Tunable RF Cavities Using Orthogonally Biased Ferrite (original) (raw)

Perpendicular Biased Ferrite Tuned Cavities for the Fermilab Booster

The aging Fermilab Booster RF system needs an upgrade to support the future experimental program. The important feature of the upgrade is a substantial enhancement of the requirements for the accelerating cavities. The new requirements include enlargement of the cavity beam pipe aperture, increase of the cavity voltage and increase in the repetition rate. The modification of the present traditional parallel biased ferrite cavities is rather challenging. An alternative to rebuilding the present Fermilab Booster RF cavities is to design and construct new perpendicular biased RF cavities, which potentially offer a number of advantages. An evaluation and a preliminary design of the perpendicular biased ferrite tuned cavities for the Fermilab Booster upgrade is described in the paper. Also it is desirable for better Booster performance to improve the capture of beam in the Booster during injection and at the start of the ramp. One possible way to do that is to flatten the bucket by introducing second harmonic cavities into the Booster. This paper also looks into the option of using perpendicularly biased ferrite tuners for the second harmonic cavities.

Ferrite Characterization for the Design of an Accelerating Cavity With Perpendicular Biasing

IEEE Transactions on Nuclear Science, 2015

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.

Study on a tuning-free network for the rf accelerating cavity

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1996

Applying a bridged-T type all-pass network to a resonator described as a parallel circuit, the output voltage of the resonator shows a band-pass feature over a certain frequency range, while the input impedance is always constant against frequency. This feature is considered to realize the ferrite-loaded tuning-free rf accelerating cavity. It has several merits such as a simple cavity structure without bias windings, an easy operation without feedback control of the bias current, applying new ferrite with favorable rf characteristics and so on. The accelerating system is applicable to a proton-synchrotron for radio therapy or a cooler-synchrotron for nuclear physics studies in a multi-GeV region. This paper presents a theory of the system, the characteristics of the new ferrite, which is currently developed, and design studies of the network based on preliminary measurements of an equivalent lumped circuit.

Proof-of-principle Experiment of a Ferroelectric Tuner for the 1.3 GHz Cavity

A novel tuner has been developed by the Omega-P company to achieve fast control of the accelerator RF cavity frequency. The tuner is based on the ferroelectric property which has a variable dielectric constant as function of applied voltage. Tests using a Brookhaven National Laboratory (BNL) 1.3 GHz electron gun cavity have been carried out for a proof-of-principle experiment of the ferroelectric tuner. Two different methods were used to determine the frequency change achieved with the ferroelectric tuner (FT). The first method is based on a S11 measurement at the tuner port to find the reactive impedance change when the voltage is applied. The reactive impedance change then is used to estimate the cavity frequency shift. The second method is a direct S21 measurement of the frequency shift in the cavity with the tuner connected. The estimated frequency change from the reactive impedance measurement due to 5 kV is in the range between 3.2 kHz and 14 kHz, while 9 kHz is the result fro...

The Effect of 2-Directional Magnetic Biasing Used for Tuning of a Ferrite-Loaded Re-entrant Cavity

IEEE Transactions on Nuclear Science, 2000

Cavities that are partially filled with ferrite material provide a tunable resonance frequency by making use of the changing µ-characteristics of ferrites when exposed to an external magnetic bias field. The concept of using either parallel or perpendicular magnetic biasing to reach a certain resonance frequency of a cavity has been known for many years. However, a cavity based on superposition of perpendicular and parallel magnetic fields to obtain improved ferrite characteristics was suggested in W. R. Smythe "Reducing ferrite tuner power loss by bias field rotation," IEEE Trans. Nucl. Sci., vol. 30, no. 4, pp. 273-275, 1983, but to our knowledge was neither tested nor built. Such a 2-directional biasing is expected to provide a reduction in RF losses for an identical tuning range as compared with the classical 1directional magnetic bias. We have successfully tested this theory with a measurement setup consisting of a ferrite-filled cavity, exposed to external biases that allow the clear separation of the two orientations of superposed magnetic bias fields. The outcome is an enlargement of tuning range with high cavity Ԛ and the possibility of fast tuning. In this paper, we describe the measurement setup and present the tuning ranges that we attained by applying different bias schemes.

Ferroelectric Based High Power Components for L-Band Accelerator Applications

2018

Euclid TechLabs LLC is developing BST based ferroelectric elements designed to be used as the basis for new advanced accelerator components operating in the 1.3 GHz frequency range and intended for Project X and ILC applications. These new ferroelectric elements are designed for the fast active tuner for SC cavities that can operate in air at low biasing DC fields in the range of 15 kV/cm. The BST(M) material (BST ferroelectric with Mg-based additives) allows fast switching and tuning both in vacuum and in air: a switching time < 10 ns of material samples has been demonstrated. The overall goal of the program was to design an L-band externallycontrolled fast ferroelectric tuner for controlling the coupling of superconducting RF cavities for future linear colliders. The tuner prototype has been built; a time response of <30 ns, or 1 deg. in 0.5 ns has been reached. The following problems are addressed: (i) lowering the losses in the ferroelectric material; (ii) improving the te...

The FNAL Booster 2nd Harmonic RF Cavity

2018

A second harmonic RF cavity which uses perpendicularly biased garnet for frequency tuning is currently being constructed for use in the Fermilab Booster. The cavity will operate at twice the fundamental RF frequency, from ~76 106 MHz, and will be turned on only during injection, and transition or extraction. Its main purpose is to reduce beam loss as required by Fermilab’s Proton Improvement Plan (PIP). After three years of optimization and study, the cavity design has been finalized and all constituent parts have been received. We discuss the design aspects of the cavity and its associated systems, component testing, and status of the cavity construction.

Ferro-Electric Fast Reactive Tuner Applications for SRF Cavities

2021

A Ferro-Electric fast Reactive Tuner (FE-FRT) is a novel type of RF cavity tuner containing a low loss ferroelectric material. FE-FRTs have no moving parts and allow cavity frequencies to be changed extremely quickly (on the timescale of 100s of ns or less). They are of particular interest for SRF cavities as they can be placed outside the liquid helium environment and without an FE-FRT it's typically very difficult to tune SRF cavities quickly. FE-FRTs can be used for a wide variety of use cases including microphonics suppression, RF switching, and transient beam loading compensation. This promises entirely new operational capabilities, increased performance and cost savings for a variety of existing and proposed accelerators. An overview of the theory and potential applications will be discussed in detail.

The FNAL Booster Second Harmonic RF Cavity

2018

A second harmonic RF cavity which uses perpendicularly biased garnet for frequency tuning is currently being constructed for use in the Fermilab Booster. The cavity will operate at twice the fundamental RF frequency, from ~76 - 106 MHz, and will be turned on only during injection, and transition or extraction. Its main purpose is to reduce beam loss as required by Fermilab's Proton Improvement Plan (PIP). After three years of optimization and study, the cavity design has been finalized and all constituent parts have been received. We discuss the design aspects of the cavity and its associated systems, component testing, and status of the cavity construction.