The Global Precipitation Measurement (GPM) Microwave Imager (GMI) instrument is a multi-channel, conicalscanning, microwave radiometer serving an essential role in the near-global-coverage and frequent-revisit-time requirements of GPM. As a part of its contribution to GPM, NASA will provide a GMI instrument and a spacecraft for the Core observatory and is considering the acquisition of a second GMI instrument for placement aboard a constellation spacecraft with a payload and orbit to be defined. In March 2005, NASA chose Ball Aerospace & Technology Corporation to provide the GMI instrument(s). This paper describes the GMI instrument, the technical performance requirements, its role within the combined passive and active microwave measurements on the Core observatory, and the timeline for GMI development and acquisition.
KEYWORDS: Amplifiers, Free electron lasers, Radio propagation, Beam propagation method, Electron beams, Extremely high frequency, Plasma, Magnetism, Iron, Fusion energy
Free electron laser amplifiers are investigated as sources of high-average-power (1 MW) millimeter to submillimeter wave radiation (200 GHz - 600 GHz) for application to electron cyclotron resonance heating of magnetically confined fusion plasmas. As a stepping-stone to higher frequencies and cw operation a pulsed amplifier (τpulse ≃ 80 ns) at 98 GHz is being developed. Status is reported on this experiment which investigates linear gain amplification with use of a sheet electron beam (transverse cross section = 0.1 cm × 2.0 cm, Vbeam = 440 keV, Ibeam ≃ 10 A) and short-period wiggler (lw = 0.96 cm) and with expected output of 140 W. Predictions of gain and efficiency from a 1-D universal formulation are presented. Beam propagation results, with wiggler focusing as a means of sheet beam confinement in both transverse dimensions, through the 54 cm (56 period) pulsed electromagnet wiggler are discussed. Peak wiggler fields of 5.1 kG on-axis have been achieved.
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