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An introduction to beamstrahlung and disruption

Description: In this lecture we review the current understanding of the beam-beam interaction in e/sup +/e/sup -/ linear colliders. Strictly speaking, the two effects, disruption and beamstrahlung, during beam-beam interaction are coupled. This is self-evident because without deflection there would be no radiation, and with radiation during bending the remaining trajectory of particles would not be the same. Fortunately, in a large range of beam parameters the average disruption angles are rather small, and the emission of hard photons are relatively rare. For these reasons the two effects can be isolated from each other to the first degree of accuracy, and our study of the issue can be greatly simplified. This happens also to be the development historically. We discuss the effects associated with disruption with negligible beamstrahlung. Here, an important parameter, the disruption parameter D, is introduced. We then discuss the maximum and rms disruption angles. The analytic scaling laws for D >> 1 and D << 1 are then compared with simulation results. Next we investigate the enhancement of luminosity due to disruption. Together with the aspect ratio R identical to sigma/sub x//sigma/sub y/, the two parameters define a scaling law for luminosity enhancement, H/sub D1/, due to the mutual pinching of the e/sup +/e/sup -/ bunches where the effective beam size sigma/sub x/sigma/sub y/ is reduced. Next we discuss beamstrahlung with negligible disruption. First we review the nature of beamstrahlung by describing the novel features of the problem. These specific features are then compared with the known radiation phenomena with emphasis on their similarities and differences. 36 refs.
Date: August 1, 1987
Creator: Chen, P.
Partner: UNT Libraries Government Documents Department

Progress on plasma accelerators

Description: Several plasma accelerator concepts are reviewed, with emphasis on the Plasma Beat Wave Accelerator (PBWA) and the Plasma Wake Field Accelerator (PWFA). Various accelerator physics issues regarding these schemes are discussed, and numerical examples on laboratory scale experiments are given. The efficiency of plasma accelerators is then revealed with suggestions on improvements. Sources that cause emittance growth are discussed briefly.
Date: May 1, 1986
Creator: Chen, P.
Partner: UNT Libraries Government Documents Department

Progress on laser plasma accelerators

Description: Several laser plasma accelerator schemes are reviewed, with emphasis on the Plasma Beat Wave Accelerator (PBWA). Theory indicates that a very high acceleration gradient, of order 1 GeV/m, can exist in the plasma wave driven by the beating lasers. Experimental results obtained on the PBWA experiment at UCLA confirms this. Parameters related to the PBWA as an accelerator system are derived, among them issues concerning the efficiency and the laser power and energy requirements are discussed.
Date: April 1, 1986
Creator: Chen, P.
Partner: UNT Libraries Government Documents Department

Quantum beamstrahlung from gaussian bunches

Description: The method of Baier and Katkov is applied to calculate the correction terms to the Sokolov-Ternov radiation formula due to the variation of the magnetic field strength along the trajectory of a radiating particle. We carry the calculation up to the second order in the power expansion of B tau/B, where tau is the formation time of radiation. The expression is then used to estimate the quantum beamstrahlung average energy loss from e/sup +/e/sup -/ bunches with gaussian distribution in bunch currents. We show that the effect of the field variation is to reduce the average energy loss from previous calculations based on the Sokolov-Ternov formula or its equivalent. Due to the limitation of our method, only an upper bound of the reduction is obtained. 18 refs.
Date: August 1, 1987
Creator: Chen, P.
Partner: UNT Libraries Government Documents Department

The nature of beamstrahlung

Description: The physical nature of beamstrahlung during beam-beam interaction in linear colliders is reviewed. We first make the distinction between a dense beam and a dilute beam. We then review the characteristics of synchrotron radiation (SR) and bremsstrahlung, and argue that for a wide range of beam parameters beamstrahlung is SR in nature, even if the beam is dilute. Some issues concerning the specific conditions in beamstrahlung as SR are then discussed. Finally we suggest that in order to suppress beamstrahlung energy loss and to improve energy resolution, it is desirable to partition a bunch into a train of bunchlets, where the length of each bunchlet is shorter than the SR convergence length.
Date: April 1, 1987
Creator: Chen, P.
Partner: UNT Libraries Government Documents Department

