107 research outputs found
Low Loss Microwave Ceramic and other Microwave Dielectric Materials for Beam Physics Applications
Introduction. Relativistic, high intensity and small emittance electron bunches are the basis of a future linear collider and free electron laser projects. Drive beam generation in a wakefield structure employing for power extraction and acceleration low loss dielectrics like microwave ceramics, fused silica and Chemical Vapor Deposition (CVD) diamond were considered.Objective. We report here our experimental testing of a ceramic material with extremely low loss tangent at GHz frequency ranges allowing the realization of high efficiency wakefield acceleration. We also present Barium Strontium Titanium oxides (BST) ferroelectric material, which is a critical tuning element of the 400 MHz superconducting radiofrequency (RF) tuner developed and tested by the CERN/Euclid Techlabs collaboration. The materials discussed here also include quartz and CVD diamonds that are capable of supporting the high RF electric fields generated by electron beams or pulsed high power microwaves. These materials have been optimized or specially designed for accelerator applications.Materials and methods. The ceramic materials for accelerators, commonly used for the dielectric based accelerating structures, have to withstand high gradient accelerating fields, and prevent potential charging by electron beams. Correspondingly, the ceramic materials, fused silica and CVD diamond were tested with high power wakefield accelerating structures at Argonne Wakefield Accelerator of Argonne National Laboratory. Some of the presented here ceramic materials were tested at X-band 11.4 GHz magnicon high power source.Results. Low loss microwave ceramics, fused silica, and CVD diamonds have been considered as materials for dielectric based accelerating structures to study of the physical limitations encountered driving > 100 MV/m at microwave and ~ GV/m at THz frequencies in a dielectric based wakefield accelerator. Various ceramic compositions were high power and electron beam tested at X-band 11.4 GHz magnicon power source and Argonne Wakefield Accelerator correspondingly. Special attention was paid to the CVD diamond cylindrical Ka-band 35 GHz wakefield structure development. Finally, the dielectric based structure tuning was demonstrated by varying the permittivity of the BST ferroelectric layer by temperature changes and by applying an external direct current electric field across the ferroelectric. This allows us to control the effective dielectric constant of the composite system and therefore, to control the structure frequency during operation. The same type of ferroelectric material was used for the Ferroelectric Fast Reactive tuner (FE-FRT) development. In a world first, CERN has tested the prototype FE-FRT with a superconducting cavity, and frequency tuning has been successfully demonstrated.Conclusion. Recent results on the development and experimental testing of advanced dielectric materials for accelerator applications are presented. Low loss microwave ceramics, quartz and CVD diamond are considered. We presented our experimental results on wakefield generation in microwave frequency ranges with the dielectric based accelerating structures. Special attention was paid to the experimental results on high power testing at X-band of the externally powered dielectric based components. Finally, we present here first experimental demonstration of ferroelectric tunable microwave ceramic for accelerator application, which includes both tunable dielectric wakefield accelerating structure and ferroelectric based fast high power tuner for superconducting cavities. The experimental results presented here are critical for the advanced dielectric wakefield accelerating structures and other components development intended for the future linear collider projects.Introduction. Relativistic, high intensity and small emittance electron bunches are the basis of a future linear collider and free electron laser projects. Drive beam generation in a wakefield structure employing for power extraction and acceleration low loss dielectrics like microwave ceramics, fused silica and Chemical Vapor Deposition (CVD) diamond were considered.Objective. We report here our experimental testing of a ceramic material with extremely low loss tangent at GHz frequency ranges allowing the realization of high efficiency wakefield acceleration. We also present Barium Strontium Titanium oxides (BST) ferroelectric material, which is a critical tuning element of the 400 MHz superconducting radiofrequency (RF) tuner developed and tested by the CERN/Euclid Techlabs collaboration. The materials discussed here also include quartz and CVD diamonds that are capable of supporting the high RF electric fields generated by electron beams or pulsed high power microwaves. These materials have been optimized or specially designed for accelerator applications.Materials and methods. The ceramic materials for accelerators, commonly used for the dielectric based accelerating structures, have to withstand high gradient accelerating fields, and prevent potential charging by electron beams. Correspondingly, the ceramic materials, fused silica and CVD diamond were tested with high power wakefield accelerating structures at Argonne Wakefield Accelerator of Argonne National Laboratory. Some of the presented here ceramic materials were tested at X-band 11.4 GHz magnicon high power source.Results. Low loss microwave ceramics, fused silica, and CVD diamonds have been considered as materials for dielectric based accelerating structures to study of the physical limitations encountered driving > 100 MV/m at microwave and ~ GV/m at THz frequencies in a dielectric based wakefield accelerator. Various ceramic compositions were high power and electron beam tested at X-band 11.4 GHz magnicon power source and Argonne Wakefield Accelerator correspondingly. Special attention was paid to the CVD diamond cylindrical Ka-band 35 GHz wakefield structure development. Finally, the dielectric based structure tuning was demonstrated by varying the permittivity of the BST ferroelectric layer by temperature changes and by applying an external direct current