Byron T. Wright

Two Electron Models of a Constant‐Frequency Relativistic Cyclotron

Two model constant‐frequency cyclotrons based on the principle of L. H. Thomas, as extended by David L. Judd, are described. Both accelerated electrons to speeds of half that of light in magnetic fields of three‐fold azimuthal periodicity. Three 60°‐wide wedge‐shaped electrodes, driven 120° out of phase, provided an energy gain per revolution of 3 eV0, where V0 is the peak electrode‐to‐ground voltage. Electrons were accelerated to 75 kv with V0=23 v, implying a minimum of one thousand revolutions in the cyclotron. The beam reached full energy without axial loss and it was demonstrated that essentially all of the circulating current will emerge from this type of accelerator without the use of additional deflecting systems. The success of this development program has shown the feasibility of a high‐current, high‐energy cyclotron based on the Thomas principle.

Design and operation of the U.C.L.A. 50 MeV spiral-ridge cyclotron

The design and operation of the U.C.L.A. 50 Mev cyclotron is described. The magnetic field is presented in a series of graphs and orbit calculations on beam stability are given. The results of experimental observations and measurements on the internal beam include beam intensity graphs and photographs, piots of / nu /sub z/ and nu /sub r/ from r.f. knockout measurements, beam intensity as a function of dee voltage, and radial oscillation amplitude of the beam. Because of iack of shielding, the beam has been restricted to 2 mu a of 50 Mev protons by use of a 5% duty cycle. An increased intensity is expected when a puller electrode is used at the source. The tuning up of the beam by means of the eight circular coils for trimming the magnetic field has been found to be quite simple in practice. Efforts to get an external beam are now proceeding in the permanent shielding vault. (auth)

An investigation of the reaction 12C(p, 6Li)7Be at 36 to 57 MeV

Abstract Differential cross sections for the reaction 12 C(p, 6 Li) 7 Be (g.s. + 0.431 MeV) have been measured at incident proton energies of 36.0, 40.7, 45.0, 50.0 and 56.8 MeV. Angular distributions are presented for the c.m. angles generally between 20° and 160°. At the lowest energy differential cross sections are as large as 200 μb/sr. Excitation functions have been taken at energies from 36 to 43 MeV at the c.m. angles 37°, 67° and 90°. The data have been analyzed using zero-range and finite-range DWBA theories assuming the pick-up of 5 He and 6 Li clusters as the dominant reaction mechanisms.

Two-Stage, Two-Gap, Light- and Heavy-Ion Cyclotron Study

A detailed study of a separated-magnet two-stage cyclotron has been made. For elements heavier than S, ions are preaccelerated by a 700 keV Cockroft-Walton and then injected into the first stage (lower gap) of the cyclotron. After acceleration, extraction and stripping (from charge Q to 4Q) they are returned to the center of the second stage (upper gap, whose center line is 15 inches above that of the lower gap) and further accelerated. For ions lighter than S, preacceleration takes place in a small cyclotron and the ions are injected directly into the second stage of the large cyclotron. Protons may be accelerated from 4 to 200 MeV, 3He from 12 to 630 MeV and U from 620 to 2130 MeV. The magnitude of external beams of heavy ions is limited by heating and sputtering of the electrostatic deflector extraction system. The turn separation for uranium ions at the final radius is 16 mm, so extraction efficiencies above 90% should be possible. At 90% it is estimated that 1 particle microampere of uranium ions will be obtained.

DESIGN OF A 720 Mev PROTON FFAG ACCELERATOR

Abstract An FFAG accelerator has advantages for use as a “meson factory”, for the production of intense pion beams. The greatest advantage is the flexibility in duty factor arising from beam stacking. Beams can be brought onto targets with duty factors varying from 10 −6 to unity, for use with different detectors. A conceptual design of an FFAG accelerator has been carried out. It is estimated that this design will accelerate more than 10 15 protons per second to an energy of 720 MeV.

The criteria and techniques of magnetic field measurement used on the UCLA 50 MeV spiral ridge cyclotron

Abstract The precision in the field measurements necessary for satisfactory operation of this cyclotron is calculated. The Hall plate detectors are described. The various methods of field measurement used to give the desired precision are presented.

STUDIES WITH A THREE-DEE THREE-PHASE PROTON CYCLOTRON

As part of the program to investigate the properties of the Thomas cyclotron, a 20‐in. diam proton cyclotron was constructed. In such a three‐dee three‐phase system it is possible to accelerate protons, deuterons, and tritons at the same setting of frequency and magnetic field but on different modes of the rf. For stable operation in the proper mode and with balanced voltages, it has been found necessary to provide both phase servos and amplifier efficiency servos. The dees could not be servoed individually until the inter‐dee capacity was neutralized. Under such conditions it was possible to attain steadily 6.0 ma of protons at 1.0 Mev in the forward mode and 6.5 ma of deuterons at 0.5 Mev in the reverse mode.

Invited Paper-Variable Energy Extraction from Negative Ion Cyclotrons

Negative hydrogen ions are accelerated at a fixed magnetic field. The energy of an extracted beam is determined by the radius of a stripping foil and its azimuth and radius determine the exit point of the beam from the cyclotron. The exit points can be adjusted so that an auxiliary magnet causes the various extracted beams to enter a common beam transport system. Since February, 1966, external beams whose energy is variable from 25 to 50 MeV have been produced by the above means at UCLA and the University of Manitoba. While this is primarily a report on the UCLA system and its performance, special features of the Manitoba system are presented.