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Strong Resonant Intersubband Magnetopolaron Effect in Heavily Modulation-Doped GaAs/AlGaAs Single Quantum Wells at High Magnetic Fields

Description: Electron cyclotron resonance (CR) has been studied in magnetic fields up to 32 T in two heavily modulation -d-doped GaAs/Al{sub 0.3}Ga{sub 0.7}As single-quantum-well. Little effect on electron CR is observed in either sample in the region of resonance with the GaAs LO phonons. However, above w{sub LO} at B > 27 T, electron CR exhibits a strong avoided-level-crossing splitting for both samples at energies close to E{sub LO} + (E{sub 2}-E{sub 1}), where E{sub 2}, and E{sub 1} are the energies of the bottoms of the second and the first subbands, respectively. The energy separation between the two branches is large, reaching a minimum of about 40 cm{sup {minus}1} around 30.5 T for both samples. This splitting is due to a three-level resonance between the second LL of the first electron subband and the lowest LL of the second subband plus a LO phonon. The large splitting in the presence of high electron densities is due to the absence of occupation (Pauli-principle) effects in the final states and weak screening for this three level process.
Date: July 20, 1999
Creator: Jiang, H.W.; Jones, E.; Lee, X.Y.; Leem, Y.A.; McCombe, B.D.; Peeters, F.M. et al.
Partner: UNT Libraries Government Documents Department

Current Drive in a Ponderomotive Potential with Sign Reversal

Description: Noninductive current drive can be accomplished through ponderomotive forces with high efficiency when the potential changes sign over the interaction region. The effect can practiced upon both ions and electrons. The current drive efficiencies, in principle, might be higher than those possible with conventional radio-frequency current-drive techniques, since different considerations come into play.
Date: July 30, 2003
Creator: Fisch, N.J.; Rax, J.M. & Dodin, I.Y.
Partner: UNT Libraries Government Documents Department

Electron Bernstein Wave Research on NSTX and CDX-U

Description: Studies of thermally emitted electron Bernstein waves (EBWs) on CDX-U and NSTX, via mode conversion (MC) to electromagnetic radiation, support the use of EBWs to measure the Te profile and provide local electron heating and current drive (CD) in overdense spherical torus plasmas. An X-mode antenna with radially adjustable limiters successfully controlled EBW MC on CDX-U and enhanced MC efficiency to {approx} 100%. So far the X-mode MC efficiency on NSTX has been increased by a similar technique to 40-50% and future experiments are focused on achieving * 80% MC. MC efficiencies on both machines agree well with theoretical predictions. Ray tracing and Fokker-Planck modeling for NSTX equilibria are being conducted to support the design of a 3 MW, 15 GHz EBW heating and CD system for NSTX to assist non-inductive plasma startup, current ramp up, and to provide local electron heating and CD in high beta NSTX plasmas.
Date: June 10, 2003
Creator: Taylor, G.; Efthimion, P.C.; Jones, B.; Bell, G.L.; Bers, A.; Bigelow, T.S. et al.
Partner: UNT Libraries Government Documents Department

ECR sources for the production of highly charged ions

Description: Electron Cyclotron Resonance Ion Sources (ECRIS) using RF between 5 and 16 GHz have been developed into stable, reliable sources of highly charged ions produced from a wide range of elements. These devices are currently used as ion sources for cyclotrons, synchrotrons, and heavy-ion linacs for nuclear and relativistic heavy-ion physics. They also serve the atomic physics community as a source of low energy multiply-charged ions. In order to improve their performance both with respect to maximum charge state and beam intensity, ECRIS builders are now designing and constructing sources which will operate at frequencies up to 30 GHz. In this paper we review the present status of operating ECRIS, review recent experimental measurements on plasma parameters, and look at the technology and potential of sources operating at frequencies up to 30 GHz. 14 refs., 4 figs., 1 tab.
Date: September 1, 1989
Creator: Lyneis, C.M.; Antaya, T.A (Lawrence Berkeley Lab., CA (USA) & Michigan State Univ., East Lansing, MI (USA))
Partner: UNT Libraries Government Documents Department

