Upgrade of the RF reference system for the J-PARC 400 MeV LINAC

Futatsukawa, Kenta; Fang, Z.*; Kobayashi, Tetsuya*; Fukui, Yuji*; Shinozaki, Shinichi 

A new RF reference signal oscillator, which can provide signals of not only 312 MHz signal but also 960 MHz in synchronism with the 12 MHz J-PARC master clock, was installed at J-PARC LINAC for the 400 MeV upgrade. The phase noise of the output signal in this module was measured by the signal source analyzer. The jitter of the output signal, which was estimated from the integration of phase noise from 10 Hz to 1 MHz, becomes about 240 fsec and was one order smaller than that of the old system (about 1700 fsec). However, the original performance of this module is expected to be better. It's thought to be due to the 12 MHz input signal in this module. Therefore, the path of the 12 MHz master clock was optimized except for unnecessary modules. In addition, necessary modules, the O/E and E/O modules, were selected for the less phase noise in some kind of modules with the same features. Then, the jitter of the output signal in the RF reference signal oscillator improved to be about 41 fsec, which is less than one fifth that before the optimization. This value satisfies the required phase stability ( 0.3). Moreover, the high-accuracy synchronism of two kinds of frequency, 324 MHz and 972 MHz, was confirmed by the sampling oscilloscope. Therefore the RF reference signal with more precision can be provided by this system after the upgrade.