a, Frequency map for different DLW dimensions when vp = 0.9999c. b, Calculated normalized energy gain for different DLW dimensions when vp = 0.9999c and f0 = 0.6 THz. c, Dispersion curve of the designed DLW. d, Normalized magnitude of the longitudinal electric field along the radial axis. e, Calculated coupling of the horn coupler. f, Simulation results of megaelectronvolt-level THz-driven acceleration using the designed DLW for single-stage and cascaded configurations.