[en] Accurate tracking in inhomogeneous and arbitrarily oriented magnetic fields requires the velocity and direction of the drifting ionization to be known to high precision. A semi-empirical method of calculating drift velocities and magnetic deflection angles is presented for non-perpendicular electric and magnetic fields. Data obtained using a drift chamber rotated in a B-field verify the calculation. The model is used to restore accuracy in the L3 forward/backward muon detector where non-orthogonal and inhomogeneous electric and magnetic fields are present. (orig.)

[en] The achievement of large volumetric power losses (dissipation) in the Alcator C-Mod divertor region is demonstrated in two operational modes: radiative divertor and detached divertor. During radiative divertor operation, the fraction of SOL power lost by radiation is P_R/P_SOL∼0.8 with single null plasmas, n_e<2x10²⁰ m^-3 and I_p<1 MA. These plasmas sometimes have very high recycling, with n_e,div≤6x10²⁰ m^-3. As the divertor radiation and density increase, the plasma eventually detaches abruptly from the divertor plates: I_SAT drops at the target and the divertor radiation peak moves to the X-point region. Probe measurements at the divertor plate show that the transition occurs when T_e∼5 eV. The critical n_e for detachment depends linearly on the input power. This abrupt divertor detachment is preceded by a comparatively long period ( similar 1-200 ms) where a partial detachment is observed to grow at the outer divertor plate. ((orig.))

[en] To cope with the high bunch crossing rates of future particle accelerators, new detectors must have short recovery times. We measured the transit time of drifting photoelectrons in straw tubes of 2.5 mm radius for magnetic fields ranging from 0 to 8 T. Six different gas mixtures, primarily CF₄ based, were studied. Long transit times and signal degradation indicate the need for careful choices in detector design. (orig.)

[en] A series of experiments has been carried out on Alcator C-Mod to compare impurity penetration between similar limiter and divertor discharges. Known amounts of recycling impurities (Ar and Ne) and non-recycling impurities (N₂ and CH₄) are injected by gas puffing, and the fraction ending up in the plasma is deduced from spectroscopic measurements. The poloidal location of the gas injection is also varied. It is found that during the most recent run campaign, limiter plasmas have 1-3 times higher impurity penetration than divertor plasmas which detached, but 5-20 times higher penetration compared to divertor plasmas which remained attached. During the previous run campaign, limiter plasmas had only 1-3 times higher penetration than attached divertor plasmas. These ratios are the same for both recycling and non-recycling species. There are strong dependencies on gas puff location as well. The reason for the difference in the two run campaigns is not understood, but may be related to gas leakage paths behind the divertor structure, which were plugged up between the two campaigns. (orig.)

[en] We construct lattice gauge theories in which the elements of the link matrices are represented by non-commuting operators acting in a Hilbert space. These quantum link models are related to ordinary lattice gauge theories in the same way as quantum spin models are related to ordinary classical spin systems. Here U(1) and SU(2) quantum link models are constructed explicitly. As Hamiltonian theories quantum link models are non-relativistic gauge theories with potential applications in condensed matter physics. When formulated with a fifth Euclidean dimension, universality arguments suggest that dimensional reduction to four dimensions occurs. Hence, quantum link models are also reformulations of ordinary quantum field theories and are applicable to particle physics, for example to QCD. The configuration space of quantum link models is discrete and hence their numerical treatment should be simpler than that of ordinary lattice gauge theories with a continuous configuration space. (orig.)

[en] We use perturbation theory to construct perfect lattice actions for quarks and gluons. The renormalized trajectory for free massive quarks is identified by blocking directly from the continuum. We tune a parameter in the renormalization group transformation such that for 1d configurations the perfect action reduces to the nearest-neighbor Wilson fermion action. The fixed point action for free gluons is also obtained by blocking from the continuum. For 2d configurations it reduces to the standard plaquette action. Classically perfect quark and gluon fields, quark-gluon composite operators and vector and axial vector currents are constructed as well. Also the quark-antiquark potential is derived from the classically perfect Polyakov loop. The quark-gluon and three-gluon perfect vertex functions are determined to leading order in the gauge coupling. This work provides a basis for the numerical construction of a lattice action for QCD, which is (approximately) perfect even beyond perturbation theory. (orig.)

[en] The effect of adding different impurity gases and ICRF heating on divertor detachment has been compared for Ohmic, L-mode and high-q _parallel (≥300 MW/m^-2), H-mode plasmas. The relative effect of all these external controls on divertor and core radiation is evaluated. Recycling gases (Ne and Ar) are found to primarily affect the main plasma as opposed to the divertor region. The lower Z non-recycling gases, N₂ and CD₄ are more efficacious in this regard. N₂ was found effective in inducing detachment for high-q _parallel, H-mode plasmas. An additional advantage of N₂ over the higher Z gases is that its injection resulted in the smallest degradation in H-mode energy confinement (∝10%). (orig.)

[en] A capillary injection system has been installed on Alcator C-Mod which allows the localized introduction of gaseous species at a variety of poloidal locations. An experimental program has been undertaken to observe impurity puffs with a CCD camera through appropriate optical filters. The comet-like shape of an ion line emission plume formed in the region of an injection graphically displays the direction of background deuterium flow as well as that of the poloidal impurity ion drift. Parallel and cross-field one-dimensional fluid models are used to characterize the plume shapes and to deduce the background plasma temperature, the parallel flow velocity and the poloidal drift velocity of the impurity ion. Model results are benchmarked against simulations of DIVIMP, a Monte Carlo code, and fast scanning probe measurements. The experiments present a novel diagnostic technique to elucidate local edge impurity transport. (orig.)

[en] A novel, simple, and inexpensive multi-point two-coordinate alignment technique based on a stretched wire approach is proposed for the axial alignment of the GEM muon chambers. The concept was simulated and tested in a laboratory. Over a very wide range (∼10 mm) of possible displacements in two directions (orthogonal to the wire), this technique is capable of providing an accuracy of a few microns for one of them and a few tens of microns for the other. (orig.)

[en] We investigate the time dependence of discontinuity factors. First, equations for the discontinuity factors which correct finite-difference and quadratic nodal models are developed. Calculations are then performed for a coolant inlet-temperature transient and a control rod motion transient of a Westinghouse 1000 MW_e PWR. These calculations demonstrate that many of the discontinuity factors may be held constant at their initial values, thus avoiding the costly task of updating the discontinuity factors during the transient. In transients involving control rod motions, however, corrections in the assemblies which contain moving control rods must be performed. (orig./DG)