Abstract
A perpendicular biased ferrite loaded accelerating cavity is studied for a possible upgrade of the CERN accelerator complex which could help to overcome the intensity limitations occurring at the SPS injection. The required accelerating cavity should cover a frequency range of 18 to 40 MHz with high cavity Q, which poses high demands on the ferrite material properties. A test setup is presented to measure the relative permeability and magnetic losses of full scale ferrite garnets (350 mm outer and 200 mm inner diameter) in a magnetic bias field within the frequency range of interest. An one-port reflection measurement provides adequate input to model the relative permeability of the ferrite in numerical simulations for different magnetic bias fields. A resonant measurement setup was used to cross-check simulation results with measurement data and to investigate the magnetic losses of the ferrite material. A numerical model of a simplified accelerating cavity is used to study the capability of the garnet G-510 as a perpendicular biased tuning ferrite.
Highlights
T HE resonance frequency of a ferrite loaded accelerating cavity shifts by applying an external magnetic bias field to the ferrite material by means of changing the relative permeability
It was shown by Earley that a magnetic bias field which is perpendicular to the RF magnetic field can lead to a much higher magnetic of the ferrite in comparison to parallel biasing [1]
In a first step the measurement setup was filled with a single ferrite ring, and in a second run two ferrite rings were placed in the cavity
Summary
T HE resonance frequency of a ferrite loaded accelerating cavity shifts by applying an external magnetic bias field to the ferrite material by means of changing the relative permeability. Different types of ferrite tiles have been evaluated [6] for use in an accelerating cavity with a frequency sweep of 18 to 40 MHz. A measurement technique was presented to calculate the relative permeability vs frequency, dependent on a static magnetic bias field of different orientations. It was shown that superposition of a magnetic bias with both perpendicular and parallel components with respect to the RF magnetic field can be advantageous in terms of frequency tuning range and quality factor. This biasing method was initially suggested by [10]. An electromagnetic design of an accelerating cavity with a frequency sweep of 18 to 40 MHz was made
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