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Summary on the Fundamental Mode Damper Experiments of the 56 MHz SRF Cavity

Description: This report summarizes the experimental results done with the fundamental damper for the 56 MHz prototype Cu cavity. Various measurements were done on the cavity including determination of the position of the fundamental damper and measurement of the frequency and Q factor changes while the damper is withdrawn. Prediction on the dissipated power while the damper is withdrawn was made by experiments.
Date: July 1, 2008
Creator: Choi,E. & Hahn, H.
Partner: UNT Libraries Government Documents Department

Higher Order Mode Damper Study of the 56 MHz SRF Cavity

Description: This report summarizes the study on the higher order mode (HOM) damper for the 56 MHz SRF cavity. The Q factors and frequencies of the HOMs with the HOM damper are measured and compared to the simulation. The high pass filter prototype for rejecting the fundamental mode is designed and tested. The filter measurement is also compared to the simulation. Based on the measurement, a new location of the HOM damper is chosen.
Date: August 1, 2008
Creator: Choi,E. & Hahn, H.
Partner: UNT Libraries Government Documents Department

Capacitive Fundamental Power Coupler and Pickup for the 56 MHz SRF Cavity

Description: The beam excited 56 MHz SRF cavity will have a power coupler for a fast frequency tuner. The calculation shows the coupling of the power coupler, {beta}{sub opt}, is around 50. Size and location of the power coupler are determined by measurements. Measurements are in good agreement with the simulation results. The axial location of the power coupler for the Nb cavity is limited by corrugations made on the cavity outer conductor for purpose of removing any multipacting. The preferred axial location is 14.5 cm away from the cavity gap start where a slow tuner plate will be. MWS simulations are done to determine the length of the power coupler inner conductor and pickup probe for the Nb cavity at the fixed axial location. Size and location of both the fundamental power coupler and the pickup probe can be decided from the simulation results.
Date: July 1, 2008
Creator: Choi,E. & Hahn, H.
Partner: UNT Libraries Government Documents Department

A Multiple-Channel Sub-Band Transient Detection System

Description: We have developed a unique multiple-channel sub-band transient detection system to record transient electromagnetic signals in carrier-dominated radio environments; the system has been used to make unique observations of weak, transient HF signals. The detection system has made these observations possible through improved sensitivity compared to conventional broadband transient detection systems; the sensitivity improvement is estimated to be at least 20 dB. The increase in sensitivity has been achieved through subdivision of the band of interest (an 18 MHz tunable bandwidth) into eight sub-band independent detection channels, each with a 400 kHz bandwidth and its own criteria. The system generates a system trigger signal when a predetermined number of channels (typically five) trigger within a predetermined window of time (typically 100 ~s). Events are recorded with a broadband data acquisition system sampling at 50 or 100 Msample/s, so despite the fact that the detection system operates on portions of the signal confined to narrow bands, data acquisition is broadband. Between May and September of 1994, the system was used to detect and record over six thousand transient events in the frequency band from 3 to 30 MHz. Approximately 500 of the events have been characterized as paired bursts of radio noise with individual durations of 2 to 10 ps and separations between the bursts of 5 to 160 ps. The paired transients are typically 5 to 40 dB brighter than the background electromagnetic spectrum between carrier signals. We have termed these events SubIonospheric Pulse Pairs (SIPPS) and presently have no explanation as to their source. Our observations of SIPPS resemble observations of TransIonospheric Pulse Pairs (TIPPs) recorded by the Blackboard instrument on the ALEXIS satellite; the source of TIPP events is also unknown. Most of the recorded SIPP events do not exhibit frequency dispersion, implying propagation along a line-of-sight (groundwave) ...
Date: November 1, 1998
Creator: Smith, David A.
Partner: UNT Libraries Government Documents Department

High-frequency electric field measurement using a toroidal antenna

Description: In this paper the author describes an innovative method of measuring high-frequency electric fields using a toroid. For typical geophysical applications the new sensor will detect electric fields for a wide range of spectrum starting from 1.0 MHz. This window, in particular the lower frequency range between 1.0 to 100 MHz, has not been used for existing electromagnetic or radar systems to detect small objects in the upper few meters of the ground. Ground penetrating radar (GPR) can be used successfully in this depth range if the ground is resistive but most soils are, in fact, conductive (0.01 to 1.0 S/m) rendering GPR inefficient. Other factors controlling the resolution of GPR system for small objects is the spatial averaging inherent in the electric dipole antenna and the scattering caused by soil inhomogeneities of dimensions comparable to the wavelength (and antenna size). For maximum resolution it is desirable to use the highest frequencies but the scattering is large and target identification is poor. Time-varying magnetic fields induce an emf (voltage) in a toroid. The electric field at the center of the toroid is shown to be linearly related to this induced voltage. By measuring the voltage across a toroid one can easily and accurately determine the electric field. The new sensor will greatly simplify the cumbersome procedure involved with GPR measurements with its center frequency less than 100 MHz. The overall size of the toroidal sensor can be as small as a few inches. It is this size advantage that will not only allow easy fabrication and deployment of multi-component devices either on the surface or in a borehole, but it will render greatly improved resolution over conventional systems.
Date: January 1, 1997
Creator: Lee, K.H.
Partner: UNT Libraries Government Documents Department

