Ion Beam Transport Research Articles

Investigation of the space-charge compensation process of ion beams using a time-resolving ion energy spectrometer

For low-energy beam transport of pulsed high perveance ion beams under space charge compensated conditions the knowledge of the build up time of compensation is of main interest. An LEBT system consisting of two solenoids has been set up to measure the rise time of compensation. Therefore, the beam potential has been in a residual gas ion energy analyser by time resolved measurements. The measured data has been used together with numerical simulation of different equilibrium states of the beam plasma to investigate the behavior of the compensation electrons as a function of time. The data acquired shows that the theoretical rise time of space-charge compensation is shorter by a factor of two than the build up time determined experimentally. An interpretation of the results is given.

Long-pulse ion induction linac

Important issues for the long-pulse induction ion accelerator are (1) the development of high-current long-pulse ion injectors, (2) a method for precise modulation of ion energy for longitudinal pulse compression, (3) core material selection of reasonable construction cost and size, and (4) a realistic scheme for the ion beam transport at low- β region. At the present stage of our project, emphasis has been placed on the characterization of magnetic materials and the development of the long pulse, high flux, low emittance ion injectors. For the precise voltage modulation and cost effective selection of magnetic cores, we measured the response of various ferromagnetic materials under fast-pulse excitation. For the intense, long-pulse ion injectors, we propose drifting point-expanding plasma sources, which compress (smooth out) and expand (cool) the source plasma. These issues are discussed based on some experimental results.

Accelerated ion beams for in-beam e- γ spectroscopy

A few accelerated ion beam requirements for in-beam e- γ spectroscopy are briefly reviewed as well as several features of the MP Tandem accelerator of IPN-Orsay and the accelerated ion-beam transport devices leading to the experimental area of in-beam e- γ spectroscopy. In particular, the main capabilities of the ion-sources, the ion pulsing system, the ion stripping and stabilizing devices as well as the versatility of the ion beam transport system are discussed from the point of view of the different kinds of in-beam e- γ experiments performed in that area.

Possibility of lowering the effective emittance of neutralized ion beams

Self-similarity conditions are determined for the steady states of a quasineutral beam plasma generated during the transport of ion beams in a gaseous medium. The self-consistent radial distribution of the beam and plasma densities is taken into account. Under the resulting conditions the radial electric field of the beam-plasma system is linear, and it is possible for beams to be transported without nonlinear distortion of their phase response characteristics or an increase in the effective emittance.

Charge compensated ion beam propagation in a reactor sized chamber

A fully electromagnetic particle in cell-Monte Carlo (PIC-MCC) code is considered for the ballistic transport of intense ion beams in a reaction chamber field with Flibe gas surrounding a pellet with a thermonuclear fuel in it. A specific emphasis is given to a self-consistent treatment of beam boundary conditions. Spurious electromagnetic waves are evacuated out of the grid, and a modified Maxwell system corrects for Gauss theorem error. A dynamical grid with self-adaptating field follows beam convergence. Final ion propagation in the Hylife II [R. Moir, Fusion Technol. 29, 306 (1991)] scheme and also in the space charge compensated one is investigated at length. For the first, a partial beam neutralization is identified only through electron background. The second displays an acceptable focalization at pellet, the background electron temperature has a significant influence on beam minimum radius. Transverse emittance is given specific attention.

Transportation of intensive ion beams (invited)

This proceeding considers excitation of ion and electron oscillations in a plasma formed by the beam of fast positive ions. Linear and nonlinear stages of the oscillations developing, and the influence of these oscillations on the beam transportation properties are described. Also briefly described are some techniques for the stabilization of instabilities of electron and ion oscillations in compensated ion beams.

Transportation of intensive ion beams (invited)

This proceeding considers excitation of ion and electron oscillations in a plasma formed by the beam of fast positive ions. Linear and nonlinear stages of the oscillations developing, and the influence of these oscillations on the beam transportation properties are described. Also briefly described are some techniques for the stabilization of instabilities of electron and ion oscillations in compensated ion beams.

