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Measurements and Studies of Secondary Electron Emission of Diamond Amplified Photocathode

Description: The Diamond Amplified Photocathode (DAP) is a novel approach to generating electrons. By following the primary electron beam, which is generated by traditional electron sources, with an amplifier, the electron beam available to the eventual application is increased by 1 to 2 orders of magnitude in current. Diamond has a very wide band gap of 5.47eV which allows for a good negative electron affinity with simple hydrogenation, diamond can hold more than 2000MV/m field before breakdown. Diamond al… more
Date: October 1, 2008
Creator: Wu, Q.
Partner: UNT Libraries Government Documents Department
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Simulation of the High-Pass Filter for 56MHz Cavity for RHIC

Description: The 56MHz Superconducting RF (SRF) cavity for RHIC places high demands High Order Mode (HOM) damping, as well as requiring a high field at gap with fundamental mode frequency. The damper of 56MHz cavity is designed to extract all modes to the resistance load outside, including the fundamental mode. Therefore, the circuit must incorporate a high-pass filter to reflect back the fundamental mode into the cavity. In this paper, we show the good frequency response map obtained from our filter's desi… more
Date: May 23, 2010
Creator: Wu, Q. & Ben-Zvi, Ilan
Partner: UNT Libraries Government Documents Department
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Optimizing of the higher order mode dampers in the 56MHz SRF cavity

Description: Earlier, we reported that a 56 MHz cavity was designed for a luminosity upgrade of the RHIC, and presented the requirements for Higher Order Mode (HOM) damping, the design of the HOM dampers, along with measurements and simulations of the HOM dampers. In this report, we describe our optimization of the dampers performance, and the modifications we made to their original design. We also optimized the number of the HOM dampers, and tested different configurations of locations for them.
Date: January 27, 2010
Creator: Wu, Q. & Ben-Zvi, Ilan
Partner: UNT Libraries Government Documents Department
open access

Optimization of Higher Order Mode Dampers in the 56MHz SRF Cavity for RHIC

Description: A 56 MHz superconducting RF cavity was designed for a luminosity upgrade of the Relativistic Heavy Ion Collider (RHIC), including requirements for Higher Order Mode (HOM) damping. In this paper, we describe our optimization of the damper's performance, and modifications made to its original design. We also show the effects of the damper geometry on the cavity's HOM impedance. To reduce the likelihood of magnetic breakdown, we lowered the magnetic field enhancement at the ports to a value less t… more
Date: May 23, 2010
Creator: Wu, Q. & Ben-Zvi, Ilan
Partner: UNT Libraries Government Documents Department
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A DFT and TDDFT Study of Alkylated Trimethylene-Bridged Bis(p-Phenylenediamines)

Description: The conclusions are: (1) LDA predicts fairly well the structures of {pi}-dimers. This has been reported before. Here we show that even the small difference between conformers can be described by LDA. Electron densities suggest a stronger bond is formed in LDA than B3LYP. (2) Though its good performance is possibly due to error cancelations, LDA may be used as a practical tool for large {pi}-dimer systems. (3) TDDFT once again does a good job for the optical transitions. The near-IR band shows a… more
Date: July 5, 2009
Creator: Wu, Q.; Jalilov, A. & Nelson, S.
Partner: UNT Libraries Government Documents Department
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Novel deflecting cavity design for eRHIC

Description: To prevent significant loss of the luminosity due to large crossing angle in the future ERL based Electron Ion Collider at BNL (eRHIC), there is a demand for crab cavities. In this article, we will present a novel design of the deflecting/crabbing 181 MHz superconducting RF cavity that will fulfil the requirements of eRHIC. The quarter-wave resonator structure of the new cavity possesses many advantages, such as compact size, high R{sub t}/Q, the absence of the same order mode and lower order m… more
Date: July 25, 2011
Creator: Wu, Q.; Belomestnykh, S. & Ben-Zvi, Ilan
Partner: UNT Libraries Government Documents Department
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The fundamental power coupler and pick-up of the 56 MHz SRF cavity for RHIC

Description: A fundamental power coupler (FPC) is designed to provide fast tuning the 56MHz SRF cavity in RHIC. The FPC will be inserted from one of the chemical cleaning ports at the rear end of the cavity with magnetic coupling to the RF field. The size and the location of the FPC are decided based on the required operational external Q of the cavity. The cavity is beam driven, and the FPC is designed with variable coupling that would cover a range of power levels. It is thermally isolated from the base t… more
Date: March 28, 2011
Creator: Wu, Q.; Bellavia, S.; Ben-Zvi, Ilan & Pai, C.
Partner: UNT Libraries Government Documents Department
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Simulations for preliminary design of a multi-cathode DC electron gun for eRHIC

