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| TU5PFP009 | Ferroelectric Based High Power Components for L-Band Accelerator Applications | 824 |
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Funding: This work was supported by the US Department of Energy 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 in vacuum and in air both; switching time of material samples < 10 ns has been demonstrated. The overall goal of the program was to design an L-band externally-controlled fast ferroelectric tuner for controlling the coupling of superconducting RF cavities for the 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 technique of the ferroelectric element metallization and brazing; and (iii) improvement breakdown threshold at high voltage bias. |
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| TU5PFP010 | Multipactor in Dielectric Loaded Accelerating Structures | 827 |
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Funding: Work supported by the US Department of Energy. The development of high gradient rf driven dielectric accelerating structures is in part limited by the problem of multipactor. The first high power experiments with an 11.424-GHz rf driven alumina accelerating structure exhibited single surface multipactor. Unlike the well understood multipactor problem for dielectric rf windows, where the rf electric field is tangential and the rf power flow is normal to the dielectric surface, strong normal and tangential rf electric fields are present from the TM01 accelerating mode in the DLA and the power flow is parallel to the surface at the dielectric-beam channel boundary. While a number of approaches have been developed, no one technology for MP mitigation is able to completely solve the problem. In this paper we report on numerical calculations of the evolution of the MP discharge, and give particular attention to MP dependence on the rf power ramp profile and the use of engineered surface features on the beam channel wall to interrupt the evolution of the multipactor discharge. |
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| WE6RFP060 | A 26 GHz Dielectric Based Wakefield Power Extractor | 2930 |
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Funding: DoE SBIR 2008 Phase II, DE-FG02-07ER84821 High frequency, high power rf sources are needed for many applications in particle accelerators, communications, radar, etc. We have developed a 26GHz high power rf source based on the extraction of wakefields from a relativistic electron beam. The extractor is designed to couple out rf power generated from a high charge electron bunch train traversing a dielectric loaded waveguide. Using a 20nC bunch train (bunch length of 1.5 mm) at the Argonne Wakefield Accelerator (AWA) facility, we expect to obtain a steady 26GHz output power of 148 MW. The extractor has been fabricated and bench tested along with a 26GHz Power detector. The first high power beam experiments should be performed prior to the Conference. Detailed results will be reported. |
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| WE6RFP061 | A Transverse Mode Damped DLA Structure | 2933 |
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Funding: DoE SBIR Phase I 2008 As the dimensions of accelerating structures become smaller and beam intensities higher, the transverse wakefields driven by the beam become quite large with even a slight misalignment of the beam from the geometric axis. These deflection modes can cause inter-bunch beam breakup and intra-bunch head-tail instabilities along the beam path, and thus BBU control becomes a critical issue. All new metal based accelerating structures, like the accelerating structures developed at SLAC or power extractors at CLIC, have designs in which the transverse modes are heavily damped. Similarly, minimizing the transverse wakefield modes (here the HEMmn hybrid modes in Dielectric-Loaded Accelerating (DLA) structures) is also very critical for developing dielectric based high energy accelerators. We have developed a 7.8GHz transverse mode damped DLA structure. The design and bench test results are presented in the article. |
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| WE6RFP062 | Development of a GHz/THz Source Based on a Diamond Structure | 2936 |
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Funding: This work is supported by the US Department of Energy There has been considerable progress in using microfabrication techniques to produce experimental rf sources. These devices have for the most part been based on micromachined copper surfaces or silicon wafers. We are developing THz diamond wakefield structures produced using Chemical Vapor Deposition (CVD) technology. The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric rf structures: high breakdown voltage (~600 MV/m), extremely low dielectric losses and the highest thermoconductive coefficient available for removing waste heat from the device. These structures are based on cylindrical diamond dielectric tubes that are manufactured via a relatively simple and inexpensive chemical vapor deposition (CVD) process, plasma assisted CVD. Use of the CVD process is a much simpler method to achieve high quality rf microcavities compared to other microfabrication techniques. We are designing a number of diamond rf structures with fundamental TM01 frequencies in the 0.1-1 THz range. Numerical simulations of planned experiments with these structures will be reported. |
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| WE6RFP063 | Studies of Beam Breakup in Dielectric Structures | 2939 |
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Funding: This work is supported by the US Department of Energy Beam breakup (BBU) effects resulting from parasitic wakefields provide a potentially serious limitation to the performance of dielectric structure based accelerators. We report here on comprehensive numerical studies and planned experimental investigations of BBU and its mitigation in dielectric wakefield accelerators. An experimental program is planned at the Argonne Wakefield Accelerator facility that will focus on BBU measurements in a number of high gradient and high transformer ratio wakefield devices. New pickup-based beam diagnostics will provide methods for studying parasitic wakefields that are currently unavailable at the AWA. The numerical part of this research is based on a particle-Green’s function beam dynamics code (BBU-3000) that we are developing. The code allows rapid, efficient simulation of beam breakup effects in advanced linear accelerators. The goal of this work is to compare the results of detailed experimental measurements with accurate numerical results and ultimately to study the use of external FODO channels for control of the beam in the presence of strong transverse wakefields. |
