4µs
5. Summaries and conclusions
In this study, development of the linac control system toward stable linac operation was presented. The results of this study are summarized and concluded as follows.
The new linac control system was successfully developed taking account of stability enhancement of the control system itself and availability enhancement of the linac operation. The MADOCA framework was applied for the control software. It newly brought enough stability, powerful data logging/archiving system and sufficient throughput of issued control commands to the linac accelerator equipment. For applying MADOCA, Solaris was newly chosen as the real-time OS for the Intel architecture VME CPU boards, according to the results of wide and profound studies of real-time functionality. The data logging/archiving system greatly contributed to the linac stabilization by providing the off-line analyses capability. The control hardware was radically renovated. The newly developed OPT-VME and MCU replaced direct I/O boards on the VMEbus. Adopting these new devices successfully brought noise immunity enhancement, function-oriented control system re-arrangement and availability enhancement of the linac operation.
In 2005, the VME systems were rebooted seven times. All the troubles were due to the UPD software problem. Nevertheless, these troubles had never interrupted the top-up operation of SPring-8. The fact showed that the approach for the availability enhancement in this study was considerably successful.
On the basis of the new linac control system, the shot-by-shot data acquisition system for the linac BPM was newly developed. The data acquisition system successfully took 376 signals from 47 BPMs synchronizing to the 60pps linac operation without any shot detection losses. Six VME computers, a PC and a dedicated database server were used for the acquisition. The SHM-net linked all the VME computers and the PC for fast real-time transfer of the acquired BPM data. The SHM-net was also used for synchronization between software processes running on the VME computers. A set of synchronized BPM data was recorded into a commercial RDB on the dedicated database server together with an event number and a time stamp for beam shot identification. All the acquired BPM data were kept permanently in the RDB and could be easily accessed by using web browsers or C function calls.
The data acquisition system presently needed about 50msec for a SQL data insertion into the RDB. The ring-buffered data bank built on the SHM-net helped the system to acquire all the data at 60Hz operation as long as the ring-buffer didn’t overflow. The system has the potential to achieve continuous 60Hz data acquisition soon by using bulk insert technique, which already achieved 100Hz data insertions of 400 signals into a DB in the test.
The accumulated BPM data successfully gave opportunities of precise analyses of beam trajectories in the linac and provided capability of feedback control of the linac electron beams to achieve long-term energy
stability. Before introducing the automatic corrections of the electron beams trajectories and energies in every 5 minutes, operators had manually corrected them whenever the injection efficiency had become worse.
The BPM data analysis successfully contributed to the achievement of long-term energy stability of 0.02%
(rms) and the beam positions stability of 30µm (rms) through the automatic feedback control.
The longtime accumulated BPM data enables reproduction of a past electron beam status. The analysis of the burst currents, which occurred very occasionally in the linac, is a good example to show the importance of the completeness of BPM dataset. An investigation of recorded BPM data brought a fruitful result to find a rare burst-current phenomenon. It was achieved by surveying a perfect dataset taken by the event-synchronized data acquisition system.
This study showed that the beam-synchronized data acquisition and the analysis of all the acquired data was effective approach for the linac stabilization. Since the BPM data acquisition system was developed as the standard framework of MADOCA for the event-synchronized data acquisition, the new framework, furthermore, can be applied to 60Hz data acquisition of the SCSS 8-GeV XFEL accelerator whose control system will be developed with MADOCA. The application will help the beam stabilization of SCSS a lot.
The approach in this study to stable linac operation is general and widely adaptable for other linac control system, which doesn’t use the MADOCA framework. The approach to hold present output signals without depending on any states of equipment control computers is very effective to availability enhancement of a linac operation. And, data acquisition synchronizing to every beam shot and accumulation of all the acquired data into a general RDB is effective approach for stabilization of a linac. A beam-shot synchronized complete BPM dataset can be used for feedback control and feed-forward control to stabilize linac beams.
Furthermore, the accumulated datasets plays an essential role to reproduce past electron beam status, providing opportunities for deeper understanding of beam phenomena to achieve ultimate beam stabilization.
In particular, the new system developed in this study is indispensable for 4th-generation 8-GeV XFEL being built in SPring-8 to produce X-ray laser of wavelength 0.06nm.