Abstract
Booster linacs for tandem accelerators and positive ion superconducting injectors have matured into standard features of many accelerator laboratories. Both types of linac are formed as an array of independently-phased resonators operating at room temperature or in a superconducting state. Each accelerating resonator needs to be individually set in phase and amplitude for optimum acceleration efficiency. The modularity of the linac allows the velocity profile along the structure to be tailored to accommodate a wide range charge to mass ratio. The linac setup procedure, described in this paper, utilizes a superconducting resonator operating in a beam bunch phase detection mode. The main objective was to derive the full set of phase distributions for quick and efficient tuning of the entire accelerator. The phase detector was operated in overcoupling mode in order to minimize de-tuning effects of microphonic background. A mathematical expression was derived to set a limit on resonator maximum accelerating field during the crossover search to enable extracting unambiguous beam phase data. A set of equations was obtained to calculate the values of beam phase advance and energy gain produced by accelerating resonators. An extensive range of linac setting up configurations was conducted to validate experimental procedures and analytical models. The main application of a superconducting phase detector is for fast tuning for beams of ultralow intensities, in particular in the straight section of linac facilities.
Highlights
Superconducting, or room temperature, short independently-phased accelerating structures have been in use for many decades in heavy ion booster linacs [1], positive ion injectors and high energy ion implanters [2]
The calibrated frequency error signal ΔF is the frequency difference between the self-excited loop (SEL) and the reference frequency
This analogue signal is available as an output from low level rf (LLRF) controller as dynamic signature of resonator mechanical frequency excursions
Summary
Superconducting, or room temperature, short independently-phased accelerating structures have been in use for many decades in heavy ion booster linacs [1], positive ion injectors and high energy ion implanters [2]. The short accelerating structures permit the velocity profile along the structure to be optimized to accommodate a wide range of charge to mass ratio. A typical linac booster is the superconducting linac operating at the Australian National University (ANU) Heavy Ion Accelerator Facility (HIAF). A bunched beam is obtained using a single or three frequency grid buncher operating at 1=16th sub-harmonic of the linac frequency of 150 MHz. The buncher is positioned at the low energy (LE) of the 14UD accelerator.
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