S. Kamada

Spatial coherence of undulator radiation beyond the van Cittert–Zernike theorem

Abstract A novel approximation for calculating the first-order spatial coherence of undulator radiation is presented. Since the far-field approximation is not used in the calculation, it is applicable even in the near-field region. Compared with numerical results based on the first principles, the approximation is proved to be quite reasonable. The spatial coherence measured at the Photon Factory, KEK is analyzed using the formula and the results are found to be consistent with the design value within experimental errors.

Experimental techniques and observations of nonlinear dynamics in particle accelerators

Experimental techniques and observations of nonlinear dynamics in particle accelerators since the invention of the phase‐space monitor in 1985 are briefly surveyed. To show recent achievements in experimental techniques and observations of nonlinear dynamics in lepton machines, a series of beam experiments conducted at the TRISTAN MR during the autumn of 1993 are presented. The treated issues are the dynamic aperture with tracking results, the amplitude‐dependent tune shift, the beam‐based measurement of errors and so on.

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.

Recent Progress at KEKB

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

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.

Gamma Ray Source Using Internal Targets in the Tristan Accumulation Ring

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

Beam-beam effects observed at KEKB

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.

Emittance measurement from the decay rate of coherent oscillation through nonlinear filamentation

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.

Accelerator design at SuperKEKB

A completely new approach to measure beam emittance is examined. It is based on measuring the decay rate of the coherent betatron-oscillation through nonlinear filamentation caused by lattice nonlinearity. Experimental results, computer simulations and an analytic approach using differential algebra are presented. This method may provide useful tools in measuring emittance at high brightness light sources, high luminosity particle factories and damping rings for linear colliders where emittance and coupling are expected to be very small.