Lithium Ion Beam Research Articles

Modification of optical, chemical and structural response of CR-39 polymer by [formula omitted] lithium ion irradiation

CR-39 polymer samples were irradiated with 50 MeV lithium ion beam; the fluence was varied in the range 10 11– 10 13 ions cm −2 . Irradiation effects were studied using UV–visible, FTIR spectroscopic and X-ray diffraction techniques. The observation of the recorded spectra shows that the detector is sensitive to swift ions irradiation and its UV absorption is influenced by the stopping power (d E/d x) e. The FTIR spectra does not show any considerable changes due to the irradiation indicating that the detector is chemically stable. No appreciable change in the diffraction pattern of CR-39 polymer after irradiation upto the fluence level of 10 13 ions cm −2 is observed, showing its structural stability also.

Resonance Ionization Diode-Laser Spectroscopy of Neutral Atomic Beam Produced by Pulsed-Ablation Charge Exchange

The lithium ion beam was neutralized in a newly developed charge-exchange cell. The charge exchange was performed with sodium, lithium and iron vapors. The lithium atom was photoionized in a three-step resonance-ionization scheme where the first-step excitation was performed with a cw external-cavity diode laser. The resonance ionization with a diode laser and a pulsed dye laser was as efficient as that with two high-power pulsed dye lasers.

Deposition and drive symmetry for light ion ICF targets

Light ion beam ICF is a concept in which intense beams of low atomic number ions would be used to drive ICF targets to ignition and gain. Three dimensional analytic approximations indicate that at least twelve beams would be required to drive an indirect drive target with adequate symmetry. Here, results from two dimensional numerical simulations are presented describing the ion deposition and drive symmetry aspects of such a target for which the ion beams are approximated as ring sources. For adequate symmetry in the two dimensional calculations, the simulations required six ring sources and two pole sources during the low power `foot' pulse and four ring sources during the main ion beam drive pulse. If each ring represents five individual beams, this corresponds to 32 beams in the foot pulse and 20 beams in the main pulse. The corresponding two dimensional integrated LASNEX calculation, simulating the target from ion beam input to ignition and burn in the same code run, produced 591 MJ of thermonuclear yield with lithium ion beam sources containing a total input energy of 16 MJ.

Laser-ablation charge exchange for collinear resonance ionization spectroscopy

A charge-exchange cell based on pulsed-laser ablation has been developed and applied to collinear resonance ionization spectroscopy. A fast lithium ion beam has been neutralized in the charge-exchange cell and resonance ionization spectra of the 2 s 2 S 1/2−2 p 2 P 1/2,3/2 0 transitions of lithium have been successfully observed. The charge-exchange efficiency of the cell is discussed.

Spectroscopic Measurements of Argon Plasma Formation by a High-Intensity Lithium Ion Beam

We describe the first measurements of plasma formation by a 20 nsec, 9 MeV, $20\mathrm{kA}/{\mathrm{cm}}^{2}$ ${\mathrm{Li}}^{+3}$ ion beam injected into 2-Torr argon, conditions similar to inertial-fusion ion-beam transport requirements. A new visible-spectroscopy diagnostic exploits ion-beam-excited Ar II transitions to measure the time-resolved plasma electron density $({10}^{15}{\mathrm{cm}}^{\ensuremath{-}3}--{10}^{16}{\mathrm{cm}}^{\ensuremath{-}3})$ and temperature (1--2 eV) during the initial breakdown phase. Stark broadening and line intensity ratios are used as diagnostics after the plasma forms. Comparisons with computer simulations examine intense-beam effects important for the transport of light- and heavy-ion beams.

