Orbit Cyclotron Research Articles

An accelerator–driven nuclear reactor

Abstract The basic parameters of the accelerator facility for a proton beam of 100 mA and 1 GeV using a superconducting separate orbit cyclotron, are given. By means of such an accelerator system one can activate a subcritical 3 GW thermal power nuclear reactor of the well known RMBK–type 1000. The system is stable against any “Chernobyl–type” power excursion. When this accelerator system will be coupled to existing RMBK–type 1000 power stations, the resulting electricity production would become substantially more safe. Associated problems and design parameters are discussed.

Orbit correction in an orbit separated cyclotron

The orbit separated proton cyclotron (OSC) described in [1] differs in concept from that of a separated orbit cyclotron (SOC) [2]. Synchronous acceleration in an OSC is based on harmonic number jumps and orbit length adjustments via reverse bending. Four-turn acceleration in the OSC enables it to have four times fewer cryogenic-cavity systems than in a superconducting linac of the same high beam power and energy range.Initial OSC studies identified a progressive distortion of the spiral beam orbits by the off-axis, transverse deflecting fields in its accelerating cavities. Compensation of the effects of these fields involves the repeated use of a cavity field map, in a 3-D linac tracking code, to determine the modified arc bends required for the OSC ring. Subsequent tracking studies confirm the compensation scheme and show low emittance growth in acceleration.

A new accelerator option for driving a sub-critical reactor

A linac and two cyclotrons, of a new type, are considered as a proton driver for an ADSR sub-critical reactor. The cyclotrons use reverse bending, for orbit length adjustments, and harmonic number jumps to achieve a synchronous acceleration. This is a different basis from that of a separated orbit cyclotron (SOC) where accelerating fields must vary over the cavity apertures in a defined manner to maintain synchronism. The new ring is called an orbit separated cyclotron (OSC) as it has the shape of an irregular SOC. An OSC design example is presented, with a six-cell superconducting cavity in each of the eight ring periods. Acceleration, over four turns, of a 10mA (cw) proton beam from 0.5 to 1.0GeV relates to input and output beam powers of 5 and 10MW, respectively. A key design issue is the unusual, spiral magnet system, with all 32 superperiods requiring different combined function magnet designs. One main advantage of an OSC ring over a linac stage is the four times fewer cryogenic and cavity systems, due to the use of the four turn acceleration.

First Beam Accelerated in the TRITRON Superconducting Separated Orbit Cyclotron

First Beam Accelerated in the TRITRON Superconducting Separated Orbit Cyclotron

Computer simulation of electromagnetic fields in the Tritron cavities

The Tritron, a superconducting separated orbit cyclotron, is under construction at Münich. The six superconducting cavities operate in the fundamental mode at 170 MHz. The higher order modes were investigated numerically by means of a three-dimensional computer code ISFEL3D. Computed results are given in comparison with some measured results.

The superconducting accelerating cavities for the Tritron

Abstract The Tritron is a separated orbit cyclotron with superconducting magnets and rf-cavities. The six cavities operate at 170 MHz. They are designed to have a small field enhancement factor. The cavities are fabricated by electroplating copper onto fibreglass shells. The copper is electroplated with PbSn as superconductor. Test results for the first two cavities are given. The values for the accelerating voltage and the quality factor Q lie above the design values for the Tritron accelerator. The highest gap field reached was 10.6 MV/m.

Superconducting cyclotrons

Superconducting cyclotrons with compact geometry and solenoidal coils are operating since several years, indicating the successful introduction of superconductivity in cyclotron design. Some of these facilities use or will use tandems as injectors, some operate as stand-alone machines. The technical problems of this concept are caused mainly by the compactness, which is the attractive feature of the design of course. In order to achieve specific energies above ∼ 300 MeV/u separated sector cyclotrons with superconducting magnets are still under consideration. Technical difficulties are related to the large stored magnetic field energy, to the strong electromagnetic forces and to the non-circular shape of the coils. A rather small separated orbit cyclotron with superconducting channel magnets and superconducting cavities is under construction in Munich. This type of cyclotron offers unique focusing properties at relaxed injection and extraction conditions. The large number of individual controllable channel magnets gives some flexibility. On the other hand it demands a high degree of reliability of many complex components, requiering simple solutions wherever possible. The present status of the Tritron-project is given in detail.

