Abstract
An energy variable ion linac consisting of multigap, constant-$\ensuremath{\beta}$ cavities was developed. The effect of phase sliding, unavoidable in any constant-$\ensuremath{\beta}$ section, is leading to a coherent rf phase motion, which fits well to the H-type structures with their long $\ensuremath{\pi}$-mode sections and separated lenses. The exact periodicity of the cell lengths within each cavity results in technical advantages, such as higher calculation accuracy when only one single period can be simulated, simpler manufacturing, and tuning. This is most important in the case of superconducting cavities. By using this concept, an improved design for a 217 MHz cw superconducting heavy ion linac with energy variation has been worked out. The small output energy spread of $\ifmmode\pm\else\textpm\fi{}3\text{ }\text{ }\mathrm{AkeV}$ is provided over the whole range of energy variation from 3.5 to 7.3 AMeV. These capabilities would allow for a competitive research in the field of radiochemistry and for a production of super heavy elements (SHE), especially. A first 19-cell cavity of that type was designed, built, and rf tested successfully at the Institute for Applied Physics (IAP) Frankfurt. A 325.224 MHz, seven-cell cavity with constant $\ensuremath{\beta}=0.16$ is under development and will be operated in a frequency controlled mode. It will be equipped with a power coupler and beam tests with Unilac beams at GSI are foreseen.
Highlights
This paper is investigating the design and possible technical parameters of a cw operated linac to perform experiments with heavy ions at the Coulomb barrier.The linac design described in this paper investigates the potential of cavities with gap numbers from 10 to 20 and with cold focusing elements located in the intertank sections
The rough energy variation is provided by just switching the sections off one after another, starting from the end of the linac as it is practiced successfully with Gesellschaft fur Schwerionenforschung (GSI)-Unilac
The phase sliding of the bunch, unavoidable in the constant-period section, has been used to form a special type of the longitudinal motion, which fits very well to the efficient, low-capacitive H-type structures with separated focusing lenses
Summary
This paper is investigating the design and possible technical parameters of a cw operated linac to perform experiments with heavy ions at the Coulomb barrier. The study results are presented in this paper This concept allows negative rf phases at the entrance and exit regions and acceleration around the crest of the wave along the middle part. Superconducting energy variable linacs are composed by two or three gap cavities of the spiral, quarter wave, half wave, or spoke type, respectively [5,6,7,8] This gives a high flexibility in beam energies and charge-tomass ratios of the beam particles—just by altering rf phase relations between cavities and matching the voltage amplitudes. The focusing elements are operated at room temperature This causes an additional effort in a high number of separated cryostats accompanied by many cold-warm transitions along the beam line. Calculation accuracy becomes much higher in this case and allows avoiding the cold rf model
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