Description: The proposed electron ion collider, eRHIC, requires a large average polarized electron current of 50 mA, which is more than 20 times higher than the present experimental output of a single, highly polarized electron source, based on cesiated super-lattice GaAs. To meet eRHIC's requirement for current, we designed a multicathode DC electron gun for injection. The twenty-four GaAs cathodes emit electrons in sequence, then are combined on axis by a rotating field (or 'funnelled'). In addition to i… more
Date: May 23, 2010
Creator: Wu, Q.; Ben-Zvi, Ilan; Chang, X. & Skaritka, J.
Partner: UNT Libraries Government Documents Department
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HOM damping and multipacting analysis of the quarter-wave crab cavity

Description: The quarter-wave crab cavity design has been analyzed further to accommodate LHC requirements. The goal for the design is to provide strong deflecting voltage to the proton bunches at the IP, while keeping the effective length as short as possible. We will evaluate the higher order mode damping with two or four magnetic coupling dampers installed in different configuration. In this paper, we also show possible multipacting locations which are simulated by 2D and 3D codes.
Date: May 20, 2012
Creator: Wu, Q.; Belomestnykh, S.; Ben-Zvi, Ilan & Calaga, R.
Partner: UNT Libraries Government Documents Department
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Interfacial structures of confined air-water two-phase bubbly flow

Description: The interfacial structure of the two-phase flows is of great importance in view of theoretical modeling and practical applications. In the present study, the focus is made on obtaining detailed local two-phase parameters in the air-water bubbly flow in a rectangular vertical duct using the double-sensor conductivity probe. The characteristic wall-peak is observed in the profiles of the interracial area concentration and the void fraction. The development of the interfacial area concentration al… more
Date: August 2000
Creator: Kim, S.; Ishii, M.; Wu, Q.; McCreary, D. & Beus, S. G.
Partner: UNT Libraries Government Documents Department
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Measurements of interfacial area concentration in two-phase flow with two-point conductivity probe. Brief communication

Description: Kataoka, Ishii and Serizawa analyzed the measurements of the local time-averaged interfacial area concentration in two-phase flow with a two-point conductivity probe. They considered the influence of the bubble velocity fluctuation on the measurement and directly transferred the mathematics concept of the local time-averaged interfacial area concentration into the measurable parameters. In the end of the derivation, however, the expression of the interfacial area concentration was inappropriate… more
Date: February 1, 1997
Creator: Wu, Q.; Zheng, D.; Ishii, M. & Beus, S.G.
Partner: UNT Libraries Government Documents Department
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One-group interfacial area transport in vertical air-water bubbly flow

Description: In the two-fluid model for two-phase flows, interfacial area concentration is one of the most important closure relations that should be obtained from careful mechanistic modeling. The objective of this study is to develop a one-group interfacial area transport equation together with the modeling of the source and sink terms due to bubble breakage and coalescence. For bubble coalescence, two mechanisms are considered to be dominant in vertical two-phase bubbly flow. These are the random collisi… more
Date: July 1, 1997
Creator: Wu, Q.; Kim, S.; Ishii, M. & Beus, S.G.
Partner: UNT Libraries Government Documents Department
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Quantitative characterizations of phasic structure developments by local measurement methods in two-phase flow

Description: An experimental study on the internal structure an a out in a 25.4 mm ID pipe. The local void fraction and interfacial area concentration were measured by a double-sensor probe. The flow structure development was visualized by measuring the radial distribution of these two parameters at three axial, locations (L/D = 12, 62, and 112). A more detailed study on the fully developed flow structure was conducted at L/D = 120. The interfacial structure were measured by the double- and four-sensor prob… more
Date: June 1, 1995
Creator: Eberle, C. S.; Leung, W. H.; Wu, Q.; Ueno, T. & Ishii, M.
Partner: UNT Libraries Government Documents Department
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Measurements of interfacial area concentration in two-phase bubbly flow

Description: Interfacial area concentration is an important parameter in the two-fluid model for two-phase flow analysis, which is defined as the total interface area per unit mixture volume and has the following local time-averaged expression: {bar a}{sup t} = 1/{Delta}T {Sigma}{sub j}(1/{vert_bar}V{sub i} {center_dot} n{sub i}{vert_bar}){sub j}, where j denotes the j-th interface that passes the point of interest in a time interval {Delta}T. V{sub i} and n{sub i} refer to the bubble interface velocity and… more
Date: December 31, 1997
Creator: Wu, Q.; Kim, S.; McCreary, D.; Ishii, M. & Beus, S.G.
Partner: UNT Libraries Government Documents Department
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Fundamental damper power calculation of the 56MHz SRF cavity for RHIC

