polarization modulation.

When polarimetric effects are large the Cotton–Mouton and Faraday effects do not combine linearly and it is not possible to separate exactly the pure Cotton–Mouton effect W1 and the pure Faraday effect, W3. Four alternative approximate expressions for W1 and W3 in terms of measurable quantities are examined for tokamak configurations. Two of these approximations proposed recently are found to be preferable, some previous statements concerning them are corrected and the errors incurred by their use are evaluated.

The combination of interferometry and polarimetry using modulation of the input polarization is considered. For this case an expression for the interferometric phase is derived showing the presence of an additional time-varying term with respect to the case without modulation. It is found that for finite plasma birefringence the additional term is always important even if a linear input polarization is used, in contrast to the case where birefringence is zero. If the contribution of the additional term is eliminated by filtering, a consequence is a loss of time resolution on the interferometric measurement.

On 13 March 1994, a fragmented, incomplete and highly fossilized, human calvarium was discovered in situ by one of the authors (I.B.) during excavations for the construction of a highway near Ceprano, a town in southern Latium, situated about 55 miles S.E. from Rome. The remains come from a clay lying below sandy volcaniclastic gravels whose age is estimated by K–Ar to be 700 ka. The shape and capacity (ca. 1185 ml) of the calvarium show that the hominid from Ceprano possesses several, but not all, of the features of Homo erectus .

It is shown that the full polarimetric transition matrix of a magnetized plasma can be determined with a good time resolution (down to 100 ns) and, furthermore, it is possible to make use mainly of phase measurements, which are less sensitive to noise than amplitude measurements. The simultaneous measurement of the nine elements of the absolute transition matrix (or of the eight elements of the normalized transition matrix) allows a significant enhancement of the information obtained for each probing beam.

It is shown that it is possible to measure both the plasma density and the poloidal magnetic field simultaneously by polarimetry, purely from phase measurements. The latter are advantageous compared with previously proposed amplitude measurements. The phase measurements can be performed either by modulating the input polarization (two alternative configurations for this modulation are considered), or by modulating the output polarization. The merits of the three schemes are discussed. The polarimeter required for these measurements is simpler and more robust than the conventional interferometer - polarimeter presently used for the combined density and magnetic field measurements.

A formalism is presented for treating plasma polarimetry when both the Cotton–Mouton and the Faraday effects are large. For this general case it is shown that, for each measuring chord, up to nine parameters related to the plasma can be determined, instead of the usual single Faraday rotation. These parameters can be measured by a convenient modulation of the polarization state of the input radiation, and they can be used in the reconstruction of the magnetohydrodynamic equilibrium. Thus, the potential of the polarimetric diagnostic can be significantly increased, and the range of plasma conditions where the latter can be used, is extended. The importance of refraction is discussed.

A method is presented for the treatment of tokamak polarimetric systems, which is a hybrid between the Jones matrix and the Poincare sphere methods. The method can be readily applied both to analytical and to numerical treatments and therefore is a useful alternative to the method described recently by Soltwisch which uses only Jones matrices and can only be used for numerical analysis. Analytical expressions are given for the case when the ellipticity of the radiation is finite, but small, and when plasma effects are also small. These expressions can supply the constraints required for MHD equilibria reconstruction.

Experimental determinations of the radial plasma flow velocity, of Zeff and of the thermal energy content, made on the Frascati Tokamak Upgrade (FTU), have been compared with the predictions of the conventional neoclassical theory, of the extended neoclassical theory and of the pseudoneoclassical theory. In the comparison only the momentum balance and continuity equations were used. The best overall agreement is found for the second of these theories, thus confirming the result of previous analyses

It is shown that the neglect of plasma birefringence in Faraday rotation measurements on tokamak experiments leads to an apparent shift of the magnetic axis and to an apparent decrease of the central safety factor, q0. The dependence of these effects on plasma parameters and on the radiation wavelength is found.

It is shown how one can measure at the same time both the electron line density and the poloidal magnetic field in a Tokamak, using only a polarimeter in order to determine the full state of polarization of radiation transmitted across the plasma. The proposed polarimeter is simpler and more flexible than the more conventional interferometer/polarimeter used on various Tokamaks.

It is shown that, within the framework of the extended neoclassical theory, for a tokamak there exists a relationship between the normalized thermalenergy content, β, and the normalized plasma current, 1/q. This relationship, which depends essentially only on plasma fuelling, is a generalization of the usual Bennett relation and it is of importance for tokamak confinement and heating.

An approximate analytic expression is given for the influence of Plasma birefringence on Faraday rotation in the tokamak and the range of validity is determined. The expression is of interest for polarimetric measurements and for the analysis of electron cyclotron emission.

This article reports on the design of the motional Stark effect diagnostic (MSE) for the Frascati Tokamak Upgrade tokamak (Rmaj=93 cm, rmin=33 cm, BT

An analytic solution is found for the evolution of the state of polarization of an electromagnetic wave propagating in a plasma with uniformly sheared magnetic field. It is the generalization of the one found previously for the special case of propagation perpendicular to the magnetic field.

Explicit use of the poloidal Ohm's law, together with the radial plasma velocity (obtained from the distribution of plasma sources), leads to a very general constraint on the possible radial profiles of plasma density and temperature. The constraint does not require any ad hoc assumption; it can place severe restrictions on the allowed profiles and is independent of energy and particle transport; also, it may be the underlying principle of profile consistency. The constraint is discussed in the framework of neoclassical theory, using results from the Frascati tokamak.

We propose ellipsometer configurations where, by conveniently modulating either the input or the output polarization, one can determine the ellipsometric parameters, D and psi, purely from phase measurements on two harmonic components of the signal from a single detector. Such phase measurements are less sensitive to noise than the conventional amplitude measurements, and the proposed modulation techniques can allow the achievement of frequencies up to tens of megahertz. Thus a very good time resolution is achieved.

