141 Matching Results

Search Results

Advanced search parameters have been applied.

Production of Neutrals and Their and Effects on the Ion Chargestates in Cathodic Vacuum Arc Plasmas

Description: Cathodic arc plasmas are considered fully ionized and theycontain multiply charged ions, yet, gaseous and metal neutrals can bepresent. It is shown that they can cause a significant reduction of theion charge states as measured far from the cathode spots. Several cathodematerials were used to study the evolution the mean ion charge state as afunction of time after arc ignition. The type of cathode material, arccurrent amplitude, intentionally increased background gas, additionalsurfaces placed near the plasma flow, and other factors influence thedegree of charge state reduction because all of these factors influencethe density of neutrals. In all cases, it was found that the mean ioncharge state follows an exponential decay of first order, Q(t) = A *exp(t/tau) + Qss, where A is a parameter describing the importance of thedecay, tau is the characteristic decay time, and Qss is a steady-statevalue approached for continuous arc operation. The extrapolated valuesQ(t-->0) indicate surprisingly high mean charge states as produced atcathode spots and not "skewed" by charge exchange collisions withneutrals.
Date: May 23, 2007
Creator: Anders, Andre; Oks, Efim M. & Yushkov, Georgy Yu.
Partner: UNT Libraries Government Documents Department

High Charge State Ions Extracted from Metal Plasmas in the Transition Regime from Vacuum Spark to High Current Vacuum Arc

Description: Metal ions were extracted from pulsed discharge plasmas operating in the transition region between vacuum spark (transient high voltage of kV) and vacuum arc (arc voltage ~;; 20 V). At a peak current of about 4 kA, and with a pulse duration of 8 ?s, we observed mean ion charges states of about 6 for several cathode materials. In the case of platinum, the highest average charge state was 6.74 with ions of charge states as high as 10 present. For gold we found traces of charge state 11, with the highest average charge state of 7.25. At currents higher than 5 kA, non-metallic contaminations started to dominate the ion beam, preventing further enhancement of the metal charge states.
Date: June 19, 2008
Creator: Yushkov, Georgy Yu. & Anders, A.
Partner: UNT Libraries Government Documents Department

Collision-induced interaction cross sections of 1-7 MeV B₂ ions incident on an N₂ gas target

Description: This article describes the measurement of collision-induced interaction cross sections for 1-7 MeV diatomic boron molecular ions incident on a nitrogen gas target by using a differentially pumped gas cell.
Date: May 5, 1995
Creator: Kim, Y. D.; Jin, J. Y.; Matteson, Samuel E.; Weathers, Duncan L.; Anthony, J. M.; Marshall, Paul et al.
Partner: UNT College of Arts and Sciences

Magnetic field effects on plasma ionization balance

Description: Magnetic fields give rise to several phenomena that can significantly affect ionization balance in a plasma. Theoretical models commonly used to determine the charge state distribution (viz., <Z>) of ions in non-magnetized plasmas are reviewed first, for both equilibrium and non-equilibrium situations. Then, after a brief survey of laboratory and cosmic plasmas with strong fields, B > 10{sup 6} Gauss, some of the ways such magnetic fields influence <Z> are highlighted. Most key problems have yet to be tackled.
Date: December 31, 1995
Creator: Weisheit, J.C.
Partner: UNT Libraries Government Documents Department

Puzzling differences in bismuth and lead plasmas: evidence for thesignificant role of neutrals in cathodic vacuum arcs

Description: Time-dependent ion charge state measurements for Pb and Bicathodic arc plasmas revealed unexpectedly strong differences: the meanBi ion charge state dropped much stronger and with a longer time constantthan the mean Pb ion charge state. It is shown that the difference inthermal conductivity led to much higher vapor pressure for Bi, which inturn much more effectively caused charge exchange collisions. The resultshave implications beyond Pb and Bi plasmas, most importantly that the"true" charge states as emitted from the cathode spot are higher thanwhat is generally measured and published.
Date: May 10, 2007
Creator: Anders, Andre & Yushkov, Georgy Yu.
Partner: UNT Libraries Government Documents Department

Influence of argon and oxygen on charge-state-resolved ion energydistributions of filtered aluminum arcs