Disruption, beamstrahlung, and beamstrahlung pair creation

Description: The two major effects from the interaction of e/sup /minus//e/sup +/ beams---beamstrahlung and disruption---are reviewed, with emphasis on flat beam collisions. For the disruption effects we discuss the luminosity enhancement factor, the maximum and rms disruption angles, and the ''kink instability''. All the results are obtained from computer simulations, and scaling laws based on these are deduced whenever possible. For the beamstrahlung effects, we concentrate only on the final electron energy spectrum and the deflection angle associated with low energy particles. In addition to the generic studies on the beam-beam effects, we also list the relevant beam-beam parameters obtained from simulations on two sample designs: the TLC and the ILC. As an addendum, the newly discovered phenomenon of coherent beamstrahlung pair creation, together with the incoherent process, are discussed. 18 refs., 15 figs., 1 tab.
Date: December 1, 1988
Creator: Chen, P.
Partner: UNT Libraries Government Documents Department

Review of linear collider beam-beam interaction

Description: Three major effects from the interaction of e/sup +/e/sup /minus// beams---disruption, beamstrahlung, and electron-positron pair creation---are reviewed. For the disruption effects we discuss the luminosity enhancement factor, the maximum and rms disruption angles, and the ''kink instability''. All the results are obtained from computer simulations. Scaling laws for the numerical results and theoretical explanations of the computer acquired phenomena are offered wherever possible. For the beamstrahlung effects we concentrate only on the final electron energy spectrum resulting from multiple photon radiation process, and the deflection angle associated with low energy particles. For the effects from electron-positron pair creation, both coherent and incoherent processes of beamstrahlung pair creation are discussed. In addition to the estimation on total number of such pairs, we also look into the energy spectrum and the deflection angle. 17 refs., 23 figs., 1 tab.
Date: January 1, 1989
Creator: Chen, P.
Partner: UNT Libraries Government Documents Department

Physical motivations of the constitutive relations for ferroelectric ceramics and the existence of butterfly and hysteresis loops

Description: The responses of ferroelectric ceramics can be quite complex depending on the physical processes to which they are subjected. Their mechanical, electromechanical and dielectric properties depend on domain switching, dipole dynamics and phase transformation which can be caused by external stimuli such as mechanical and electrical loadings, and temperature variations. A theory, taking into account the effects of domain switching and dipole dynamics, has been formulated, and in its present stage of development is sufficient to characterize various observable resonses. Specifically, a special case of the theory predicts the nature of the butterfly and hysteresis loops. The butterfly and hysteresis loops are manifestations of the mechanical, electro-mechanical and dielectric responses due to domain switching produced by cyclic electric fields. Comparisons of the predictions of the theory with experimental results are made in a pseudo one dimensional context.
Date: January 1, 1982
Creator: Chen, P.J.
Partner: UNT Libraries Government Documents Department

Plasma accelerators

Description: In this paper we discuss plasma accelerators which might provide high gradient accelerating fields suitable for TeV linear colliders. In particular we discuss two types of plasma accelerators which have been proposed, the Plasma Beat Wave Accelerator and the Plasma Wake Field Accelerator. We show that the electric fields in the plasma for both schemes are very similar, and thus the dynamics of the driven beams are very similar. The differences appear in the parameters associated with the driving beams. In particular to obtain a given accelerating gradient, the Plasma Wake Field Accelerator has a higher efficiency and a lower total energy for the driving beam. Finally, we show for the Plasma Wake Field Accelerator that one can accelerate high quality low emittance beams and, in principle, obtain efficiencies and energy spreads comparable to those obtained with conventional techniques.
Date: March 1, 1986
Creator: Ruth, R.D. & Chen, P.
Partner: UNT Libraries Government Documents Department

Comparison of the plasma beat wave accelerator and the plasma wake field accelerator

Description: In this paper we compare the Plasma Beat Wave Accelerator and Plasma Wake Field Accelerator. We show that the electric fields in the plasma for both schemes are very similar, and thus the dynamics of the driven beams are very similar. The differences appear in the parameters associated with the driving beams. In particular to obtain a given accelerating gradient, the Plasma Wake Field Accelerator has a higher efficiency and a lower total energy for the driving beam. 7 refs., 2 tabs.
Date: March 1, 1985
Creator: Chen, P. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Plasma wake field accelerator

Description: A new scheme of electron acceleration, employing relativistic electron bunches in a cold plasma, is analyzed. The wake field of a leading bunch is derived in a single-particle model. We then extend the model to include finite bunch length effect. In particular, we discuss the relation between the charge distributions of the driving bunch and the energies transformable to the trailing electrons. It is shown that for symmetric charge distribution of the driving bunches, the maximum energy gain for a driven electron is 2..gamma../sub 0/mc/sup 2/. This limitation can be overcome by introducing asymmetric charge distributions. 13 refs., 5 figs.
Date: March 1, 1985
Creator: Chen, P. & Dawson, J.M.
Partner: UNT Libraries Government Documents Department

