N.M. Kroll

Bio: N.M. Kroll is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Photonic crystal & Collider. The author has an hindex of 12, co-authored 48 publications receiving 938 citations.

Wakefield and beam centering measurements of a damped and detuned X-band accelerator structure

Abstract: We present wakefield measurements of a prototype Next Linear Collider (NLC) accelerator structure that was built with dipole mode damping and detuning to suppress the long-range transverse wakefield induced by a beam. In addition, we describe beam centering tests that use as a guide the dipole power coupled out of the structure for damping purposes.

A spectral function method applied to the calculation of the wake function for the NLCTA

Abstract: The equivalent circuit representation of the dipole modes of the SLAC damped detuned structure (DDS) which is being fabricated at LAC has been analyzed by three different methods. The first two are based upon a modal analysis: in the first, damped modes are found by a first order perturbation in the cell to damping manifold coupling strength; while in the second, preferred when the coupling strength is large (as is the case for the SLAC structure) they are determined exactly (a time consuming procedure). The third method, which the authors report here, expresses the wake as a modal sum for modes whose frequencies place them outside the propagation bands of the manifolds (a minor contribution) plus a Fourier like integral of a spectral function over the propagation band of the manifolds (the major contribution). They will present comparisons to previous calculations, assessment of appropriate domains of applicability, and applications to the SLAC structure with matched and mismatched manifold terminations.

Studies of a metal photonic bandgap cavity

Abstract: We describe work on a metal photonic bandgap (PBG) cavity for potential use in high gradient, high Q accelerator structures The configuration we discuss is a square periodic array of metal cylinders, with one cylinder removed from the center The unit is bounded on top and bottom by conducting plates, and terminated on the periphery by microwave absorber Numerical simulations suggest that the metal PBG cavity should have only one high Q resonant mode with monopole symmetry Experimental measurements confirm the existence of the predicted mode, but also reveal higher order, low Q, resonances We examine the origin of these resonances, and suggest possible methods of removing them, to eventually produce a structure with no significant higher order modes

Accelerator and RF System Development for NLC

Abstract: An experimental station for an X-band Next Linear Collider has been constructed at SLAC. This station consists of a klystron and modulator, a low-loss waveguide system for RF power distribution, a SLED II pulse-compression and peak-power multiplication system, acceleration sections and beam-line components (gun, pre-buncher, pre-accelerator, focussing elements and spectrometer). An extensive program of experiments to evaluate the performance of all components is underway. The station is described in detail in this paper, and results to date are presented.<>

Physics and technology of the Next Linear Collider : a report submitted to Snowmass '96

Abstract: We present the current expectations for the design and physics program of an e+e- linear collider of center of mass energy 500 GeV -- 1 TeV. We review the experiments that would be carried out at this facility and demonstrate its key role in exploring physics beyond the Standard Model over the full range of theoretical possibilities. We then show the feasibility of constructing this machine, by reviewing the current status of linear collider technology and by presenting a precis of our `zeroth-order' design.

High-impedance electromagnetic surfaces with a forbidden frequency band

Abstract: A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas.

Microwave transmission through a two-dimensional, isotropic, left-handed metamaterial

Abstract: We present experimental data, numerical simulations, and analytical transfer-matrix calculations for a two-dimensionally isotropic, left-handed metamaterial (LHM) at X-band microwave frequencies. A LHM is one that has a frequency band with simultaneously negative eeff(ω) and μeff(ω), thereby having real values of index of refraction and wave vectors, and exhibiting extended wave propagation over that band. Our physical demonstration of a two-dimensional isotropic LHM will now permit experiments to verify some of the explicit predictions of reversed electromagnetic-wave properties including negative index of refraction as analyzed by Veselago [Usp. Fiz. Nauk 92, 517 (1964), Sov. Phys. Usp. 10, 509 (1968)].

Comparative analysis of edge- and broadside- coupled split ring resonators for metamaterial design - theory and experiments

Abstract: This paper develops a quasi-analytical and self-consistent model to compute the polarizabilities of split ring resonators (SRRs). An experimental setup is also proposed for measuring the magnetic polarizability of these structures. Experimental data are provided and compared with theoretical results computed following the proposed model. By using a local field approach, the model is applied to the obtaining of the dispersion characteristics of discrete negative magnetic permeability and left-handed metamaterials. Two types of SRRs, namely, the so-called edge coupled- and broadside coupled- SRRs, have been considered. A comparative analysis of these two structures has been carried out in connection with their suitability for the design of metamaterials. Advantages and disadvantages of both structures are discussed.

Homogenization of metamaterials by field averaging (invited paper)

Abstract: Over the past several years, metamaterials have been introduced and rapidly been adopted as a means of achieving unique electromagnetic material response. In metamaterials, artificially structured—often periodically positioned—inclusions replace the atoms and molecules of conventional materials. The scale of these inclusions is smaller than that of the electromagnetic wavelength of interest, so that a homogenized description applies. We present a homogenization technique in which macroscopic fields are determined via averaging the local fields obtained from a full-wave electromagnetic simulation or analytical calculation. The field-averaging method can be applied to homogenize any periodic structure with unit cells having inclusions of arbitrary geometry and material. By analyzing the dispersion diagrams and retrieved parameters found by field averaging, we review the properties of several basic metamaterial structures. © 2006 Optical Society of America OCIS codes: 160.0160, 160.1190, 260.2110, 350.5500.