Description: The charge-state-resolved ion energy distributions (IEDs) in filtered aluminum vacuum arc plasmas were measured and analyzed at different oxygen and argon pressures in the range 0.5 8.0 mTorr. A significant reduction of the ion energy was detected as the pressure was increased, most pronounced in an argon environment and for the higher charge states. The corresponding average charge state decreased from 1.87 to 1.0 with increasing pressure. The IEDs of all metal ions in oxygen were fitted with shifted Maxwellian distributions. The results show that it is possible to obtain a plasma composition with a narrow charge-state distribution as well as a narrow IED. These data may enable tailoring thin-film properties through selecting growth conditions that are characterized by predefined charge state and energy distributions.
Date: March 23, 2006
Creator: Rosen, Johanna; Anders, Andre; Mraz, Stanislav; Atiser, Adil & Schneider, Jochen M.
Partner: UNT Libraries Government Documents Department

Measurement of total ion current from vacuum arc plasmasources

Description: The total ion current generated by a vacuum arc plasma source was measured. The discharge system investigated allowed ion collection from the arc plasma streaming through a hemispherical mesh anode with geometric transparency of 72 percent. A range of different cathode materials was investigated, and the arc current was varied over the range 50-500 A. We find that the normalized ion current (Iion/Iarc) depends on the cathode material, with values in the range from 5 percent to 19 percent and generally greater for elements of low cohesive energy. The application of a strong axial magnetic field in the cathode and arc region leads to increased normalized ion current, but only by virtue of enhanced ion charge states formed in a strong magnetic field.
Date: July 1, 2005
Creator: Oks, Efim M.; Savkin, Konstantin P.; Yushkov, Georgiu Yu.; Nikolaev, Alexey G.; Anders, A. & Brown, Ian G.
Partner: UNT Libraries Government Documents Department

A Summary of Recent Experimental Research on Ion Energy and Charge States of Pulsed Vacuum Arcs

Description: The paper reviews the results of vacuum arc experimental investigations made collaboratively by research groups from Berkeley and Tomsk over the last two years, i.e. since the last ISDEIV in 2006. Vacuum arc plasma of various metals was produced in pulses of a few hundred microseconds duration, and the research focussed on three topics: (i) the energy distribution functions for different ion charge states, (ii) the temporal development of the ion charge state distribution, and (iii) the evolution of the mean directed ion velocities during plasma expansion. A combined quadruple mass-to-charge and energy ana-lyzer (EQP by HIDEN Ltd) and a time-of-flight spectrometer were employed. Cross-checking data by those complimen-tary techniques helped to avoid possible pitfalls in interpre-tation. It was found that the ion energy distribution func-tions in the plasma were independent of the ion charge state, which implies that the energy distribution on a substrate are not equal to due to acceleration in the substrate&#39;s sheath. In pulsed arc mode, the individual ion charge states fractions showed changes leading to a decrease of the mean charge state toward a steady-state value. This decrease can be re-duced by lower arc current, higher pulse repetition rate and reduced length of the discharge gap. It was also found that the directed ion velocity slightly decreased as the plasma expanded into vacuum.
Date: June 16, 2008
Creator: Oks, Efim M.; Yushkov, Georgy Yu. & Anders, Andre
Partner: UNT Libraries Government Documents Department

Ion Species and Charge States of Vacuum Arc Plasma with Gas Feed and Longitudinal Magnetic Field

Description: The evolution of copper ion species and charge state distributions is measured for a long vacuum arc discharge plasma operated in the presence of a longitudinal magnetic field of several 10 mT and working gas (Ar). It was found that changing the cathode-anode distance within 20 cm as well as increasing the gas pressure did not affect the arc burning voltage and power dissipation by much. In contrast, burning voltage and power dissipation were greatly increased as the magnetic field was increased. The longer the discharge gap the greater was the fraction of gaseous ions and the lower the fraction of metal ions, while the mean ion charge state was reduced. It is argued that the results are affected by charge exchange collisions and electron impact ionization.
Date: June 23, 2010
Creator: Oks, Efim & Anders, Andre
Partner: UNT Libraries Government Documents Department

Temporal Development of Ion Beam Mean Charge State in PulsedVacuum Arc Ion Sources

