Gyrotron transmitting tube

An electromagnetic wave generator operating in the 20 GHz to 500 GHz range and comprising:

• a gyrotron tube having an electron emitting cathode at one end;
• an electron collector disposed at the other end of said gyrotron tube, said other end having disposed thereat a focusing ring through which electrons are injected into said collector;
• a solenoid disposed around said gyrotron tube establishing a first magnetic field which causes electrons emitted by said cathode to follow helical paths;
• and
• means for establishing a second magnetic field between said first magnetic field and said focusing ring, said second magnetic field being characterized by decreasing from the B value of said first magnetic field to substantially zero over an axial distance of from 1.lambda..sub.c to 3.lambda..sub.c in a direction away from said cathode, and at such a rate as to establish optimum conversion of spiral energy of the spent electrons into forward motion.