Extension of Alcator C-mod's ICRF Experimental Capability

Description: A new 4-strap single-ended ICRF antenna has been added to the Alcator C-Mod tokamak. PPPL designed, fabricated, and tested the antenna up to 45 kV on an rf test stand. It is capable of symmetric phasing for ICRF heating studies, and asymmetric phasing with an improved directed wave spectrum for current drive. Two new 2 MW transmitters, tunable from 40-80 MHz, allow operation in plasma at 43, 60, and 78 MHz to match a variety of toroidal fields and plasma conditions. This addition increases the total available ICRF power to 4 MW at 80 MHz plus 4 MW at 40-80 MHz. Plasma heating and current drive experiments at the extended power levels and new frequencies are planned, and initial system performance will be discussed.
Date: June 1, 1999
Creator: Schilling, G.; Hosea, J.C.; Wilson, J.R.; Bonoli, P.T. & Lee, W.D.
Partner: UNT Libraries Government Documents Department

The LASI high-frequency electromagnetic subsurface-imaging system: System description and demonstration site-characterization survey at the Idaho National Engineering Laboratory

Description: A high-frequency, high-resolution, electromagnetic imaging system has been developed for environmental geophysics surveys. Some key features include: (1) rapid surveying to allow dense spatial sampling over a large area, (2) high-accuracy measurements which are used to produce a high-resolution image of the subsurface, (3) measurements which have excellent signal-to-noise ratio over a wide bandwidth (31 kHz to 32 MHz), (4) large-scale physical modeling to produce accurate theoretical responses over targets of interest in environmental geophysics surveys, (5) rapid neural network interpretation at the field site, and (6) visualization of complex structures during the survey. A field survey was conducted at INEL, Nov. 28-Dec. 1, 1995, over the Cold Test Pit, which simulates waste pits at INEL and other DOE sites.
Date: December 31, 1996
Creator: Sternberg, B.K. & Poulton, M.M.
Partner: UNT Libraries Government Documents Department

Connection between NMR and electrical conductivity in glassy chalcogenide fast ionic conductors

Description: The work documented in this thesis follows the traditional order. In this chapter a general discussion of ionic conduction and of glassy materials are followed by a brief outline of the experimental techniques for the investigation of fast ionic conduction in glassy materials, including NMR and impedance spectroscopy techniques. A summary of the previous and present studies is presented in the last section of this introductory chapter. The details of the background theory and models are found in the Chapter II, followed by the description of the experimental details in Chapter III. Chapter IV of the thesis describes the experimental results and the analysis of the experimental observations followed by the conclusions in chapter V.
Date: November 1, 1995
Creator: Kim, K.H.
Partner: UNT Libraries Government Documents Department

Sintering of ceramics using low frequency rf power

Description: Sintering with low frequency rf power ({approximately}50 MHz) is a new technique with unique capabilities that has been used to sinter a variety of ceramic materials, including zirconia-toughened alumina, alumina, silicon carbide, and boron carbide. Processing with low frequencies offers many advantages compared to processing with conventional microwave frequencies (915 MHz and 2.45 GHz). Because of the longer wavelength, the rf electric field penetrates materials more than microwaves. This effect allows the processing of a wider variety of materials and allows for an increase in the physical size of the material being processed. In addition, the material is heated in a single mode cavity with a uniform electric field, which reduces the occurrence of hot-spot generation and thermal runaway effects. This technique has been used to sinter large crack-free alumina samples (3 inch square) to > 97% density. The sintering and/or annealing of a number of carbide materials has been demonstrated as well, including silicon carbide, boron carbide, tungsten carbide, and titanium carbide.
Date: July 1, 1995
Creator: Caughman, J.B.O.; Hoffman, D.J.; Baity, F.W.; Akerman, M.A.; Forrester, S.C. & Kass, M.D.
Partner: UNT Libraries Government Documents Department

Reduction of the beam breakup mode Q values in the ETA/ATA Accelerating Cells

Description: Earlier Microwave Measurements of the ETA Accelerating Cells has uncovered eleven resonances in the frequency range of 0 > 850 MHz. The Q values of these modes ranged from 14 to 70. A three phase program directed at substantially reducing these Q values is reported. In particular the dampening methods described below resulted in a decrease of Q value from 40 to 5 for the beam breakup mode (TM/sub 110/) with a corresponding reduction for most of the other cavity modes.
Date: May 20, 1980
Creator: Birx, D.L.
Partner: UNT Libraries Government Documents Department

Basalt nuclear-waste repository remote sensing using electromagnetic techniques

Description: The electromagnetic permittivity and attenuation rate of basalt, from the Near Surface Test Facility of the Basalt Waste Isolation Project at Hanford, Washington, have been measured in the laboratory as a function of water content at frequencies from 25 MHz to 1000 MHz. Both the permittivity and the attenuation rate are strongly related to water content of basalt in this frequency range. Completely dehydrated, the rock has a frequency-independent relative permittivity of about 8 and attenuation rates (inverse skin depths) of 0.04 m/sup -1/ and 3.2 m/sup -1/ at 25 MHz and 1000 MHz, respectively. When completely saturated by tap water to 6% by volume, the relative permittivity ranges from 16.5 to 10.0 and the attenuation ranges from 0.3 m/sup -1/ to 5.5 m/sup -1/ between 25 MHz and 1000 MHz. The data indicate that high-frequency electromagnetic remote sensing techniques, such as those used in radar, cross-borehole tomography, and borehole logging, may be useful in characterizing proposed basalt repositories and monitoring established waste repositories. Electromagnetic methods are particularly suited to delineating water content of the rock and, when completely saturated, crack and pore porosity of the rock mass within a repository. 7 references, 3 figures.
Date: January 1, 1984
Creator: Daily, W.D. & Buettner, H.M.
Partner: UNT Libraries Government Documents Department