We discuss a new circuit theory of multi-conductor transmission lines. According to the theorem, a symmetrical three-line (S3L) circuit gives an excellent noise reduction compared with a nominal two-line circuit. The practice of this S3L circuit was proposed by the author for power supplies of the twin synchrotrons of HIMAC (Heavy Ion Medical Accelerator in Chiba) 20 years ago, and the theory has recently been established by Prof. Hiroshi Toki, who has found a new principle of circuit theory based on the retarded potential and coefficients of potential. This theory provides a clear mathematical definition of common-, normal-, and antenna-modes for electromagnetic phenomena with a set of coupled integro differential equations among three modes. A signal contamination by noise is understood as coupling among these three modes. A relation between the “noise and signal”, and the three modes is generally complicated, however, such a relation is simplified very much in the case of the S3L circuit. The normal mode is decoupled from the common- and antenna-modes, so that a pure signal is obtained without any contamination of noise with a common-mode filter. This article describes the essence of both the practice and theory of the method in three parts; “Part 1 Outline”, “Part 2 Practice”, and “Part 3 Theory”.

Beam loading compensation is a key for acceleration of a high intensity proton beam in the synchrotrons, the RCS and MR, of the Japan Proton Accelerator Research Complex (J-PARC). Magnetic alloy loaded rf cavities are used to achieve high accelerating voltages without a tuning bias loop. The frequency response of the RCS cavity covers the fundamental accelerating harmonic (h = 2) and higher harmonics up to the third (h = 6) harmonic. In case of the MR, the accelerating harmonic (h = 9) and the neighbors (h = 8, 10) are covered. wake voltages in the MA cavities are multiharmonic, and multiharmonic beam loading compensation is necessary for both of the RCS and MR. We developed the multiharmonic feedforward systems for the J-PARC synchrotrons. A commissioning methodology of the feedforward patterns has been established. We describe the system architecture and the commissioning methodology of the feedforward patterns. The commissioning of the feedforward using high intensity proton beams was successfully performed in the RCS and MR. We report the commissioning results. The multiharmonic beam loading compensation is necessary for the high intensity user operation.

Modern accelerators require the microwave technology and typical devices are klystrons. This article describes the developments of klystrons other than S-band, since developments of S-band klystron and linac were already described in the last volume of this journal. Recent progress of computer simulation enables us to manufacture tailored klystron mating with the accelerator having the desired frequency. Sometimes klystron engineers had to face to the difficulties involving the oscillations and instabilities, and spent a lot of efforts to solve them. In this article, such oscillation and instabilities which author experienced before are mentioned.

Compact Energy Recovery Linac (cERL) project is ongoing at KEK in order to demonstrate the ERL performance which satisfies various advanced requirements of future light sources. The cERL injector with its diagnostic beamline was constructed and its initial commissioning was successfully done at June 2013. The cERL recirculation loop with a main superconducting linac, merger and dump sections was then constructed. The commissioning with the loop has been started from December 2013. In the commissioning, a significant progress has so far been made. In this paper, we will report the status of the cERL commissioning including the construction work.