Production and control of high current ion beams in plasma-optical systems

A brief review of investigations carried out in the Institute of Physics is presented along with an analysis of processes determining production of ions as well as formation and transport of intense ion beams in plasma-optical systems. All these systems have a common mechanism of space charge equipotentialization. When a noncompensated beam’s self-potential exceeds significantly an external potential, a charge compensation is mainly provided by secondary electron emission. Two systems are considered, a magnetically isolated diode gap (MDG) operating in the plasma-optical regime, and a high-current electrostatic plasma lens. It is demonstrated that a MDG can be used for production of hydrogen ions with unique parameters (current 6 A, density of current 6 A/cm2, energy up to 20 keV, pulse duration up to 100 μs). An effective method of intense ion beam low pressure transport is proposed.

High brightness He3 ion source and plasma target for nuclear astrophysical applications

The design of a compact low-energy, high-current accelerator for the study of fusion reactions in the field of nuclear astrophysics is reported. The accelerator can produce an intense beam of several ion species, including proton, deuteron, and helium isotopes, of more than 1 mA. In order to provide extremely fine, cross-sectional measurements for fusion reactions at 40 to 50 keV, analyses of ion beam production, extraction and transport to a windowless gas target are made using the GIOS and FUGUN computer codes. The use of multielectrodes for the ion extraction and the application of these electrodes to the NANOGUN ion source is expected to improve the beam quality and to raise the luminosity for the beam-to-gas-target interaction. To study the electron screening effects, an experimental apparatus is proposed and constructed.

Status report on ECR ion source operation at the GSI accelerator facilities

The Caprice electron cyclotron resonance (ECR) ion source of the high charge state injector (HLI) as standard injection line for the UNILAC at GSI is now in permanent operation during all beam time periods of a year. So the ECR test stand which is equipped with the same version of Caprice mainly has to be used for preparatory work. Ion beams of a great variety of elements are demanded covering beam time periods of up to six weeks. Besides the stable and reliable operation with diverse gases the application of our high-temperature oven has become a standard method for all solid materials attaining a vapor pressure of 10−3 mbar between 800 and 1500 °C. It has been operated not only with pure metal samples but also with especially produced isotopic zinc oxide samples providing a stable beam of Zn10+68 ions. Alternatively a low-temperature evaporator was constructed for high vapor pressure materials and was used for the production of Se and Zn ions. Experiences gained with the oven and evaporator method will be reported and results will be summarized. In order to investigate and improve ion extraction and beam transport through the low energy beam line under conditions equivalent to the HLI a new ECR injector setup is being built which is equipped with an identical analyzing system. The basic concept of the new setup is described.

Developments on the KSU-CRYEBIS, a user facility for low energy, highly charged ions

The KSU-CRYEBIS, a CRYogenic electron beam ion source, supplies experiments with low-energy, highly charged ions of numerous species. The supplied charge states cover the range from 1+ to 52+, with typical beam currents of a nA for low charge states and a few pA for the highest charge states. The ion energies cover the range from 0.3 to 165 keV per charge. This is an unusually broad range of final ion energies and hence requires an unusual dynamic ion transport system. This paper presents advances made with respect to the CRYEBIS ion beam transport, diagnostics, and identification. In addition, an update on the developments of ion beams with very high duty cycles is given.

Array of neutral particle analyzers at DIII-D

Local measurements of the fast-ion distribution in auxiliary-heated plasmas are key to understanding the behavior of energetic particles under a variety of conditions, such as beam–ion transport during Alfvén instabilities and the acceleration of beam ions by fast waves. For the first time at DIII-D, line-averaged and local measurements of the energetic-particle density (for E=5–75 keV) are possible using an array of four compact charge–exchange analyzers [P. Beiersdorfer et al., Rev. Sci. Instrum. 58, 2092 (1987)]. The installation consists of three vertically viewing analyzers with fixed sightlines, measuring particles with χ=90° (where χ is the angle between the particle’s velocity and the toroidal direction), and one horizontally viewing analyzer with a variable sightline, measuring particles with 2°≲χ≲60°. All the analyzers can make passive measurements while three detectors, with sightlines that intersect deuterium heating beams, can make active charge–exchange measurements.

