Development and experimental studies of Plane Wave Transformer (PWT) linac structures

Multiple, S-band (2856 MHz), Standing Wave (SW), Plane Wave Transformer (PWT) Linear Accelerator (Linac) structures of 4, 8, 12 and 20 cells have been designed and developed by Free Electron Laser and Utilization Section (FEL and US) of Raja Ramanna Centre for Advanced Technology (RRCAT), Indore. A RF tuning method has been evolved to tune the structures to desired RF parameters viz. pi mode frequency, waveguide to cavity coupling and field flatness. The structures are characterized by low and high RF power testing. A PWT linac structure typically provides 1 MeV energy gain per cell. Hence, to increase the energy gain, it is desired to increase the number of cells. However, by increasing the number of cells, the RF field profile is also adversely affected due to the SW nature of the structure, which is studied by cold test measurements to find out the optimum number of cells. The variation in field profile with number of cells also affects the waveguide to cavity coupling coefficient, which needs to be corrected. This paper presents the design, fabrication, RF testing, tuning and characterization results of these structures. A comparison of RF parameters of different structures is also presented. (author)