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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

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

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

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

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

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

Recent developments on ECR sources at LBL

Description: After a number of refinements, the stability and ease of tuning of the LBL AECR ion source are greatly improved. Several nuclear science experiments have now used cyclotron ion beams injected by the AECR ion source and have taken advantage of its good short and long term-stability and high performance. Refinements include installation of a dc filament power supply for the electron gun, improved gas flow control.and temperature stabilization of parts of the microwave transmission network. Measurements of the mean plasma potential and plasma potential difference were made on the AECR and the LBL ECR sources. The absolute. mean potentials of plasmas of oxygen, argon, and argon mixed with oxygen in the AECR have been determined. These plasma potentials are positive with respect to the plasma wall and are on the order of a few tens of volts for microwave power up to 600 W and normal operating gas flow. Electrons injected by an electron gun into the AECR plasma reduce the plasma potentials. Beam energy spreads of oxygen, argon and argon mixed with oxygen have also been measured. Measurement of the plasma potential difference between the first and the second stage of the LBL ECR ion source shows that the plasma potential in the first stage is higher than the second stage. Such plasma potential differences range from about 10 to 200 volts depending on the microwave power and density of neutral atoms. With these potential differences, typically of 10 to 40 V at the LBL ECR running conditions, most of the 1+ ions produced by the first stage are probably not be confined by the second state plasma. Thus it appears that the main function of a microwave-driven first stage is to provide electrons to the second stage plasma, as is done with an electron gun in the ...
Date: May 5, 1993
Creator: Xie, Z. Q. & Lyneis, C. M.
Partner: UNT Libraries Government Documents Department

Comprehensive research on stability and performance of a-Si:H and alloys. Phase I team annual technical report, 31, May 1994--30, May 1995

Description: This report covers the research done during the first phase of the subcontract. During this period, we have concentrated on two areas: improving the voltage and stability of a-Si:H devices made using ECR deposition, and improving the properties of a-(Si,Ge):H films also using ECR deposition.
Date: August 1, 1996
Creator: Dalal, V.
Partner: UNT Libraries Government Documents Department

Photoionization of FE3+ Ions

Description: Photoionization of Fe3+ ions was studied for the first time using synchrotron radiation from the Advanced Light Source (ALS) and the merged-beams technique. Fe3+ ions were successfully produced using ferrocene in an electron cyclotron resonance ion source (ECR). The measured yield of Fe4+ photoions as a function of photon energy revealed the presence of resonances that correspond to excitation of autoionizing states. These resonances are superimposed upon the photoion yield produced by direct photoionization, which is a smooth, slowly decreasing function of energy. The spectra for the photoionization of Fe3+ will be analyzed and compared with theory. The data collected will also serve to test models for the propagation of light through ionized matter.
Date: January 1, 2003
Creator: Ovchinnikov, O. & Schlachter, F.
Partner: UNT Libraries Government Documents Department

Development of Nb and Alternative Material Thin Films Tailored for SRF Applications

Description: Over the years, Nb/Cu technology, despite its shortcomings due to the commonly used magnetron sputtering, has positioned itself as an alternative route for the future of superconducting structures used in accelerators. Recently, significant progress has been made in the development of energetic vacuum deposition techniques, showing promise for the production of thin films tailored for SRF applications. JLab is pursuing energetic condensation deposition via techniques such as Electron Cyclotron Resonance and High Power Impulse Magnetron Sputtering. As part of this project, the influence of the deposition energy on the material and RF properties of the Nb thin film is investigated with the characterization of their surface, structure, superconducting properties and RF response. It has been shown that the film RRR can be tuned from single digits to values greater than 400. This paper presents results on surface impedance measurements correlated with surface and material characterization for Nb films produced on various substrates, monocrystalline and polycrystalline as well as amorphous. A progress report on work on NbTiN and AlN based multilayer structures will also be presented.
Date: September 1, 2011
Creator: Valente-Feliciano, A -M; Reece, C E; Spradlin, J K; Xiao, B; Zhao, X; Gu, Diefeng et al.
Partner: UNT Libraries Government Documents Department


Description: Third generation Electron Cyclotron Resonance (ECR) ion sources operate at microwave frequencies between 20 and 30 GHz and employ NbTi superconducting magnets with a conductor peak field of 6-7 T. A significant gain in performance can be achieved by replacing NbTi with Nb{sub 3}Sn, allowing solenoids and sextupole coils to reach a field of 15 T in the windings. In this paper we describe the design of a Nb{sub 3}Sn superconducting magnet for a fourth generation ECR source operating at a microwave frequency of 56 GHz. The magnet design features a configuration with an internal sextupole magnet surrounded by three solenoids. A finite element magnetic model has been used to investigate conductor peak fields and the operational margins. Results of the numerical analysis are presented and discussed.
Date: May 4, 2009
Creator: Ferracin, P.; Caspi, S.; Felice, H.; Leitner, D.; Lyneis, C. M.; Prestemon, S. et al.
Partner: UNT Libraries Government Documents Department

ECR plasma cleaning: an in-situ processing technique for RF cavities

Description: A condition for Electron Cyclotron Resonance (ECR) can be established inside a fully assembled RF cavity without the need for removing high-power couplers. As such, plasma generated by this process can be used as a final cleaning step, or as an alternative cleaning step in place of other techniques. Tests showed filtered dry air plasma can successfully remove sulfur particles on niobium surface while the surface oxygen content remains intact.
Date: January 1, 2008
Creator: Wu, G.; /Fermilab; Moeller, W-D.; /DESY; Antoine, C.; /Saclay et al.
Partner: UNT Libraries Government Documents Department

Optimization of electron-cyclotron-resonance charge-breeder ions : Final CRADA Report.