Investigation of nonthermal particle effects on ionization dynamics in high current density ion beam transport experiments

Light ion inertial fusion experiments require the presence of a moderate density background gas in the transport region to provide charge and current neutralization for a high current density ion beam. In this article, we investigate the effects of nonthermal particles such as beam ions or non-Maxwellian electron distributions on the ionization dynamics of the background gas. In particular, we focus on the case of Li beams being transported in an argon gas. Nonthermal particles as well as thermal electrons are included in time-dependent collisional-radiative calculations to determine time-dependent atomic level populations and charge state distributions in a beam-produced plasma. We also briefly discuss the effects of beam ions and energetic electrons on the visible and vacuum ultraviolet (VUV) spectral regions. It is found that the mean charge state of the gas, and hence the electron density, is significantly increased by collisions with energetic particles. This higher ionization significantly impacts the VUV spectral region, where numerous resonance lines occur. On the other hand, the visible spectrum tends to be less affected because the closely spaced excited states are populated by lower energy thermal electrons.

Light ion beam driven inertial confinement fusion: Requirements and achievements

In this paper we compare the requirements for a light ion beam driven inertial confinement fusion (ICF) reactor with the present achievements in pulsed power technology, ion diode performance, beam transport, and target physics. The largest gap exists in beam quality and repetition rate capability of high-power ion diodes. Beam quality can very likely be improved to a level sufficient for driving a single-shot ignition facility, if the potential of two-stage acceleration is used. Present schemes for repetition rate ion diodes allow either too low power densities or create too large beam divergence. On the other hand, repetitively operating pulsed-power generators meeting the requirements for an ICF reactor driver can be built with present technology. Also, a rather mature target concept has been developed for indirect drive with light ion beams.

Self-pinched transport for ion-driven inertial confinement fusion

Efficient transport of intense ion beams is necessary for ion-driven inertial confinement fusion (ICF). The self-pinched transport scheme involves the focusing of an ion beam to a radius of about 1 cm or less. At this radius, using the beam's self-magnetic field for confinement, the ion beam propagates through the reactor chamber to an ICF target. A promising regime for self-pinched transport involves the injection of a high current beam into an initally neutral gas at about 200 mTorr less. A simple equilibrium theory of a beam with a temporally pinching radial envelope predicts that large confining magnetic fields are possible with net currents of more than 50% of the beam current. The magnitude of these fields is strongly dependent on the rate of ionization of the given ion species. We have simulated ion-beam propagation, using the hybrid code IPROP, which self-consistently calculates the gas breakdown and electromagnetic fields. In agreement with the theory, a propagation window of 20–200 mTorr of argon is calculated for a 50 kA, 5 MeV proton beam similar to the parameters of the SABRE accelerator at Sandia National Laboratories. We present simulations of the focusing and propagation of the SABRE beam, with the purpose of designing a self-pinch experiment.

The high current plasma lens: investigations of fine focusing of high energy heavy ion beams

Fine focusing and transport of heavy ion beams in plasma lenses and z-discharge channels is a significant issue for inertial confinement fusion. Therefore, some of the corresponding questions are addressed in an experimental programme at GSI, using a wall-stabilized discharge as an active plasma lens for fine focusing experiments of heavy ion beams. Very accurate and reproducible focusing of ion beams (Ne, C, Ar, Au) at energies between 10 and 300 MeV a.m.u. −1 is now achieved. Emittance measurements and the determination of the emittance growth that results from scattering in thin foils of the heavy ion beam have been possible with the plasma lens. The minimum achieved spot diameter was 390 μm in the vertical plane at a target distance of 53 mm and 150 kA plasma current, with a plasma column of length 100 mm and diameter 14 mm. The corresponding beam emittance was 40 π mm mrad (r.m.s.).

