R. Chasman

Preliminary Design of a Dedicated Synchrotron Radiation Facility

An electron storage ring to be used solely as a synchrotron radiation source has been designed for a maximum energy of 1.5 GeV, expandable to 2 GeV, and a maximum current of 1 A, High field superconducting magnet wigglers to serve as hard radiation ports have been incorporated into the ring to make available a wide range of wavelengths for simultaneous experiments. The regular lattice consists of a series of small achromatic bends forming the arcs. The wiggler magnets are placed in low-ß in the center of insertions separating these arcs. The arrangement minimizes the electron emittances and yields high source brightness. Other machine parameters are dictated by experimental requirements and apparatus as well as by cost constraints.

A Method for Calculating Resonant Frequencies, Mode Structure and Field Flatness in an Alvarez Type Linac Cavity

The method of Walkinshaw, Sabel and Outram has been extended to cavities consisting of drift tube loaded cells with varying lengths in order to determine the field flatness and sensitivity to errors for the various modes of a realistic linac. A computational program has been written which gives the resonant frequency and field pattern for a multi-cell cavity with arbitrary drift tube lengths and gap lengths. The object of the study is to obtain the following information: 1) Mode structure and resonant frequencies of a cavity consisting of several identical cells in order to obtain the dispersion curve. 2) Sensitivity of the field flatness to dimensional errors for the zero and 7/2 modes. 3) Mode structure and field flatness for a cavity consisting of several cells with differing geometrical parameters. Results of these computations are presented and discussed.

Benton et al: Computer calculations of effect of space charge computer calculations of effect of space charge on longitudinal beam dynamics in proton linear accelerators

A machine program for calculating the effect of space charge on the longitudinal motion in a proton linac was presented at the 1966 Los Alamos Linear Accelerator Conference. This program assumes a uniformly charged ellipsoidal bunch of constant transverse semi-axes throughout the calculation. Since then, numerical results for transmitted current and longitudinal beam quality have been obtained with this program. These results showed that with increasing current, the assumption of a uniformly charged ellipsoidal bunch becomes less and less justified. It was, therefore, decided to also try other space charge force models which would allow for any longitudinal charge distribution. Three additional models, assuming cylindrical symmetry and a fixed transverse beam radius, were programmed. In all of these, the charge density is assumed to vary only longitudinally and the bunch can, therefore, be represented by a succession of thin disks, each uniformly charged. In the point-disk (PD) program, the contributions of the individual disks to the force at a point on the axis are summed the point-diskimage (PDI) (model used by Morton ) is obtained in the same way but includes the effects of image charges induced on drift tubes and the influence of neighboring bunches; the disk-disk (DD) calculation starts from the force between two coaxial charged disks and sums the contribution from all other disks to the force on any one of them. All computations were done on the CDC 6600 computer at the Brookhaven National Laboratory.

ISABELLE e-p Option

During the ISABELLE preliminary design study it became clear from the response of the high energy physics community that the addition of an electron ring to the proposed 200-GeV colliding proton beam facility would be very attractive. It was felt that with the capability of this ring to reach an energy of 15 GeV the already wide range of experimental possibilities of ISABELLE would be greatly extended. Basic design features for such an electron ring have been worked out. Lattice parameters, rf system, injection scheme and characteristics of its interaction with one of the proton rings will be presented. The resulting luminosity was estimated to range from ? 1033 to ? 0.5 × 1032 cm-2 sec-1 for c.m. energies from 65 to 109 GeV.

The Effects of Sextupole Fields on Slow Extraction in a High Field Superconducting Accelerator

