Detector and imaging systems for the Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument

摘要

Hard X-ray and gamma-ray emission during solar flares encode information about electron/ion dynamics and provide a proxy to deduce solar atmospheric parameters. Enhanced imaging, spectroscopy and polarimetry of HXR/gamma-ray flare emissions over ~20 keV to ≥10MeV is needed to study particle transport; the Gamma-Ray Imager/Polarimeter for Solar Flares (GRIPS) instrument is designed to meet these goals. GRIPS' key technological improvements over the current solar state of the art in HXR/gamma-ray energies (RHESSI) include 3D position-sensitive germanium detectors (3D-GeDs) and a single-grid modulation collimator, the Multi-Pitch Rotating Modulator (MPRM). The 3D-GeDs allow GRIPS to reconstruct Compton-scatter tracks of energy deposition, providing enhanced background reduction and polarization measurements. Each of GRIPS' sixteen detectors has 298 electrode strips, each of which has dedicated ASIC/FPGA electronics. In GRIPS' energy range, indirect Fourier imaging provides higher resolution than focusing optics or Compton imaging techniques. The MPRM grid-imaging system has a single-grid design which provides 2x the throughput of a bigrid imaging system like RHESSI. Quasi-continuous resolution from 12.5 - 162 arcsecs is achieved by varying the grid pitch between 1 - 13mm. This spatial resolution will be capable of imaging the separate footpoints in a variety of flare sizes. In comparison, RHESSI's minimum 35 arcsec resolution at the same energy makes footpoints resolvable in only the largest flares. We discuss GRIPS' science goals, the instrument overall, and recent developments in GRIPS' detector and imaging systems. GRIPS is scheduled for an engineering flight from Fort Sumner in September 2014,followed by two long-duration balloon flights from Antarctica in 2015/16.