Molecular uranates - laser synthesis of uranium oxide anions in the gas phase

Description: Laser ablation of solid UO{sub 3} or (NH{sub 4}){sub 2}U{sub 2}O{sub 7} yielded in the gas phase molecular uranium oxide anions with compositions ranging from [UO{sub n}]{sup -} (n = 2-4) to [U{sub 14}O{sub n}]{sup -} (n = 32-35), as detected by Fourier transform ion cyclotron resonance mass spectrometry. The cluster series [U{sub x}O{sub 3x}]{sup -} for x {le} 6 and various [U{sub x}O{sub 3x-y}]{sup -}, in which y increased with increasing x, could be identified. A few anions with H atoms were also present, and their abundance increased when hydrated UO{sub 3} was used in place of anhydrous UO{sub 3}. Collision-induced dissociation experiments with some of the lower m/z cluster anions supported extended structures in which neutral UO{sub 3} constitutes the building block. Cationic uranium oxide clusters [U{sub x}O{sub n}]{sup +} (x = 2-9; n = 3-24) could also be produced and are briefly discussed. Common trends in the O/U ratios for both negative and positive clusters could be unveiled.
Date: December 14, 2009
Creator: Marcalo, Joaquim; Santos, Marta; Pires de Matos, Antonio & Gibson, John K
Partner: UNT Libraries Government Documents Department

Plasma and Beam Production Experiments with HYBRIS, aMicrowave-assisted H- Ion

Description: A two-stage ion source concept had been presented a few years ago, consisting of a proven H- ion source and a 2.45-GHz Electron Cyclotron-Resonance (ECR) type ion source, here used as a plasma cathode. This paper describes the experimental development path pursued at Lawrence Berkeley National Laboratory, from the early concept to a working unit that produces plasma in both stages and creates a negative particle beam. Without cesiation applied to the second stage, the H{sup -} fraction of this beam is very low, yielding 75 micro-amperes of extracted ion beam current at best. The apparent limitations of this approach and envisaged improvements are discussed.
Date: September 13, 2006
Creator: Keller, R. AUTHOR-Kwan, S.; Hahto, S.; Regis, M. & Wallig, J.
Partner: UNT Libraries Government Documents Department

Modeling the shell type TeV supernove remnant RX J1713-3946

Description: We simulate the shock waves of shell type supernova remnants with a prototype progenitor of 15 M{sub {circle_dot}} and fit the size and lifetime of SNR RX J1713-3946 with a density of {approx} 1O{sup -26}g cm{sup -3} for the shocked downstream plasma. Such a density is required for efficient stochastic electron acceleration and leads to a thermal X-ray flux more than one order of magnitude lower than the observed featureless X-ray flux. Fast mode waves must be excited to have efficient stochastic electron acceleration. We find that (1) the acceleration efficiency needs to be at least 10 times higher than that through the cyclotron resonances, implying much more efficient acceleration through the transit-time damping process, and (2) the distribution of the accelerated electrons is very sensitive to the ratio of the speed in the downstream to the shock suggesting a dynamo process that can regulate the magnetic field in such a way that the electron distribution doesn't change dramatically throughout the evolution history of the shock waves.
Date: January 1, 2009
Creator: Fryer, Christopher Lee; Fan, Zhonghui & Liu, Siming
Partner: UNT Libraries Government Documents Department

Cyclotron resonance and quasiparticles

Description: This introductory paper contains personal perspectives about the importance of cyclotron resonance in forming our modern view of solids. The papers following this one will discuss the discovery, refinements, and some of the latest developments. Although I will touch on some of these subjects, I leave the details to the other authors and in the main focus on the conceptual impact of the work. I propose that it was experiments based on cyclotron resonance which established the quasiparticle concept.
Date: January 15, 2005
Creator: Cohen, Marvin L.
Partner: UNT Libraries Government Documents Department

Concluding remarks for ECRIS '02

Description: ECRIS'02 was held in Jyvaeskylae Finland at the edge of Lake Jyvaeskylae, which was beautiful location to meet and discuss the state of Electron Cyclotron Resonance ion sources. It was the 15th ECR Ion Source Workshop in a series stretching back to the first workshop held November 6, 1978 in Karlsruhe Germany. Overall, the workshop reports could be characterized as showing solid achievements and steady progress without any spectacular breakthroughs or highly controversial new ideas. In this short report, I will mention some of the highlights and surprises of the workshop that I observed during the meeting and reported on at the close of the meeting. As such, it will be relatively brief and not meant to be all encompassing. A short list of items that made this workshop memorable is given.
Date: September 9, 2002
Creator: Lyneis, Claude
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

