X-ray spectra of n = 2 to 1 transitions in hydrogen-like Ca19 +, helium-like Ca18 + and nearby satellites have been obtained from Alcator C-Mod tokamak plasmas using a spatially imaging high resolution x-ray spectrometer system. For Ca19 +, the intensity ratio of Lyα2 (1s 1S1/2–2p 2P1/2) to Lyα1 (1s 1S1/2–2p 2P3/2) was found to be ∼0.531 ± 0.005 over a range of plasma parameters, which is somewhat greater than the ratio of the statistical weights of the upper n = 2 levels, 1/2. This difference is mainly due to interaction with the 2S1/2 fine structure sub-level. Experimental results are compared to calculations from COLRAD, a collisional-radiative modelling code, and good agreement is shown. For Ca18 +, the intensity ratio of the dielectronic satellite k (1s22p 2P1/2–1s2p2 2D3/2) to the resonance line w (1s2 1S0–1s2p 1P1) is sensitive only to the electron temperature. The observed brightness ratio scaling with Te is in good agreement with the calculated ratio of the respective dielectronic recombination to the collisional excitation rates.

Temporal summation is an important feature of the visual system which combines visual signals that arrive at different times. Previous research estimated complete summation to last for 100ms for stimuli judged "just detectable." We measured the full range of temporal summation for much weaker stimuli using a new paradigm and a novel light source, developed in the field of quantum optics for generating small numbers of photons with precise timing characteristics and reduced variance in photon number. Dark-adapted participants judged whether a light was presented to the left or right of their fixation in each trial. In Experiment 1, stimuli contained a stream of photons delivered at a constant rate while the duration was systematically varied. Accuracy should increase with duration as long as the later photons can be integrated with the proceeding ones into a single signal. The temporal integration window was estimated as the point that performance no longer improved, and was found to be 650ms on average. In Experiment 2, the duration of the visual stimuli was kept short (100ms or <30ms) while the number of photons was varied to explore the efficiency of summation over the integration window compared to Experiment 1. There was some indication that temporal summation remains efficient over the integration window, although there is variation between individuals. The relatively long integration window measured in this study may be relevant to studies of the absolute visual threshold, i.e., tests of single-photon vision, where "single" photons should be separated by greater than the integration window to avoid summation.

Changes in the core intrinsic toroidal rotation velocity following L-to Hand Lto I-mode transitions have been investigated in Alcator C-Mod tokamak plasmas. The magnitude of the co-current rotation increments is found to increase with the pedestal temperature gradient and q 95 , and to decrease with toroidal magnetic field. These results are captured quantitatively by a model of fluctuation entropy balance which gives the Mach number M i ∼ = ρ * /2 L s /L T ∼ ∇T q 95 /B T in an ITG turbulence dominant regime. The agreement between experiment and theory gives confidence for extrapolation to future devices in similar operational regimes. Core thermal Mach numbers of ∼0.07 and ∼0.2 are expected for ITER and ARC, respectively.