# Presentation: 042321

## Gamma-Ray Imager/Polarimeter for Solar Flares (GRIPS)

**Gamma-Ray Imager/Polarimeter for Solar Flares (GRIPS)**

_**Fundamental Goal:**_
- Understand energy release at the Sun and its effect on Earth and the solar system by studying particle acceleration associated with solar flares
_**Science Objectives:**_
- Determine the spatial distribution of flare-accelerated ions and electrons
- Determine the angular distribution of relativistic electrons
- Study the trapping of relativistic electrons in flare loops
- Determine the accelerated-ion spectrum and associated elemental abundances
_**Associated RFAs:**_
- F2. Understand the plasma processes that accelerate and transport particles.
- H1. Understand the causes and subsequent evolution of solar activity that affects Earth’s space climate and environment.
- J2. Develop the capability to predict the origin and onset of solar activity and disturbances associated with potentially hazardous space weather events.

_**Enabling and Enhancing Technology Development:**_
- 3D-GeDs with 0.5-mm strip pitch — detectors with coarser pitch and the associated electronics have been built and flown on *NCT* balloon payloads
- Multi-Pitch Rotating Modulator grid — straightforward to fabricate (minimum pitch of 1 mm), and tungsten grids have been used on *RHESSI* and *HEIDI*
- 20-meter extendable boom — already been developed for other space missions

_**Mission Implementation Description:**_
- One spacecraft in an equatorial or near-equatorial, ~600-km low-Earth orbit
- Three-axis stabilized, mass: 190 kg, power: 340 W, data: 4 GB/day
- Imaging: angular resolution ranging from 5 arcseconds to hundreds of arcseconds
- Polarization:  ~1% minimum detectable polarization at 150–650 keV energies
- Spectroscopy: 3 keV to 17 MeV, spectral resolution of 1.8 keV FWHM at 662 keV
- 3D spatially resolving germanium detectors (3D-GeDs): excellent spectral resolution (see above) and spatially locates energy depositions to within <0.1 mm3
- Single-grid tungsten Multi-Pitch Rotating Modulator (MPRM): exploits detector spatial resolution to provide a point-response function virtually free from sidelobes
- 20-meter extendable boom separates the MRPM and the spectrometer to provide the angular resolution (see above), with loose requirements on twist and stability
- Compton scatter reconstruction techniques used to determine the polarization of incident photons and to provide background rejection
_**Measurement Strategy:**_
- Resolve gamma-ray line sources and X-ray sources
- Measure the polarization of electron >150 keV bremsstrahlung emission
- Determine source size and shape using high-quality images
- Measure the spectral parameters of the various gamma-ray lines
- Perform imaging spectral polarimetry

- Ions accelerated in solar flares produce gamma-ray lines through nuclear interactions that reflect the nature and location of their acceleration.  Relativistic electrons accelerated in solar flares produce polarized bremsstrahlung emission depending on their angular distribution.
- Images from *RHESSI* (e.g. Hurford et al. 2006) indicate that accelerated ions are interacting in localized regions that are spatially shifted from the locations of accelerated-electron interactions.