Future prospects for ECR ion sources with improved charge state distributions

Description: Despite the steady advance in the technology of the ECR ion source, present art forms have not yet reached their full potential in terms of charge state and intensity within a particular charge state, in part, because of the narrow band width. single-frequency microwave radiation used to heat the plasma electrons. This article identifies fundamentally important methods which may enhance the performances of ECR ion sources through the use of: (1) a tailored magnetic field configuration (spatial domain) in combination with single-frequency microwave radiation to create a large uniformly distributed ECR ``volume`` or (2) the use of broadband frequency domain techniques (variable-frequency, broad-band frequency, or multiple-discrete-frequency microwave radiation), derived from standard TWT technology, to transform the resonant plasma ``surfaces`` of traditional ECR ion sources into resonant plasma ``volume``. The creation of a large ECR plasma ``volume`` permits coupling of more power into the plasma, resulting in the heating of a much larger electron population to higher energies, thereby producing higher charge state ions and much higher intensities within a particular charge state than possible in present forms of` the source. The ECR ion source concepts described in this article offer exciting opportunities to significantly advance the-state-of-the-art of ECR technology and as a consequence, open new opportunities in fundamental and applied research and for a variety of industrial applications.
Date: December 31, 1995
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Design of fast tuning elements for the ITER ICH system

Description: The coupling between the ion cyclotron (IC) antenna and the ITER plasma (as expressed by the load resistance the antenna sees) will experience relatively fast variations due to plasma edge profile modifications. If uncompensated, these will cause an increase in the amount of power reflected back to the transmitter and ultimately a decrease in the amount of radio frequency (rf) power to the plasma caused by protective suppression of the amount of rf power generated by the transmitter. The goals of this task were to study several alternate designs for a tuning and matching (T&M) system and to recommend some research and development (R&D) tasks that could be carried out to test some of the most promising concepts. Analyses of five different T&M configurations are presented in this report. They each have different advantages and disadvantages, and the choice among them must be made depending on the requirements for the IC system. Several general conclusions emerge from our study: The use of a hybrid splitter as a passive reflected-power dump [``edge localized mode (ELM)-dump``] appears very promising; this configuration will protect the rf power sources from reflected power during changes in plasma loading due to plasma motion or profile changes (e.g., ELM- induced changes in the plasma scrape-off region) and requires no active control of the rf system. Trade-offs between simplicity of design and capability of the system must be made. Simple system designs with few components near the antenna either have high voltages over considerable distances of transmission lines, or they are not easily tuned to operate at different frequencies. Designs using frequency shifts and/or fast tuning elements can provide fast matching over a wide range of plasma loading; however, the designs studied here require components near the antenna, complicating assembly and maintenance. Capacitor-tuned resonant systems may offer a ...
Date: May 1, 1996
Creator: Swain, D.W. & Goulding, R.H.
Partner: UNT Libraries Government Documents Department

A new 14 GHz electron-cyclotron-resonance ion source (ECRIS) for the heavy ion accelerator facility ATLAS: a status report

Description: A new 14 GHz ECRIS has been designed and built over the last 2 years. The source, a modification of the Berkeley AECR, incorporates the latest results from ECR developments to produce intense beams of highly charged ions, i.e., an improved electron confinement with an axial magnetic mirror ratio of 3.5 and a radial magnetic field inside the plasma chamber of 1.0 T. The aluminium plasma chamber and extraction electrode as well as a biased disk on axis at the microwave injection side donate additional electrons to the plasma, making use of the large secondary electron yield from Al oxide. Slots in the plasma chamber allow for radial pumping which increases the AECR performance. The source will also be capable of additional ECR plasma heating using two frequencies simultaneously to increase the electron energy gain for producing high charge states. To be able to deliver usable intensities of the heaviest ion beams, the design will also allow for axial access for metal evaporation ovens and solid material samples using plasma sputtering. Main design goal is to produce several e{mu}A of U{sup 34+} in order to obtain Coulomb- barrier energies from ATLAS without further stripping.
Date: November 1, 1996
Creator: Schlapp, M.; Vondrasek, R.C.; Szczech, J.; Billquist, P.J.; Pardo, R.C. & Xie, Z.Q.
Partner: UNT Libraries Government Documents Department