Description: At each injection period during RHIC's operation, the beam's frequency sweeps across a wide range, and some of its harmonics will cross the frequency of the 56MHz SRF cavity. To avoid excitation of the cavity at these times, we designed a fundamental damper for the quarter-wave resonator to damp the cavity heavily. The power extracted by the fundamental damper should correspond to the power handling ability of the system at all stages. In this paper, we discuss the power output from the fundame… more
Date: March 28, 2011
Creator: Wu, Q.; Bellavia, S.; Ben-Zvi, Ilan; Grau, M.; Miglionico, G. & Pai, C.
Partner: UNT Libraries Government Documents Department
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Tellurium-Containing Conjugated Materials for Solar Cells: From Sulfur to Tellurium

Description: A series of diketopyrrolopyrrole(DPP)-based small molecules have been synthesized by palladium-catalyzed coupling reactions. Electron-donating moieties (benzothiophene, benzoselenophene, and benzotellurophene) are bridged by an electron-withdrawing DPP unit to generate donor-acceptor-donor (D-A-D) type molecules. We observe red-shifts in absorption spectra of these compounds by varying heteroatoms from sulfur to tellurium. In bulk heterojunction solar cells with [6,6]phenyl-C61-butyric acid met… more
Date: April 3, 2013
Creator: S., Park Y.; Kale, T.; Wu, Q.; Ocko, B.M. & Black, C.T., Grubbs, R.B.
Partner: UNT Libraries Government Documents Department
open access

Secondary-electron emission from hydrogen-terminated diamond

Description: Diamond amplifiers demonstrably are an electron source with the potential to support high-brightness, high-average-current emission into a vacuum. We recently developed a reliable hydrogenation procedure for the diamond amplifier. The systematic study of hydrogenation resulted in the reproducible fabrication of high gain diamond amplifier. Furthermore, we measured the emission probability of diamond amplifier as a function of the external field and modelled the process with resulting changes in… more
Date: May 20, 2012
Creator: Wang, E.; Ben-Zvi, Ilan; Rao, T.; Wu, Q.; Dimitrov, D. A. & Xin, T.
Partner: UNT Libraries Government Documents Department
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Thermal Emittance Measurement Design for Diamond Secondary Emission

Description: Thermal emittance is a very important characteristic of cathodes. A carefully designed method of measuring the thermal emittance of secondary emission from diamond is presented. Comparison of possible schemes is carried out by simulation, and the most accessible and accurate method and values are chosen. Systematic errors can be controlled and maintained at small values, and are carefully evaluated. Aberration and limitations of all equipment are taken into account.
Date: June 25, 2007
Creator: Wu, Q.; Ben-Zvi, Ilan; Burrill, A.; Chang, X.; Kayran, D.; Rao, T. et al.
Partner: UNT Libraries Government Documents Department
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Quantum efficiency temporal response and lifetime of a GaAs cathode in SRF electron gun

Description: RF electron guns with a strained super lattice GaAs cathode can generate polarized electron beam of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface. In a normal conducting RF gun, the extremely high vaccum required by these cathodes can not be met. We report on an experiment with a superconducting SRF gun, which can maintain a vacuum of nearly 10-12 torr because of cryo-pumping at the temperature of 4.2K. With conventional activ… more
Date: May 23, 2010
Creator: Wang, E.; Ben-Zvi, Ilan; Kewisch, J.; Burrill, A.; Rao, T.; Wu, Q. et al.
Partner: UNT Libraries Government Documents Department
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Testing a GaAs cathode in SRF gun

Description: RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10{sup -12… more
Date: March 28, 2011
Creator: Wang, E.; Kewisch, J.; Ben-Zvi, Ilan; Burrill, A.; Rao, T.; Wu, Q. et al.
Partner: UNT Libraries Government Documents Department
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Diamond Amplified Photocathodes

Description: High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while … more
Date: November 26, 2007
Creator: Smedley, J.; Ben-Zvi, Ilan; Bohon, J.; Chang, X.; Grover, R.; Isakovic, A. et al.
Partner: UNT Libraries Government Documents Department
open access

Recent Progress on the Diamond Amplified Photo-Cathode Experiment.

Description: We report recent progress on the Diamond Amplified Photo-cathode (DAP). The use of a pulsed electron gun provides detailed information about the DAP physics. The secondary electron gain has been measured under various electric fields. We have achieved gains of a few hundred in the transmission mode and observed evidence of emission of electrons from the surface. A model based on recombination of electrons and holes during generation well describes the field dependence of the gain. The emittance… more
Date: June 25, 2007
Creator: Chang,X.; Ben-Zvi, Ilan; Burrill, A.; Grimes, J.; Rao, T.; Segalov, Z. et al.
Partner: UNT Libraries Government Documents Department
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