Measurements of electromagnetic properties of ferrites as a function of frequency and temperature

A Chmielinska,F Caspers,C Vollinger,M J Barnes,B Popovic

doi:10.1088/1742-6596/1067/8/082018

Abstract

Fast kicker magnets are used to inject beam into and extract beam out of the CERN accelerator rings. These kickers are often ferrite loaded transmission line type magnets with a rectangular shaped aperture through which the beam passes. The interaction of the beam with the resistive part of the longitudinal beam coupling impedance leads to power dissipation and heating of different elements in the accelerator ring. In particular, power deposition in the kicker magnets can be a limitation: if the temperature of the ferrite yoke exceeds the Curie temperature, the beam will not be properly deflected. In addition, the imaginary portion of the beam coupling impedance contributes to beam instabilities. A good knowledge of electromagnetic properties of materials up to GHz frequency range is essential for a correct impedance evaluation. This paper presents the results of transmission line measurements of complex initial permeability and permittivity for different ferrite types. We present an approach for deriving electromagnetic properties as a function of both frequency and temperature; this information is required for simulating ferrite behaviour under realistic operating conditions.

Highlights

In circular accelerators, injection and extraction systems place newly injected or extracted particles onto the correct trajectory while aiming to minimize the beam losses
Since the transmission line method is more prone to error at higher frequencies, the short-circuit line technique was predominantly used in these studies
The results show that, above 40 MHz, μr decreases with increasing ferrite temperature: for a given beam, this would result in a reduction in beam induced power deposition as the ferrite heats up

Summary

Introduction

Injection and extraction systems place newly injected or extracted particles onto the correct trajectory while aiming to minimize the beam losses. A major component of these systems are fast kicker magnets, which are typically ferrite loaded transmission line type magnets. These magnets consists of multiple cells to approximate a transmission line, where C-shape yokes of magnetic material (typically NiZn ferrites) are sandwiched between high voltage capacitance plates [1]. A key parameter of a ferrite is permeability, which effects the strength and homogeneity of the magnetic field. An accurate model of the ferrite’s permeability is critical to understanding its behaviour and for proper beam coupling impedance simulations. The permeability is of particular interest as the ferrite approaches its Curie temperature (Tc)

Methods

Results

Discussion

Conclusion