Resonant interaction of fast particles with Alfven waves in spherical tokamaks

The Spherical Tokamak (ST) concept has become one of the main avenues in magneticnuclear fusion research since STs successfully demonstrated plasma operationat [Beta] = 2P[mu]0=B2~1. Next step ST machines aiming at achieving burning plasmaconditions in high [Beta] plasmas are being planned, such as the Spherical TokamakPower Plant (STPP) and the Component Testing Facility (CTF). Instabilities offast particle-driven Alfven eigenmodes are often observed in present-day STs. Suchinstabilities, driven by fusion-born alpha particles as well as by fast ions producedwith auxiliary heating schemes, in the next step STs may pose a major problem asthese instabilities may affect confinement and losses of the fast ions.A theory of compressional Alfven eigenmodes (CAE) with frequencies above thedeuterium cyclotron frequency,[omega] > [omega]cD, is developed for plasma parameters of aSTPP, and modes in the ion-ion hybrid frequency range, [omega]cT < [omega] < [omega]cD, are alsoinvestigated in order to assess the potential of diagnosing the deuterium-tritium(D-T) ratio. For the 1-D character of a STPP equilibrium with [Beta]~1 , a `hollowcylinder toroidal plasma model is employed for studying CAEs with arbitrary valuesof the parallel wave-vector k[||] = k[.]B/|B|. The existence of weakly-damped CAEs,free of mode conversion, is shown to be associated with the `well in the magneticfield profile, B = B (R), that can exist at the magnetic axis.A significant part of this thesis focusses on the experimentally observed effectsof resonant wave-particle interaction between Alfven waves and fast particles in theMega Amp Spherical Tokamak (MAST) device at the Culham Laboratory, UK, andin the LArge Plasma Device (LAPD) in the University of California, Los-Angeles,USA. New robust experimental scenarios for exciting CAEs in the MAST spherical tokamak are developed, and interpretation of the observed CAEs in the frequencyrange [omega]cD/3 < [omega] < [omega]cD is given in the context of the 1-D ST model and the Dopplershifted cyclotron resonance. The e ciency of the Doppler resonance between coand counter directed fast ions and left and right hand polarised Alfven waves isfurther assessed experimentally on the LAPD device, with probe ions injected inthe presence of Alfv en waves launched by an external antenna.The developed theory of CAEs is then applied to a calculation of the linear kineticdrive of CAEs in the MAST experiments. A model representation of the fast iondistribution function, produced by neutral beam injection (NBI), is used by fittingto the TRANSP Monte-Carlo NBI modelling results. The main free energy sourcesassociated with temperature anisotropy and bump-on-tail are estimated analytically,and the CAE stability boundary is qualitatively assessed.In order to explain the experimentally observed difference between steady-stateand pulsating Alfvenic modes, the non-linear theory of fast particle driven modesnear marginal stability is extended to include dynamical friction (drag). For thebump-on-tail problem, the drag is shown to always give an explosive amplitudeevolution in contrast to diffusion in velocity space in the vicinity of the wave-particleresonance. This is then extended to the case of experimentally observed NBI-driventoroidal Alfven eigenmodes (TAEs) in the MAST machine. The experimentallyobserved differences between TAEs driven by fast ions produced with ion cyclotronresonance heating (ICRH) and NBI are then interpreted. The problem of dragdominated collisions for modes excited by fusion-born alpha particles in burningplasmas such as a STPP and ITER is underlined.Imperial Users onl

RGE Behaviour of SUSY with a U(2)^3 symmetry

The first LHC results seem to disfavour, from the point of view of naturalness, any constrained MSSM realization with universal conditions at the SUSY-breaking scale. A more motivated scenario is given by split-family SUSY, in which the first two generations of squarks are heavy, compatible with a U(2)^3 flavour symmetry. We consider this flavour symmetry to be broken at a very high scale and study the consequences at low energies through its RGE evolution. Initial conditions compatible with a split scenario are found, and the preservation of correlations from minimal U(2)^3 breaking are checked. The various chiral operators in $\Delta F=2$ processes are analyzed, and we show that, due to LHC gluino bounds, the (LL)(RR) operators can not always be neglected. Finally, we also study a possible extension of the U(2)^3 model compatible with the lepton sector.Comment: 22 pages, 9 Figures; v2: minor corrections, improved discussion on (LL)(RR) operators, main results unchange

