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Theory of Electron-Ion Collisions

Description: Collisions of electrons with atoms and ions play a crucial role in the modeling and diagnostics of fusion plasmas. In the edge and divertor regions of magnetically confined plasmas, data for the collisions of electrons with neutral atoms and low charge-state ions are of particular importance, while in the inner region, data on highly ionized species are needed. Since experimental measurements for these collisional processes remain very limited, data for such processes depend primarily on the results of theoretical calculations. Over the period of the present grant (January 2006 – August 2009), we have made additional improvements in our parallel scattering programs, generated data of direct fusion interest and made these data available on The Controlled Fusion Atomic Data Center Web site at Oak Ridge National Laboratory. In addition, we have employed these data to do collsional-radiative modeling studies in support of a variety of experiments with magnetically confined fusion plasmas.
Date: October 2, 2009
Creator: Griffin, Donald C.
Partner: UNT Libraries Government Documents Department

Design of Electron and Ion Crabbing Cavities for an Electron-Ion Collider

Description: Beyond the 12 GeV upgrade at the Jefferson Lab a Medium Energy Electron-Ion Collider (MEIC) has been considered. In order to achieve the desired high luminosities at the Interaction Points (IP), the use of crabbing cavities is under study. In this work, we will present to-date designs of superconducting cavities, considered for crabbing both ion and electron bunches. A discussion of properties such as peak surface fields and higher-order mode separation will be presented. Keywords: super conducting, deflecting cavity, crab cavity.
Date: July 1, 2012
Creator: Alejandro Castilla Loeza, Geoffrey Krafft, Jean Delayen
Partner: UNT Libraries Government Documents Department

Crab Crossing Schemes and Studies for Electron Ion Collider

Description: This report shows our progress in crab crossing consideration for future electron-ion collider envisioned at JLab. In this design phase, we are evaluating two crabbing schemes viz., the deflecting and dispersive. The mathematical formulations and lattice design for these schemes are discussed in this paper. Numerical simulations involving particle tracking through a realistic deflecting RF cavity and optics illustrate the desired crab tilt of 25 mrad for 1.35 MV. Evolution of beam propagation are shown which provides the physical insight of the crabbing phenomenon.
Date: September 1, 2011
Creator: S. Ahmed, Y. Derbenev, V. Morozov, A. Castilla, G.A. Krafft, B. Yunn, Y. Zhang, J.R. Delayen
Partner: UNT Libraries Government Documents Department

Theoretical atomic physics for fusion. 1995 annual report

Description: The understanding of electron-ion collision processes in plasmas remains a key factor in the ultimate development of nuclear fusion as a viable energy source for the nation. The 1993--1995 research proposal delineated several areas of research in electron-ion scattering theory. In this report the author summarizes his efforts in 1995. The main areas of research are: (1) electron-impact excitation of atomic ions; (2) electron-impact ionization of atomic ions; and (3) electron-impact recombination of atomic ions.
Date: December 31, 1995
Creator: Pindzola, M.S.
Partner: UNT Libraries Government Documents Department

ECR-based atomic collision physics research at ORNL

Description: After a brief summary of the present capability and configuration of the ORNL Multicharged Ion Research Facility (MIRF), and of upcoming upgrades and expansions, the presently on-line atomic collisions experiments are described. In the process, the utility of intense, cw ion beams extracted from ECR ion sources for low-signal rate experiments is illustrated.
Date: April 1997
Creator: Meyer, F. W.; Bannister, M. E.; Hale, J. W. & Havener, C. C.
Partner: UNT Libraries Government Documents Department

EM-PIC simulations of e-beam interaction with field emitted ions from bremsstrahlung targets

Description: We investigate electron beam defocusing caused by field emitted ions from the bremsstrahlung target of a radiography machine using fully electromagnetic particle-in-cell simulations. This possibly deleterious effect is relevant to both current radiography machines (FXR) and machines being built (DARHT-2) or planned (AHF). A simple theory of the acceleration of ions desorbed from the heated target, and subsequent beam defocusing due to partial charge neutralization is in reasonable agreement with the more detailed simulations. For parameters corresponding to FXR (I{sub b}=2.3 kA, {epsilon}{sub b}=16 MeV), simulations assuming space-charge-limited emission of protons predict prompt beam defocusing. Time integrated spot-size measurement, however, is dominated by early-time small spot brightness, and so is not a sensitive diagnostic. Comparisons are made to available FXR data. We also investigate use of a recessed target geometry to mitigate field emitted ion acceleration; only modest improvements are predicted.
Date: August 13, 1998
Creator: Rambo, P. W., LLNL
Partner: UNT Libraries Government Documents Department