Measurements of planar target heating by an intense lithium ion beam

The heating of a planar multilayer (CH-Au-Al-CH) foil target by an intense lithium ion beam is measured using time-integrated spectroscopy of $K$\ensuremath{\alpha} x-ray satellite emission from the Al layer. The time-resolved beam irradiance, kinetic energy, and focal spot size are simultaneously measured using lithium ions Rutherford scattered from the foil. The approximately 20 ns full width at half maximum, 10 MeV peak kinetic energy, Li${}^{3+}$ ion beam deposited up to 435 TW/g (\ifmmode\pm\else\textpm\fi{}30%) in the Al layer. The peak electron temperature reached in the Al layer is estimated to be 38--43 eV by comparing the relative emission intensities from the He-like and Li-like Al with collisional-radiative-equilibrium (CRE) calculations. The data are used to examine one-dimensional radiation-hydrodynamic simulations that calculate the target plasma temperature and density using the measured beam parameters as input. It was found that a detailed CRE treatment of the atomic level populations and the line transport is essential for accurate calculations of the radiation loss from the ion heated target. Simulations that include such a treatment embedded within the radiation-hydrodynamic calculations are in good agreement with the data, within the experimental uncertainties. The methods developed here for observation and analysis of $K$\ensuremath{\alpha} spectra provide a sensitive tool suitable for the more stringent examinations of intense ion beam-matter interaction models that will ultimately be required for light-ion driven fusion.

Numerical Simulation of Radiation-driven Targets for Light-ion Inertial Confinement Fusion

Light ion beam inertial confinement fusion (ICF) is a concept in which intense beams of low atomic number ions would be used to drive ICF targets to ignition and gain. Here, results from numerical simulations are presented describing the operation of an indirect-drive light-ion ICF target designed for a commercial power plant application. The simulations indicate that the ICF target, consisting of an X-ray-driven capsule embedded in a spherical foam-filled hohlraum, will produce a fusion energy output of over 500 MJ when driven with lithium ion beams containing a total input energy of 8 MJ.

PBFA II lithium beam characterization from inner-shell x-ray images

The Particle Beam Fusion Accelerator (PBFA II) is now driving targets with ICF-relevant lithium ion beams. During the most recent lithium beam target series, time-integrated x-ray pinhole cameras viewed the ion-induced inner-shell x-ray fluorescence from the central gold cone target and a titanium-coated strip. Ion-beam profiles at a nominal 10-mm radius and fixed azimuthal direction were obtained from images of the Ti Kα fluorescence of a Ti-coated Al diagnostic wire. The gold cone gave us beam profiles at a nominal 3-mm radius and at all azimuthal angles from the Au Lα fluorescence. From these profiles, we obtained the ion-beam vertical focus position, the full width at half maximum, and the degree of azimuthal uniformity for the lithium target shots. For these initial results, beam steering problems were evident. Azimuthal uniformity was measured from the ion-beam footprint on the outer Au case (predominantly Au Lα) of the hohlraum target and was found to be in the same range (up to 30%) as for previous proton beam target series.

Temporal response of a lithium nitrate electrohydrodynamic ion source

The first measurements of electrohydrodynamic (EHD) ion emission from thin films of molten lithium nitrate under pulsed field conditions are presented. Pulse widths from ∼20 ns to 50 μs were used to initiate ion emission from the apex of a stainless-steel field emitter tip coated with molten lithium nitrate. Current densities ≳100 A/cm2 were obtained from a single emission site. As the pulse width was increased from 20 ns to several microseconds the electric field required to initiate ion emission decreased and asymptotically approached the electric field value characteristic of dc operation. In contrast to dc operation, Li+ was the dominant species (≳90%) for pulse durations less than 1 μs. The abundance of Li+ was independent of pressure between 10−3 and 10−8 Torr of water vapor. The use of a lithium nitrate EHD ion source for the production of intense lithium ion beams in light-ion inertial confinement fusion reactors is foreseen.

A lithium liquid metal ion source with a narrow angle emission for writing beam lithography

Abstract Parameters of a lithium liquid metal ion source have been determined. The angular intensity is the highest yet reported for liquid metal ion sources. This high angular intensity and the large range of light ions suggest the liquid metal ion source to be applied for writing beam lithography. PMMA resist layers were exposed by a focused lithium ion beam.