Description: Vacuum arc ion sources, commonly also known as "Mevva" ionsources, are used to generate intense pulsed metal ion beams. It is knownthat the mean charge state of the ion beam lies between 1 and 4,depending on cathode material, arc current, arc pulse duration, presenceor absence of magnetic field at the cathode, as well background gaspressure. A characteristic of the vacuum arc ion beam is a significantdecrease in ion charge state throughout the pulse. This decrease can beobserved up to a few milliseconds, until a "noisy" steady-state value isestablished. Since the extraction voltage is constant, a decrease in theion charge state has a proportional impact on the average ion beamenergy. This paper presents results of detailed investigations of theinfluence of arc parameters on the temporal development of the ion beammean charge state for a wide range of cathode materials. It is shown thatfor fixed pulse duration, the charge state decrease can be reduced bylower arc current, higher pulse repetition rate, and reduction of thedistance between cathode and extraction region. The latter effect may beassociated with charge exchange processes in the dischargeplasma.
Date: June 21, 2007
Creator: Oks, Efim M.; Yushkov, Georgy Yu. & Anders, Andre
Partner: UNT Libraries Government Documents Department

High intensity production of high and medium charge state uraniumand other heavy ion beams with VENUS

Description: The next generation, superconducting ECR ion source VENUS(Versatile ECR ion source for NUclear Science) started operation with 28GHzmicrowave heating in 2004. Since then it has produced world recordion beam intensities. For example, 2850 e mu A of O6+, 200 e mu A of U33+or U34+, and in respect to high charge state ions, 1 e mu A of Ar18+, 270e mu A of Ar16+, 28 e mu A of Xe35+ and 4.9 e mu A of U47+ have beenproduced. A brief overview of the latest developments leading to theserecord intensities is given and the production of high intensity uraniumbeams is discussed in more detail.
Date: November 15, 2007
Creator: Leitner, Daniela; Galloway, Michelle L.; Loew, Timothy J.; Lyneis, Claude M.; Rodriguez, Ingrid Castro & Todd, Damon S.
Partner: UNT Libraries Government Documents Department

Status of DPIS development in BNL

Description: Direct injection scheme was proposed in 2000 at RIKEN in Japan. The first beam test was done at Tokyo Institute of Technology using a CO{sub 2} laser and an 80 MHz 4 vane RFQ in 2001, and further development continued in RIKEN. In 2006, all the experimental equipment were moved to BNL and a new development program was started. We report on our recent activities at BNL including the use of a frozen gas target for the laser source, low charge state ion beam production and a newly developed laser irradiation system.
Date: September 29, 2008
Creator: Okamura,M.; Tamura, J. & Kanesue, T.
Partner: UNT Libraries Government Documents Department

Target life time of laser ion source for low charge state ion production

Description: Laser ion source (LIS) produces ions by irradiating pulsed high power laser shots onto the solid state target. For the low charge state ion production, laser spot diameter on the target can be over several millimeters using a high power laser such as Nd:YAG laser. In this case, a damage to the target surface is small while there is a visible crater in case of the best focused laser shot for high charge state ion production (laser spot diameter can be several tens of micrometers). So the need of target displacement after each laser shot to use fresh surface to stabilize plasma is not required for low charge state ion production. We tested target lifetime using Nd:YAG laser with 5 Hz repetition rate. Also target temperature and vacuum condition were recorded during experiment. The feasibility of a long time operation was verified.
Date: June 23, 2008
Creator: Kanesue,T.; Tamura, J. & Okamura, M.
Partner: UNT Libraries Government Documents Department

Injection and acceleration of Au31+ in the BNL AGS.

Description: Injection and acceleration of ions in a lower charge state reduces space charge effects, and, if further elcctron stripping is needed, may allow elimination of a stripping stage and the associated beam losses. The former is of interest to the accelerators in the GSI FAIR complex, the latter for BNL RHIC collider operation at energies lower than the current injection energy. Lower charge state ions, however, have a higher likelihood of electron stripping which can lead to dynamic pressures rises and subsequent beam losses. We report on experiments in the AGS where Au{sup 31+} ions were injected and accelerated instead of the normally used Au{sup 77+} ions. Beam intensities and the average pressure in the AGS ring are recorded, and compared with calculations for dynamic pressures and beam losses. The experimental results will be used to benchmark the StrahlSim dynamic vacuum code and will be incorporated in the GSI FAIR SIS100 design.
Date: June 23, 2008
Creator: Fischer,W.; Ahrens, L.; Brown, K.; Gardner, C.; Glenn, W.; Huang, H. et al.
Partner: UNT Libraries Government Documents Department

ION SOURCES FOR ENERGY EXTREMES OF ION IMPLANTATION.

