Intrabeam Scattering Analysis of ATF Beam Measurements

At the Accelerator Test Facility (ATF) at KEK intrabeam scattering (IBS) is a strong effect for an electron machine. It is an effect that couples all dimensions of the beam, and in April 2000, over a short period of time, all dimensions were measured as functions of current. In this report we derive a simple relation for the growth rates of emittances due to IBS. We apply the theories of Bjorken-Mtingwa, Piwinski, and a formula due to Raubenheimer to the ATF parameters, and find that the results all agree (if in Piwinski's formalism we replace the dispersion squared over beta by the dispersion invariant). Finally, we compare theory, including the effect of potential well bunch lengthening, with the April 2000 measurements, and find reasonably good agreement in the energy spread and horizontal emittance dependence on current. The vertical emittance measurement, however, implies that either: there is error in the measurement (equivalent to an introduction of 0.6% x-y coupling error), or the effect of intrabeam scattering is stronger than predicted (35% stronger in growth rates).Comment: 4 pages, 3 figures, Presented at IEEE Particle Accelerator Conferenc

Impedance Analysis of Bunch Length Measurements at the ATF Damping Ring

We present energy spread and bunch length measurements at the Accelerator Test Facility (ATF) at KEK, as functions of current, for different ring rf voltages, and with the beam both on and off the coupling resonance. We fit the on-coupling bunch shapes to those of an impedance model consisting of a resistor and an inductor connected in series. We find that the fits are reasonably good, but that the resulting impedance is unexpectedly large.Comment: 9 pages, 5 figures, presented at 10th International Symposium on Applied Electromagnetics and Mechanics (ISEM2001

Tunable Photoluminescence via Thermally Evaporated ZnS Ultra Thin Films

ZnS thin films have been deposited by thermal evaporation at various deposition rates. By controlling the deposition rate, the position of the maximum in the photoluminescence spectra could be easily tuned from 2.9 to 2.0 eV, which produced a corresponding change in the emission color. The optical and morphological characteristics of the ZnS thin films were measured. The photoluminescence spectra had broad peaks, suggesting a distribution of ZnS nanocrystallites dimensions. Nanocrystallites dimensions were in the range of 1 nm to 3 nm via TEM analyses. The changes in optical properties were potentially attributable to the lattice defects of ZnS crystals, including Schottky defects and the substation of sulfur atoms by oxygen atoms. The color of the resulting light emission was obtained by controlling the deposition rate of ZnS

Evidence for a rapid decrease in Pluto's atmospheric pressure revealed by a stellar occultation in 2019

We report observations of a stellar occultation by Pluto on 2019 July 17. A single-chord high-speed (time resolution $= 2\,$s) photometry dataset was obtained with a CMOS camera mounted on the Tohoku University 60 cm telescope (Haleakala, Hawaii). The occultation light curve is satisfactorily fitted to an existing Pluto's atmospheric model. We find the lowest pressure value at a reference radius of $r = 1215~{\rm km}$ among those reported after 2012, indicating a possible rapid (approximately $21^{+4}_{-5} \%$ of the previous value) pressure drop between 2016 (the latest reported estimate) and 2019. However, this drop is detected at a $2.4\sigma$ level only and still requires confirmation from future observations. If real, this trend is opposite to the monotonic increase of Pluto's atmospheric pressure reported by previous studies. The observed decrease trend is possibly caused by ongoing ${\rm N_2}$ condensation processes in the Sputnik Planitia glacier associated with an orbitally driven decline of solar insolation, as predicted by previous theoretical models. However, the observed amplitude of the pressure decrease is larger than the model predictions.Comment: 7 pages, 3 figures, accepted for publication in Astronomy and Astrophysic