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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

Bootstrap planning: Theory and application

Description: We identify a general framework for weak planning called bootstrap planning, which is defined as global planning using only a local planner along with some memory for learning intermediate subgoals. We present a family of algorithms for bootstrap planning, and provide some initial theory on their performance. In our theoretical analysis, we develop a random digraph problem model and use it to make some performance predictions and comparisons of these algorithms. We also use it to provide some techniques for approximating the optimal resource bound on the local planner to achieve the best global planner. We validate our theoretical results with empirical demonstration on the 15-puzzle. We show how to reduce the planning cost of a global planner by 2 orders of magnitude using bootstrap planning. We also demonstrate a natural but not widely recognized connection between search costs and the lognormal distribution.
Date: February 1, 1994
Creator: Chen, P. C.
Partner: UNT Libraries Government Documents Department

Adaptive robot path planning in changing environments

Description: Path planning needs to be fast to facilitate real-time robot programming. Unfortunately, current planning techniques are still too slow to be effective, as they often require several minutes, if not hours of computation. To overcome this difficulty, we present an adaptive algorithm that uses past experience to speed up future performance. It is a learning algorithm suitable for incrementally-changing environments such as those encountered in manufacturing of evolving products and waste-site remediation. The algorithm allows the robot to adapt to its environment by having two experience manipulation schemes: For minor environmental change, we use an object-attached experience abstraction scheme to increase the flexibility of the learned experience; for major environmental change, we use an on-demand experience repair scheme to retain those experiences that remain valid and useful. Using this algorithm, we can effectively reduce the overall robot planning time by re-using the computation result for one task to plan a path for another.
Date: August 1, 1994
Creator: Chen, P. C.
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

Coherent pair creation as a positron source for linear colliders

Description: We propose a positron source for future linear colliders which uses the mechanism of coherent pair creation process from the collision of a high energy electron beam and a monochromatic photon beam. We show that there is a sharp spike in the pair-produced positron energy spectrum at an energy much lower than the primary beam energy. The transverse emittance is ``damped``, yielding final positrons with lower normalized emittance than the initial electrons. Numerical examples invoking conventional lasers and Free Electron Lasers (FEL) for the photon beams are considered.
Date: November 1, 1992
Creator: Chen, P. & Palmer, R. B.
Partner: UNT Libraries Government Documents Department

Beamstrahlung spectra in next generation linear colliders

Description: For the next generation of linear colliders, the energy loss due to beamstrahlung during the collision of the e{sup +}e{sup {minus}} beams is expected to substantially influence the effective center-of-mass energy distributions of the colliding particles. In this paper, we first derive analytical formulae for the electron and photon energy spectra under multiple beamstrahlung processes, and for the e{sup +}e{sup {minus}} and {gamma}{gamma} differential luminosities. We then apply our formalism to various classes of 500 GeV e{sup +}e{sup {minus}} linear collider designs currently under study.
Date: February 1, 1992
Creator: Barklow, T.; Chen, P. & Kozanecki, W.
Partner: UNT Libraries Government Documents Department