M. K. Craddock

High Transition Energy Magnet Lattices

Several methods have been investigated to raise the transition energies of the TRIUMF KAON Factory accelerators, designed to provide 100 ¿A proton beams at 30 GeV, above their acceleration ranges. This would completely avoid beam loss at transition, which, even at the few percent level, would be unacceptable for these beam currents. The methods require a periodic perturbation in either the bending properties of the lattice or the focusing properties or both. In a combined-function lattice the perturbation is provided by clustering the magnets within each superperiod. The effects on the lattice functions are described. The long drifts resulting from the magnet distribution provide natural gaps for beam extraction and injection elements and for rf accelerating cavities.

Production of Simultaneous, Variable Energy Beams from the Triumf Cyclotron

An extracted beam at the design energy of 500 MeV was obtained at TRIUMF in December, 1974. Later, beams of varying energies between 180 and 520 MeV were extracted down beam line 4 and further work resulted in the simultaneous extraction of a 506 MeV beam down beam line 1 while variable energy beams were brought down line 4. In order to reduce initial activation of cyclotron components, time average beams have been restricted to 100 nA but 12 ¿A in a pulsed beam was very easily obtained at 500 MeV. Without much optimization of the injection conditions and without use of the harmonic trim coils an energy spread (full width) of 2.5-3.0 MeV has been observed. Ordinarily, the macro-duty factor has been 100% and the micro-duty factor corresponds to a 5 ns pulse every 44 ns. The transmission to 500 MeV is consistent with the expected loss due to gas stripping.

Improvements to the Beam Properties of the TRIUMF Cyclotron

The behaviour of the internal H- and external proton beams has been considerably improved during the past year. Better steering near the centre has resulted in the internal vertical emittance being reduced to hTr mm-mrad, while the external beam emittances are now 37¿ mm-mrad vertically and 3¿ mm-mrad horizontally, for 90% of the beam. Digitization of probe data together with computer-aided trim coil tuning has enabled the beam to be centred vertically to within ±6 mm; this has been important in simplifying the simultaneous extraction of two beams at independently variable energies (183 to 520 MeV) and intensities (split-ratios from 1/1 to 1/5000). Beam losses in the cyclotron are <20%; direct evidence is presented for gas and electromagnetic stripping, and also for a loss of a few per cent by resonant processes. New techniques have been developed to measure the phase, and have enabled the phase excursions (¿sin¿) to be reduced from ± 0.7 to <± 0.2 below 400 MeV. At high energies the phase excursions reach ±0.4, as anticipated from the magnetic field survey. However, a method is proposed by which separated turns could still be achieved and the energy spread reduced to 0.1 MeV, just as in a perfectly isochronous field.

Optimization of the Phase Acceptance of the Triumf Cyclotron

The horizontal and vertical beam behaviour in the TRIUMF cyclotron has been calculated numerically up to 20 MeV. Effects limiting the cyclotron phase acceptance for an extracted beam with good emittance and energy resolution are discussed, as wel1 as ways of overcoming these effects. Two effects which are critical because of their strong phase dependence are vertical electric focusing at the dee gaps and coupling between the radial and longitudinal motions. With only the RF fundamental present it is shown that the second of these effects can be reduced considerably by the use of local bumps in either the average magnetic field or its second harmonic component, or both. The addition of a third harmonic RF component suitably phase shifted from the fundamental results in the phase dependence of both effects being considerably reduced over a wide phase range. For an initial beam emittance of 0.5π in.‐mrad and an extracted energy resolution of ±600 keV the net phase acceptance is expected to be ∼30 deg with fu...

Central Region Orbit Dynamics in the TRIUMF Cyclotron

Orbit dynamics in the central region have been studied with the aim of optimizing the design for beam quality and RF phase acceptance. Axial ion motion near the centre is dominated by the strong phase dependent RF electric forces at the dee gaps; the consequent restriction of the phase acceptance to ions lagging the RF voltage peak can be lifted both by using an asymmetric dee gap geometry and by the addition of third harmonic to the RF fundamental. A transition from six- to three-sector magnet geometry at the centre to increase the axial focusing was also tried, but was found to give rise to unacceptable ±9° phase oscillations if the dee gap were oriented to avoid the usual gap crossing resonance. Other effects producing coherent radial oscillations, such as first harmonic magnetic field components and dee-voltage asymmetries, have been assigned tight tolerances. The proposed design also makes possible near perfect centring for ions of all phases. Numerical orbit tracking has shown that a beam with the emittance of the external ion source can be accelerated to 20 MeV within 0.25 ? in. mrad for an RF phase band at least 25° wide: in the absence of inflationary effects at higher energies this would yield a 500 MeV beam with ±600 keV energy resolution.

