Criteria for comparing the suitability of microwave amplifiers for driving TeV linear colliders

Many types of microwave amplifiers are being considered at various institutions as candidate sources for driving future linear colliders. The choice of operating frequency ranges from 2.85 GHz to 35 GHz. Peak microwave output power and pulse duration also vary widely. In this paper, we propose three criteria for evaluating and comparing amplifier options. These are as follows: 1) N_t, the number of amplifiers required to drive an accelerator with a given final energy and a given accelerating gradient; 2) V, the voltage required to operate the microwave amplifier; and 3) η_T, the overall efficiency including the output efficiency of the amplifier, the efficiency of the pulse compression circuit if any is used, and the high voltage modulator pulse-shape efficiency. All of these criteria will affect the cost of a linear collider system. The cost of the microwave amplifiers will, of course,equal the cost of each amplifier (with its associated power supplies, magnets, and pulse compression circuit) multiplied by the number of amplifiers, system. The cost of each amplifier and its power supply/modulator will increase with the voltage, V. In fact, we have chosen to restrict our consideration of specific amplifiers to those in which V<1 MV; at voltages above 1 MV very large insulators and more exotic pulsed power supplies such as induction linacs would be required and these might be excessively costly. Overall efficiency will, of course, influence average power consumption as well as the size and cost of power supplies