# CMAG: A Mission to Study and Monitor the Inner Corona Magnetic Field
## 1 Introduction
### Scientific Goals of the CMAG Mission  
The mission aims to answer the overarching question, \"How does magnetic energy transformation occur in the inner corona, driving coronal heating and all eruptive phenomena relevant to space weather effects on Earth?\" This global question breaks down into specific questions described below.  
1. What is the structure of the inner coronal magnetic field? Understanding the magnetic field's structuring in coronal loops and streamers and its evolution and relationship with photospheric fields is crucial. CMAG's high spatial resolution (2.5\({}^{\prime\prime}\)) and cadence (\(\approx\)1 min) will determine the strength and direction of the vector magnetic field from close to the surface to the higher layers for providing an empirical basis that help validate and refine current extrapolations and improve coronal magnetic models.
2. What is the coronal origin of the solar wind? The solar wind has distinct components: slow and fast, related to coronal streamers, coronal hole boundaries, and the solar network. CMAG will investigate the magnetic connection between coronal holes, streamers, and the solar wind, aiding the understanding of how the solar wind propagates through the heliosphere and its relationship with coronal waves.
3. How are flares and CMEs generated? Flares and CMEs are phenomena with different effects on the heliosphere and the Earth's environment. CMAG will reveal the inner corona's internal structure and evolution and follow the magnetic field vector during the CME onset and the generation of associated waves. At a resolution of 2.5\({}^{\prime\prime}\), it could also provide a glimpse of the evolution of the magnetic field structure at the reconnection sites.
* What is the origin of solar coronal heating? Measurements of magnetic field strength will provide a quantitative basis for assessing the origin of non-thermal heat observed in the Sun's inner coronal layers.
* What is the role of the inner corona in space weather? CMAG's measurements of inner coronal magnetic fields at L5, provided in almost real time, will greatly enhance space weather nowcasting and forecasting capabilities, crucial for predicting radiation and energetic particle impacts on Earth as a consequence of flares and CMEs.  
\begin{table}
\begin{tabular}{l l} \hline Spatial resolution & 2.5\({}^{\prime\prime}\) at 750 nm \\ Aperture & 10 cm \\ Cadence & \(\approx\)1 min for S/N = 1000 in Stokes Q, U, and V \\ Field of view (FoV) & \(\approx\)2400\({}^{\prime\prime}\) (\(\approx\)0.66\({}^{\circ}\) = 2.5 R\({}_{\odot}\)) \\ Targets spectral lines & Fe XIV 530 nm; Fe XI 789 nm; Fe XIII 1074 nm \\ Spectral resolution & 20 pm; 30 pm; 40 pm \\ Maximum spectral shift over the FoV & 25 pm; 30 pm; 50 pm \\ Detector dimensions & 4 k \(\times\) 4 k pixels \\ Etalon max. incidence angle 1  & 1.28\({}^{\circ}\) \\ Etalon diameter & \(\approx\)60 mm \\ Polarization modulator interm. image diameter & \(\approx\)55 mm \\ dimensions & \(<\)1 m\({}^{3}\) \\ stray light requirements & \(<\)0.1\% @ 1.02 R\({}_{\odot}\) \\ \hline \end{tabular}
\end{table}
Table 1: CMAG spacecraft main instrument baseline requirements.  
Figure 2: Detectability diagram. Calculations assume the weak field approximation on lines with a Doppler width of 20 km/s [31]. Emission intensities at different regions are represented with shaded areas. Diagram regions below blue lines indicate magnetic field strength detectability for Fe XIII 1074 nm and no atomic alignment. Diagram regions below green lines indicate the reached S/N in Stokes V for the given exposure times with a 10 cm aperture telescope (Table 1) at 1 au from the Sun and a total transmission of 0.4, sensor quantum efficiency of 50%, and a polarimetric efficiency of 0.5.