A prototype of the JET ITER-like Ion Cyclotron Range of Frequencies (ICRF) launcher is presently being constructed by a collaboration between Oak Ridge National Laboratory (ORNL) and Princeton Plasma Physics Laboratory (PPPL). The launcher is being designed to couple power at high density (8 MW/m2, 7 MW total) into an ELMy H-mode plasma with a characteristic resistive loading > 2/m. The two-strap High Power Prototype (HPP) closely approximates in geometry and materials the left upper quadrant of the actual antenna. High power tests will be performed in vacuum with the HPP installed in the Radio Frequency Test Facility (RFTF) at ORNL. These include long pulse (20 s) tests at the design current (920 A rms) and voltage (35 kV peak) limits, with shorter pulses (10 s) at currents up to 1250 A rms. The design of the HPP together with the set of diagnostics and test plan that will be employed are discussed.