[en] This proposal presents the design of the Test Bed and the engineering development on crucial components, and describes the experimental and theoretical program that will answer uncertainties regarding beam behavior. The 160 meter-long Test Bed will accelerate Cs⁺¹ at a beam charge of 20 micro-coulombs. The ions will originate from a large contact ionization source and transit through two drift tubes before injection into the approximately 80 induction modules of the linac. The output energy will be 25 MeV. The Test Bed will be located on a long pad behind an existing building on the LBL site. Depending on the funding schedule, the project could span from 30 to 44 months, as described in the Cost and Schedule section