Electron collisions with positive ions. Final report, June 15, 1990--June 14, 1992

Description: This report concerns a program of computation of cross sections for electron impact excitation and ionization of ions. A review of progress made in the 1980s for calculations on electron impact excitation of atoms and ions for low and intermediate energy ranges concludes that the effect of continuum channels is very important to include in close coupling calculations. This may be achieved by use of pseudostates or the coupled-channels optical-potential method or the intermediate energy R-matrix method. Those methods have been applied mainly to electron atom scattering to date and much remains to be accomplished in electron-ion scattering. Further, for multicharged ions, contributions of excitation-autoionization and resonant-excitation-double-autoionization to total ionization cross sections are important and underscore the role of two-electron correlation effects.
Date: May 1, 1997
Creator: Henry, R.J.
Partner: UNT Libraries Government Documents Department

Searching for the Optimal Working Point of the MEIC at JLab Using an Evolutionary Algorithm

Description: The Medium-energy Electron Ion Collider (MEIC), a proposed medium-energy ring-ring electron-ion collider based on CEBAF at Jefferson Lab. The collider luminosity and stability are sensitive to the choice of a working point - the betatron and synchrotron tunes of the two colliding beams. Therefore, a careful selection of the working point is essential for stable operation of the collider, as well as for achieving high luminosity. Here we describe a novel approach for locating an optimal working point based on evolutionary algorithm techniques.
Date: March 1, 2011
Creator: Terzic, Balsa; KRamer, Matthew & Jarvis, Colin
Partner: UNT Libraries Government Documents Department

Single and multiple electron dynamics in the strong field limit

Description: High precision photoelectron energy and angular distributions in helium and neon atoms for a broad intensity range reflect the change in the continuum dynamics that occurs as the ionization process evolves into the pure tunneling regime. Elastic rescattering of the laser-driven free electron from its parent ion core leaves a distinct signature on the spectra, providing a direct quantitative test of the various theories of strong field multiphoton ionization. We show that it takes a relatively complete semi-classical rescattering model to accurately reproduce the observed photoelectron distributions. However, the calculated inelastic rescattering rate fails to reproduce the measured nonsequential double ionization yields. 18 refs., 5 figs.
Date: October 1, 1996
Creator: Sheehy, B.; Walker, B.; Lafon, R.; Widmer, M.; Gambhir, A.; DiMauro, L.F. et al.
Partner: UNT Libraries Government Documents Department

Collisions of highly charged ions with electrons, atoms and surfaces

Description: At the Oak Ridge Multicharged Ion Source Facility, an experimental atomic collisions physics program is centered around a recently upgraded Electron Cyclotron Resonance (ECR) multicharged ion source. The 10 GHz CAPRICE source has been in operation since October 22, 1992, and has provided more intense, higher charge ion beams than our previous ECR ion source. Intense metallic beams have recently become available with the installation of a metallic oven on the source. In addition to measurements of electron-impact excitation, carried out in collaboration with the Joint Institute for Laboratory Astrophysics (JILA), experiments are presently on-line to study electron-impact ionization, low-energy ion-atom collisions, and ion-surface interactions. A brief summary of our various activities with an emphasis on the new capabilities is presented.
Date: September 30, 1994
Creator: Havener, C.C.; Bannister, M.E.; Folkerts, L.; Hale, J.W.; Pieksma, M.; Shinpaugh, J. et al.
Partner: UNT Libraries Government Documents Department

The uses of electron beam ion traps in the study of highly charged ions

Description: The Electron Beam Ion Trap (EBIT) is a relatively new tool for the study of highly charged ions. Its development has led to a variety of new experimental opportunities; measurements have been performed with EBITs using techniques impossible with conventional ion sources or storage rings. In this paper, I will highlight the various experimental techniques we have developed and the results we have obtained using the EBIT and higher-energy Super-EBIT built at the Lawrence Livermore National Laboratory. The EBIT employs a high-current-density electron beam to trap, ionize, and excite a population of ions. The ions can be studied in situ or extracted from the trap for external experiments. The trapped ions form an ionization-state equilibrium determined by the relative ionization and recombination rates. Ions of several different elements may simultaneously be present in the trap. The ions are nearly at rest, and, for most systems, all in their ground-state configurations. The electron-ion interaction energy has a narrow distribution and can be varied over a wide range. We have used the EBIT devices for the measurement of electron-ion interactions, ion structure, ion-surface interactions, and the behavior of low-density plasmas.
Date: November 2, 1994
Creator: Knapp, D.
Partner: UNT Libraries Government Documents Department