Determination of the on-target polarization of an optically-pumped polarized lithium ion beam

An optically-pumped polarized lithium ion source has been built and is currently producing highly polarized 6Li − beams with on-target 6Li 3+ currents up to 150 nA. An absolute measurement of the on-target tensor polarization was made during a one week calibration run, which yielded t 20 = −0.938±0.013, averaged over the entire run. The on-target vector polarization is typically t 10 = 1.02±0.06. The nuclear polarization of the atomic beam at the source has been measured by laser-induced fluorescence to be typically t 10 = 1.14±0.06 and t 20 = −1.14±0.06. A 4He gas polarimeter has been calibrated as a secondary standard for monitoring both vector and tensor polarizations.

The charge stripping interactions of energetic lithium ions and the implications for magnetic fusion applications

This paper describes the first experimental measurements of sigma 23P, the cross section for removal of the final electron from lithium by charge exchange and impact ionization with protons. The implications that this cross section has with regard to lithium ion beam heating and/or current drive in tokamaks are discussed. Since the expected cross section is quite small, non-standard techniques were employed to make this measurement. Singly ionized lithium ions, formed in a magnetically insulated racetrack diode, were passed through an energy selector and then directed along the axis of a theta pinch produced hydrogen plasma. The selector restricted the energy range of the lithium beam to the neighbourhood of 400 keV. The theta pinch coil was 71 cm long and had an inner diameter of 10.5 cm. It was energized by a 25 kj main capacitor bank operating at 150 kHz. After exiting the theta pinch plasma the ion charge states were analysed with a Thomson spectrometer.

Ion mass separation by use of spatial cyclotron resonance

Spatial cyclotron resonance of an ion beam in a wavy magnetic field is investigated to realize the separation of stable isotopes. To perform the experiment, a surface-ionizing lithium ion beam source, which is collisionless and charge-neutralized, has been developed. A wavy magnetic field is produced by setting two magnet-arrays face to face. At the resonance condition, clear scattering of the lithium ion beam is observed and the concentration of 6Li is obtained on a target.

Multicusp ion source for production of negative lithium ions

A beam of negative lithium ions (Li−) with a current density as high as 3×10−5 A/cm2 was extracted from a 5 cm diam, 7 cm long multicusp ion source. The extracted Li− current was correlated to the plasma temperature and density measured with Langmuir probes heated to avoid Li condensation. The neutral lithium flux from the ion source was measured with a Langmuir–Taylor detector, and it showed a linear correlation with the extracted Li− current. Further increase in efficiency to produce Li− current is expected by improving the plasma confinement of the ion source.

An intense lithium ion beam source using vacuum baking and discharge cleaning techniques

We have developed a high-purity, intense, lithium ion beam source which operates at 500 kV and 120 A/cm2 with pulse widths of 125 ns full width half maximum. The beams were generated using a lithium chloride anode in planar magnetically insulated geometry. We have found that the combination of vacuum baking of the anode at 250 °C followed by the application of 100 W of pure argon, steady-state, glow discharge cleaning reduced the impurity concentration in the beam to approximately 10% (components other than chlorine or lithium were considered impurities). Although the impurities were low, the concentration of chlorine in the 1+ and 2+ charge states was significant (∼25%). The remaining 65% of the beam consisted of Li+ ions. Without the special cleaning process, over half the beam particles were impurities. It was determined that these impurities entered the beam at the anode surface but came originally from material in the vacuum chamber. After the cleaning process, recontamination was observed to occur in approximately 6 min. This long recontamination time, which was much greater than the expected monolayer formation time, was attributed to the elevated temperature of the anode. We also compared the electrical characteristics of the beams produced by LiCl anodes to those generated by a standard polyethylene proton source. In contrast to the polyethylene anode, the LiCl source exhibited a higher impedance, produced beams of lower ion current efficiency and had longer turn on times.

リチウムイオンビームの空間的サイクロトロン共鳴現象

The behavior of lithium ion beams in a periodic wavy magnetic field is investigated experimentally to prove the spatial cyclotron resonance of selected isotope. Surface-ionized lithium ion beam source, which is collisionless and charge-neutralized, has been developed to perform the experiment. The wavy magnetic field is produced by setting arrays of magnets face to face in a homogeneous magnetic field. The spatial cyclotron resonance is clearly observed at the resonance condition. This resonance can be used to perform the lithium mass separation.