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| WE6RFP064 | Accelerator Applications of New Nonlinear Ferroelectric Materials | 2942 |
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Funding: Work supported by the US Department of Energy. Materials possessing large variations in the permittivity as a function of the electric field exhibit a rich variety of phenomena for electromagnetic wave propagation such as frequency multiplication, wave steepening and shock formation, solitary waves, and mode mixing. New low loss nonlinear microwave ferroelectric materials present interesting and potentially useful applications for both advanced and conventional particle accelerators. Accelerating structures (either wakefield-based or driven by an external rf source) loaded with a nonlinear dielectric may exhibit significant field enhancements. Nonlinear transmission lines can be used to generate short, high intensity rf pulses to drive fast rf kickers. In this paper we will explore the large signal permittivity of these new materials and applications of nonlinear dielectric devices to high gradient acceleration, rf sources, and beam manipulation. We describe planned measurements using a planar nonlinear transmission line to study the electric field dependence of the permittivity of these materials. Diagnostics include appearance of harmonics with a cw drive signal and sharpening of a pulse waveform as it propagates. |
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| TH5PFP051 | Numerical Algorithms for Dispersive, Active, and Nonlinear Media with Applications to the PASER | 3318 |
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Funding: Work supported by the US Department of Energy. The PASER is one of the first advanced accelerator modeling applications that requires a more sophisticated treatment of dielectric and paramagnetic media properties than simply assuming a constant permittivity or permeability. So far the PASER medium has been described by a linear, frequency-dependent, single-frequency, scalar dielectric function. We have been developing algorithms to model the high frequency response of dispersive, active, and nonlinear media with an emphasis on areas most useful for PASER simulations. The work described also has applications for modeling of other electromagnetic problems involving realistic dielectric and magnetic media. Results to be reported include treatment of multiple Lorentz resonances based on auxiliary differential equation, Fourier, and hybrid approaches, and Kerr, Brillouin, and Raman optical nonlinearities. |
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| TH5RFP001 | Development of Metamaterials for Cherenkov Radiation Based Particle Detectors | 3432 |
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Funding: DOE Metamaterials (MTMs) are periodic artificially constructed electromagnetic structures. The periodicity of the MTM is much smaller than the wavelength of the radiation being transported. With this condition satisfied, MTMs can be assigned an effective permittivity and permeability. Areas of possible application of MTMs in accelerator science are Cherenkov detectors and wakefield devices. MTMs can be designed to be anisotropic and dispersive. The combination of engineered anisotropy and dispersion can produce a Cherenkov radiation spectrum with a different dependence on particle energy than conventional materials. This can be a basis for novel non-invasive beam energy measurements. We report on progress in the development of these media for a proof-of-principle demonstration of a metamaterial-based beam diagnostic. |
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| TH6REP038 | High Precision Beam Energy Measurement with Cherenkov Radiation in an Anisotropic Dispersive Metamaterial Loaded Waveguide | 4033 |
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Funding: SBIR DOE (DE-FG02-08ER85031); Russian Foundation for Basic Research (06-02-16442-a); Physical Faculty of St.Petersburg State University (Russia) (14.10.08) We consider microwave Cherenkov radiation in a waveguide containing an engineered medium, and show that the properties of the radiation can be used to determine the energy of charged particle beams. These properties can form the basis of a new technique for bunch diagnostics in accelerators. We propose to use a material characterized by a diagonal permittivity tensor with components depending on frequency as in the case of a plasma but with the constant terms not equal to unity. These properties can be realized in a metamaterial with a relatively simple structure. In contrast to previous work in the present paper a vacuum channel in the waveguide is taken into account. The particle energy can be determined by measurement of mode frequencies. It is shown that a strong dependence of mode frequencies on particle energy for some predetermined narrow range can be obtained by appropriate choice of the metamaterial parameters and radius of the channel. It is also possible to obtain energy measurements over a wider range at the cost of a weaker frequency dependence. *A.V.Tyukhtin, S.P.Antipov, A.Kanareykin, P.Schoessow, PAC07, p.4156. |
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| FR5RFP001 | Microwave Active Media Studies for PASER | 4535 |
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Funding: DOE Particle Acceleration by Stimulated Emission of Radiation (PASER) is method of particle acceleration in which a beam gains energy from an active medium through stimulated emission. To obtain the required sitmulated emission for the PASER effect the particle beam intensity is modulated at the frequency corresponding to the energy difference between the levels in which population inversion is achieved in the active medium. We propose to use solid-state active medium based on the Zeeman effect (triplet systems) for the PASER. Modulation of the beam at the frequency of the transition to obtain stimulated emission can be produced by means of a deflecting cavity. A transverse "beamlet" pattern will be produced on the AWA photocathode gun by using a laser mask. The transverse beam distribution will be transformed into a longitudinal beam modulation as the beam passes through the deflecting cavity. In this paper we report on the development of active media and the first RF bench test. |