In equatorial single null diverted discharges in TEXT-Upgrade, up-down asymmetries have been noted, the sign and magnitude of which depend on plasma conditions such as electron density and X point position. Geometrical effects do not play a role in these plasmas, which are topologically up-down symmetric, so the asymmetry must come from physical driving mechanisms. Several such mechanisms will be investigated, both computationally and experimentally, and compared with data from tokamak discharges. An analysis is included of the E × B, diamagnetic and rT × B drifts as well as plasma rotation. The B2-EIRENE plasma simulation code is used to evaluate the respective influences of the rT × B driving terms. Scans of the X point position relative to the divertor plates and of the electron density are performed. The X point is brought in all the way to the divertor plates so as to assess the importance of the private region in the drift flow patterns and to break the flow loops. The low recycling regime typical of TEXT-Upgrade single null plasmas allows separation and identification of the influence of individual flows. It is concluded that E × B drift is the dominant effect and that it qualitatively explains the reported behaviour. * Current affiliation: Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA. the ∇T ×B associated flows. Mathematically, E ×B drift motion can be expressed as v E = E × B/B 2 . The diamagnetic velocity is

Scanning tunneling microscopy (STM) observations are performed on intrinsic hydrogenated amorphous silicon (a-Si:H) surfaces under monochromatic visible light irradiation. Tunneling spectroscopy results show rectifying behavior in the dark, and tunneling current increases dramatically at a negative (reverse) sample bias when the surface is continuously exposed to monochromatic visible light. It is elucidated that the increase of tunneling current under the irradiation is caused by the photoexcited electrons, which leads to the appearance of a larger voltage across the vacuum between the probe apex and the a-Si:H surface than that in the dark. A high tunneling current under the irradiation enables us to perform stable STM observations of the intrinsic a-Si:H surface. The current image at a negative sample bias under the irradiation was different from the topographic one at a positive sample bias, which may indicate that topographic images of a-Si:H surfaces reflect not only surface electronic structures but also subsurface information determined by the growth process of a-Si:H films.

We have constructed a high speed digital autocorrelation spectrometer suitable for use as a sensitive receiver in millimetre spectral line astronomy. The instrument has 32 channels and employs the one-bit digitization technique to analyse spectra contained in bandwidths available between 0.94 and 30 MHz. Schottky clamped transistortransistor logic is used in the digital processor to permit a maximum sampling rate of GO MHz, which is three times faster than any similar instrument of which we are aware. Stability tests indicate that for 1000 s integration times the receiver sensitivity is within 15 % of its theoretical value at all available bandwidths. The receiver is presently being used to study emission at 22.2 GHz from interstellar water molecules.

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