M. Tejima

KEKB beam instrumentation systems

For the stable high-luminosity operation and luminosity increase, the electron and positron storage rings of the KEK B-Factory (KEKB) is equipped with various beam instrumentations, which have been working well since the start of the commissioning in December, 1998. Details and performance of the beam-position monitor system based on the spectrum analysis using DSPs, the turn-by-turn BPM with four-dimensional function available for measurements of the individual bunch position, phase and intensity, the parametric beam-DCCTs designed so as to avoid the magnetic-core-selection problems for the parametric flux modulation, the bunch-by-bunch feedback system indispensable to suppress the strong multibunch instabilities in KEKB, the various optical beam diagnostic systems, such as synchrotron radiation interferometers for precise beam-size measurement, the tune meters, the bunch length monitors and the beam-loss monitors are described. Delicate machine tuning of KEKB is strongly supported by these instrumentations.

Sensitivity calculation of beam position monitor using boundary element method

Abstract The position sensitivity for two types of beam position monitors has been calculated using the boundary element method (BEM). A cylindrical beam position monitor was first chosen to compare between BEM and analytical calculations. The results of the BEM fall within 1% of the analytical calculations. Next we applied the BEM to aracetrack type position monitor and compared the BEM results with measured values.

Operational Results of Optics Handling and Closed Orbit Correction in the Tristan Accumulation Ring

The optics handling system of the TRISTAN accumulation ring (AR) is facilitated by the general purpose computer of KEK as well as the machine control computers and has been dealing with many kinds of optics successfully since November 1983. Also a series of correction procedures has reduced r.m.s. values of closed orbit distortion(c.o.d.) at position monitors from 8.5mm to 0.6mm horizontally, and from 2.3mm to 0.3mm vertically in the typical optics of AR. Using the estimated errors, the pre-correction facility has been installed in AR to make an orbit correction possible in a completely new optics before beam injection.

Beam Diagnostics of the Tristan Accumulation Ring

The beam diagnostic system of the TRISTAN Accumulation Ring consists of beam position monitors, visible radiation monitors, x-ray monitors, tune measurement setup, etc.. Eighty-six position monitors are installed around the ring. For the closed orbit measurement, a superheterodyne circuit is used to pick up the 479-th harmonic of the revolution frequency (795 kHz) out of beam pulse trains. Synchrotron light is observed in the visible region and in the x-ray region. Visible radiation is used in three ways: profile monitoring by TV cameras, beam current measurement and bunch shape observation by a streak camera. In the x-ray channel a multi-wire ionization chamber is used to get a digitized profile of the x-ray source. Stripline pickxps are installed to detect transverse oscillations of e+ and e- bunches. The envelope signal of pulse trains will be sent to an FFT processor for tune number identification. At the same time the signals are amplified and fed back to wideband deflection electrodes for damping of the oscillaitons.

Recent Progress at KEKB

We summarize the machine operation of KEKB during past one year focusing on progress for this period.

Refinement Procedures of Beam Position Measurement in the Tristan Accumulation Ring

High precision of about 0. 1 mm is required in the beam position measurement of TRISTAN MR(main ring) which is now under construction. In this respect, position measurement in the TRISTAN AR(accumulation ring) is reviewed. We found that the statistical study of the accumulated measuremnent data gives very useful information on the performance of the monitor system. For example, repeated COD measurements during a beam storage showed not only reproducibility of the position measurement (0. 05 mm) in the beam intens ity range of factor 50 but also pointed out troubles caused by poor contact in coaxial switches. Moreover, it suggested the criterion to abandon erroneous data. Programs for such check has been prepared and has improved the efficiency of COD correction. Improvements have also been made in the calibration and in the mechanical setting of the monitor chambers.

Gamma Ray Source Using Internal Targets in the Tristan Accumulation Ring

As an alternative electron source TRISTAN AR is now operational, and is a

PF-ring and PF-AR operational status

le to accelerate and store an electron beam of more than 5 GeV. We planned to extract high energy gamma rays by inserting a internal target into the AR, because a direct beam extraction is not easy. Two gamma ray lines are prepared by the two detector groups. Each detector group has its own target and gamma ray line. It is also required that the gamma rays should be simultaneously produced at the two targets with the least interference between them. The circulating electron beams gradually collide with the target and produce gamma rays, which are extracted from the AR through a Be-foil window. By a converter the gamma ray is changed into high energy electrons and positrons, which are finally used for the calibration of the lead glass counter. The momentum of the electron beam is defined by an analyzer magnet. At present two gamma ray lines, IT1 and IT4, are available as shown in Fig. 1, and are able to produce the electron beams for the two detector groups simultaneously. Target System Each internal target is located in the beam duct at a bending magnet gap and inserted horizontally from the outside of the beam orbit. The target is suffered from enormous synchrotron radiation and hence is made of molybdenum which is heat-resistive and easy to fabricate. The target head is 3 mm thick and 6 mm high, and is cooled by water flowing through a hole inside the target holder. The target position is monitored by a potentiometer and can be precisely adjusted within 0.05 mm by a remote control.

Movement of BPMS due to Thermal Stress in KEKB

The present operational status of the Photon Factory storage ring (PF-ring) and the Photon Factory advanced ring (PF-AR) in KEK is reported. The scheduled user times of them were more than 4000 hours in FY2006. In the last summer shutdown, new undulators were installed in both of the rings and have been stably operated. A top-up operation in a single-bunch mode was demonstrated for six days in February 2007 druring the shutdown of KEKB at the PF-ring.

Measurement of Transverse Dipole and Quadrupole Moments with the BPMS in the J-PARC 3-50 BT

Movements of Beam Position Monitors due to thermal stress in high beam current operation were observed in KEKB. For high luminosity operation of KEKB, the beam current as high as 1.7 A is accumulated in the positron ring and a precise control of the beam orbit based on the BPM system is required. Though every BPM chamber is fixed firmly on a support of each quadrupole magnet, the BPM chamber moves several hundred microns from the setting position depending on the beam current due to heating of beam pipe by strong synchrotron light irradiation. Such movement introduces an unavoidable offset error in the BPM measurement, and is a serious problem not only for KEKB but also for the next generation of B-factory operated with extremely high beam current. We report the measurement of the movement by gap detectors and an attempt to correct the BPM offset error in real-time operation.