K. Oide

The KEKB injector linac

Abstract An 8-GeV electron/3.5-GeV positron injector for KEKB was completed in 1998 by upgrading the existing 2.5-GeV electron/positron linac. The main goals were to upgrade its accelerating energy from 2.5 to 8 GeV and to increase the positron intensity by about 20 times. This article describes not only the composition and features of the upgraded linac, but also how these goals were achieved, by focusing on an optics design and commissioning issues concerning especially high-intensity single-bunch acceleration to produce positron beams.

LEP3: A High Luminosity

A strong candidate for the Standard Model Scalar boson, H(126), has been discovered by the Large Hadron Collider (LHC) experiments. In order to study this fundamental particle with unprecedented precision, and to perform precision tests of the closure of the Standard Model, we investigate the possibilities offered by An e+e- storage ring collider. We use a design inspired by the B-factories, taking into account the performance achieved at LEP2, and imposing a synchrotron radiation power limit of 100 MW. At the most relevant centre-of-mass energy of 240 GeV, near-constant luminosities of 10^34 cm^{-2}s^{-1} are possible in up to four collision points for a ring of 27km circumference. The achievable luminosity increases with the bending radius, and for 80km circumference, a luminosity of 5 10^34 cm^{-2}s^{-1} in four collision points appears feasible. Beamstrahlung becomes relevant at these high luminosities, leading to a design requirement of large momentum acceptance both in the accelerating system and in the optics. The larger machine could reach the top quark threshold, would yield luminosities per interaction point of 10^36 cm^{-2}s^{-1} at the Z pole (91 GeV) and 2 10^35 cm^{-2}s^{-1} at the W pair production threshold (80 GeV per beam). The energy spread is reduced in the larger ring with respect to what is was at LEP, giving confidence that beam polarization for energy calibration purposes should be available up to the W pair threshold. The capabilities in term of physics performance are outlined.

e^+e^-

The 8 GeV accumulation ring and the 30 GeV main ring of TRISTAN, an accelerator-storage ring complex at KEK, are controlled by a highly computerized control system. Twenty-four minicomputers are linked by optical fiber cables to form an N-to-N token ring network. The transmission speed on the cables is 10 Mbps. From each minicomputer, a CAMAC serial highway extends to the controlled equipment. At present, twenty minicomputers are connected to the network and are used to control the accumulation ring. The software system is based on the NODAL language devised at the CERN SPS. The KEK NODAL system retains main features of the original NODAL: the interpretive scheme, the multi-computer programming facility, and the data-module concept. In addition, it has the following features: (1) fast execution due to the compiler-interpreter method, (2) a multi-computer file system (3), a full-screen editing facility, and (4) a dynamic linkage scheme for data modules and NODAL functions. The accelerators are operated through five operator consoles, each of which is managed by one minicomputer in the network. An operator console contains two 20-inch high-resolution color graphic displays, a pair of touch-panels, and ten small TV monitors. One touch-panel is used to select a program and a piece of equipment to be controlled; the other is used mainly to perform the console actions.

Collider to Study the Higgs Boson

An electronic feedback circuit designed for suppression of the statistical voltage fluctuation across an impedance is described. Characteristics of the ensuing artificial cold resistor are presented. Application of the circuit to transducers of antennas for gravitational radiation is discussed.

The TRISTAN control system

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.

Artificial Cold Resistors

As an introduction, let us begin with a brief introduction of particle colliders related to KEKB. There have been two colliders. The first one was TRISTAN,1) a single ring electron-positron collider with a circumference of 3 km, at the centerof-mass energy up to 64 GeV. TRISTAN was approved in 1981, and experiments started in 1987. Its main object was the discovery of the t-quark, whose mass was not known when it was started. The second collider in Japan is KEKB, a double-ring collider with asymmetric energy 3.5 GeV positrons and 8 GeV electrons, built in the same tunnel as TRISTAN. KEKB was approved in 1994, experiments started in 1999, and then have continued through 2009. KEKB’s energy is tuned around the resonance Υ (4S) ≈ 10.56 GeV to observe the asymmetry in the decay of Band B-mesons. KEKB’s luminosity reached 1.96×1034 cm−2 s−1 in 2009, which is twice as high as its design luminosity. PEP-II2) is also a double-ring collider with 3.1 GeV positrons and 9 GeV electrons built in the same tunnel as PEP, which was a single-ring collider with 2.2 km circumference at SLAC. It was a peculiar situation in the history of colliders in the world that the two machines, KEKB and PEP-II were designed, constructed, and operated at the same time in parallel, with the same scientific goal. This was a severe head-to-head competition. At the beginning PEP-II made a good start in the luminosity, but KEKB has taken a lead since 2001. PEP-II ended its operation in 2008, with the highest luminosity 1.2 × 1034 cm−2 s−1. The competition between the two machines provided various benefits to both. It was not hostile but rather cooperative. Most information was open to each other via meetings, web, and visiting people. Both sides invited reviewers from the other to participate in machine review committees.

The gravitational field of a rotating bar.

In attempts to minimize the impedance of an accelerator by smoothing out its vacuum chamber, improvements are typically first made by reducing the inductive part of the impedance. As the inductance is reduced, however, the impedance becomes increasingly relatively resistive, and as a consequence, the nature of potential well distortion changes qualitatively. An inductive impedance lengthens the bunch (above transition) while maintaining more or less a head-tail symmetry of the bunch longitudinal distribution. A resistive impedance does not change the bunch length as much, but tends to cause a large head-tail asymmetry.

KEKB B-factory, the luminosity frontier

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 80s) 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.

A weak microwave instability with potential well distortion and radial mode coupling

A small angle crab scheme is being considered for the LHC luminosity upgrade. In this paper we present a 400 MHz superconducting cavity design and discuss the pertinent RF challenges. We also present a study on the beam-beam performance and proton-beam emittance growth in the presence of crab compensation, with RF noise sources.

KEK NODAL System

A beam test of the multi-bunch energy compensation system (ECS) was performed using the ΔF method with the 2856±4.327 MHz accelerating structures in the accelerator test facility (ATF) at KEK. The 1.54 GeV S-band linac of the ATF was designed to accelerate a multi-bunch beam that consists of 20 bunches with 2.8 ns spacing. The multi-bunch beam with 2.0×1010 electrons/bunch has an energy deviation of about 8.5% at the end of the linac due to transient beam loading without ECS. The ATF linac is the injector of the ATF damping ring (DR), whose energy acceptance is ±0.5%. The beam loading compensation system is necessary in the ATF linac for the successful injection of multi-bunch into DR. The rf system of the linac consists of 8 regular rf units with the SLED system and 2 ECS rf units without the SLED system. The accelerating structures of the regular units are driven at 2856 MHz and the 2 ECS structures are operated with slightly different rf frequencies of 2856±4.327 MHz. In the beam test, we have succeeded in compressing the multi-bunch energy spread within the energy acceptance of the DR using ΔF ECS. The principle of the beam loading compensation system of KEK-ATF and the experimental results are described in this paper.