A new 14 GHz Electron-Cyclotron-Resonance Ion Source (ECRIS) for the heavy ion accelerator facility ATLAS

Description: A 14 GHz Electron-Cyclotron-Resonance Ion Source (ECRIS) has been designed and built at Argonne National Laboratory. The source is a modification of the AECR at Berkeley and incorporates the latest results from ECR developments to produce intense beams of highly charged ions, including an improved magnetic confinement of the plasma electrons with an axial mirror ratio of 3.5. The aluminum plasma chamber and extraction electrode as well as a biased disk on axis at the microwave injection side donates additional electrons to the plasma, making use of the large secondary electron yield from aluminum oxide. The source is capable of ECR plasma heating using two different frequencies simultaneously to increase the electron energy gain for the production of high charge states. The main design goal is to produce several e{mu}A of at least {sup 238}U{sup 35+} in order to accelerate the beam to coulomb-barrier energies without further stripping. First charge state distributions for gaseous elements have been measured and 210 e{mu}A {sup 16}O{sup 7+} has been achieved. A normalized 90% emittance from 0.1 to 0.2 {pi} mm{sm_bullet}mrad for krypton and oxygen beam has been found.
Date: November 1997
Creator: Schlapp, M.; Pardo, R. C.; Vondrasek, R. C.; Billquist, P. J. & Szczech, J.
Partner: UNT Libraries Government Documents Department

Experimental studies of auroral arc generators

Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). An all-sky video camera system was deployed in Eagle, Alaska at the foot of the magnetic field line that threads geosynchronous satellite 1989-046 as part of a campaign to study correlations of ground-based auroral activity with satellite-based plasma and energetic particle measurements. The overall intent of the project was to study magnetosphere-ionosphere coupling as it relates to the aurora, and, in particular, to look for signatures that may help to identify various auroral generator mechanism(s). During this study, our efforts were primarily directed towards identifying the generator mechanism(s) for pulsating aurora. Our data, though not conclusive, are found to support theories that propose a cyclotron resonance mechanism for the generation of auroral pulsations.
Date: August 1, 1997
Creator: Suszcynsky, D.M.; Borovsky, J.E. & Thomsen, M.F.
Partner: UNT Libraries Government Documents Department

Recent developments in ECRIS technology at Argonne National Laboratory and the New ATLAS 14 GHz ECRIS Project

Description: A summary of recent developments in ECRIS technology taking place at Argonne National Laboratory is presented in this paper. A pulsed laser for ablation of solid material into the source plasma has been used online with the ATLAS PII-ECRIS and has allowed direct time measurements to be made which verify and quantify sequential, step-by-step ionization taking place in an ECRIS. In addition, during the course of these laser studies a method was discovered which, from an operational viewpoint, represents an important new method for incorporating solid materials into an ECRIS. We also report on a new 14 GHz ECRIS currently under construction at Argonne. This new ECRIS, along with a new 300 kV high voltage platform and building addition, will further the capabilities of the ATLAS facility by providing the accelerator with a second, independent ECRIS.
Date: May 1, 1995
Creator: Harkewicz, R.; Billquist, P.J. & Pardo, R.C.
Partner: UNT Libraries Government Documents Department

Determination of wall reflectivity for ECE frequencies in DIII-D

Description: The significance of cyclotron radiation losses in next-generation tokamaks depends on the reflectivity of first wall materials. An experimental study of the effective reflectivity for electron cyclotron frequencies in the graphite-walled DIII-D tokamak is reported. Measurements of optically-thin harmonics ({omega} = n{omega}{sub ce}, n > 4) are made for two polarizations from thermal plasma discharges using an absolutely calibrated Michelson interferometer. The reflectivity r and polarization transfer fraction p are obtained by matching measured spectra to simulations from an ECE radiation transport code with adjustable wall parameters. For the frequency range 150-400 GHz average values of r = 0.76 and p = 0.19 are found.
Date: May 1, 1997
Creator: Austin, M.E.; Ellis, R.F. & Luce, T.C.
Partner: UNT Libraries Government Documents Department

Ion heating in the field-reversed configuration (FRC) by rotating magnetic fields (RMF) near cyclotron resonance

