Kishiro, J

Nakagawa, H

Nakamura, E

Sato, H

Shirakata, M

Yamanaka, S

CERN Document Server

ORBIT CONTROL AND ABS TRIAL AT KEK 12GEV PROTONSYNCHROTRON MAIN RINGH. Nakagawa, J. Kishiro, H. Sato, E. Nakamura, S. Yamanaka and M. ShirakataHigh Energy Accelerator Research Organization (KEK), Oho 1-1, Tsukuba, Ibaraki, JapanAbstractA new physics experiment of neutrino oscillation requires the high beam in-tensity at KEK 12 GeV Proton Synchrotron. The machine physics study andthe improvements of machine equipment are now going on to increase thebeam intensity for this experiment. The automated beam orbit control is oneof the subjects for this intensity up-grade project. During the ABS implemen-tation in the PS, we investigated how to reject the position monitor anomalyand an improvement of the orbit correction algorithm by including the correla-tion analysis of the orbit data with the beam loss around the machine. A briefdescription of the current ABS system in KEK PS is described in this article.1. INTRODUCTIONThe long-baseline neutrino oscillation experiment [1] requires a stable beam more than  	 ppp,which are nearly equals to the current maximum achievement of the KEK PS. The ABS has to installfor control the beam orbit continuously and precisely during the operation to keep this intensity. Asan example, the beam orbit causes day by day drift from 3 mm to 10 mm in horizontal plane duringthe daily operation. This drift is speculated coming from (a) the exact orbit shift by a deformation ofthe accelerator floor etc. [2] [3] and (b) an anomalous signal level shift of a beam position monitorelectronics or the pickup itself. In the case (a), we must correct the beam orbit. On the other hand, incase (b) we do not use data of such pickups. For separating these problems, it needs to identify the twotypes of cause in orbit measurement. To solve such problem, some trial was done to identify some failedposition monitors. Nevertheless, in our case, results were not good. We need alternate method to do so.At operation of KEK PS, the beam loss signal has been used many works. When operators control theobit, also, they use the beam loss signal to control each local bump. Then, we are planning to use thebeam loss signal for automated orbit control.2. ORBIT MEASUREMENT2.1 Typical orbit of our main ringAt KEK PS Main Ring, 56 beam position monitors are installed in four super periods [4]. Horizontalorbit data is shown in Fig. 1. In this figure, vertical scale is time from injection to near flat top. Eachorbit trajectory stands side by side. Each group corresponds to a superperiod. The figure shows that thereare some failed monitors and there are orbit deformation at both injection and extraction areas.2.2 Drift of beam orbitThe orbits were corrected by operators day by day. Orbit distortion was checked and its result is shown inFig. 2. The figure shows that our corrected orbits were drifted from 10 mm to 3 mm (selected monitors’rms).Many causes are conjectured and many studies are doing now. Because relations between causesare complex, identification of main part of the cause of drift is not so easy. Therefore, we must improvethe problem by automated correction engineering.121Fig. 1: Typical orbit trajectory from injection to near flat top.Fig. 2: Orbit RMS drifts day by day. (In 1998)122Fig. 3: Data flow of our study.      Fig. 4: Beam loss data when test of ABS.Left: Before correction. Right: After correction.3. STUDY OF SEMI-AUTOMATED ORBIT CORRECTION3.1 Correction method in this testSimple automated orbit correction studies were done a few times to get an information which is used tobuild a full automated orbit correction system. Manual orbit correction system of KEK PS was built onthe VME-MAP control system [5]. Position monitor signals were got and displayed by VME computer.The steering magnets were controlled also by the VME. In this study, a Unix computer was used toconnect the two subsystems. Because the VME computers were operated under ”OBJP” environment[6], this part is so easy. The data/command flow is shown in Fig. 3.3.2 Results of testSimple programs of orbit correction were made of our own. Data flow shown in Fig. 3 was used forboth orbit correction and making response matrix. Unix calculation server gets response matrixes andcurrent orbit information and makes a set of current value of steering magnets. This process can doautomatically. At the calculation of a set of current, monitor control table is used, which holds monitorslive/dead information. At the study, these tables were manipulated by hand for correction state control.The result of orbit correction by position monitors were checked both intensity monitors and beam lossmonitors [7]. One of the results of orbit correction is shown in Fig. 4, which is beam loss signals beforeand after orbit correction.In this case, orbit was corrected, but locations of beam loss caused were moved but we can notdecrease the beam losses. When we manipulated the monitor control table, we could get various results.123Fig. 5: Orbit correction system includes beam loss monitor.4. IMPROVEMENT OF OUR SYSTEMWhen that study were done, the beam loss monitoring system was separated from VME computers. Fromthat time on, the loss monitoring system has been connected to a VME computer. It thus appears that theorbit correction can be done automatically when beam loss increase. In addition, finish condition of theautomated orbit correction will be determined beam loss status. Decision of location where orbit must becorrected will be done from information of large beam loss areas. Operators corrected the orbit by localbump method using such information, and then we think that automated orbit correction system can dosame method. Therefore, we are planning the automated orbit correction system shown in Fig. 5.5. CONCLUSIONWe think that beam steering is not performed only by BPM-steering system, but also it should be includedboth beam loss or intensity monitor to certify its performance. We are intending to make an eventdriven automated orbit correction architecture. Event  beam loss monitor In addition, the result of orbitcorrection is checked by the data from the beam loss monitor. A criterion to generate an event by beamloss is now investigating. They are now plan and study, but we would like to make complete automatedorbit correction system.ACKNOWLEDGEMENTSWe thank the member of the KEK PS group for their ideas of beam handling. We also acknowledge theencouragement of Prof. I. Yamane. We thank Dr. K. Takayama for his helpful advice. Thanks are due toMr. K. Hiraishi for his help about many technical problems.References[1] M. Sakuda, The KEK-PS Long Baseline Neutrino Oscillation Experiment (E362) KEK Preprint97-254, Feb. 1998 (Submitted to APCTP-WS).[2] MJ. Shirakata et al., Floor Level Fluctuation in Accelerator Tunnel , Proceedings of the 11th Sym-posium on Accelerator Science and Technology, 1997, Harima, Japan, p.516.[3] H. Sato, Floor Level Fluctuation in the KEK-PS Tunnel , Proceedings of the 1st Asian ParticleAccelerator Conference KEK, Tsukuba, Japan, March 23-27, 1998, p.263.[4] D. Arakawa et al., Proceedings of the 3rd Symposium on Accelerator Science and Technology,1980, Osaka, Japan, p.169.124[5] Y. Shoji et al., Proceedings of the 8th Symposium on Accelerator Science and Technology, 1991,Saitama, Japan, p.332.[6] H. Nakagawa et al., A Program Development Tool for KEK VME-MAP Control System, Proc.ICALEPCS’91 at KEK, KEK Proceedings 92-15(1992) p.322.[7] H. Nakagawa et al., Beam-Loss monitoring System with Free-Air Ionization Chambers, Nucl. In-strum. Methods 174 (1980) 401.125

Orbit control and ABS trial at KEK 12 GeV proton synchrotron main ring

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