[en] This thesis deals with the fundamental photorefractive and photovoltaic properties of iron-doped lithium niobate crystals. Experimental observations of a strong magnetic field effect on the energy coupling and grating formation in a vectorial interaction scheme are presented. To the author's knowledge these are the first reported results in the field. It is shown that an enhancement of the diffraction efficiency of 60% is possible by applying even a moderate magnetic field of 0.23 T. A new theoretical model of the magnetophotorefractive effect in the vectorial interaction scheme is presented. It describes the space-charge field formation, two-wave mixing and grating formation under the influence of an externally applied magnetic field. Good agreement with the experimental results and the first measurement of nondiagonal components of the magnetophotovoltaic tensor are reported. A theoretical model for the temperature properties of photorefractive interference filters with subangstrom bandwidths are presented and compared favourably with experimental investigations. A novel method for determining the spectral response of these filters from a combined thermal and angular response measurements is described. (au) 9 tabs., 30 ills., 84 refs

[en] The Beta Beam, the concept of generating a pure and intense (anti) neutrino beam by letting accelerated radioactive ions beta decay in a storage ring called the Decay Ring (DR), is the basis of one of the proposed next generation neutrino oscillation facilities, necessary for a complete study of the neutrino oscillation parameter space. Sensitivities of the unknown neutrino oscillation parameters depend on the DR's ion intensity and of its duty factor (the filled ratio of the ring). Different methods, including analytical calculations and multiparticle tracking simulations, were used to estimate the DR's potential to contain enough ions in as small a part of the ring as needed for the sensitivities. Studies of transverse blow up of the beams due to resonance wake fields show that a very challenging upper limit of the transverse broadband impedance is required to avoid instabilities and beam loss.

[en] Second-harmonic emission produced by the interaction of a 130-fs laser pulse with solid aluminum has been spectrally analyzed. For an angle of incidence near 20 degree sign , the specular second harmonic is blueshifted when the laser intensity exceeds 5x10¹⁶ W /cm² . This effect is also observed in particle-in-cell simulations of the experiment. The blueshift is interpreted as a signature of the onset of absorption due to the anomalous skin effect. (c) 1999 The American Physical Society

[en] A data analysis procedure is proposed for a τ neutrino appearance experiment in which the Cherenkov light from τ leptons created in neutrino-nucleon interactions is imaged using an HPD-based RICH counter. In particular, the problem of eliminating the two orders of magnitude more abundant Cherekov light from the long-lived charged particles, that originate from the τ decay and from the neutrino interaction vertex, is treated. It is tentatively concluded that it would be feasible to reach a τ signal detection efficiency of the order of 5-10%

[en] The detection of an umbrella-shaped plume extending about 280 km above the bright limb of Io was one of the most important discoveries made during the Voyager 1 encounter with the jovian system. This discovery proves that Io is volcanically active at present, and the number and magnitude of these eruptions indicate that Io is the most volcanically active body so far discovered in the Solar System. Preliminary analyses of these eruptive plumes are presented. (U.K.)

[en] Collisionless shielding in one dimensional (highly magnetized) plasmas is paradoxical. The insertion of a positive test charge into such a plasma locally accelerates the plasma electrons, causing them to move faster in the vicinity of the test charge. Since flux conservation requires that faster moving electrons have lower density, the density of the negatively charged electrons will decrease around the test charge. The plasma anti-shields the test charge; instead of decreasing the net positive charge near the test particle, the plasma will increase the net charge. While the authors observe anti-shielding in a pure electron plasma when they employ unusual initial conditions, more commonly they observe the converse--shielding. They show here that this shielding results from the presence of electrons trapped in the potential well of the test charge. While several different mechanisms are observed to trap electrons, a ubiquitous, fast acting, transit-time mechanisms always traps electrons when the test charge is introduced adiabatically. That one dimensional (1-d), collisionless shielding requires trapping does not appear to have been previously recognized, and the explanation of shielding given in many textbooks and papers is incorrect or incomplete. Because the trapping results from dynamical processes, they call the resulting shielding ''dynamic'' shielding

[en] A comprehensive simulation study of the feasibility of an earlier proposed tau-neutrino appearance experiment based on a RICH with liquid radiator (C₆F₁₄) has been performed. Tau leptons, that are created in charged current interactions of incident tau neutrinos with the same momentum spectrum as that of the planned Gran Sasso beam (average 17 GeV/c), have an average track length of about 0.5 mm. Cherenkov photons emitted in the liquid radiator from the short track of the tau lepton provide a characteristic pattern for tau-neutrino appearance. In the present report it is shown, on the basis of simulations performed with the GEANT4 code, that Cherenkov radiation from delta electrons, originating from the interaction of the long-lived tau decay products with the Cherenkov radiator, constitutes a severe background that renders the detection of the millimeter-short tau track unfeasible. Increasing the incident neutrino beam momentum results in longer tau tracks and therefore more signal photons, but this does not solve the background problem since the kink angle between the tau track and the secondary decay particle decreases with increasing neutrino momentum, leading to an increased overlap between the Cherenkov rings of these two particles

[en] The response of a collisionless plasma to an external perturbation does not necessarily obey the standard Debye result. In some cases, the plasma will behave in a manner opposite to the manner predicted by Debye theory; i.e. the plasma becomes more positive in the neighborhood of a positive test charge. In general, the plasma shields out an external perturbation, but this shielding results solely from electrons dynamically trapped in the neighborhood of the test charge. A new theory of dynamic shielding is in good agreement with experiments in pure-electron plasmas

[en] We are developing an antenna coupled micro-bolometer using high temperature superconductors (HTS) for detection in the far infrared. A prototype consisting of a thin-film strip of Y₁Ba₂Cu₃O_x on MgO, coupled to a logarithmic periodic silver antenna has been fabricated. The measured responsivity was 10 V/W, giving an NEP of 8.10^-10W/Hz^1/2 at 500 Hz. Measurements of the DC responsivity indicate that the intrinsic responsivity is larger, pointing to a poor coupling efficiency of the antenna. Excess noise is found to be proportional to the bolometer resistance at a fixed bias current. Currently we investigate the possibility of using self-supporting bufferlayers for high sensitivity microbolometers on silicon. Some success with Y₁Ba₂Cu₃O_x on silicon with an YSZ bufferlayer has been achieved. (orig.)

[en] Beta Beam, the concept of letting accelerated radioactive ions generate a pure and intense (anti-) neutrino beam by beta decay, is the basis of one of the proposed next generation neutrino oscillation facilities, necessary for a complete study of the neutrino oscillation parameter space. The first CERN based scenario, using ¹⁸Ne and ⁶He as ν_e and ν-bar_e emitters respectively, has shown a shortfall in ¹⁸Ne production. We have now entered the era of the studies of an alternative CERN based baseline. This alternative investigates how the ions ⁸B and ⁸Li can be produced in high quantities in a 'Production Ring', accelerated and then accumulated in a 'Decay Ring'. The idea of an alternative RF scheme for the Decay Ring, to use RF barriers to collect all ions in one 'Barrier Bucket', has been tested. Longitudinal phase space simulations show that with the Barrier Bucket method it is unfeasible to optimize between ion intensity in the bucket and the duty cycle the bucket occupies. Therefore the prior RF scheme, which proved to accomplish a duty cycle that satisfied the requirements, will have to be investigated also for the new ions.