Description: The trajectories of ions confined in a Solovev FRC equilibrium magnetic geometry and heated with a small-amplitude, odd-parity rotating magnetic field, have been studied with a Hamiltonian computer code. When the RMF frequency is in the ion-cyclotron range, explosive heating occurs. Higher-energy ions are found to have betatron-type orbits, preferentially localized near the FRC midplane. These results are relevant to a compact magnetic-fusion-reactor design.
Date: July 20, 2000
Creator: Cohen, Samuel A. & Glasser, Alan H.
Partner: UNT Libraries Government Documents Department

ICRF heating on helical devices

Description: Ion cyclotron range of frequency (ICRF) heating is currently in use on CHS and W7-AS and is a major element of the heating planned for steady state helical devices. In helical devices, the lack of a toroidal current eliminates both disruptions and the need for ICRF current drive, simplifying the design of antenna structures as compared to tokamak applications. However the survivability of plasma facing components and steady state cooling issues are directly applicable to tokamak devices. Results from LHD steady state experiments should be available on a time scale to strongly influence the next generation of steady state tokamak experiments. The helical plasma geometry provides challenges not faced with tokamak ICRF heating, including the potential for enhanced fast ion losses, impurity accumulation, limited access for antenna structures, and open magnetic field lines in the plasma edge. The present results and near term plans provide the basis for steady state ICRF heating of larger helical devices. An approach which includes direct electron, mode conversion, ion minority and ion Bernstein wave heating addresses these issues.
Date: September 1, 1995
Creator: Rasmussen, D.A.; Lyon, J.F.; Hoffman, D.J.; Murakami, M.; England, A.C.; Wilgen, J.B. et al.
Partner: UNT Libraries Government Documents Department

Plasma chemistry dependent ECR etching of GaN

Description: Electron cyclotron resonance (ECR) etching of GaN in Cl{sub 2}/H{sub 2}/Ar, C1{sub 2}/SF{sub 6}/Ar, BCl{sub 3}/H{sub 2}/Ar and BCl{sub 3}/SF{sub 6}/Ar plasmas is reported as a function of percent H{sub 2} and SF{sub 6}. GaN etch rates were found to be 2 to 3 times greater in Cl{sub 2}/H{sub 2}/Ar discharges than in BCl{sub 3}/H{sub 2}/Ar discharges independent of the H{sub 2} concentration. In both discharges, the etch rates decreased as the H{sub 2} concentration increased above 10%. When SF{sub 6} was substituted for H{sub 2}, the GaN etch rates in BCl{sub 3}-based plasmas were greater than those for the Cl{sub 2}-based discharges as the SF{sub 6} concentration increased. GaN etch rates were greater in Cl{sub 2}/H{sub 2}/Ar discharges as compared to Cl{sub 2}SF{sub 6}/Ar discharges whereas the opposite trend was observed for BCl{sub 3}-based discharges. Variations in surface morphology and near-surface stoichiometry due to plasma chemistries were also investigated using atomic force microscopy and Auger spectroscopy, respectively.
Date: December 31, 1995
Creator: Shul, R.J.; Ashby, C.I.H. & Rieger, D.J.
Partner: UNT Libraries Government Documents Department

Fast symplectic mapping, quasi-invariants, and long-term stability in the LHC

Description: A systematic program to explore stability of orbits in hadron storage rings is based on the following steps: (a) beginning with a symplectic tracking code, construct the mixed-variable generator of the full-turn map in a Fourier-spline basis; (b) use the resulting fast mapping to follow long orbits and estimate the long-term dynamic aperture; (c) contruct quasi-invariants and examine their variation in time to set long-term bounds on the motion for any initial condition in a specified region. First results from an application of the program to the Large Hadron Collider (LHC) are reported. Maps can be constructed in a few hours and evaluated at a speed 60 times greater than that of one-turn tracking, on a workstation computer. Orbits of 10{sup 7} turns take 3.6 hours. The value of a ``stroboscopic`` view of the synchro-betatron motion is emphasized. On a Poincare section at multiples of the synchrotron period, one can study resonances and invariant surfaces in two dimensions, thereby taking advantage of techniques that have proved effective in treating pure betatron motion.
Date: January 1, 1996
Creator: Warnock, R.L. & Berg, J.S.
Partner: UNT Libraries Government Documents Department