The Distribution of Nearby Stars in Velocity Space Inferred from Hipparcos Data

(abridged) The velocity distribution f(v) of nearby stars is estimated, via a maximum- likelihood algorithm, from the positions and tangential velocities of a kinematically unbiased sample of 14369 stars observed by the HIPPARCOS satellite. f(v) shows rich structure in the radial and azimuthal motions, v_R and v_phi, but not in the vertical velocity, v_z: there are four prominent and many smaller maxima, many of which correspond to well known moving groups. While samples of early-type stars are dominated by these maxima, also up to 25% of red main-sequence stars are associated with them. These moving groups are responsible for the vertex deviation measured even for samples of late-type stars; they appear more frequently for ever redder samples; and as a whole they follow an asymmetric-drift relation, in the sense that those only present in red samples predominantly have large |v_R| and lag in v_phi w.r.t. the local standard of rest (LSR). The question arise, how these old moving groups got on their eccentric orbits. A plausible mechanism, known from solar system dynamics, which is able to manage a shift in orbit space involves locking into an orbital resonance. Apart from these moving groups, there is a smooth background distribution, akin to Schwarzschild's ellipsoidal model, with axis ratio of about 1:0.6:0.35 in v_R, v_phi, and v_z. The contours are aligned with the $v_r$ direction, but not w.r.t. the v_phi and v_z axes: the mean v_z increases for stars rotating faster than the LSR. This effect can be explained by the stellar warp of the Galactic disk. If this explanation is correct, the warp's inner edge must not be within the solar circle, while its pattern rotates with frequency of about 13 km/s/kpc or more retrograde w.r.t. the stellar orbits.Comment: 16 pages LaTeX (aas2pp4.sty), 6 figures, accepted by A

Microlensing toward crowded fields: Theory and applications to M31

We present a comprehensive treatment of the pixel-lensing theory and apply it to lensing experiments and their results toward M31. Using distribution functions for the distances, velocities, masses, and luminosities of stars, we derive lensing event rates as a function of the event observables. In contrast to the microlensing regime, in the pixel-lensing regime (crowded or unresolved sources) the observables are the maximum excess flux of the source above a background and the full width at half-maximum (FWHM) time of the event. To calculate lensing event distribution functions depending on these observables for the specific case of M31, we use data from the literature to construct a model of M31, reproducing consistently photometry, kinematics and stellar population. We predict the halo- and self-lensing event rates for bulge and disk stars in M31 and treat events with and without finite source signatures separately. We use the M31 photon noise profile and obtain the event rates as a function of position, field of view, and S/N threshold at maximum magnification. We calculate the expected rates for WeCAPP and for a potential Advanced Camera for Surveys (ACS) lensing campaign. The detection of two events with a peak signal-to-noise ratio larger than 10 and a timescale larger than 1 day in the WeCAPP 2000/2001 data is in good agreement with our theoretical calculations. We investigate the luminosity function of lensed stars for noise characteristics of WeCAPP and ACS. For the pixel-lensing regime, we derive the probability distribution for the lens masses in M31 as a function of the FWHM timescale, flux excess and color, including the errors of these observables.Comment: 45 pages, 27 figures LaTeX; corrected typos; published in the Astrophysical Journal Supplemen

Tracy-Widom asymptotics for q-TASEP

We consider the q-TASEP that is a q-deformation of the totally asymmetric simple exclusion process (TASEP) on Z for q in [0,1) where the jump rates depend on the gap to the next particle. For step initial condition, we prove that the current fluctuation of q-TASEP at time t are of order t^{1/3} and asymptotically distributed as the GUE Tracy-Widom distribution, which confirms the KPZ scaling theory conjecture.Comment: 24 pages, 5 figure

Tomographic approach to resolving the distribution of LISA Galactic binaries

The space based gravitational wave detector LISA is expected to observe a large population of Galactic white dwarf binaries whose collective signal is likely to dominate instrumental noise at observational frequencies in the range 10^{-4} to 10^{-3} Hz. The motion of LISA modulates the signal of each binary in both frequency and amplitude, the exact modulation depending on the source direction and frequency. Starting with the observed response of one LISA interferometer and assuming only doppler modulation due to the orbital motion of LISA, we show how the distribution of the entire binary population in frequency and sky position can be reconstructed using a tomographic approach. The method is linear and the reconstruction of a delta function distribution, corresponding to an isolated binary, yields a point spread function (psf). An arbitrary distribution and its reconstruction are related via smoothing with this psf. Exploratory results are reported demonstrating the recovery of binary sources, in the presence of white Gaussian noise.Comment: 13 Pages and 9 figures high resolution figures can be obtains from http://www.phys.utb.edu/~rajesh/lisa_tomography.pd

ZZH coupling : A probe to the origin of EWSB ?

We argue that the $ZZH$ coupling constitutes a simple probe of the nature of the scalar sector responsible for electroweak symmetry breaking. We demonstrate the efficacy of this measure through an analysis of four-dimensional models containing scalars in arbitrary representation of $SU(2) \times U(1)$, as well as extra-dimensional models with a non-factorizable geometry. A possible role for the $t \bar t H$ couplings is also discussed.Comment: Minor modifications in the text. Version to appear in Nucl. Phys.