Description: For the past four years a joint research and development effort designed to develop steady state, intense ion sources has been in progress with the ultimate goal to develop ion sources and techniques, which meet the two energy extreme range needs of mega-electron-volt and 100's of electron-volt ion implanters. This endeavor has already resulted in record steady state output currents of high charge state of Antimony and Phosphorous ions: P{sup 2+} (8.6 pmA), P{sup 3+} (1.9 pmA), and P{sup 4+} (0.12 pmA) and 16.2, 7.6, 3.3, and 2.2 pmA of Sb{sup 3+} Sb{sup 4+}, Sb{sup 5+}, and Sb{sup 6+} respectively. For low energy ion implantation our efforts involve molecular ions and a novel plasmaless/gasless deceleration method. To date, 1 emA of positive Decaborane ions were extracted at 10 keV and smaller currents of negative Decaborane ions were also extracted. Additionally, Boron current fraction of over 70% was extracted from a Bemas-Calutron ion source, which represents a factor of 3.5 improvement over currently employed ion sources.
Date: August 26, 2007
Creator: HERSCHCOVITCH,A.; JOHNSON, B.M.; BATALIN, V.A.; KROPACHEV, G.N.; KUIBEDA, R.P.; KULEVOY, T.V. et al.
Partner: UNT Libraries Government Documents Department

HIGH-ENERGY HEAVY-ION BEAMS AS IGNITERS FOR COMMERCIAL-SCALE INTERTIAL-FUSION POWER PLANTS

Description: Commercial-scale inertial-fusion power can be generated by producing a steady succession of thermonuclear microexplosions of small pellet targets whose ignition requires supplying a few magajoules in a few nanoseconds, a goal well beyond the present single-shot capabilities of high-power pulsed laser and electron-beam systems which also lack the needed repetition-rate capability of order one per second. However, existing high-energy accelerator technology with straightforward engineering extrapolations, applied to pulsed beams of heavy ions in low charge states, can meet all requirements. The relevant accelerator capabilities are discussed; three widely differing types of accelerators show promise. Needed developmental work is mostly on lower-energy components and can be conducted at relatively low cost. Some of the work started at several accelerator laboratories on this new approach within the past year are described, and possible goals of an early demonstration construction project are indicated.
Date: December 1, 1977
Creator: Judd, D. L.
Partner: UNT Libraries Government Documents Department

Formation of High Charge State Heavy Ion Beams with intense Space Charge

Description: High charge-state heavy-ion beams are of interest and used for a number of accelerator applications. Some accelerators produce the beams downstream of the ion source by stripping bound electrons from the ions as they pass through a foil or gas. Heavy-ion inertial fusion (HIF) would benefit from low-emittance, high current ion beams with charge state &gt;1. For these accelerators, the desired dimensionless perveance upon extraction from the emitter is {approx}10{sup -3}, and the electrical current of the beam pulse is {approx}1 A. For accelerator applications where high charge state and very high current are desired, space charge effects present unique challenges. For example, in a stripper, the separation of charge states creates significant nonlinear space-charge forces that impact the beam brightness. We will report on the particle-in-cell simulation of the formation of such beams for HIF, using a thin stripper at low energy.
Date: March 1, 2011
Creator: Seidl, P.A. & Vay, J-L.
Partner: UNT Libraries Government Documents Department

High-Resolution Spectroscopy of K-shell Praseodymium with a High-Energy Calorimeter

Description: We present a measurement of the K-shell spectrum of He-like through Be-like praseodymium ions trapped in the Livermore SuperEBIT electron beam ion trap using a bismuth absorber pixel on the XRS/EBIT microcalorimeter. This measurement is the first of its kind where the n=2 to n=1 transitions of the various charge states are spectroscopically resolved. The measured transition energies are compared with theoretical calculations from several atomic codes.
Date: June 5, 2007
Creator: Thorn, D B; Brown, G V; Clementson, J T; Chen, H; Chen, M H; Beiersdorfer, P et al.
Partner: UNT Libraries Government Documents Department

Milestones in EBIT Spectroscopy and Why it Almost Didn't Work

Description: The EBIT spectroscopy that now seems routine would not be possible without considerable good luck in several areas of EBIT technology. Among these are x-ray background, ion cooling, neutral gas density, and electron current density and energy control. A favourable outcome in these areas has enabled clean x-ray spectra, sufficient intensity for high resolution spectroscopy, production of very high charge states, and a remarkable variety of spectroscopic measurements. During construction of the first EBIT 20 years ago, it was not clear that any of this was possible.
Date: July 17, 2007
Creator: Marrs, R E
Partner: UNT Libraries Government Documents Department

