| Paper | Title | Page |
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| MOPE044 | Particle Energy Determination Technique Based on Waveguide Mode Frequency Measurement | 1071 |
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We consider the particles energy measurement method offered in our papers (footnotes). It is based on measurement of the modes frequencies in waveguide loaded with certain material. For this method, the modes frequencies must depend on the particles energy strong enough. Here we discuss the problem of selection of materials for this technique. It is shown that high precision of energy measurement can be reached by use of the system of specific parallel conductors. The approximate analytical approach for obtaining effective permittivity of such structure is developed. It is shown that selection of parameters of the structure allows ruling an effective permittivity characterized by both frequency dispersion and spatial one. The structure is simple enough for production. It allows measuring the particles energy for different predetermined ranges. The other ways of realization of the method are discussed as well. One of them consists in use of thin layer of ordinary dielectric. Selection of the layer thickness and dielectric constant allows obtaining strong enough dependence of frequency on Lorentz-factor in the relatively wide range. A.V. Tyukhtin, S.P. Antipov, A. Kanareykin, P. Schoessow, PAC07, p.4156; |
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| TUPEC081 | Simulations and Measurements of Beam Breakup in Dielectric Wakefield Structures | 1904 |
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Beam breakup (BBU) effects resulting from parasitic wakefields are a serious limitation to the performance of dielectric structure based accelerators. We report here on numerical studies and experimental investigations of BBU and its mitigation. An experimental program is underway at the Argonne Wakefield Accelerator facility that will focus on BBU measurements in dielectric wakefield devices. We examine the use of external FODO channels for control of the beam in the presence of strong transverse wakefields. We present calculations based on a particle-Green's function beam dynamics code (BBU-3000) that we are developing. We will report on new features of the code including the ability to treat space charge. The BBU code is being incorporated into a software framework that will significantly increase its utility (Beam Dynamics Simulation Platform). The platform is based on the very flexible Boinc software environment developed originally at Berkeley for the SETI@home project. The package can handle both task farming on a heterogeneous cluster of networked computers and computing on a local grid. User access to the platform is through a web browser. |
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| WEPE100 | Dielectric Collimators for Linear Collider Beam Delivery System | 3587 |
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In this presentation, dielectric collimator concepts for the linear collider will be described. Cylindrical and planar dielectric collimator designs for CLIC and ILC parameters will be presented, and results of simulations to minimize the beam impedance will be discussed. The prototype collimator system is planned to be fabricated and experimentally tested at Facilities for Accelerator Science and Experimental Test Beams (FACET) at SLAC. |
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| THPEA045 | Development of a Dielectric-loaded Accelerating Structure with Built-in Tunable Absorption Mechanism for High Order Modes | 3777 |
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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. These deflection modes can cause inter-bunch beam breakup and intra-bunch head-tail instabilities along the beam path. We propose a built-in tunable absorption mechanism for damping the parasitic transverse modes without affecting the operational modes in dielectric loaded accelerating (DLA) structures and wakefield power extractors. The new principle for HOM absorption is based on electron paramagnetic resonance. The dielectric tube of the DLA has to be doped with a material exhibiting high EPR, for example ruby, Al2O3 overdoped ~1% with Cr3+. The absorption frequency can be tuned by an external DC magnetic field to match the frequency of the transverse mode. At the resonance imaginary part of permeability becomes significant and the dielectric tube acts as an absorber for the transverse modes. The external DC magnetic field is solenoidal and has to have a magnitude of about 3 kG. This configuration in fact is desirable to focus the beam and provide additional control of beam break up. |
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| THPEB051 | Observation of an Anomalous Tuning Range of a Doped BST Ferroelectric Material Developed for Accelerator Applications | 3987 |
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The BST based ferroelectric-oxide compounds have been found as suitable materials for a fast electrically-controlled RF switches and phase shifters that are under development for accelerator applications in X, Ka and L - frequency bands. 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*. One of the problems related to accelerator application of BST ferroelectric is its high dielectric constant. Decreasing the permittivity however is usually strongly correlated with a decrease in the tunability (k(E)=ε(0)/ε(E)) of ferroelectrics. The use of linear dielectric inclusions in BST ceramics could result in significant suppression of the mentioned k(E) dependence, with the best case being that the tunability vs. ε decrease could be unchanged. On the basis of our measurements we report here two unusual phenomena observed**: (i) the increase both the dc and the dynamic tunability with a decrease of the dielectric constant; (ii) the dynamic tunability was observed to exceed the static tunability at specific magnitudes of the applied field. * A.Kanareykin et al, Proceedings PAC'09. |