The Superconducting Separated Orbit Cyclotron Tritron

At the Munich 13 MV-Tandem Laboratory the TRITRON is under development, which will be the prototype of a superconducting separated orbit cyclotron for acceleration of heavy ions with 0.04 < i 0.14 and 0.1 0.3. It consists of 12 flat, superconducting sector magnets with 20 neighbouring channels for the spiral-orbit (rin = 70 cm, re, = 150 cm). Due to the individual magnetic channels the transversal and longitudinal focusing properties are as in synchrotrons. The constant turn separation of Ar = 4 cm requires a maximum accelerating voltage of 3 MV per turn, which will be provided by 6 superconducting cavities positioned in each second field free sector gap (see contribution of L. Dietl). Due to the longitudinal focusing the RFfrequency (-170 MHz) may be a high harmonic (h 2 20) of the revolution frequency. Thus the frequency range for acceleration of ions with different revolution frequency can be kept small (+3 %). The magnets as well as the cavities are contained in the same cavity.

Lead Alloys for Superconducting Cavities

For the superconducting separated orbit cyclotron Tritron six large, wedge shaped cavities for simultaneous acceleration of 19 parallel ions beams are needed. The indirectly cooled superconducting cavities with frequencies of ~170 MHz ± 3 % will be made of copper electroplated with lead alloy. With PbSn and PbBi as superconductor stable surfaces without chemical polishing can be obtained. The results of measurements on a 500 MHz test cavity (PbSn) are reported.

Particle acceleration in the drift orbit cyclotron

The drift orbit cyclotron was investigated both theoretically and experimentally. A drift orbit cyclotron was designed and constructed, and acceleration experiments using electrons in high vacuum were performed. Theoretical calculations using the guiding center approximation match the experimental results. Improvement of the acceleration efficiency was observed by using the stochastic acceleration technique.

Design considerations for a separated turn isochronous cyclotron

The objective of this machine is the production of large proton currents at energies from 200 to 1000 MeV with clear turn separations so that 100% beam extraction is achieved. Each stage of the cyclotron consists of a “ring” of identical magnet sectors interpersed with an appropriate set of rf acceleration cavities. The beam is injected from a linac thereby eliminating the central region problems associated with present isochronous cyclotrons. As a result of the narrow magnet gaps, the machine has relatively strong axial focusing throughout. The orbital frequency is high enough so that the beam can be accomodated within the space charge limits. Additional small third harmonic cavities provide for a “flat-top” on the resultant voltage wave form thereby allowing a relatively large phase width in the accelerated beam. Conditions for achieving clear turn separation are analysed and found feasible. For a reasonable total number of turns, the isochronous field trimming requirements are quite tractable. Tentative design figures are presented and compared with the present Separated Orbit Cyclotron (SOC) designs.

A Sector Magnet for a 10-50 MeV Soc

A full-scale prototype magnet sector of a 12-sector, 10-50 MeV separated orbit cyclotron has been built and tested. Eleven pairs of alternating-gradient pole tips are mounted on a yoke structure which provides a common magnetic return path. The pole tips are all excited by a single pair of coils which surround the pole tip mounting bases at the upper and lower yoke faces. The pole tips combine both the negative- and positive-gradient sections in a single unit; the magnetic field gradients are about 800 gauss/in. The pole tips are 4.5 in. wide and have a mean gap of 1.75 in. They were machined by the numeric controlled milling process. Special edge contours were developed to achieve a useful radial aperture of 3 inches. Experience with the prototype magnet demonstrates that magnets for separated orbit cyclotrons present no special difficulty in design, construction, or alignment.

