Slab symmetric dielectric micron scale structures for high gradient electron acceleration

A class of planar microstructure is proposed which provide high accelerating gradients when excited by an infrared laser pulse. These structures consist of parallel dielectric slabs separated by a vacuum gap; the dielectric or the outer surface coating are spatially modulated at the laser wavelength along the beam direction so as to support a standing wave accelerating field. We have developed numerical and analytic models of the accelerating mode fields in the structure. We show an optimized coupling scheme such that this mode is excited resonantly with a large quality factor. The status of planned experiments on fabricating and measuring these planar structures will be described

Plane wave synthesis : a new approach to the problem of antenna near-field / far field transformation.

In the recently evolved fields of satellite and space communications as well as in a number of related areas, a vital requirement is an accurate knowledge of the radiating and receiving characteristics of the transmitting and receiving antennas as they appear at a large distance (in the so called far-field region). It is often impossible to obtain a direct measurement of the performance of an antenna and in such cases where it is possible, the accuracy obtainable is frequently limited by the many difficulties associated with the process. Over recent years, a number of techniques have begun to appear which allow measurement of data close to the test antenna (in the near-field region) and then by mathematical processing (the transformation) predict what the far-field performance will be. The earlier techniques while being basically simple from a mathematical viewpoint, were not completely general and tended to involve special, sophisticated, hardware. The later techniques use the most general spherical scanning system but involve much more complicated processing. A new approach to the problem is presented in which much of the computational burden is pre-processed so that the size and complexity of the ultimate prediction task is reduced. The various measurement systems are considered briefly and the spherical system is formulated in detail. Simulated and experimental predictions are carried out and studies are included of the various errors likely to be present and their effects. The important parameters, including the sampling criterion, are discussed in some detail. It is shown that this technique has the potential for producing rapid and accurate predictions of antenna far-field patterns including the facility of compensation for the characteristics of the measurement probe

Report on holographic tests at S-band and K-band on the DSS-63 64 metre antenna

High resolution holographic tests were carried out on DSS-63 at S-band and K-band during May l985. These tests followed a mechanical retrofit which involved the addition of structural bracing to the backing structure. Geosynchronous satellite beacons were used as sources for the tests. At a resolution of 0.4m the S-band and K-band tests revealed rms deviations of the surface to be 2.73mm and 1.53mm, respectively. The difference between these two results is thought to be due mainly to contamination of the S-band surface error map by expected and generally predictable subreflector diffraction effects. The S-band map is also known to be contaminated by diffraction from the subreflector support struts and has a higher noise level than the K-band map. A list of corrections to be applied to the reflector panels is derived from the K-band map. These corrections are predicted to reduce the rms deviation from 1.53mm to 0.86mm at 0.4m resolution. Comparison with results obtained before the mechanical retrofit suggests the major effect of the added structural bracing to be reduction of a third order deformation of the reflector about its axis

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

Design and construction of a high charge and high current 1 - 1/2 cell L-band RF photocathode gun

The Argonne Wakefield Accelerator has been successfully commissioned and used for conducting wakefield experiments in dielectric loaded structures and plasmas. Although the initial wakefield experiments were successful, higher drive beam quality would substantially improve the wakefield accelerating gradients. In this paper we present a new 1-1/2 cell L-band photocathode RF gun design. This gun will produce 10-100 nC beam with 2-5 ps rms pulse length and normalized emittance less than 100 mm mrad. The final gun design and numerical simulations of the beam dynamics are presented

High Energy Physics Division. Semiannual report of research activities, January 1, 1995--June 30, 1995

This report describes the research conducted in the High Energy Physics Division of Argonne National Laboratory during the period of January 1, 1995-July 31, 1995. Topics covered here include experimental and theoretical particle physics, advanced accelerator physics, detector development, and experimental facilities research. Lists of division publications and colloquia are included