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It is shown that there is an essential limit on the focusing of electron beams due to synchrotron radiation in the final focusing lens of a linear collider. The minimum possible beam size is determined almost only by an invariant emittance of a beam which is given at the entrance of a linear accelerator.

An N-to-N token ring network of twenty-four minicomputers controls the TRISTAN accelerator complex. The computers are linked by optical fiber cables with 10 Mbps transmission speed. The software system is based on the NODAL, a multi-computer interpreter language developed at CERN SPS. Typical messages exchanged between computers are NODAL programs and NODAL variables transmitted by the EXEC and the REMIT commands. These messages are exchanged as a cluster of packets whose maximum size is 512 bytes. At present, eleven minicomputers are connected to the network and the total length of the ring is 1.5 km. In this condition, the maximum attainable throughput is 980 kbytes/s. The response of a pair of an EXEC and a REMIT transactions which transmit a NODAL array A and one line of program `REMIT A' and immediately remit the A is measured to be 95+0.039x ms, where x is the array size in byte. In ordinary accelerator operations, the maximum channel utilization is 2%, the average packet length is 96 bytes and the transmission rate is 10 kbytes/s.

The KEK NODAL system, which is based on the NODAL devised at the CERN SPS, works on an optical-fiber token ring network of twenty-four minicomputers (Hitachi HIDIC 80's) to control the TRISTAN accelerator complex, now being constructed at KEK. KEK NODAL retains main features of the original NODAL: the interpreting scheme, the multi-computer programming facility, and the data-module concept. In addition, it has the following characteristics: (1) fast execution due to the compiler-interpreter method, (2) a multicomputer file system, (3) a full-screen editing facility, and (4) a dynamic linkage scheme of data modules and NODAL functions. The structure of the KEK NODAL system under PMS, a real-time multitasking operating system of HIDIC 80, is described; the NODAL file system is also explained.

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.

The dynamic gravitational field around a rotating bar, and the forced oscillation of a resonant antenna located in this field, are treated in terms of the quadrupole-quadrupole interaction. Some of these calculations have been confirmed by observation of the resonant oscillation of a quadrupole antenna in several orientations.

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

KEKB has achieved the peak luminosity of 4.1 x 10{sup 33} cm{sup -2} sec{sup -1} and the present capability for delivering integrated luminosity is 224 pb{sup -1}/day. This paper describes (1) the recent performance and the problems of KEKB and (2) the comparison of beam-beam simulations with experiments at KEKB.

A beam optics scheme has been designed [ 1 ] for the Future Circular Collider- e + e − (FCC-ee). The main characteristics of the design are: beam energy 45 to 175 GeV, 100 km circumference with two interaction points (IPs) per ring, horizontal crossing angle of 30 mrad at the IP and the crab-waist scheme [ 2 ] with local chromaticity correction. The crab-waist scheme is implemented within the local chromaticity correction system without additional sextupoles, by reducing the strength of one of the two sextupoles for vertical chromatic correction at each side of the IP. So- called “tapering" of the magnets is applied, which scales all fields of the magnets according to the local beam energy to compensate for the effect of synchrotron radiation (SR) loss along the ring. An asymmetric layout near the interaction region reduces the critical energy of SR photons on the incoming side of the IP to values below 100 keV, while matching the geometry to the beam line of the FCC proton collider (FCC-hh) [ 3 ] as closely as possible. Sufficient transverse/longitudinal dy- namic aperture (DA) has been obtained, including major dynamical effects, to assure an adequate beam lifetime in the presence of beamstrahlung and top-up injection. In particular, a momentum acceptance larger than ± 2% has been obtained, which is better than the momentum acceptance of typical collider rings by about a factor of 2. The effects of the detector solenoids including their compensation elements are taken into account as well as synchrotron radiation in all magnets. The optics presented in this paper is a step toward a full conceptual design for the collider. A number of issues have been identified for further study.