Channeled particle acceleration by plasma waves in metals

Description: A solid state accelerator concept utilizing particle acceleration along crystal channels by longitudinal electron plasma waves in a metal is presented. Acceleration gradients of order 100 GV/cm are theoretically possible. Particle dechanneling due to electron multiple scattering can be eliminated with a sufficiently high acceleration gradient. Plasma wave dissipation and generation in metals are also discussed.
Date: January 1, 1987
Creator: Chen, P. & Noble, R.J.
Partner: UNT Libraries Government Documents Department

Applications of a plasma lens with bootstrap disruption

Description: In this work, we examine the viability of employing the mechanism of ''bootstrap disruption'' with an underdense plasma lens to enhance the luminosity in linear colliders. We discuss the optics of an underdense plasma lens for electrons and positrons. We present results of such a scheme for the SLC, and hetero-energetic B-factory designs. 11 refs., 4 figs., 2 tabs.
Date: March 1, 1989
Creator: Rajagopalan, S.; Chen, P. & Rosenzweig, J.
Partner: UNT Libraries Government Documents Department

Beamstrahlung and the QED, QCD backgrounds in linear colliders

Description: The intense radiation, called beamstrahlung, during the collision of e{sup +}e{sup -} beams in a linear collider, is reviewed, with attention to the influence of beam-beam disruption on the beamstrahlung spectrum. We then discuss the various detector backgrounds induced by these hard beamstrahlung photons, as well as the Weiszacker-Williams photon, through various QED and QCD processes, namely the coherent and incoherent e{sup +}e{sup -} pair creation and the hadron production and minijet yields.
Date: September 1, 1992
Creator: Chen, P.
Partner: UNT Libraries Government Documents Department

Prospects of High Energy Laboratory Astrophysics

Description: Ultra high energy cosmic rays (UHECR) have been observed but their sources and production mechanisms are yet to be understood. We envision a laboratory astrophysics program that will contribute to the understanding of cosmic accelerators with efforts to: (1) test and calibrate UHECR observational techniques, and (2) elucidate the underlying physics of cosmic acceleration through laboratory experiments and computer simulations. Innovative experiments belonging to the first category have already been done at the SLAC FFTB. Results on air fluorescence yields from the FLASH experiment are reviewed. Proposed future accelerator facilities can provided unprecedented high-energy-densities in a regime relevant to cosmic acceleration studies and accessible in a terrestrial environment for the first time. We review recent simulation studies of nonlinear plasma dynamics that could give rise to cosmic acceleration, and discuss prospects for experimental investigation of the underlying mechanisms.
Date: September 21, 2006
Creator: Ng, J. S. T. & Chen, P.
Partner: UNT Libraries Government Documents Department

Plasma lens experiments at the final focus test beam

Description: The authors intend to carry out a series of plasma lens experiments at the Final Focus Test Beam facility at SLAC. These experiments will be the first to study the focusing of particle beams by plasma focusing devices in the parameter regime of interest for high energy colliders, and is expected to lead to plasma lens designs capable of unprecedented spot sizes. Plasma focusing of positron beams will be attempted for the first time. They will study the effects of lens aberrations due to various lens imperfections. Several approaches will be applied to create the plasma required including laser ionization and beam induced tunneling ionization of a working gas--the latter which has never been observed before. The compactness of the device should prove to be of interest for applications at the SLC and the next generation linear colliders.
Date: February 1, 1995
Creator: Barletta, W.; Chattopadhyay, S. & Chen, P.
Partner: UNT Libraries Government Documents Department

Instructors Adoption of a Web-based Learning System at Rajabhat Universities in Thailand: a Study Using the Unified Theory of Acceptance and Use of Technology