Heavy ion beam transport in an inertial confinement fusion reactor

A new code, btrac, is under development to determine whether a beam of heavy ions can be focused to the necessary spot size radius of about 2 mm within an inertial confinement reactor chamber where the background gas densities are on the order of 10 14-10 15 cm −3 of lithium (or equivalent). Beam transport is expected to be strongly affected by stripping and collective plasma phenomena; if propagation is possible in this regime, it could lead to simplified reactor designs. The beam is modeled using a 2 1 2 -dimensional particle-in-cell (PIC) simulation code coupled with a Monte Carlo (MC) method for analyzing collisions. The MC code follows collisions between the beam ions and neutral background gas atoms that account for the generation of electrons and background gas ions (ionization), and an increase in the charge state of the beam ions (stripping). The PIC code models the complete dynamics of the interaction of the various charged particle species with the self-generated electromagnetic fields. Details of the code model and preliminary results are presented.

Intense heavy ion beam transport with electric and magnetic quadrupoles

As part of the small induction recirculator development at LLNL we are testing an injector and transport line that delivers 4 μs beams of potassium with repetition rates up to 10 Hz at a nominal current of 2 mA. The normalized edge equivalent emittance of the beams is near 0.02 mm mrad and is mostly determined by the temperature of the source (0.1 eV). K + ions generated at 80 keV in a Pierce diode are matched to an alternating gradient transport line by seven electric quadrupoles. Two additional quads have been modified to serve as two-axis steerers. The matching section is followed by a transport section comprised of seven permanent magnet quadrupoles. Matching to this section is achieved by adjusting the voltages on the electric quadrupoles to voltages calculated by an envelope matching code. Measurements of beam envelope parameters are made at the matching section entrance and exit as well as at the end of the permanent magnet transport section. Beam current waveforms along the experiment are compared with results from a one-dimensional longitudinal dynamics code. Initial experiments show particle loss occurring at the beam head as a result of overtaking. Except for this, the beam is transported with essentially no loss of current through the 4.8 m of electric and magnetic focused transport. During transport the emittance increases by approximately 50% from the intrinsic emittance of the source. Some electron effects that have little apparent influence on transport have also been seen. The apparatus is also being used for the development of non- or minimally intercepting diagnostics for future recirculator experiments. These include capacitive monitors for determining beam line change density and position in therecirculator, flying wire scanners for beam position, and gated TV scanners for measuring beam profiles and emittance.

Plasma lens focusing and plasma channel transport for heavy ion fusion

The capabilities of adiabatic, current-carrying plasma lenses for the final focus problem in heavy-ion-beam-driven inertial confinement fusion are explored and compared with the performance of non-adiabatic plasma lenses, and with that of conventional quadrupole lenses. A final focus system for a fusion reactor is proposed, consisting of a conventional quadrupole lens to prefocus the driver beams to the entrance aperture of the adiabatic lens, the plasma lens itself, and a high current discharge channel inside the chamber to transport the focused beam to the fusion pellet. Two experiments are described that address the issues of adiabatic focusing, and of transport channel generation and stability for ion beam transport. The test of the adiabatic focusing principle shows a 26-fold current density increase of a 1.5 MeV potassium ion beam during operation of the lens. The lens consist of a discharge of length 300 mm, filled with helium gas at a pressure of 1 Torr and is pulsed with a current between 5 and 15 kA. The investigations of discharge channels for ion beam transport show that preionization of the discharge channels with a UV laser can be an efficient way to direct and stabilize the discharge.

Space-charge compensation of highly charged ion beam from laser ion source

The problem of matching an ion beam delivered by a high-intensity ion source with an accelerator is considered. The experimental results of highly charged ion beam transport with space-charge compensation by electrons are presented. A tungsten thermionic cathode is used as a source of electrons for beam compensation. An increase of ion beam current density by a factor of 25 is obtained as a result of space-charge compensation at a distance of 3 m from the extraction system. The process of ion beam space-charge compensation, requirements for a source of electrons, and the influence of recombination losses in a spacecharge-compensated ion beam are discussed.