DESIGN AND TEST RESULTS ON THE PERVEANCE MONITOR FOR MEASURING A 80-MW KLYSTRON CHARACTERISTICS*

Total 12 units of high power klystron-modulator systems are under continuous operation in the Pohang Light Source (PLS) linac. The peak powers of the modulator and the klystron are 200 MW and 80 MW, respectively. The total heater run time of an oldest klystron system has been accumulated over 75,000-hours as of now. Therefore, it is necessary to monitor the klystron operational status for stable beam operation. It can be achieved by measuring the klystron perveance to diagnose characteristics of klystron. Up to now, the operator manually performs it. We have designed the perveance monitor by processing the sensing signal of a beam voltage and current of the klystron. It takes advantage of the time saving in diagnosing klystron performance. In addition, a highly accurate current and voltage sensor is one of the critical components of the measuring system. This paper presents the design concepts and initial test results of the perveance monitor to diagnose characteristics of klystron. Perveance definition The klystron is a device for amplifying signals at microwave radio frequencies. The perveance is an important design parameter since it is totally determined by electron gun dimensions. When the cathode is operated in the space-charge-limited region, the emission current will be a specific function of the applied voltage [2]. The constant, k, is a function of the geometry of the cathode-anode structure, and is termed perveance. It is space-charge characteristic between electrodes in a klystron tube. It is equal to the current (Ik) divided by the electronic potential (Vk) of the collector raised to the 3/2 powers [3]. Basic design concept The perveance monitor can be divided into two major sections: a pulse conditioning & peak hold module (PCPHM) section, a perveance processor module (PPM) section. The basic concept governing the klystron perveance monitor may be understood via the block diagram shown in Figure 1. The operational function for it can be expressed as an equation (1).