# CMAG: A Mission to Study and Monitor the Inner Corona Magnetic Field
## 1 Introduction
### Observing the Inner Solar Corona  
Observing the inner solar corona presents a significant challenge primarily due to the faintness of the emitted light from the coronal material compared to the overall brightness of the Sun. Consequently, observing the solar corona requires blocking the light emitted by the solar disk. This can be accomplished during a solar eclipse, which only lasts for a few minutes, or through the use of specialized instruments called coronagraphs. However, the solar coronal light becomes intermingled with background signals originating from scattered light, mainly from the occulter but also from the instrument optics. Despite these difficulties, extensive efforts have been made to carry out coronal observations using both ground- and space-based assets. Instruments for coronal observations include LASCO [6] and UVCS [7], both aboard SoHO [8]; STEREO/SECCHI [9]; METIS [10] and SoloHI [11] on Solar Orbiter [12]; WISPR [13] onboard the Parker Solar Probe [14]; ASPMICS [15] on Proba-3; the High-Altitude Observatory (HAO)/National Center for Atmospheric Research (NCAR) Coronal Multichannel Polarimeter (CoMP) [16] and the upgraded version uCoMP [17]; and CRYO-NIRSP [18] on DKIST [19]. However, while imaging the corona poses challenges, determining its magnetic field is even more difficult due to the need for differential photometry to measure the four Stokes parameters of polarized light. The aforementioned ground-based instruments, uCoMP and CRYO-NIRSP, have capabilities for magnetic field measurements and provide valuable insights into coronal dynamics, which is known to be driven by the conversion of magnetic energy into radiative energy (in the case of flares) and the kinetic energy of material (in the case of coronal mass ejections or CMEs). Nevertheless, these measurements are significantly hampered by atmospheric turbulence, solar scattered light, and long integration times, resulting in a limited understanding of the intricate details of these energy transformations. However, new diagnostics have emerged that can provide insights into the magnetic fields of the inner corona. For instance, a newly developed diagnostic technique that involves atomic radiation modeling of the contribution of a magnetically induced transition to the Fe x 25.7262 nm spectral line intensity was presented in [20; 21; 22] and used, later, to obtain the magnetic field in active region loops [23] using [PERSON]'s [24] Extreme-ultraviolet Imaging Spectrometer EIS [25]. More recently, [PERSON] and collaborators [26] presented a method that utilizes spectroscopic measurements and MHD assumptions to indirectly estimate the strength of the coronal magnetic field. These techniques may be very useful in the future, in the context of other space missions such as SPARK [27]. However, what is truly needed is direct observation of the polarization signals associated with the magnetic field (see a review in [28]). In this respect, it is of interest to note that in 2015, the Chromospheric Lyman-alpha Spectropolarimeter (CLASP) mission obtained the first observations of the linear polarization due to scattering processes in the hydrogen Lyman-alpha line of the solar-disk radiation, while in 2019 and 2021, the Chromospheric Layer Spectropolarimeter (CLASP2 and CLASP2.1) missions obtained unprecedented observations of the linear and circular polarization signals caused by scattering processes and the Hanle and Zeeman effects in the near-UV region of the Mg II h and k lines. These suborbital space experiments opened a window for probing the magnetism and geometry of the plasma in the upper chromosphere and transition region of the Sun [28]. The magnetic field in the inner corona can also be determined using measurements at radio wavelengths [29]. These measurements, in addition to providing fundamental information to understand how the magnetic field is structured, can be of great importance for obtaining simultaneous observations of the inner corona.