  This study presents the first ion temperature (\(T_i\)) measurements from the
MAST-U divertor using a Retarding Field Energy Analyzer (RFEA). Embedded within
the flat tile of the closed divertor chamber, the RFEA captures \(T_i\)
profiles across various plasma scenarios, including transitions to the Super-X
configuration. Measurements were conducted under steady-state and transient
plasma conditions characterized by a plasma current (\(I_p\)) of 750 kA,
electron density (\(n_e\)) between \(2.2 \times 10^{19}\) and \(4.45 \times
10^{19}\,\text{m}^{-3}\), and Neutral Beam Injection (NBI) power ranging from
3.0 MW to 3.2 MW. The ion temperatures, peaking at approximately 20 eV in
steady state, were compared with electron temperatures (\(T_e\)) obtained from
Langmuir probes (LP) at identical radial positions. The study also examined ion
saturation current density (\(J_{\text{sat}}\)) signals to using methodologies
similar to previous MAST experiments. Preliminary findings reveal a \(T_i/T_e\)
ratio ranging from 1 to 2.5. Additionally, high temporal resolution
measurements (100 $\mu s$) captured the dynamics of Edge Localized Modes
(ELMs), showing \(T_i\) peaks at 16.03 +- 1.84 eV during ELM events, nearly
three times higher than inter-ELM temperatures.