Simulation of ion beam diagnostics on extraction geometry ion diodes (abstract)

Lithium ion beams are a prime driver candidate for light‐ion inertial confinement fusion. LEVIS/LIBORS lithium ion sources are being developed for the HELIA extraction ion diode. Beam diagnostics to measure beam intensity, energy, composition, and purity are also being developed. Difficulties in diagnosing the beam are encountered because the diagnostics cannot interfere with the plasma forming and ionizing lasers of the LEVIS/LIBORS source. Efforts to model the transport of lithium ions in the self‐ and applied‐magnetic fields of the HELIA ion diode as well as the calculation of beam diagnostics using the PICDIAG computer code are described. The results directly affect the choice and design of diagnostics to be fielded. Results of the simulations are presented and comparisons with available experimental data are emphasized. This work was supported by the U.S. Department of Energy under contract No. DE‐AC04‐76DP00789.

Electric field measurement in the ionosphere using the time‐of‐flight technique

The first successful electric field measurement in the ionosphere using the time‐of‐flight technique with a lithium ion beam was carried out on a S‐520 sounding rocket launched from Kagoshima Space Center, Japan on January 15, 1987. The purpose of this experiment was to prove the validity of the time‐of‐flight technique when it is applied to the measurement of the dc electric field in the ionosphere. A time‐coded ion beam was ejected from the rocket in the direction perpendicular to the Earth's magnetic field. The beam returned to the rocket twice per rocket spin when the initial beam direction was nearly perpendicular to the electric field. The electric field and the magnetic field were derived from the travel time of these return lithium ions. The accuracy of the electric field determination was ±0.3mV/m. The direction of the electric field was obtained from the direction of the returning ion beam after about one ion gyration. The main constituent of the measured electric field was a V × B field due to the rocket motion across the geomagnetic field. The ambient field was less than 1 mV/m. The magnetic field was measured with an accuracy of ±2.T nT in this experiment.

An integrated diagnostic package for intense proton and lithium-ion beam measurements on the sandia national laboratories' PBFA-II accelerator

A review of the diagnostic packages used at Sandia National Laboratories to measure the parameters of intense proton and lithium beams generated on the PBFA-II accelerator will be presented. These diagnostics consist of several types, namely: K α X-ray pinhole cameras, a multiframe dE/ dx ion pinhole camera, a p-i-n diode array ion pinhole camera, Thomson parabola spectrographs, a Rutherford magnetic spectrograph, plasma visible spectroscopy and several nuclear activation diagnostics. These components, when taken together, provide a rather thorough description of the 5 MV, 10 TW ion beams presently being produced. Specifically, the beam parameters measured by the diagnostic array include spatial profile (off and on axis), absolute number, species, voltage, current density and focal power density. A unique feature of these diagnostics is that they are capable of operating in hard (several MeV) X-ray bremsstrahlung backgrounds of some 10 9–10 11rad/s. The operating principles of each diagnostic will be summarized in the paper, along with a discussion of how the diagnostics are integrated together to form a complete system. The paper will close with a discussion of a new nuclear track counting system that has been developed for automatic counting of solid-state nuclear track detectors.

Production of negative lithium ions from the surface immersed in magnetic-field-free plasmas

A beam of negative lithium ions was produced from a 2.5 cm diameter Li metal-coated surface immersed in a magnetic-field-free plasma. The Li − current produced at the surface increased as the negative bias applied to the surface was increased, but did not increase in proportion to the ion current density irradiating the surface. Among He, Ne, Ar, Kr, and Xe plasmas, the Li − yield was higher for a plasma of heavier inert gas, and was also dependent upon the condition of the production surface. In particular, the Cs coverage and the oxygen adsorption on the surface seemed to play an important role to enhance the Li − sputtering yield.