T. Ieiri

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.

A real time bunch-length monitor using the beam spectrum and measurements of bunch lengthening

Abstract A bunch length monitor used for detecting two frequency components of a beam spectrum has been developed for the TRISTAN accumulation ring (AR). The principle, design and performance of the monitor are described. The monitor comprises a stripline electrode, a coaxial cable and two identical synchronous detectors. Calibration of the monitor was carried out using the natural bunch length at a low beam current. The bunch length was measured at an injection energy of 2.5 GeV by the monitor and a streak camera. The imaginary part of the longitudinal coupling impedance was estimated by the potential well bunch lengthening and synchrotron tune shift.

Measurement of the beam-beam parameter by exciting coherent betatron oscillation

Abstract Four coherent betatron oscillation modes induced by the beam-beam interaction we observed in the TRISTAN Main Ring (MR) during two e+ and two e− bunches colliding operation. These modes are extracted using a phase mixing technique and used for measuring beam-beam parameters. The luminosity, the coupling coefficient and the emittance are estimated from the observation. The emittance agrees with the expected value to within 15% accuracy.

Status of Solenoid System to Suppress the Electron Cloud Effects at the KEKB

A large number of solenoids have been installed in the KEKB LER to remove the electron cloud. This paper describes recent solenoid winding work and the effect of it on electron cloud effects.

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.

Observation and simulation of nonlinear behavior of betatron oscillations during the beam-beam collision

It is pointed out that, when electron and positron beams collide in a storage ring, the space charge force of one of the beams gives the other beam a transverse kick. This beam-beam force is nonlinear. When an additional kick is applied to the beam, coherent oscillations will occur. It is difficult to solve such a nonlinear forced oscillation analytically and exactly. In the present work, the nonlinear oscillation was studied experimentally using a tune measurement system. In addition, a simple program was used to simulate the nonlinear beam-beam force.<<ETX>>

High-resolution bunch-length monitor capable of measuring an rms value of a few mm

Abstract A bunch-length monitor based on detecting the beam spectrum is presented. The monitor comprises a stripline electrode and a heterodyne detector with a switch. The detailed performance of the monitor was examined on a bench as well as with a beam of the TRISTAN main ring. Calibration was carried out at a low beam current. The measured bunch lengths agree well with the calculated values. It has been demonstrated that the monitor can measure an rms bunch length of 3 mm. The repeatability of the measurement was within ±0.2 mm when the bunch length was 5.7 mm.

Beam Behavior in the Tristan Accumulation Ring

This paper describes the machine studies, particularly on the single bunch effect. Two impedance sources, RF cavities and bellows, are assumed in the AR. A short summary in the bunch lengthening effect is presented. In the transverse direction the betatron tune shift is in reasonable agreement with the estimated impedance. A vertical instability is observed but its reason is still unknown. The preliminary result of the measurement on the stability condition and the beam behavior is described.

Beam-beam effects observed at KEKB

At KEKB, a dedicated machine experiment on crab crossing has been carried out for about 4.5 months. Some of the beam-beam effects observed with crab crossing, which include a beam lifetime issue, are discussed in comparison with those with a finite crossing angle of plusmn11 mrad.

Status of PF-AR

The PF‐AR is a full‐time single‐bunch light source for SR experiments in the X‐ray region. Electrons are injected at 3.0 GeV and ramped up to the final energy of 6.5 GeV for normal user operation or 5.0 GeV for medical application. The typical initial beam current is 55 mA at 6.5 GeV and the beam lifetime is 15 h at 50 mA. The initial single‐bunch impurity better than 10−8 was achieved, however, degradation of the impurity during the users’ run has to be solved. Since the present emittance of 290nm⋅rad is not satisfactory, we are making an effort to realize the minimum attainable emittance of 160nm⋅rad. The high quality of pulse X‐ray has brought us abundant occasions to do time‐domain and/or time‐resolved measurements.