Description: Web-based learning has become an important component of education. Higher education institutions in Thailand have become increasingly aware of the widespread use and effectiveness of web-based learning systems. However, the adoption of such learning systems is growing at a slow pace in Thailand. The purpose of this study was to test the Unified Theory of Acceptance and Use of Technology (UTAUT), that performance expectancy, effort expectancy, social influence, and facilitating conditions have a positive effect on usage intention and adoption of web-based learning systems by instructors, in the Departments of Education at the Rajabhat Universities, Thailand; and to test whether experience of use, age, and gender have moderating effects in the adoption of web-based learning systems there. The research design used in this study was a cross-sectional survey design. Data were collected by means of a self-administered paper questionnaire. The study was conducted among the instructors in the departments of education at the Rajabhat Universities in Thailand. A total of 725 surveys were sent out, 454 questionnaires were returned by the respondents, and 14 were eliminated as outliers; thus, the final data set for the study was 440 samples. The two-step approach of SEM was used to test the model and the study's hypotheses; first, the measurement model was measured to examine the validity and reliability of the data; next, the structural model was measured to test the hypotheses of the study and the fitness of the data to the model. The results of this study revealed several factors that can affect instructors’ adoption of a web-based learning system and which can enhance the web-based learning performance of instructors in the Rajabhat Universities and throughout higher education in Thailand.
Date: August 2014
Creator: Boonsong, Ratchadaporn
Partner: UNT Libraries

Collinear wake field acceleration

Description: In the Voss-Weiland scheme of wake field acceleration a high current, ring-shaped driving bunch is used to accelerate a low current beam following along on axis. In such a structure, the transformer ratio, i.e., the ratio of maximum voltage that can be gained by the on-axis beam and the voltage lost by the driving beam, can be large. In contrast, it has been observed that for an arrangement in which driving and driven bunches follow the same path, and where the current distribution of both bunches is gaussian, the transformer ratio is not normally greater than two. This paper explores some of the possibilities and limitations of a collinear acceleration scheme. In addition to its application to wake field acceleration in structures, this study is also of interest for the understanding of the plasma wake field accelerator. 11 refs., 4 figs.
Date: April 1, 1985
Creator: Bane, K.L.F.; Chen, P. & Wilson, P.B.
Partner: UNT Libraries Government Documents Department

Estimation of wind characteristics at potential wind energy conversion sites. Volume 1. Technical report

Description: To achieve the DOE goal of placing the most economically viable wind energy conversion system at a site, it becomes necessary to determine the accuracy of the climatology development technique, and to determine the extent of its applicability to sites of differing geographic settings and data station locations. To achieve this goal, the Climatology Development Methodology was applied to eight candidate wind energy sites of differing site geographic settings and data station locations. The performance of the methodology was evaluated by examining the accuracy of the hub-height wind climatologies generated for each type of site and station geographic setting. The validity of the site wind climatology for a given setting helped establish the accuracy of the Climatology Development Methodology and the extent of its applicability. The Climatology Development Methodology developed in this study is presented and the techniques of the methodology discussed. Also presented are the eight candidate site hub-height wind climatologies generated, and a description of each site&#x27;s geographic setting and data station proximity. The report concludes with an evaluation of the Climatology Development Methodology and a discussion of the study&#x27;s conclusions and recommendations.
Date: March 1, 1978
Creator: Howard, S. M. & Chen, P. C.
Partner: UNT Libraries Government Documents Department

Pair Creation at Large Inherent Angles

Description: In the next-generation linear colliders, the low-energy e{sup +}e{sup -} pairs created during the collision of high-energy e{sup +}e{sup -} beams would cause potential deleterious background problems to the detectors. At low collider energies, the pairs are made essentially by the incoherent process, where the pair is created by the interaction of beamstrahlung photons on the individual particles in the oncoming beam. This problem was first identified by Zolotarev, et al[1]. At energies where the beamstrahlung parameter {Upsilon} lies approximately in the range 0.6 {approx}&lt; {Upsilon} {approx}&lt; 100, pair creation from the beamstrahlung photons is dominated by a coherent process, first noted by Chen[2]. The seriousness of this pair creation problem lies in the transverse momenta that the pair particles carry when leaving the interaction point (IP) with large angles. One source of transverse momentum is from the kick by the field of the oncoming beam which results in an outcoming angle {theta} {proportional_to} 1/{radical}x, where x is the fractional energy of the particle relative to the initial beam particle energy[2,3]. As was shown in Ref. 131, there in fact exists an energy threshold for the coherent pairs, where x{sub th} {approx}&gt; 1/2{Upsilon}. Thus within a tolerable exiting angle, there exists an upper limit for {Upsilon} where all coherent pairs would leave the detector through the exhaust port[4]. A somewhat different analysis has been done by Schroeder[5]. In the next generation of linear colliders, as it occurs, the coherent pairs can be exponentially suppressed[2] by properly choosing the {Upsilon}({approx}&lt; 0.6). When this is achieved, the incoherent pairs becomes dominant. Since the central issue is the transverse momentum for particles with large angles, we notice that there is another source for it. Namely, when the pair particles are created at low energies, the intrinsic angles of these pairs when produced may ...
Date: April 25, 2007
Creator: Chen, P.; Tauchi, T.; Schroeder, D.V. & /SLAC
Partner: UNT Libraries Government Documents Department