Laboratory x-ray spectroscopy experiments in support of NASA`s x-ray satellite missions

Description: With support from NASA, we are performing a series of laboratory astrophysics investigations designed to address fundamental uncertainties in basic atomic physics processes relevant to the interpretation of discrete X-ray spectra of cosmic plasmas. Moderate resolution spectra acquired by the ASCA Observatory already demonstrate the inadequacy of currently available spectral modelling codes for this wavelength band. With the upcoming launches of AXAF, XMM, ASTRO E, and Spektrum Roentgen-Gamma, the demand for significant advances in this field will increase dramatically. Our program is based on the exploitation of the Electron Beam Ion Trap facility at the Lawrence Livermore National Laboratory, and a unique set of spectrometers and experimental techiques specifically developed for this purpose. Recent experiments have been devoted to definitive measurements of line emissivities for iron L-shell ions in optically thin, collisional plasmas.
Date: May 22, 1998
Creator: Kahn, S. M., Columbia University
Partner: UNT Libraries Government Documents Department

Measurements of cross sections and resonance structures following electron-impact excitation/ionization of Na-like Kr and Xe

Description: We report high-resolution measurements of electron impact excitation and ionization cross sections for the Na-like ions Kr{sup 25+} and Xe{sup 43+}. Ions with ionization states centered on the Na-like configurations were produced in an electron beam ion trap (EBIT) using electrons with energies below the L shell ionization thresholds. The Na-like ions were exposed to an electron beam with an energy between 3 and 7 keV. The Na- and Ne-like ions were then extracted and their intensities measured as a function of the electron beam energy. Theoretical ionization cross sections were calculated using relativistic distorted wave methods. Complex resonance structures that appear in the computed cross sections are observed in the experimental results. These results are the first experimental observation of resonant-excitation-double-autoionization (REDA) in highly charged high-Z ions.
Date: September 28, 1994
Creator: Schneider, D.; Dewitt, D.; Knapp, D.A.; Reed, K.J. & Chen, M.H.
Partner: UNT Libraries Government Documents Department

A fast beam-ion instability

Description: Mutually driven transverse oscillations of an electron beam and residual gas ions may result in a fast transverse instability. This effect arises either during a single pass of a train of electron bunches or it is caused by ionization electrons oscillating within a single positron bunch. In both cases, the beam oscillations grow exponentially with an exponent proportional to the square root of time. In this report, instability rise times are calculated analytically and compared with computer simulations. The effect considered could be a significant limitation in many future designs.
Date: June 1, 1995
Creator: Zimmermann, F.; Raubenheimer, T.O. & Stupakov, G.
Partner: UNT Libraries Government Documents Department

Recent experiments on near-threshold electron-impact excitation of multiply charged ions

Description: Some recent measurements of excitation of multiply charged ions by electrons studied in beam-beam experiments are highlighted. The emphasis is on absolute total cross sections measured with the merged electron-ion beams energy-loss (MEIBEL) technique, although some results obtained with the crossed-beams fluorescence method are also presented. The MEIBEL technique allows the investigation of optically-allowed and forbidden transitions with sufficient energy resolution, typically about 0.2 eV, to resolve resonance structures in the cross sections. Results from the JILA/ORNL MEIBEL experiment on dipole-allowed transitions in several ions demonstrate the success of various theoretical methods in predicting cross sections in the absence of resonances. Comparisons of R-matrix calculations and measured cross sections for spin-forbidden transitions in Mg-like Si{sup 2+} and Ar{sup 6+}, however, show that further refinements to the theory are needed in order to more accurately predict cross sections involving significant contributions from dielectric resonance`s and interactions between neighboring resonances.
Date: April 1, 1998
Creator: Bannister, M.E.; Djuric, N.; Woitke, O.; Dunn, G.H.; Chung, Y.S.; Smith, A.C.H. et al.
Partner: UNT Libraries Government Documents Department

Plasma discreteness effects in the presence of an intense, ultrashort laser pulse

