2023, Borrero, J.M., Pastor Yabar, A.

Electric currents play an important role in the energy balance of the plasma in the solar atmosphere. They are also indicative of non-potential magnetic fields and magnetic reconnection. Unfortunately, the direct measuring of electric currents has traditionally been riddled with inaccuracies. Aims. We study how accurately we can infer electric currents under different scenarios. Methods. We carry out increasingly complex inversions of the radiative transfer equation for polarized light applied to Stokes profiles synthesized from radiative three-dimensional magnetohydrodynamic (MHD) simulations. The inversion yields the magnetic field vector. B. from which the electric current density, ./, is derived by applying Ampere's law. Results. We find that the retrieval of the electric current density is only slightly affected by photon noise or spectral resolution. However, the retrieval steadily improves as the Stokes inversion becomes increasingly elaborated. In the least complex case (a Milne- Eddington-like inversion applied to a single spectral region), it is possible to determine the individual components of the electric current density (jx, jy, jz) with an accuracy of cr = 0.90 - l.OOdex, whereas the modulus (|[/

2022, Quintero Noda, C., Schlichenmaier, R., Bellot Rubio, L.R., Löfdahl, M.G., Khomenko, E., Jurčák, J., Leenaarts, J., Kuckein, C., González Manrique, S.J., Gunár, S., Nelson, C.J., Giovannelli, L., González, F., González, J.B., González-Cava, J.M., González García, M., Gömöry, P., Gracia, F., Grauf, B., Greco, V., Grivel, C., de la Cruz Rodríguez, J., Guerreiro, N., Guglielmino, S.L., Hammerschlag, R., Hanslmeier, A., Hansteen, V., Heinzel, P., Hernández-Delgado, A., Hernández Suárez, E., Hidalgo, S.L., Hill, F., Tziotziou, K., Hizberger, J., Hofmeister, S., Jägers, A., Janett, G., Jarolim, R., Jess, D., Jiménez Mejías, D., Jolissaint, L., Kamlah, R., Kapitán, J., Tsiropoula, G., Kašparová, J., Keller, C.U., Kentischer, T., Kiselman, D., Kleint, L., Klvana, M., Kontogiannis, I., Krishnappa, N., Kučera, A., Labrosse, N., Aulanier, G., Lagg, A., Landi Degl’Innocenti, E., Langlois, M., Lafon, M., Laforgue, D., Le Men, C., Lepori, B., Lepreti, F., Lindberg, B., Lilje, P.B., Aboudarham, J., López Ariste, A., López Fernández, V.A., López Jiménez, A.C., López López, R., Manso Sainz, R., Marassi, A., Marco de la Rosa, J., Marino, J., Marrero, J., Martín, A., Allegri, D., Martín Gálvez, A., Martín Hernando, Y., Masciadri, E., Martínez González, M., Matta-Gómez, A., Mato, A., Mathioudakis, M., Matthews, S., Mein, P., Merlos García, F., Alsina Ballester, E., Moity, J., Montilla, I., Molinaro, M., Molodij, G., Montoya, L.M., Munari, M., Murabito, M., Núñez Cagigal, M., Oliviero, M., Orozco Suárez, D., Amans, J.P., Ortiz, A., Padilla-Hernández, C., Paéz Mañá, E., Paletou, F., Pancorbo, J., Pastor Cañedo, A., Pastor Yabar, A., Peat, A.W., Pedichini, F., Peixinho, N., Asensio Ramos, A., Peñate, J., Pérez de Taoro, A., Peter, H., Petrovay, K., Piazzesi, R., Pietropaolo, E., Pleier, O., Poedts, S., Pötzi, W., Podladchikova, T., Bailén, F.J., Prieto, G., Quintero Nehrkorn, J., Ramelli, R., Ramos Sapena, Y., Rasilla, J.L., Reardon, K., Rebolo, R., Regalado Olivares, S., Reyes García-Talavera, M., Riethmüller, T.L., Balaguer, M., Rimmele, T., Rodríguez Delgado, H., Rodríguez González, N., Rodríguez-Losada, J.A., Rodríguez Ramos, L.F., Romano, P., Roth, M., Rouppe van der Voort, L., Rudawy, P., Ruiz de Galarreta, C., Baldini, V., Rybák, J., Salvade, A., Sánchez-Capuchino, J., Sánchez Rodríguez, M.L., Sangiorgi, M., Sayède, F., Scharmer, G., Scheiffelen, T., Schmidt, W., Schmieder, B., Balthasar, H., Scirè, C., Scuderi, S., Siegel, B., Sigwarth, M., Simões, P.J.A., Snik, F., Sliepen, G., Sobotka, M., Socas-Navarro, H., Sola La Serna, P., Barata, T., Solanki, S. K., Soler Trujillo, M., Soltau, D., Sordini, A., Sosa Méndez, A., Stangalini, M., Steiner, O., Stenflo, J.O., Štěpán, J., Strassmeier, K.G., Barczynski, K., Sudar, D., Suematsu, Y., Sütterlin, P., Tallon, M., Temmer, M., Tenegi, F., Tritschler, A., Trujillo Bueno, J., Turchi, A., Utz, D., Barreto Cabrera, M., van Harten, G., van Noort, M., van Werkhoven, T., Vansintjan, R., Vaz Cedillo, J.J., Vega Reyes, N., Verma, M., Veronig, A.M., Viavattene, G., Vitas, N., Baur, A., Vögler, A., von der Lühe, O., Volkmer, R., Waldmann, T.A., Walton, D., Wisniewska, A., Zeman, J., Zeuner, F., Zhang, L.Q., Zuccarello, F., Béchet, C., Collados, M., Beck, C., Belío-Asín, M., Bello-González, N., Belluzzi, L., Bentley, R.D., Berdyugina, S.V., Berghmans, D., Berlicki, A., Berrilli, F., Berkefeld, T., Bettonvil, F., Bianda, M., Bienes Pérez, J., Bonaque-González, S., Brajša, R., Bommier, V., Bourdin, P.-A., Burgos Martín, J., Calchetti, D., Calcines, A., Calvo Tovar, J., Campbell, R.J., Carballo-Martín, Y., Carbone, V., Carlin, E.S., Carlsson, M., Castro López, J., Cavaller, L., Cavallini, F., Cauzzi, G., Cecconi, M., Chulani, H.M., Cirami, R., Consolini, G., Coretti, I., Cosentino, R., Cózar-Castellano, J., Dalmasse, K., Danilovic, S., De Juan Ovelar, M., Del Moro, D., del Pino Alemán, T., del Toro Iniesta, J. C., Denker, C., Dhara, S.K., Di Marcantonio, P., Díaz Baso, C.J., Diercke, A., Dineva, E., Díaz-García, J.J., Doerr, H.-P., Doyle, G., Erdelyi, R., Ermolli, I., Escobar Rodríguez, A., Esteban Pozuelo, S., Faurobert, M., Felipe, T., Feller, A., Feijoo Amoedo, N., Femenía Castellá, B., Fernandes, J., Ferro Rodríguez, I., Figueroa, I., Fletcher, L., Franco Ordovas, A., Gafeira, R., Gardenghi, R., Gelly, B., Giorgi, F., Gisler, D.

The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope, the German Vacuum Tower Telescope and GREGOR, the French Télescope Héliographique pour l'Étude du Magnétisme et des Instabilités Solaires, and the Dutch Open Telescope. With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems.