Abstract Details
| Name: Mohana Krishna.R Affiliation: IISc - ISRO Conference ID: ASI2018_864 Title : Optimum modulation for coronal field measurements on a space based observatory Authors and Co-Authors : Sankarasubramanian K Abstract Type : Poster Abstract Category : Instrumentation and Techniques Abstract : Many activities in the solar atmosphere are caused due to the presence of magnetic field. The influence of the magnetic fields on dynamic events range from the corona upto the heliosphere. Phenomenon like solar flares, CMEs and coronal loop oscillations are not understood complete. A vector magnetograph of coronal magnetic field provides insight into the configuration of the fields which in-turn helps in understanding the dynamics during such events. There are several theoretical models on coronal field strength and their variation with solar activity and there have been indirect ways of measuring coronal field strength through models of non-linear force free field extrapolation to estimate upper chromosphere and coronal field strength from photospheric field. These results form the basis for expected field strength and estimates of 3-40 G from solar minima to maxima. Though statistical estimates of magnetic field using stokes vector-V have been performed the vector magnetic field measurements of the corona are yet to be done. As the corona is faint with weak fields, such measurements become extremely difficult for a ground based observatory while a higher SNR can be achieved using a space based observatory. Unlike a ground based instrument a space based instrument has several constraints including mass, number of moving parts and shelf life of the components used in it. In order to have minimum mass, less moving parts and high shelf life we choose a single crystal continuously rotating retarder as modulator and a pair of polarizing beam displacers as dual beam analyzer for the polarimeter unit. We present a modulation scheme for the solar corona to measure the vector magnetic field of coronal loops. The design takes into account the crosstalk due to satellite jitter and minimizes the crosstalk from linear into weak circular polarization. A laboratory setup is made to verify the capabilities of the modulation scheme. Typical jitter of a low earth orbit satellite is recreated and linear to circular polarization crosstalk is measured. It is found that the crosstalk reduces with an increase in the number of frames that are averaged according to the curve obtained from simulations. |