Fig, 1. (a) Cell of separated function lattice, (b) Complete lattice with extraction sextupoles and correction elements. Two eEfects on resonant extraction are considered: (1) due to bending magnet saturation and (2) due to errors in positioning of the coils within the magnet aperture. The magnet saturation produces a sextupole term in the field (b = 4 B”/B) within the aperture, Thus motion of the beam of particles will be influenced by what is essentially a zeroth harmonic azimuthal sextupole distribution. What happens is as follows: Resonant extraction is attained with a set of sextupoles (four in this case), giving a 22nd harmonic (u 17-l/3 at extract ion), and causing the betatron oscillation amplitude to increase with time. However, the presence of a zeroth harmonic sextupole distribution has the effect of :;hifting the u value away from the resonance as the betatron amplitude increases.” Thus, for sufficiently large values of b, particles become retrapped and cannot be extracted. When looked at in particle phase space, the presence of a large enough value of b shows up as a distortion of the separatrix (which is the trajectory along which particles are extracted under ideal conditions), as can be seen in Fig. 2. This effect can be corrected by removing the sextupole component, b, in each magnet, Another and more practical way of achieving this correction is to use compensating sextupole magnets, For the CMS, it is proposed to use 48 such sextupoles, located at vertical @ function maxima. However, one must also consider the fact that the sextupole component causes a u variation with average radius, R. As the bending magnets saturate, i.e., as b increases, av/aR which is proportional to b, increases, for the beam.3 thus limiting the available aperture Now, if discrete sextupole magnets (rather than pole face windings) are used as compensating devices, the corrections for the two effects, i.e., the v variation with average radius and with betatron amplitude during resonant extraction, require different sextupole magnet strengths .2 That is, correcting au/aR leaves a v variation with amplitude during extraction. In order to correct the remaining part of the U versus betatron amplitude effect, an independent correction

Preliminary Design of a 30 MeV Deuteron Linear Accelerator for the Production of Intense Beams of 14 MeV Neutrons

The study of radiation damage to materials used to build containers for a fusion reactor requires a beam of neutrons with energy peaked at 14 MeV and with a total flux of 2 1014 neutrons/cm2 sec in order to carry out tests in a reasonable time scale. This report describes a Deuteron Linear Accelerator, utilizing an Alvarez structure, which is designed to produce neutron energy and flux of the above values by allowing a 30 MeV deuteron beam of 100 mA continuous current to strike a liquid lithium target. A second report1 describes the neutron spectrum obtained by this process.

Extrapolation of the Isabelle Design to 400 × 400 GeV

Consideration of a national program for the development of new high energy facilities during the next ten years suggests that the most appropriate energy for proton storage rings may be higher than the 200 × 200 GeV of the present ISABELLE design. It has been indicated that 300 × 300 GeV or 400 × 400 GeV may provide a more reasonable step to maximize the scientific potential of the next major proton storage ring facility. A preliminary analysis of the design consequences of changing the ISABELLE energy to 300 × 300 GeV and 400 × 400 GeV is given, keeping the luminosity, maximum field and most of the original design parameters unchanged. It is concluded that the ISABELLE concept can be extrapolated to 400 × 400 GeV without any unmanageable technical problems and that even higher energies seem to be feasible.

Injection into the ISA

Three modes of injection into the ISA storage accelerators are discussed. The three are: 1) Energy stacking in the ISA. 2) Acceleration of 12 bunches in the AGS followed by single bunch transfer to the ISA. Application of a moving bucket technique then allows the transferred bunch to be brought closer to the bucket train circulating in the ISA. 3) Acceleration on the first harmonic in the AGS. The single bunch is then transferred directly to the ISA into a matched bucket.

Experimental Insertions for the ISA

The general design features of experimental insertions for the ISA storage accelerators are presented. Various insertions which satisfy the requirements for specific high energy particle experiments are discussed. Some consideration is given to a) the distribution of the insertions in the lattice; b) the separation of experimental areas from those used for injection and protective extraction; c) the subject of beam crossing; d) the implications of high s, high quadrupole gradient conditions required in the insertions; and e) general characteristics, including luminosity and beam momentum spread.

Lattice and Aperture Considerations in the Cold Magnet Synchrotron (CMS)

With either superconducting or cold aluminum coils the optimum design of bending magnets for a synchrotron tends to have approximately equal horizontal and vertical apertures. It is therefore advantageous to tailor the lattice and beam parameters so that horizontal and vertical requirements are equal; this imposes the severest constraints on the horizontal aperture, and the vertical tune vz may be allowed to be less than vx. A lattice has been designed with 48 focusing periods, six magnet superperiods each containing an 8-m straight section, vz = 7-1/ 3, vx = 10.45. This choice avoids low-order superperiod resonances and facilitates resonant vertical beam extraction. With 30-GeV injection from the AGS, a gross semiaperture of 20 mm accommodates all requirements, provided field error corrections are obtained from beam position measurements.