K. Egawa

Performance of the eight superconducting quadrupole magnets for the TRISTAN low-beta insertions

The low-beta insertion quadrupoles are iron-free superconducting magnets with an inner coil diameter of 140 mm, an effective length of 1.14 m, and a nominal gradient of 70 T/m. The coils, which are of the cos 2 Theta type, are made from four layers of 27-strand NbTi Rutherford-type cable with Kapton insulation and are firmly clamped with 316LN stainless steel collars. Following the development of prototype magnets, eight magnets have been produced and were thoroughly tested and measured prior to installation in the TRISTAN main ring. A brief description of the design and manufacturing technique and the results of tests and measurements are presented.

The vertical emittance in the ATF damping ring

Abstract The results of calculations and simulations of the vertical emittance in the KEK Accelerator Test Facility damping ring are described. Both systematic and random alignment tolerances and a skew correction scheme are presented which limit the normalized vertical emittance to γϵ y −8 m rad. The effect of intrabeam scattering on the vertical emittance is calculated.

Conceptual design of a 5 T/mm quadrupole for linear collider final focus

The luminosity required of a future linear e/sup +/e/sup -/ collider in the teraelectronvolt energy range puts high demands on the final focus elements. In particular, if a classical quadrupole arrangement is chosen, the last magnet should be capable of producing a gradient of several tesla per millimeter. The authors have studied the performance limits of a quadrupole having soft ferromagnetic poles of sufficiently simple geometry to allow fabrication to submicron tolerances, excited by blocks of commercial permanent magnet material. It is shown that it should be possible to obtain a good quality quadrupole of less than 1-mm aperture, with up to 1.4-T pole-tip field.<<ETX>>

Magnet system for the KEKB main ring

Abstract KEKB is a two-ring electron–positron collider with asymmetric energies of 8 and 3.5 GeV to study CP violation in B meson decay. In KEKB, there are 21 types of magnets; about 1600 in total. About 430 dipole and quadrupole magnets were recycled from TRISTAN, the preceding program. All quadrupole magnets are equipped with vertical and horizontal steering dipole magnets. The number of steering magnets is about 1700. There are 212 sextupole magnets, and all of them are fixed on remotely controlled movers to adjust their positions to the beam passage. All main dipole magnets have back-leg coils to steer beams precisely. All quadrupole and sextupole magnets are equipped with correction coils to have a capability for beam-based alignment. Also one-turn coils are installed as well to each magnetic pole of the main magnets to monitor the magnetic flux in the case of trouble. The magnetic field in all magnets was measured and its quality strictly checked. After field measurement, the magnets were installed and precisely aligned. A cooling water system and a power supply system for these magnets were constructed. Magnet design was started in 1994, and construction of the two rings was completed in November 1998. The parameters of the magnets and the construction of the KEKB magnet system are described. Some of the problems experienced during this construction work are also presented.

Accelerator plan for a light‐source study at the TRISTAN MR

A three‐month operation with a beam is scheduled for the autumn of 1995 at the TRISTAN MR for the sake of light‐source development and research programs using it. The lattice will be modified so as to enable the installation of an undulator 5.4 m long and achieve a very low‐emittance beam of 5 nm at 10 GeV. The emittance damping wigglers will enhance the radiation‐damping rate, which will stabilize the coherent beam instabilities as well as reduce the emittance more. A considerable number of accelerating cavities will be removed from the ring in order to minimize the impedance of the higher‐order modes of the cavities that may cause coupled‐bunch instabilities and limit the intensity of the stored beam. For the stability of the light beam, a local feedback system will be applied to the electron orbit in the MR. The beam emittance will be measured by detecting the angular distribution of the Compton scattering of laser photons from the beam electrons. To measure the beam emittance in an independent way, vi...

Superconducting quadrupole magnet system for TRISTAN mini-beta insertions

Superconducting quadrupoles for the mini-beta insertions were installed close to every interaction point and their performances were tested successfully. The system consists of four subsystems, which can be operated individually at the local control rooms located near the subsystems and/or at the remote central cryogenic control room.<<ETX>>

Field measurement of superconducting quadrupole magnets for TRISTAN mini-beta insertions

Eight superconducting quadrupole magnets for TRISTAN minibeta insertions (QCS) have been measured by the rotating coil method before installation in the TRISTAN electron-positron colliding ring. Following the alignment of the magnet to the measuring system by use of a movable QCS-support, harmonics and field gradients were measured as functions of current and the median plane was determined for each magnet. Details of the measuring systems and results of the measurements are presented. The results of the field measurements show that the relative errors of the integral field gradient can be kept within +or-0.001 for all the magnets and that the higher multipole components are small enough for the tolerance required to the QCS.<<ETX>>

Response of a large CsI(Tl) crystal to electrons and pions below 1.5 GeV/c

Abstract A CsI(Tl) crystal of 9.5 cm diameter and 30 cm length was tested with electrons and pions in the momentum range from 0.2 to 1.5 GeV/ c . Photodiode and photomultiplier readouts were used for comparison. In the photodiode readout, the fwhm energy resolution for electrons was 6.7% at 1 GeV in agreement with the EGS simulation. The e/π separation for momentum analyzed particles was found to be 1/1000 at 1 GeV/ c with a simple energy cut. The pulse heith nonuniformity along the longitudinal position, scanned with a pencial beam of 1 GeV/ c pions, was smaller than ±4% between 4 and 27 cm from photomultiplier.

Fabrication and Testing of a Model Quadrupole Magnet for Linear Accelerators

A model of a quadrupole magnet for linear accelerators was designed, fabricated, and tested at KEK in order to gain fabrication experience and a better understanding of superconducting magnet characteristics. The assembly has a design field gradient of 56.5 T/m, an aperture of 92 mm, and a cold mass length of 680 mm. Furthermore, it is designed as a superferric magnet with four racetrack coils wound with a specially fabricated ribbon cable of eight superconducting strands. In this paper, we present details of the magnet design, fabrication, and the results of its cold tests. Data of the field measurements are also presented in brief.

Recent Progress at KEKB

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