Description: Measurements of 1+ beam properties and associated performance of ECR Charge Breeder source determined by total efficiency measurement and charge state distributions from the ECR Charge Breeder. These results were communicated to Far-Tech personnel who used them to benchmark the newly developed programs that model ion capture and charge breeding in the ECR Charge Breeder Source. Providing the basic data described above and in the discussion below to Far-Tech allowed them to improve and refine their calculational tools for ECR ion sources. These new tools will be offered for sale to industry and will also provide important guidance to other research labs developing Charge Breeding ion sources for radioactive beam physics research.
Date: October 9, 2009
Creator: Pardo, R.; Physics & Far-Tech, Inc.
Partner: UNT Libraries Government Documents Department

Electron cyclotron current drive in DIII-D

Description: Clear measurements of the localized current density driven by electron cyclotron waves have been made on the DIII-D tokamak. Direct evidence of the current drive is seen on the internal magnetic field measurements by motional Stark effect spectroscopy. Comparison with theoretical calculations in the collisionless limit shows the experimental current drive exceeds the predictions by a substantial amount for currents driven near the half radius. In all cases the experimental current density profile is broader than the predicted one.
Date: May 1, 1999
Creator: Luce, T.C.; Lin-Liu, Y.R.; Lohr, J.M.; Petty, C.C.; Politzer, P.A.; Prater, R. et al.
Partner: UNT Libraries Government Documents Department

Broadband frequency ECR ion source concepts with large resonant plasma volumes

Description: New techniques are proposed for enhancing the performances of ECR ion sources. The techniques are based on the use of high-power, variable-frequency, multiple-discrete-frequency, or broadband microwave radiation, derived from standard TWT technology, to effect large resonant ``volume`` ECR sources. 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, the effect of which is to produce higher charge state distributions and much higher intensities within a particular charge state than possible in present forms of the ECR ion source. If successful, these developments could significantly impact future accelerator designs and accelerator-based, heavy-ion-research programs by providing multiply-charged ion beams with the energies and intensities required for nuclear physics research from existing ECR ion sources. The methods described in this article can be used to retrofit any ECR ion source predicated on B-minimum plasma confinement techniques.
Date: December 31, 1995
Creator: Alton, G.D.
Partner: UNT Libraries Government Documents Department

Radially localized measurements of superthermal electrons using oblique electron cyclotron emission

Description: It is shown that radial localization of optically tin Electron Cyclotron Emission from superthermal electrons can be imposed by observation of emission upshifted from the thermal cyclotron resonance in the horizontal midplane of a tokamak. A new and unique diagnostic has been proposed and operated to make radially localized measurements of superthermal electrons during Lower Hybrid Current Drive on the PBX-M tokamak. The superthermal electron density profile as well as moments of the electron energy distribution as a function of radius are measured during Lower Hybrid Current Drive. The time evolution of these measurements after the Lower Hybrid power is turned off are given and the observed behavior reflects the collisional isotropization of the energy distribution and radial diffusion of the spatial profile.
Date: May 1, 1996
Creator: Preische, S.; Efthimion, P.C. & Kaye, S.M.
Partner: UNT Libraries Government Documents Department

ECR, ICP, and RIE plasma etching of GaN

Description: The group III-nitrides continue to generate interest due to their wide band gaps and high dielectric constants. These materials have made significant impact on the compound semiconductor community as blue and ultraviolet light emitting diodes (LEDs). Realization of more advanced devices; including lasers and high temperature electronics, requires dry etch processes which are well controlled, smooth, highly anisotropic and have etch rates exceeding 0.5 {mu}m/min. In this paper, we compare electron cyclotron resonance (ECR), inductively coupled plasma (ICP), and reactive ion etch (RIE) etch results for GaN. These are the first ICP etch results reported for GaN. We also report ECR etch rates for GaN as a function of growth technique.
Date: June 1, 1996
Creator: Shul, R.J.; McClellan, G.B.; Rieger, D.J. & Hafich, M.J.
Partner: UNT Libraries Government Documents Department

Current profile modification with electron cyclotron current drive in the DIII-D tokamak

Description: Proof-of-principle experiments on the suitability of electron cyclotron current drive (ECCD) for active current profile control are reported. Experiments with second harmonic extraordinary mode absorption at power levels near 1 MW have demonstrated ability to modify the current profile. This modification is manifested in changes in the internal inductance and the time at which sawteeth appear. Measurements of the local current density and internal loop voltage using high resolution motional Stark effect spectroscopy to half of the minor radius in discharges with localized deposition clearly demonstrate localized off-axis ECCD at the predicted location. Comparison with theory indicates the detrimental effect of trapped electrons on the current drive efficiency is less than predicted. Modification of the theory for finite collisionality is the leading candidate to explain the observations.
Date: November 1998
Creator: Luce, T. C.; Lin-Liu, Y. R. & Lohr, J. M.
Partner: UNT Libraries Government Documents Department