A Phenomenological Study of Gay and Lesbian College Students' Spiritual Experiences at Religious Higher Education Institutions

Description: Despite recent scholarly interest in college students' spirituality and spiritual development, as well as research indicating that students are interested in spirituality and have a strong desire to integrate spirituality into their lives, few researchers have addressed the spiritual experiences of gay and lesbian college students. Utilizing a phenomenological qualitative approach, I explored the spiritual experiences of nine gay and lesbian college students at two religiously affiliated universities in the southwest region of the United States. The ages of the participants ranged from 19 to 23, with a mean of 21. There were five female, three male, and one gender queer participants. Seven participants identified as white, while the other two participants identified as Hispanic. I identified three major themes related to their lived experience of spirituality: (1) spiritual quest characterized by struggle and pain, (2) finding reconciliation and acceptance, and (3) the importance of support from the university, student groups, friends, and family. Implications for practice included the importance of establishing an official recognized student organization to support gay and lesbian students, creating spaces for personal reflection, meditation, prayer, and solitude as well as safe spaces, the need for educational and outreach programs for faculty, staff, and students, and an evaluation of institutional policies the might negatively impact gay and lesbian students. Suggestions for future research are discussed including the exploration of the impact that faculty members have on students' spiritual growth.
Date: May 2017
Creator: Bryan, Vanessa Roberts
Partner: UNT Libraries

The Lived Experiences of African American Community College Achievers in Developmental Education

Description: Developmental education courses are typically defined as courses offered at postsecondary institutions below college level instruction. More than 60% of community college students are deemed non-college ready and required to enroll in non-credit bearing developmental education courses. Research shows that developmental education can be either a bridge or barrier to degree attainment for racial/ethnic minority students, particularly African Americans, who require developmental education more than any other racial/ethnic groups. The purpose of this study was to explore the lived experiences of African American community college achievers who were required to enroll in two or more developmental education courses. Achievers were defined as students who passed all developmental education courses and were enrolled in their final college gateway course at the time of the interviews. Utilizing a phenomenological approach and anti-deficit framework, 15 semi-structured interviews were conducted to capture the essence of how African American achievers described, interpreted, and understood their journeys from developmental education to becoming college ready to completing college level courses. Twelve participants were female and three were male, ranging from 20 to 52 years old. Results revealed seven major themes. The first research question addressed how achievers described their developmental education experience from pre-collegiate years through inside the classroom, and four themes emerged: (a) Achievers experienced difficulty from childhood through college matriculation; (b) achievers experienced support from familial and institutional agents; (c) achievers experienced chilly instructional environments; and (d) achievers experienced positive interactions with peer tutors. The second research question addressed factors that contributed to the persistence of achievers, and three themes emerged: (a) Achievers persisted because of clearly defined goals; (b) achievers persisted because of help seeking behaviors; and (c) achievers persisted because of intrinsic motivation that stemmed from difficult life experiences. Although the majority of participants were discouraged by the requirement to enroll in two ...
Date: May 2017
Creator: Hicks, Janice Marie
Partner: UNT Libraries

A Panel Analysis of Institutional Finances of Medical Residencies at Non-University-Based Independent M.D. Granting Medical Schools in the United States

Description: Traditionally, medical residency positions have been primarily funded by the federal government. However, due to declining governmental funding support over time, medical schools have resorted to fund these programs through other means such as clinical fees and payments for services. This change has affected the number and types of residencies available to medical school graduates. The purpose of this study was to measure how the availability of fiscal resources shape mission-related outputs, particularly medical residency positions at medical schools. Using academic capitalism as the theoretical framework provided a lens through which to examine how federal policies have shaped the availability and funding of medical residencies today at the institutional level. This concept has been studied in traditional colleges and universities and how they balance mission and money, but less so in the context of medical schools. This study used a fixed effect panel analysis to study the impact of selected variables over a 10-year period on financing of medical residencies. Findings included that tuition revenues, paid for by undergraduate medical students, are increasingly funding medical residency positions. There was little to no effect from hospital revenues and federal research monies on increasing the number of medical residency positions. The funding of university based medical education is particularly timely and of national importance to understand the consequences of federal policies for medical schools and how medical residency funding caps and limits have affected one of the missions of medical schools which is to train physicians.
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Date: May 2017
Creator: Cho, Ah Ra
Partner: UNT Libraries