S. Antipov

Observation of wakefield generation in left-handed band of metamaterial-loaded waveguide

We report on a design of a TM-mode based metamaterial-loaded waveguide. Network analyzer measurements demonstrated a left-handed propagation region for the TM11 mode at around 10 GHz. A beamline experiment was performed with the metamaterial-loaded waveguide. In this experiment, a 6 MeV electron beam passes through the waveguide and generates a wakefield via the Cherenkov radiation mechanism. We detected a signal in the left-handed frequency band at 10 GHz. This is an indirect demonstration of reverse Cherenkov radiation as predicted in the work of Veselago [Sov. Phys. Usp. 10, 509 (1968)] and discussed in the works of Lu et al. [Opt. Express 11, 723 (2003)], Averkov and Yakovenko [Phys. Rev. B 72, 205110 (2005)], and Tyukhtin et al. [IEEE, Proceedings of the PAC, 2007 (unpublished), pp. 4156–4158]. Cherenkov radiation in artificially constructed materials [metamaterials (MTMs)] can provide unusual engineered features that can be advantageous for particle detector design.

Wakefield generation in metamaterial-loaded waveguides

Metamaterials (MTMs) are artificial structures made of periodic elements and are designed to obtain specific electromagnetic properties. As long as the periodicity and the size of the elements are much smaller than the wavelength of interest, an artificial structure can be assigned a permittivity and permeability, just like natural materials. Metamaterials can be customized to have the permittivity and permeability desired for a particular application. When the permittivity and permeability are made simultaneously negative in some frequency range, the metamaterial is called double-negative or left-handed and has some unusual properties. For example, Cherenkov radiation (CR) in a left-handed metamaterial is backward; radiated energy propagates in the opposite direction to particle velocity. This property can be used to improve the design of particle detectors. Waveguides loaded with metamaterials are of interest because the metamaterials can change the dispersion relation of the waveguide significantly. Sl...

The Argonne Wakefield Accelerator Facility capabilities and experiments.

A description of the Argonne Wakefield Accelerator is presented, pointing out the unique capabilities of the facility. A photocathode RF gun produces electron bunches with tens of nanocoulombs of charge, which are used to excite wakefields. A second photocathode RF gun generates electron bunches that are used to probe these wakefields. An overview of the experimental program carried out at the facility is also presented.

Metamaterial-loaded waveguides for accelerator applications

Metamaterials (MTM) are artificial periodic structures made of small elements and designed to obtain specific electromagnetic properties. As long as the periodicity and the size of the elements are much smaller than the wavelength of interest, an artificial structure can be described by a permittivity and permeability, just like natural materials. Metamaterials can be customized to have the permittivity and permeability desired for a particular application. Waveguides loaded with metamaterials are of interest because the metamaterials can change the dispersion relation of the waveguide significantly. Slow backward waves, for example, can be produced in an LHM-loaded waveguide without corrugations. In this paper we present theoretical studies and computer modeling of waveguides loaded with 2D anisotropic metamaterials, including the dispersion relation for a MTM-loaded waveguide. The dispersion relation of a MTM-loaded waveguide has several interesting frequency bands which are described. It is shown theoretically that dipole mode suppression may be possible. Therefore, metamaterials can be used to suppress wakefields in accelerating structures.

High Gradient Wakefields in Dielectric Loaded Structures

Dielectric loaded wakefield structures have potential to be used as high gradient accelerator components. Using the high current drive beam at the Argonne Wakefield Accelerator Facility, we employed cylindrical dielectric loaded wakefield structures to generate accelerating fields of up to 86 MV/m, at 10 GHz. Short electron bunches of up to 86 nC are used to drive these fields, either as single bunches or as bunch trains. The structures consist of cylindrical ceramic tubes (cordierite) with a dielectric constant of 4.76, inserted into cylindrical copper waveguides. These standing‐wave structures have a field probe near the outer diameter of the dielectric, in order to sample the RF fields generated by the electron bunches. Monitoring the field probe signal serves to verify the absence of electric breakdown in the structures. MAFIA simulations are used to calculate the amplitude of the fields generated by the traversing electrons bunches.

