We describe an experiment to measure the spatial charge distribution produced by a microchannel plate intensifier with a new type of charge division readout, the ‘‘split strip’’ anode. This anode is a modified strip and strip anode which determines both the amount of charge deposited on each half of the anode and the centroid position for each event. We present experimental measurements of microchannel plate charge cloud distributions for a variety of detector operating conditions. We find that, as a first-order approximation, one can assume the charge cloud to be azimuthally symmetric. Additionally, the charge cloud remains virtually unchanged from event to event and pore to pore. The general form of the radial distribution is best described by the sum of two exponential components whose scale and relative weights vary with detector operating conditions. The central component of the distribution is three to six times smaller than the outer, or ‘‘wing’’ component. Typically most of the charge is in the central component. We have determined the scale and relative weights of the two exponentials for a fixed microchannel plate/anode gap of 6.2 mm and a range of detector operating conditions. The most significant variable determining the charge cloud distribution is the voltage between the back of the microchannel plates and the anode. As this voltage is increased from 50 to 800 V, the scale length of the central component shrinks from 1.4 to 0.5 mm and the weight increases from 50% to 85%.
Balanced receivers are under development at the Caltech Submillimeter Observatory (CSO) for the 230/460 GHz and 345/660 GHz atmospheric windows. The mixers are tunerless, implemented in a balanced configuration, have a 4-8 GHz IF, and can be used in dual frequency observation mode. As shall be seen, the balanced arrangement provides a high level of amplitude noise immunity and allows all of the available LO power to be used. In turn, this permits complete automation of the receivers by means of synthesized LO source(s). A disadvantage of balanced mixers is, perhaps, that the sidebands at the IF remain convolved (DSB), unlike sideband separating (2SB) receivers. The latter, however are unbalanced and do not have the noise and LO injection advantages of balanced mixers. For the CSO, balanced mixers covering the range 180-720 GHz were judged most promising to facilitate many of the astrophysical science goals in the years to come.In parallel, a dual polarization 280-420 GHz continuous comparison (correlation) receiver is in an advanced state of development. The instrument has two beams on the sky; a reference and a signal beam. Using only cooled reflecting optics, two polarizing grids, and a quadrature hybrid coupler, the sky beams are coupled to four tunerless SIS mixers (both polarizations). The 4-12 GHz mixer IF outputs are, after amplification, correlated against each other. In principle, this technique results in flat baselines with very low RMS noise, and is especially well suited for high redshift Galaxy work.Not only do these changes greatly enhance the spectroscopic capabilities of the CSO, they will also enable the observatory to be integrated into the Harvard-Smithsonian Submillimeter Array (SMA), as an additional telescope.Keywords: Balanced mixer theory, continuous comparison receiver, radial probe, full-height waveguide to thinfilm microstrip transition, split-block, high current density superconducting-insulating-superconducting (SIS) tunnel junction, broad bandwidth quadrature waveguide hybrid, DC-break, IF match, Wilkinson in phase power combiner, Low noise amplfier (LNA), 4-8 GHz intermediate frequency (IF).
The CAltech Submillimeter Interstellar Medium Investigations Receiver (CASIMIR) is a multichannel, heterodyne spectrometer being developed for the Stratospheric Observatory for Infrared Astronomy (SOFIA). It has a very high resolution, up to a million, over the submillimeter and far-infrared wavelength range of 150 to 600 jim, or 2.0 to 0.5 THz. CASIMIR is extremely well suited to the investigation of both the galactic and extragalactic warm, approximately 100 K, interstellar medium. A combination of advanced 515 and Hot Electron Bolometers (HEB) receivers will be used to cover this frequency range with very high sensitivity. CASIMIR will use only solid state local oscillators, with quasioptical coupling to the mixers. We present a description of the instrument and its capabilities, including detailed discussions of the receivers, local oscillators and IF systems.
We describe a technique to measure the spatial extent and magnitude of gain depression in the quiescent pores surrounding an active region of an MCP and present preliminary results. We find that significant gain depression occurs up to 1.5 mm from the center of the active region. The magnitude of the reduction in gain decreases linearly with radius and is proportional to the count rate. We evaluate two possible mechanisms for gain depression. We find that the pore deactivating model in which the electric field from the discharging of a pore distorts the electric fields in surrounding pores is more successful than the transfer of charge from quiescent pores.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.