Design study of the heliospheric imager

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Research of a new instrument for imaging heliosphere (heliospheric imager) and related studies have been done.(1) Heliospheric ImagerIn the first year, we designed the heliospheric imager. Very large effective area at least 3000mィイD12ィエD1 and reducing urban noise about 30dB are required to observe weak radio sources. For these reasons. a phase array antenna surrounded by metallic-fence with 10m height was adopted for the heliospheric imager. Thus we designed a phased array which consists of 16384 λ/2-dipole elements (256E-W) x 64(N-S), 3500mィイD12ィエD1). The sensitivity of the antenna is expected to be 0.2 Jy which will be the highest one among those of the current IPS network in our laboratory.Various parts such as a dipole element, a schpertop balun and connectors are developed and tested electric performance. Especially these are designed for mass production to cut down the cost. We success to develop a low ohmic-loss (-0.02dB) connector which can be used in the heliospheric imager. And also suitable cable (MFH-8AC) was found which have enough strength and low velocity factor.In the second year, we built a small phased array antenna (16(E-W) x 8(N-S), 32mィイD12ィエD1 to check our design. The antenna impedance is measured to be about 170Ω which well agrees with design calculation. The Sun and QSOs (3C273, 3C405) were observed to measure beam size, system temperature and aperture area, and they are 6.5 degree (FWHP), 290 K and 17mィイD12ィエD1 respectively. These values also agree with calculated ones. In conclusion, the design can be applied to the heliospheric imager.(2) Related StudiesOrigin compact very low speed solar wind and propagation of interplanetary disturbances measured with IPS were studied in these two years. These analysis techniques will be applied to new observations with the heliospheric imager. We expect that the new data will provide us further insights of dynamical phenomena in heliosphere.