Comparison of Wavebeam Phase Front Retrieval Methods Based on Iterative Algorithm and Irradiance Moments

Two methods for phase front reconstruction of quasi-optical wavebeams are discussed. Both of them allow phase reconstruction using only wavebeam intensity measurements in a few cross sections. The first method applies the iterative convergence procedure for phase synthesis. The second one is based on averaged description of wavebeams, using the irradiance moments. By means of these two methods the field structures was reconstructed in some numerical and practical experiments in mm-range. Since the methods are based on general principles they may be used not only for microwaves, but also for optics and acoustics. It was shown that depending on measurement quality, wavebeam amplitude geometry and number of measured planes, one or another method is more preferable. The optimization of phase retrieval technique by combining iteration algorithm with irradiance moment method is proposed.

Numerical studies of International Linear Collider positron target and optical matching device field effects on beam

For an International Linear Collider (ILC) undulator-based positron source target configuration, a strong optical matching device (OMD) field is needed inside the target to increase the positron yield (by more than 40%) [Y. K. Batygin, Proceedings of the 2005 ALCPG and ILC Workshops, Snowmas, CO, 14–27 August 2005 (unpublished)] It is also required that the positron target be constantly rotated to reduce thermal and radiation damages. Eddy currents, produced by an OMD field in turn, interact with the magnetic field and produce a drag (stopping) force. This force not only produces heat in the disk but also creates a dipole deflecting field, which affects the beam. Therefore it is important to simulate such a system in detail to design the motor and cooling system and also a correction magnet system. In order to guide the ILC target design, an exact simulation of the spinning disk in a magnetic field is required. In this paper we present a simulation method implemented using COMSOL and compare it with the e...

Observation of Wakefield Generation in Left-Handed Band of Metamaterial-Loaded Waveguide

We report on a design of a TM‐mode based metamaterial‐loaded waveguide. Network analyzer measurements demonstrated a left‐handed propagation region for the TM11 mode at around 10 GHz. A beamline experiment was performed with the metamaterial‐loaded waveguide. In this experiment, a 6 MeV electron beam passes through the waveguide and generates a wakefield, via the Cherenkov radiation mechanism. We detected a signal in the left‐handed frequency band at 10 GHz. This is an indirect demonstration of reverse Cherenkov radiation as discussed in several papers. Cherenkov radiation in artificially constructed materials (metamaterials, MTM) can provide unusual, engineered features that can be advantageous for particle detector design.

Applications of Cherenkov radiation in dispersive and anisotropic metamaterials to beam diagnostics

We present theoretical and numerical analyses of Cherenkov radiation in bulk anisotropic and dispersive metamaterials and in waveguides loaded with these materials. Anisotropy and dispersion of both permittivity and permeability are taken into account. It is shown that the properties exhibited by these materials allow the design of detectors with unusual and previously unavailable characteristics.

Simulations of the rotating positron target in the presence of omd field

For an International Linear Collider (ILC) undulator-based positron source target configuration, a strong optical matching device (OMD) field is needed inside the target to increase the positron yield (by more than 40%). It is also required that the positron target is constantly rotated to reduce thermal and radiation damage. We report on a simulation of the rotating metal target wheel under a strong magnetic field. By rearranging Maxwells equations for a rotating frame and using Comsol, we have solved the detailed magnetic field distribution and eddy current of a rotating metal disk in magnetic field, and so the required power to drive the target wheel. In order to validate the simulation process, we have compared our results with previous experimental data and found they are in very good agreement. Here we give detailed results on the proposed ILC target system, such as induced magnetic field (dipole and higher orders), eddy current distribution and the driving force requirements. The effect of these higher order fields on the positron beam dynamics is also considered.