electric field across the ferroelectric. This allows us to control the effective dielectric constant of the composite system and therefore, to control the structure frequency during operation. The same type of ferroelectric material was used for the Ferroelectric Fast Reactive tuner (FE-FRT) development. In a world first, CERN has tested the prototype FE-FRT with a superconducting cavity, and frequency tuning has been successfully demonstrated.Conclusion. Recent results on the development and experimental testing of advanced dielectric materials for accelerator applications are presented. Low loss microwave ceramics, quartz and CVD diamond are considered. We presented our experimental results on wakefield generation in microwave frequency ranges with the dielectric based accelerating structures. Special attention was paid to the experimental results on high power testing at X-band of the externally powered dielectric based components. Finally, we present here first experimental demonstration of ferroelectric tunable microwave ceramic for accelerator application, which includes both tunable dielectric wakefield accelerating structure and ferroelectric based fast high power tuner for superconducting cavities. The experimental results presented here are critical for the advanced dielectric wakefield accelerating structures and other components development intended for the future linear collider projects
Wakefields Generated by Electron Beams Passing Through a Waveguide Loaded With an Active Medium
The wakefields of a relativistic electron beam passing through a waveguide
loaded with an active medium with weak resonant dispersion have been
considered. For the calculations in this paper the parameters of the medium are
those of a solution of fullerene (C60) in a nematic liquid crystal that
exhibits activity in the X-band. It was shown that several of the TM
accelerating modes can be amplified for the geometries under consideration;
structures in which higher order modes are amplified exhibit essential
advantages as PASERs. In particular, the amplification of the highest mode
occurs in a structure loaded with a rather thick active medium layer that
maximizes the energy stored by the active medium.Comment: 7 pages, 6 figures, submitted to 2006 Advanced Accelerator Concept
Intention Awareness in the Nutshell
Intention awareness is a necessary condition for collective structures to cooperate. This short paper explains the concept of intention awareness, both internal and external. It highlights the importance of adopting a view of intention as an emergent as well as for system design
Heat exchange between the fuel element of a nuclear reactor made of uranium oxide and its shell under boundary conditions of the fourth kind
The work is devoted to the heat exchange of a nuclear reactor. Attention was paid to the mathematical modeling of the temperature field of the fuel element and the thin gas layer. It is assumed that the thermal contact between the solid–interlayer system is ideal. Methods of differentiation, integration and approximate methods were used for numerical modeling. The dependence of the thermal conductivity of uranium oxide on temperature was also taken into account. Based on the obtained expression, the linear heat transfer coefficient and linear thermal resistance were also found
Three-cell traveling wave superconducting test structure
Use of a superconducting traveling wave accelerating (STWA) structure with a
small phase advance per cell rather than a standing wave structure may provide
a significant increase of the accelerating gradient in the ILC linac. For the
same surface electric and magnetic fields the STWA achieves an accelerating
gradient 1.2 larger than TESLA-like standing wave cavities. The STWA allows
also longer acceleration cavities, reducing the number of gaps between them.
However, the STWA structure requires a SC feedback waveguide to return the few
hundreds of MW of circulating RF power from the structure output to the
structure input. A test single-cell cavity with feedback was designed,
manufactured and successfully tested demonstrating the possibility of a proper
processing to achieve a high accelerating gradient. These results open way to
take the next step of the TW SC cavity development: to build and test a
traveling-wave three-cell cavity with a feedback waveguide. The latest results
of the single-cell cavity tests are discussed as well as the design of the test
3-cell TW cavity.Comment: 3 pp. Particle Accelerator, 24th Conference (PAC'11) 28 Mar - 1 Apr
2011: New York, US
Fast Switching Ferroelectric Materials for Accelerator Applications
Fast switching (< 10 nsec) measurement results on the recently developed
BST(M) (barium strontium titanium oxide composition with magnesium-based
additions) ferroelectric materials are presented. These materials can be used
as the basis for new advanced technology components suitable for high-gradient
accelerators. A ferroelectric ceramic has an electric field-dependent
dielectric permittivity that can be altered by applying a bias voltage.
Ferroelectric materials offer significant benefits for linear collider
applications, in particular, for switching and control elements where a very
short response time of <10 nsec is required. The measurement results presented
here show that the new BST(M) ceramic exhibits a high tunability factor: a bias
field of 40-50 kV/cm reduces the permittivity by a factor of 1.3-1.5. The
recently developed technology of gold biasing contact deposition on large
diameter (110 cm) thin wall ferroelectric rings allowed ~few nsec switching
times in witness sample experiments. The ferroelectric rings can be used at
high pulsed power (tens of megawatts) for X-band components as well as at high
average power in the range of a few kilowatts for the L-band phase-shifter,
under development for optimization of the ILC rf coupling. Accelerator
applications include fast active X-band and Ka-band high-power ferroelectric
switches, high-power X-band and L-band phase shifters, and tunable
dielectric-loaded accelerating structures.Comment: 7 pages, 6 figures, submitted to Proceedings of 2006 Advanced
Accelerator Concepts Worksho
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