The transfer impedance is a very important parameter of a beam position monitor (BPM) which relates its output signal with the beam current. The coaxial wire method is a standard technique to measure transfer impedance of the BPM. The conventional coaxial wire method requires impedance matching between coaxial wire and external circuits (vector network analyzer and associated cables). This paper presents a modified coaxial wire method for bench measurement of the transfer impedance of capacitive pickups like button electrodes and shoe box BPMs. Unlike the conventional coaxial wire method, in the modified coaxial wire method no impedance matching elements have been used between the device under test and the external circuit. The effect of impedance mismatch has been solved mathematically and a new expression of transfer impedance has been derived. The proposed method is verified through simulation of a button electrode BPM using CST STUDIO SUITE. The new method is also applied to measure transfer impedance of a button electrode BPM developed for insertion devices of Indus-2 and the results are also compared with its simulations. Close agreement between measured and simulation results suggests that the modified coaxial wire setup can be exploited for the measurement of transfer impedance of capacitive BPMs like button electrodes and shoe box BPM.
A 3 kW and 1 MHz pulsed solid state RF amplifier has been designed and developed to drive TH581 tetrode tube based RF amplifier to realise 100 kW pulsed RF source. The driver amplifier is operated with 1 ms pulse width at 50 Hz repetition rate. The 3 kW RF power is obtained by operating two Gemini pair LDMOS transistors (VDD=50 V) in parallel configuration at device itself and having single ended topology with common lumped element based input and output matching network. The amplifier delivers 3 kW RF power when fed by 25 dBm RF input drive from the signal generator. This scheme eliminates the need of RF combiner and divider which results in low loss, high efficiency, lesser number of components, simple and compact design.
A 5 kW and 1 MHz pulsed solid-state RF amplifier has been designed and developed to drive TH581 tetrode tube-based RF amplifier to realize 100 kW pulsed RF source. The driver amplifier is operated with a 1 ms pulse width at a 50 Hz repetition rate. The 5 kW RF power is obtained by operating four Gemini pair LDMOS transistors (VDD=50V) in parallel configuration at the device itself and having single-ended topology with common lumped element based input and output matching network. The amplifier delivers 5 kW RF power when fed by 25 dBm RF input drive from the signal generator. This scheme eliminates the need for RF combiner and divider which results in low loss, high efficiency, lesser number of components, simple and compact design. The measured saturated drain efficiency of the power amplifier is around 62%.
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