Generation of a 28 GHz annular power distribution with high power gyrotron and its application to microwave driven in...

The microwave-driven in-tube accelerator (MITA) concept, which installs the center body of the thruster inside the waveguide and generates thrust via millimeter-wave beam irradiation from the front side of the center body, was experimentally demonstrated using 210-kW and 28-GHz gyrotron device. For the 28-GHz beams, a vortex phase plate was newly designed to change the incident beam profile from a Gaussian to a donut-shaped pattern, which was installed in front of the thruster's center body. Without the vortex phase plate, gas breakdown occurred at the center-body head, providing a negative impulse. However, as the electric field concentration at the center-body head was avoided using the vortex phase plate, plasma and strong shock wave generation were obtained at the rear side of the vehicle, inducing a positive impulse to accelerate the thruster toward the beam source direction. The MITA thrust performance increased as the incident beam pulse width increased because gas heating was enhanced at the rear side of the center body.