Optimization of starting conditions of terahertz range gyrotons by increasing of electron interaction time in the “depressed” resonator

Summary form only given. In the last few years a substantial progress has been achieved in development of submillimeter gyrotrons [1-3]. At the frequency of 1 THz the radiation power amounts several kilowatts in conventional gyrotron with tubular helical beam formed by a magnetron injection gun [1,2] as well as in so-called large-orbit gyrotron (LOG) with pencil paraxial electron beam [3]. A typical problem for all short wave devices including gyrotons it is insufficient level of driving current. To satisfy threshold conditions one should increase the interaction length above value strongly corresponding to maximum efficiency. The length increasing is also accompanied by additional increasing of Ohmic losses. To avoid these problems in short wavelength gyrotrons we suggest to decelerate electrons inside interaction space by imposing lower voltage at microwave resonator. Such “depressed” resonator should be separated electrically from anode and collector. Obviously, when rotating electrons pass through decelerating gap rotating velocity doesn't change while axial velocity falls. As a result we can increase electrons life-time in interaction space and drastically decrease starting an operating current. It should be noted that this method of optimization can be applied exclusively to gyrotrons were only transverse electron energy associated with rotation in magnetic field is converted in electromagnetic radiation. Thus deceleration of electrons doesn't affect on maximal electron orbital efficiency but improves starting and operating conditions.