This work explores the plasmonic properties of parallel double-walled carbon nanotube arrays. It is shown that ultraslow surface plasmon polariton (SPP) modes possessing a phase velocity some orders of magnitude lower than the speed of light in vacuum and high Q-factor can be generated in such arrays. It is demonstrated that nonrelativistic electron beams with the velocity less than 10 6 m s −1 can be used to excite SPPs in arrays of double-walled carbon nanotubes. For the SPP modes excited by an electron beam, the frequency range of SPP waves and electron beam velocities corresponding to the phase matching within a wide frequency range are determined. It opens the way to design slow-wave structures based on the dense arrays of multiwalled carbon nanotubes employing an efficient energy transfer from the pump to the SPPs.