Magnet System for a 4-MeV Experimental Separated Orbit Cyclotron

One of six sector-magnets for the 4-MeV Separated Orbit Cyclotron Experiment (SOCE) has been assembled and tested. The magnets for the SOCE are quite different and much simplified from previous SOC magnet concepts; all pole tips are of the same radius of curvature and each set is excited by a separate coil-pair. The pole-tip fields vary smoothly from 3.5 kilogauss at injection (1 MeV) to 6.6 kilogauss at full energy. The field index, n, varies from 0.58 to 0.52. A unique pole-tip design with an integral vacuum chamber has been developed. The ampere-turn requirements for the main pole-tip coils and trimming coils have been determined. A simple but highly precise magnetic field scanning device has been developed for use with the SOCE magnets.

The Oak Ridge Separated Orbit Cyclotron Project; Progress and Status, January 1966

The Oak Ridge Separated Orbit Cyclotron Project; Progress and Status, January 1966

A Low Energy Separated Orbit Cyclotron

Acceleration in the SOC is achieved by rf cavities placed at equal angular intervals about a ring of alternating gradient guide field magnets wrapped in a flat spiral. Coaxial cavities with two accelerating gaps and having voltage uniform with radius appear to be more economical than tapered rectangular cavities, for machines up to 100 MeV. Deuterons and alpha particles can also be accelerated in a proton machine by operating it on a harmonic number differing by a factor of two. About 5% adjustment in magnetic field is necessary to correct Hρ when ßp is twice ßd.

Magnet for an 800-MeV Separated Orbit Cyclotron

The Separated Orbit Cyclotron consists of individual sector magnets and rf cavities placed alternately in a circular arrangement. The beam is bent and focused by alternating gradient fields produced by pole tips with a minimum radial spacing of 4. 5 inches. Magnet design and construction problems are minimized by using the same pole-surface contour and the same mean-field intensity throughout the entire machine. All pole tips in one sector are mounted on a common yoke and driven by a common pair of coils. Shimming gaps are provided between the yoke and the pole tips so that the same mean field intensity can be achieved for all orbits. Only the azimuthal length of the poles is changed to maintain the correct focusing and bending properties of the magnets.

Stability and Tolerances of the Separated Orbit Cyclotron

The physical arrangement of the magnets and rf cavities in a Separated Orbit Cyclotron are described, and the equations of motion and their solution are discussed. The stability limits are determined for triplet and singlet lens systems, and the choice of operating values to give maximum acceptance are examined. The treatment of random misalignment errors of the magnets is described; the six types of errors whose relative strengths are compared lead to bench alignment errors of ~l mil. The alignment of adjacent lenses and alignment over a distance long compared with a betatron oscillation wavelength are shown, however, to have relatively relaxed tolerances.

Accelerating Cavities for an 800 MeV Soc

The minimum required energy gain per turn for the 800-MeV Separated Orbit Cyclotron increases by a factor of about five from the injection radius to maximum orbit radius. Ordinary rectangular cavities operating in the TM11O mode can be used to provide the accelerating voltage; however, the cavity length is then about twice the distance between the inner and outer orbits (~18 ft). This length, and the rf power loss, can be reduced by shaping the cavity to excite in addition the TM210 and TM310 modes. Inclusion of these higher order modes shifts the maximum voltage from the midpoint of the cavity out toward the end, resulting in a shorter cavity and lower losses. The performance of a 1/4-scale model of the "shaped rectangular cavity" was found to agree quite well with theory. "Wedge-shaped" cavities were also investigated. In this cavity, which is a sector of a cylinder, the length of the accelerating gap increases with machine radius. The upper and lower boundaries of either type of cavity can be shaped to excite higher order Mlodes.

Determination of Carrier Sign by Skipping Orbit Cyclotron Resonance

Determination of Carrier Sign by Skipping Orbit Cyclotron Resonance