The design of FCC-ee is relying on the accumulated experience of $$\mathrm {e^{+}e^{-}}$$ e + e - colliders that have been designed, constructed and operated in the past 40 years. FCC-ee will surpass the 26.7 km long Large Electron Positron collider LEP by a factor 4 in size. Like for LEP the large size is justified by the need to control the synchrotron radiation losses that for both machines reach a few percent per turn. To that end LEP had the first large super-conducting (SC) RF system with around 3.8 GV of accelerating voltage. LEP achieved for the first time very large beam-beam parameters of around 0.08, and it relied on transversely polarized beams to determine accurately the beam energy for the experiments. The DA$$\varPhi $$ Φ NE collider, together with PEP II and KEKB split the two beams into separate vacuum chambers to reach much higher Ampere-level beam currents. To overcome beam-beam lifetime and performance issues DA$$\varPhi $$ Φ NE used for the first time the Crab Waist concept for the interaction region (IR) optics. The B-factories, PEP-II and KEKB have verified the double-ring $$\mathrm {e^{+}e^{-}}$$ e + e - collider with multi-ampere stored currents for over 1000 bunches, small $$\beta ^*$$ β ∗ , top-up injection, and achieved then-highest luminosity. KEKB has applied 22-mrad crossing angle at the IP with crab crossing. Both machines inherited accelerator techniques from their predecessors, PEP and TRISTAN, which was a small-scale LEP. Currently the next generation SuperKEKB collider is starting up. It has already achieved some milestones required for FCC-ee such as small $$\beta ^*$$ β ∗ (0.8 mm) and virtual crab-waist scheme with a large Piwinski angle (>10).

As the accumulation current of positrons increases in the KEKB ring, the injection time is becoming longer. It will thus be one of the most important issues affecting the accumulation of the integrated luminosity. As one of the steps, we introduced a high-intensity two-bunch acceleration scheme at the KEKB linac to intensify positrons by means of doubling the primary electrons. We recently obtained test results of 0.54 nC for the first bunch and 0.49 nC for the second bunch at the linac end. This scheme increased the positron intensity by nearly 65%. Since the linac frequency is not a harmonic number of the LER frequency, the best time interval between two bunches is 96.29 ns, corresponding to 49 LER-buckets. Even with this limitation, it is undoubtedly a very useful scheme for increasing the positron injection rate. The beam test results are described.

A low beta lattice with /spl beta/x*//spl beta/y*=100/1 cm has been realized in the KEKB colliding rings. The basic optical parameters have been measured and compared with the model.

The 8 GeV accumulation ring and the 30 GeV × 30 GeV main ring of TRISTAN, an accelerator-storage ring complex at KEK, are controlled by a single computer system. About twenty minicomputers (Hitachi HIDIC 80-E's) are linked to each other by optical fiber cables to form an N-to-N token-passing ring network of 10 Mbps transmission speed. The software system is based on the NODAL interpreter developed at CERN SPS. The KEK version of NODAL uses the compiler-interpreter method to increase its execution speed. In addition to it, a multi-computer file system, a screen editor, and dynamic linkage of datamodules and functions are the characteristics of KEK NODAL.

Although well established in the realm of celestial mechanics, gravitation between two masses has not yet been thoroughly examined in a laboratory. There have been several tests of the interaction since the Cavendish's celebrated experiment1–6, most of them measuring the static attraction between two spherical masses at a distance R less than 0.8 m. The gravitational interaction is weak and, in contrast with the electromagnetic interaction, there is no effective means to shield it. It has therefore proved difficult to increase the distance R over 1 m. Under the circumstances several authors7–9 have noted that the existing experimental data do not exclude a possible term which is added to the newtonian 1/R potential. Meanwhile, on the grounds of elementary particle physics, a number of theoretical papers7,10–14 have been published predicting additional terms which vanish rapidly at R = ∞. We now report a test of the law of gravitation in a range of R up to 4.2 m. The experiment is based on a low frequency dynamical quadrupole–quadrupole interaction between two masses, which was first observed by Sinsky and Weber15,16. Our result agrees with the inverse square law within the accuracy of the experiment.

Nature of an electronic feedback system to suppress the Johnson noise of resistors is discussed.

It is shown that a scheme of beam-beam collisions which makes a head-on collision in a transversely boosted frame is applicable to storage-ring colliders. This scheme allows a large crossing angle at the collision point without an excitation of synchrotron-betatron resonances, and will give merits in designing high-luminosity colliders.