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| THPD048 | First High-gradient Tests of the Single-cell SC Cavity with the Feedback Waveguide | 4390 |
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Use of a superconducting travelling wave accelerating (STWA) structure with a small phase advance per cell rather than a standing wave structure may provide a significant increase in 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. In addition, the STWA allows 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 and manufactured to demonstrate the possibility of a proper processing to achieve a high accelerating gradient. The first results of high-gradient tests of a prototype 1.3 GHz single-cell cavity with feedback waveguide will be presented. |
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| THPD057 | The Analysis of Tunable Dielectric Loaded Wakefield Accelerating Structure of Rectangular Geometry | 4413 |
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The analysis of Vavilov-Cherenkov radiation generated by wide high current relativistic electronic bunch in a rectangular waveguide with multilayered dielectric filling is carried out. One ceramic layer of the structure possesses ferroelectric properties, which allow the waveguide frequency spectrum to be controlled by varying the permittivity of this ferroelectric layer by external electric field. On the basis of decomposition on orthogonal eigenmodes of a rectangular multilayered waveguide analytical expressions are received and numerical modeling of wakefield electromagnetic fields and the radial forces deflecting the bunch is spent. |
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| THPD058 | Definition of Focusing System Parameters on the Basis of the Analysis of a Transverse Bunch Dynamics in Dielectric Loaded Wakefield Accelerator | 4416 |
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The strong focusing of high current relativistic electron beams in multi-bunch wakefield acceleration is investigated. These beams are used for generating wake fields in dielectric loaded accelerating structures. We consider ramped charge distribution in the sequence of high current drive bunch. It is shown that the beam focusing system dumping beam break-up effect and elongating of a maximum distance the high current beam can travel determines the effectiveness of the energy transfer to the accelerated electron bunch. The optimal parameters of the focusing system on the basis of self-consistent transverse dynamics analysis are determined. |
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| THPD067 | The First Experiment of a 26 GHz Dielectric Based Wakefield Power Extractor | 4434 |
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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. The first high beam experiment has been performed at Argonne Wakefield Accelerator facility. The experimental results successfully demonstrate the 15ns 26GHz rf pulse generated from the wakefield extractor with a bunch train of 16 bunches. Meanwhile, ~ 30MW short rf pulse has been achieved with a bunch train of 4 bunches. Beam Breakup has prevented charge transport through the power extractor beyond 10nC. We are doing simulations and developing methods to alleviate the BBU effect. |
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| THPD068 | Experiment on a Tunable Dielectric-Loaded Accelerating Structure | 4437 |
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Dielectric-Loaded Accelerating (DLA) structures are generally lack of approaches to tune frequency after the fabrication. A tunable DLA structure has been developed by using an extra nonlinear ferroelectric layer. Dielectric constant of the applied ferroelectric material is sensitive to temperature and DC voltage. Bench test shows the +14MHz/°C, and 6MHz frequency tuning range for a 25kV/cm of DC bias field. A beam test is planned at Argonne Wakefield Accelerator facility before the IPAC conference. Detailed results will be reported. |
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| THPD069 | Studies of Nonlinear Media with Accelerator Applications | 4440 |
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Materials possessing variations in the permittivity as a function of the electric field exhibit a 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. 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 characterize in detail the electric field dependence of the permittivity of these materials. We will present a concept for a nonlinear transmission line that can be used to generate short, high intensity rf pulses to drive fast rf kickers. |
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| THPD070 | Numerical and Experimental Studies of Dispersive, Active, and Nonlinear Media with Accelerator Applications | 4443 |
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Current advanced accelerator modeling applications require a more sophisticated treatment of dielectric and paramagnetic media properties than simply assuming a constant permittivity or permeability. So far active media have 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. 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. We will also report on recent measurements of paramagnetic active microwave materials using EPR spectroscopy. Comparison of the results to numerical simulations will be presented. |