Description: Discrete effects of the plasma irradiated by an ultrashort, intense laser pulse are investigated. Although, for most plasmas of interest, the damping of the laser pulse is due to collective plasma effects, in certain regimes the energy absorbed in the plasma microfields can be important. A scattering matrix is derived for an electron scattering off an ion in the presence of an intense laser field.
Date: March 1, 1996
Creator: Savchenko, V.I. & Fisch, N.J.
Partner: UNT Libraries Government Documents Department


Description: In this talk, we discussed the physics case for an eA collider. We emphasized the novel physics that might be studied at small x. The interesting physics at intermediate x's has been discussed elsewhere [3]. Plans for an electron-ion collider include, as a major part of the program, the possibility of doing polarized electron-polarized proton/light ion scattering. A discussion of the combined case for high energy electron nucleus and polarized electron-polarized proton scattering will be published separately [66].
Date: September 14, 2001
Partner: UNT Libraries Government Documents Department

Spin Rotator Optics for MEIC

Description: A unique de­sign fea­ture of a po­lar­ized Medi­um En­er­gy Elec­tron-Ion Col­lid­er (MEIC) based on CEBAF is its 'Fig­ure-8' stor­age rings for both elec­trons and ions, which sig­nif­i­cant­ly sim­pli­fies beam po­lar­iza­tion main­te­nance and ma­nip­u­la­tion. While elec­tron (positron) po­lar­iza­tion is main­tained ver­ti­cal in arcs of the ring, a sta­ble lon­gi­tu­di­nal spin at four col­li­sion points is achieved through solenoid based spin ro­ta­tors and hor­i­zon­tal orbit bends. The pro­posed MEIC lat­tice was de­vel­oped in order to pre­serve a very high po­lar­iza­tion (more than 70%) of the elec­tron beams in­ject­ed from the CEBAF ma­chine. The oth­er­wise cou­pled beam tra­jec­to­ry due to solenoids used in the spin ro­ta­tors was de­cou­pled by de­sign. Aspin match­ing tech­nique needs to be im­ple­ment­ed in order to en­hance quan­tum self-po­lar­iza­tion and min­i­mize de­po­lar­iza­tion ef­fects.
Date: March 1, 2010
Creator: H. K. Sayed, S.A. Bogacz, P. Chevtsov
Partner: UNT Libraries Government Documents Department

Controls system developments for the ERL facility

Description: The BNL Energy Recovery LINAC (ERL) is a high beam current, superconducting RF electron accelerator that is being commissioned to serve as a research and development prototype for a RHIC facility upgrade for electron-ion collision (eRHIC). Key components of the machine include a laser, photocathode, and 5-cell superconducting RF cavity operating at a frequency of 703 MHz. Starting with a foundation based on existing ADO software running on Linux servers and on the VME/VxWorks platforms developed for RHIC, we are developing a controls system that incorporates a wide range of hardware I/O interfaces that are needed for machine R&D. Details of the system layout, specifications, and user interfaces are provided.
Date: October 7, 2011
Creator: Jamilkowski, J.; Altinbas, Z.; Gassner, D.; Hoff, L.; Kankiya, P.; Kayran, D. et al.
Partner: UNT Libraries Government Documents Department

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 mode, and easy higher order mode damping. We will present the properties and characteristics of the new cavity in detail. As the accelerator systems grow in complexity, developing compact and efficient deflecting cavities is of great interest. Such cavities will benefit situations where the beam line space is limited. The future linac-ring type electron-ion collider requires implementation of a crab-crossing scheme for both beams at the interaction region. The ion beam has a long bunches and high rigidity. Therefore, it requires a low frequency, large kicking angle deflector. The frequency of the deflecting mode for the current collider design is 181 MHz, and the deflecting angle is {approx}5 mrad for each beam. At such low frequency, the previous designs of the crab cavities will have very large dimensions, and also will be confronted by typical problems of damping the Lower Order Mode (LOM), the Same Order Mode (SOM), and as usual, the Higher Order Modes (HOM). In this paper we describe how one can use the concept of a quarter-wave (QW) resonator for a deflecting/crabbing cavity, and use its fundamental mode to deflect the beam. The simplicity of the cavity geometry and the large separation between its fundamental mode and the first HOM make it very attractive.
Date: July 25, 2011
Creator: Wu, Q.; Belomestnykh, S. & Ben-Zvi, I.
Partner: UNT Libraries Government Documents Department