High Brightness Ion Beams Research Articles

A compact radio-frequency ion source for high brightness and low energy spread negative oxygen ion beam production.

A high brightness and low energy spread (∆E) ion source is essential to the production of a high-quality primary ion beam applied in secondary ion mass spectrometry (SIMS). A compact 13.56MHz radio-frequency (RF) ion source with an external planar spiral antenna has been developed as a candidate ion source for the production of negative oxygen ion beams for SIMS application. This ion source is designed with a three-and-a-half-turn water-cooled planar antenna for RF power coupling, a multi-cusp magnetic field for effective plasma confinement, and a three-electrode extraction system. The experimental results show that more than 50 µA negative oxygen ion beams have been extracted, which consist of 56% O-, 25% O2-, and 19% O3-. The ion energy distribution of the negative oxygen ion beam exhibits a Gaussian distribution with a minimum ∆E of 6.3eV. The brightness of the O- beam is estimated to be 82.4Am-2 Sr-1V-1. The simulation, design, and experimental study results of this RF ion source will be presented in this paper.

Development of a surface plasma method for negative ion beams production

By now, the fluxes of accelerated negative ions of steel an indispensable tool for accelerators, plasma physics, solid state physics, chemistry, biology, medicine, important areas of new technique and technology. It arouses increased interest to the development of intensive sources of these particles.The cesiation effect - a significant increase in the emission of negative ions from the discharge with a simultaneous decrease in the flux of accompanying electrons below the current of negative ions after adding a small amount of cesium or other substances with a low ionization potential to the discharge was discovered 50 years ago, on July 1, 1971 in the Budker Institute of Nuclear Physics (BINP), Novosibirsk, Russia.The cesiation effect has opened the door to high-intensity, high-brightness negative ion beams production. The efficiency of generating beams of negative ions was significantly increased due to the invention at the BINP of geometric focusing of generated negative ions. Based on the cesiation effect a surface-plasma method for producing beams of negative ions was developed at the BINP, which provided the creation of surface plasma sources of negative ions for accelerators with a current of hundreds of mA and sources for Controlled Nuclear Fusion with a current of tens of A. (the previous intensity record was 5 mA).Surface plasma sources are being developed all over the world in England, France, Germany, Switzerland, Italy, Japan, Korea, China, India, USA, Canada, Sweden, Spain, New Zealand, Russia, Ukraine, Finland with investments in billions of USD. Specialists in surface plasma sources are trained at the Plasma Physics Department of Novosibirsk State University.

Transport dynamics in a high-brightness magneto-optical-trap Li ion source

Laser-cooled gases offer an alternative to tip-based methods for generating high-brightness ion beams for focused ion beam applications. These sources produce ions by photoionization of ultracold neutral atoms, where the narrow velocity distribution associated with microkelvin-level temperatures results in a very low emittance, high-brightness ion beam. In a magneto-optical trap-based ion source, the brightness is ultimately limited by the transport of cold neutral atoms, which restricts the current that can be extracted from the ion-generating volume. We explore the dynamics of this transport in a 7Li magneto-optical trap ion source by performing time-dependent measurements of the depletion and refilling of the ionization volume in a pulsed source. An analytic microscopic model for the transport is developed, and this model shows excellent agreement with the measured results.

Development of a Radio Frequency Coupled Broad Beam Ion Source for Material Processing

The development of a radio frequency (RF) broad beam ion sources for generating a high brightness ion beams for material processing is presented. The source was able to deliver ion beams from 100 eV up to 2000 eV and with beam currents 100 µA up to 25 mA. The beams divergence do not exceed 7 degrees when using nominally flat grids. The current of ions extracted from a plasma source depends on the plasma parameters particularly the electron number density and electron temperature of the plasma. The Optical Emission Spectroscopy (OES) is employed to determine the plasma electron density and temperature. The effects of argon filling pressures and RF power on electron temperature and density plasma parameters are investigated. The electron density of Ar plasma is between 4x1011 cm-3 and 7x1012 cm-3 whereas electron temperatures 0.6 - 5 eV at pressures from 5x10-4 - 8.5 x10-3 mbar over the RF powers deposited within the plasma from 25 W to 200 W. The ion source is installed on a homemade accelerating tube. The beam optics is extensively studied with space charge compensation by TRANSPORT code. A solenoid magnet located between the ion source and the accelerating tube is used to focus and get the beam divergence under control. The performance of the accelerating facility is reported and applications for material modification is examined.