Properties of the TRIUMF Cyclotron Beam

8% of the 300 keV d. c. beam from the ion source can be transmitted to 500 MeV in the TRIUMF cyclotron, without using the buncher. The beam losses are entirely accounted for by the 40° phase acceptance at injection, 20% gas stripping and 6% Lorentz stripping; there are no significant losses due to orbit dynamic problems during 1500 turns of acceleration. The phase history, like \( v_z^2, \) is in good agreement with predictions based on the magnetic field survey. The effect of the harmonic coils and injection parameters on beam quality has been investigated; they can be used, with a chopper, to reduce the energy resolution of the extracted beam to 0.9 MeV FWHM and the emittance for 90% of the beam to 4π mm. mrad horizontally and 11π mm. mrad vertically.

Invited Paper-Polarized Ion Sources for Cyclotrons

Since their advent six years ago polarized ion sources have been successfully installed in 15 accelerators of various types around the world, including FF, FM, and isochronous cyclotrons. The advantages of sources over nuclear reactions for providing polarized particles are (1) greater intensity, (2) control of polarization mode and direction, and (3) freedom from background radiation from the primary target. Currently operating polarized ion sources can produce several tenth-microamperes of up to 80% polarized protons or 100% polarized deuterons and negative ion currents a thousand times smaller. Basic principles and recent developments in polarized ion source design and technology will be reviewed, with particular reference to the problems peculiar to cyclotrons. Some of the major contributions to polarized ion source development have been made at cyclotrons laboratories, first at CERN and later at Saclay, where the powerful adiabatic passage process for inducing hyperfine transitions has been extensively developed. More recently, the achievement of axial injection at Birmingham and the successful acceleration of polarized particles in the isochronous cyclotrons there and at Saclay indicate that polarized ion sources installed on this latest range of cyclotrons could provide the most powerful tool yet for examining nuclear polarization phenomena in the intermediate energy region.

Effects of Axial Misalignment of the Dees and Their Correction

Axial misalignment of the dees near the centre of a cyclotron can lead to the build‐up of large coherent axial oscillations. Numerical computations made for the TRIUMF cyclotron are shown to be in agreement with an analytic treatment of the problem. General formulae are given, applicable to all cyclotrons. In the case of TRIUMF the tolerance allowed on the vertical positions of the dee lips in order to maintain beam quality is ±0.25 mm, quite tight considering the size of the cyclotron.Various methods of reducing the effects of dee misalignment are considered. For TRIUMF a system of specially shaped electrostatic deflecting plates acting over the first few turns has been proposed; these could relax the misalignment tolerance by a factor four. Other advantages and disadvantages of this scheme are discussed, including its effects on the radial motion.

Magnet Lattices for the Proposed TRIUMF KAON Factory

The magnet lattices of a chain of two proton synchrotron and three dc storage rings for the proposed TRIUMF KAON Factory are described. The KAON Factory will provide pulsed and dc proton beams of 30 GeV and 100 PA and will be fed from the existing TRIUMF cyclotron. The rapid cycling Booster (50 Hz) accelerates from 440 MeV to 3 GeV; the 10 Hz main ring is 5 times larger and brings the energy to 30 GeV. The lattices are all of the separated-function type. For avoiding serious beam losses at transition the transition energy is driven far above the top energy of the accelerators. This feature is obtained mainly by creating a superperiodic structure with missing magnet cells and by choosing the horizontal tune just below the number of superperiods. A special arrangement of the rf accelerating cavities is used to avoid synchro-betatron coupling. Fast extraction systems are described.

Magnetic Field Tolerances for the TRIUMF 500 MeV H-Cyclotron

The mass of steel in the TRIUMF magnet will be approximately 4000 tons. In designing this magnet it has been found that there is considerable interplay between manufacturing methods and their tolerances on the one hand, and the tolerances required by beam dynamics on the. other. This paper reviews the magnet tolerances needed to achieve adequate isochronism and axial focusing, and limit first-harmonic induced radial oscillations and electric dissociation of H-ions. The possibility of separated turn acceleration is also considered.