  Our aim is to test potential solar prominence plasma diagnostics as obtained
with the new solar capability of the Atacama Large Millimeter / submillimeter
Array (ALMA). We investigate the thermal and plasma diagnostic potential of
ALMA for solar prominences through the computation of brightness temperatures
at ALMA wavelengths. The brightness temperature, for a chosen line of sight, is
calculated using densities of hydrogen and helium obtained from a radiative
transfer code under non local thermodynamic equilibrium (NLTE) conditions, as
well as the input internal parameters of the prominence model in consideration.
Two distinct sets of prominence models were used: isothermal-isobaric
fine-structure threads, and large-scale structures with radially increasing
temperature distributions representing the prominence-to-corona transition
region. We compute brightness temperatures over the range of wavelengths in
which ALMA is capable of observing (0.32 - 9.6mm), however we particularly
focus on the bands available to solar observers in ALMA cycles 4 and 5, namely
2.6 - 3.6mm (Band 3) and 1.1 - 1.4mm (Band 6). We show how the computed
brightness temperatures and optical thicknesses in our models vary with the
plasma parameters (temperature and pressure) and the wavelength of observation.
We then study how ALMA observables such as the ratio of brightness temperatures
at two frequencies can be used to estimate the optical thickness and the
emission measure for isothermal and non-isothermal prominences. From this study
we conclude that, for both sets of models, ALMA presents a strong thermal
diagnostic capability, provided that the interpretation of observations is
supported by the use of non-LTE simulation results.
