In this article we describe the theoretical motivation and experimental development of low‐energy (2 keV) neutral beams for fueling the central cell of the TMX‐U thermal‐barrier tandem mirror experiment at Lawrence Livermore National Laboratory. Theoretical estimates are given for the beam current required to build up a low‐density plasma (nc=0.5–2.5×1012cm−3) to a final‐state high‐density plasma (nc=1×1013cm−3). The design of low‐divergence (±3°) beam modules is described together with test stand measurements of beam‐neutral current, divergence, and species fractions. Experimental results are given for injection of 45 aA of low‐energy neutral‐beam current into the central cell of TMX‐U.