High Z materials, as possible plasma facing components for a fusion reactor, are being re-evaluated due to their advantages connected to the low sputtering yield and small erosion. A data base of experimental results related to their use on present Tokamak is missing. FTU has carried out a series of experiments with different medium and high Z limiter materials, Ni, Mo, and W, to improve the knowledge of the plasma behavior in these conditions. The results on plasma operation, core parameters, impurity content, and corresponding radiation losses are presented, and compared with those obtained with a low Z dominant impurity (siliconization). A simple model coupling the SOL and the plasma core is able to reproduce the experimental results, indicating that sputtering and self-sputtering are the main physical mechanisms of impurity production. © 1995 American Institute of Physics.

For an electromagnetic wave propagating in an inhomogeneous plasma with a sheared magnetic field, the conditions are found under which a wave can remain a local characteristic mode during its propagation. Extending previous work, the conditions are determined for the general case of propagation in an arbitrary direction with respect to the local magnetic field.

We develop a numerical procedure, based upon the periodic scattering transform, for determining the spatial and temporal evolution of solutions to the Korteweg-de Vries (KdV) equation with periodic boundary conditions. In this approach solutions to KdV are found in terms of the “μ-representation”, i.e. the wave amplitude is given by a “trace formula” consisting of a linear superposition of hyperelliptic functions, μ j ( x,t ) (1≤ j ≤ N ), which are governed by N nonlinearly coupled ordinary differential equations. Our approach consists of the numerical integration of these equations using a second-order Taylor series expansion with variable integration step size. It is well known that the μ j are generalizations of elliptic functions to the hyperelliptic class; nevertheless we find that the μ j ( x,t ) bear little or no resemblance to elliptic functions except in the small amplitude, linear limit or for the case of a single soliton. We study in particular the most difficult numerical case which occurs for the N -soliton wave-train solution of the periodic KdV equation.

A mechanism for neutron emission from deuterated metals is proposed, which is based on some known phenomena, concerning hydrogen precipitation in supersaturated metals. Transient electric fields are assumed to produce energetic deuterons and hence neutrons from D(d, n)3He reactions. The mechanism predicts neutron yields compatible with those reported in some of the experiments and implies a certain degree of experimental irreproducibility.

With reference to the change of polarization of an electromagnetic wave traversing a plasma, two alternative numerical schemes are discussed for computing the plasma transition matrix for given profiles of plasma parameters. Such a computation is required for the reconstruction of magnetohydrodynamic equilibria, when the elements of the matrix are included among the measured quantities used in the best fit procedure. Both schemes, which are especially useful when the Cotton–Mouton effects are not small, ensure that the matrix remains unitary during the numerical integration.

The optical ray properties of the cube-corner retroreflector (CCR) are first recalled. The change of polarization of the radiation due to CCR reflection is then derived by use of the Mueller matrix calculus. It is found that, in general, when the faces are not ideal reflectors, the useful cross section of the CCR consists of six zones, each of which produces a different change of polarization, i.e., it gives a different Mueller matrix. All the Mueller matrices depend on wavelength. The results are quite general and can be used directly also for partially polarized radiation.

It has been suggested by various authors over the past 15 years, and also recently, that in tokamaks the perpendicular resistivity η⊥ is between 102 and 103 times the parallel (Spitzer) resistivity. Here it is shown that on the contrary the measurements on the FTU tokamak [Proceedings of the 16th Symposium on Fusion Technology, London, 1990 (North‐Holland, Amsterdam, 1991), Vol. 1, p. 218] are consistent with η⊥/η∥=2 when the extended neoclassical theory is used (which is preferable to the conventional neoclassical theory for reasons which are here reviewed).

First, the analytic expressions are derived that describe some properties of the Poincare sphere that are related to the coherent sum of two waves having different polarizations. Then these expressions are used to obtain the differential equation that describes the evolution of the state of polarization of radiation propagating in a medium that is nonuniform, birefringent, optically active, and dichroic. Finally, an important example is presented: that of a magnetized plasma in which particle collisions are not negligible, such as the earth’s ionosphere or certain laboratory plasmas. The evolution equation is the basis of plasma polarimetry.

The polarimeter system for ITER features 10 viewing chords covering almost the full poloidal cross section of the plasma in a fan-like arrangement. The 10 laser beams all enter the plasma via 150 mm diam penetrations through the diagnostic plug at the low-field side. Small retroreflectors at the high-field side mirror the laser beams back towards the penetrations at the low-field side. Extensive feasibility calculations have led to the conclusion that the optimum wavelength for the polarimeter is around 100 mu m. At this wavelength counterproductive effects like refraction and electron cyclotron absorption are negligibly small. However, the anticipated Faraday rotation angles are still very large, such that several important plasma parameters can be measured within the requirements set by the ITER team. In this article the status of the conceptual design of the polarimeter system for ITER will be presented. (C) 1999 American Institute of Physics. [S0034-6748(99)63801-1].

Three methods of density modulation have been used in FTU discharges (gas puffing, pellet injection and current rampup). The analysis of particle balance confirms that the neoclassical theory is not adequate and the experimental results obtained by the three methods are used to verify the validity of an empirical expression for the radial particle flux. Such an expression is relevant for the design of future experiments and constitutes a constraint for any satisfactory theory.

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Experiments with different dominant impurities (C, Si, Ni, Mo) have been carried out on the FTU tokamak. Density limit, marfe, Z(eff) and radiation losses are compared and discussed. An analytical model that couples in a self consistent way the parameters of the SOL and the transport of the impurities generated at the limiter to the bulk plasma parameters has been used to reproduce the experimental data.