Electronic Structure Calculations of an Oxygen Vacancy in KH2PO4

Description: We present first-principles total-energy density-functional theory electronic structure calculations for the neutral and charge states of an oxygen vacancy in KH{sub 2}PO{sub 4} (KDP). Even though the overall DOS profiles for the defective KDP are quite similar to those of the perfect KDP, the oxygen vacancy in the neutral and +1 charge states induces defect states in the band gap. For the neutral oxygen vacancy, the gap states are occupied by two electrons. The difference between the integral of the total density of states (DOS) and the sum of the DOS projected on the atoms of 0.98 |e|, indicates that one of the two electrons resulting from the removal of the oxygen atom is trapped in the vacancy, while the other tends to delocalize in the neighboring atoms. For the +1 charge oxygen vacancy, the addition of the hole reduces the occupation of the filled gap-states in the neutral case from two to one electron and produces new empty states in the gap. The new empty gap states are very close to the highest occupied states, leading to a dramatic decrease of the band gap. The difference between the integral of the total DOS and the sum of the DOS projected on the atoms is 0.56 |e|, which implies that more than 56% of the redundant electron is trapped in the oxygen vacancy, and 44% spreads over the neighboring atoms. In sharp contrast, no defect states appear in the energy gap for the +2 charge O vacancy. Thus, the addition of the two holes completely compensates the two redundant electrons, and removes in turn the occupied gap states in the neutral case.
Date: February 18, 2005
Creator: Liu, C S; Hou, C J; Kioussis, N; Demos, S & Radousky, H
Partner: UNT Libraries Government Documents Department

Designing double-gap linear accelerators for a wide mass range

Description: For applications like ion implantation, rf linacs using double-gap structures with external resonators can be used because they are practical at low frequencies. However, since the two gaps associated with a given resonator cannot be individually phased, it is not obvious how to build a linac that can efficiently accelerate particles having different mass/charge ratios. This paper describes the beam dynamics of double-gap rf linacs and shows how to maximize the range of mass/charge ratios. The theory also tells one how to rescale a linac tune (i.e., reset the voltages and phases) so that a new particle, having a different mass or charge, will behave similarly to the original particle.
Date: December 31, 1998
Creator: Lysenko, W.P.; Wadlinger, E.A.; Rusnak, B.; Krawczyk, F.; Saadatmand, K. & Wan, Z.
Partner: UNT Libraries Government Documents Department

Status report of a compact 10 GHz electron cyclotron resonance (ECR) ion source for atomic physics experiments

Description: A summary of recent modifications and developments of a compact, fully permanent magnet ECR ion source will be given in this paper. To improve the confinement of the plasma electrons the axial magnetic mirror ratio has been enhanced to 2.5. This results in a more efficient plasma heating at low microwave power levels and therefore ion currents up to 320 e{mu}A could be extracted with a microwave power of less than 10 Watts. The maximum intensities for different charge states and various gases obtained so far will be shown.
Date: August 1, 1997
Creator: Trassl, R.; Broetz, F. & Pawlowsky, M.
Partner: UNT Libraries Government Documents Department

High energy implantation with high-charge-state ions in a vacuum arc ion implanter

Description: Ion implantation energy can in principal be increased by increasing the charge states of the ions produced by the ion source rather than by increasing the implanter operating voltage, providing an important savings in cost and size of the implanter. In some recent work the authors have shown that the charge states of metal ions produced in a vacuum arc ion source can be elevated by a strong magnetic field. In general, the effect of both high arc current and high magnetic field is to push the distribution to higher charge states--the mean ion charge state is increased and new high charge states are formed. The effect is significant for implantation application--the mean ion energy can be about doubled without change in extraction voltage. Here they describe the ion source modifications, the results of time-of-flight measurements of ion charge state distributions, and discuss the use and implications of this technique as a means for doing metal iron implantation in the multi-hundreds of keV ion energy range.
Date: August 1, 1996
Creator: Oks, E. M.; Anders, A.; Brown, I. G.; Dickinson, M. R. & MacGill, R. A.
Partner: UNT Libraries Government Documents Department