High spatial resolution and high brightness ion beam probe for in-situ elemental and isotopic analysis

A high spatial resolution and high brightness ion beam from a cold cathode duoplasmatron source and primary ion optics are presented and applied to in-situ analysis of micro-scale geological material with complex structural and chemical features. The magnetic field in the source as well as the influence of relative permeability of magnetic materials on source performance was simulated using COMSOL to confirm the magnetic field strength of the source. Based on SIMION simulation, a high brightness and high spatial resolution negative ion optical system has been developed to achieve Critical (Gaussian) illumination mode. The ion source and primary column are installed on a new Time-of-Flight secondary ion mass spectrometer for analysis of geological samples. The diameter of the ion beam was measured by the knife-edge method and a scanning electron microscope (SEM). Results show that an O2- beam of ca. 5 µm diameter with a beam intensity of ∼5 nA and an O- beam of ca. 5 µm diameter with a beam intensity of ∼50 nA were obtained, respectively. This design will open new possibilities for in-situ elemental and isotopic analysis in geological studies.

Field ionization of Rydberg atoms for high-brightness electron and ion beams

We present an ionization mechanism for use in a cold atom electron source with the goal of producing highly monochromatic electron beams. We experimentally produce a map of the Stark states of $^{85}\mathrm{Rb}$ below the ionization threshold and identify states that undergo selective field ionization. The properties of an electron beam produced by field-assisted ionization of such states are quantified. A theoretical framework is established to predict the improvement to beam quality when ionization is conducted above the ionization threshold, where ionization conditions are typically more favorable than below the threshold. Calculations suggest that selective ionization of Rydberg states may offer a pathway to the production of high-brightness, highly monochromatic ion and electron beams.

Performance predictions for a laser-intensified thermal beam for use in high-resolution focused-ion-beam instruments

Photo-ionization of a laser-cooled and compressed atomic beam from a high-flux thermal source can be used to create a high-brightness ion beam for use in Focus Ion Beam (FIB) instruments. Here we show using calculations and Doppler cooling simulations that an atomic rubidium beam with a brightness of $2.1 \times 10^7 A/(m^2\,sr\,eV)$ at a current of 1 nA can be created using a compact 5 cm long 2D magneto-optical compressor which is more than an order of magnitude better than the current state of the art Liquid Metal Ion Source.

The proton injector for the accelerator facility of antiproton and ion research (FAIR)

The new international accelerator facility for antiproton and ion research (FAIR) at GSI in Darmstadt, Germany, is one of the largest research projects worldwide and will provide an antiproton production rate of 7 × 10(10) cooled pbars per hour. This is equivalent to a primary proton beam current of 2 × 10(16) protons per hour. For this request a high intensity proton linac (p-linac) will be built with an operating rf-frequency of 325 MHz to accelerate a 35 mA proton beam at 70 MeV, using conducting crossed-bar H-cavities. The repetition rate is 4 Hz with beam pulse length of 36 μs. The microwave ion source and low energy beam transport developed within a joint French-German collaboration GSI/CEA-SACLAY will serve as an injector of the compact proton linac. The 2.45 GHz ion source allows high brightness ion beams at an energy of 95 keV and will deliver a proton beam current of 100 mA at the entrance of the radio frequency quadrupole (RFQ) within an acceptance of 0.3π mm mrad (norm., rms).

High-flux monochromatic ion and electron beams based on laser-cooled atoms

We propose a source for high-brightness ion and electron beams based on the ionization of an effusive atomic beam which is transversely laser cooled and compressed. The very low transverse temperature (mK range) and the relative low density of the starting atomic sample ensure excellent initial conditions for obtaining bright and monochromatic charge sources. In contrast to the standard photoionization techniques used by similar sources, we utilize field ionization of Rydberg atoms. This approach allows a substantial reduction of the required laser power and copes differently with the problems of the energy spread created during the ionization process and of the stochastic space-charge effect. Theoretical modeling and prospective ideas of this emerging technology are given.

Vacuum electrospray of volatile liquids assisted by infrared laser irradiation

Current large cluster sources such as C(60) or argon utilize gas-phase sources which are of low-brightness and cannot be focused efficiently to better than 1 micron diameter spot size. The development of a high-brightness large cluster ion source is of critical importance to achieve high resolution in secondary ion mass spectrometry (SIMS) imaging of organics. We propose a new high-brightness large cluster ion source, and a technique for producing a stable electrospray of volatile liquids under vacuum. It is known that vacuum electrospray of volatile liquids such as water is extremely difficult because of freezing of the liquids introduced in vacuum by evaporative cooling. To avoid freezing, the tip of the electrospray emitter was irradiated by a continuous wave infrared laser. Without continuous laser irradiation the vacuum electrospray of a water/methanol solution was unstable with respect to the shapes of the Taylor cone and current, whereas continuous laser irradiation produced a stable electrospray of water. The typical modes of electrospray were clearly observed with an optical microscope even under vacuum conditions. A stable vacuum electrospray could be achieved by improving the vacuum pressure to suppress electric discharge and by using the laser to maintain the liquid state. This is the first description of the production of a stable vacuum electrospray of volatile liquids such as water. This vacuum electrospray technique can be expected to produce a novel high-brightness large cluster ion beam source.

Phase-Space Manipulation of Ultracold Ion Bunches with Time-Dependent Fields

All applications of high brightness ion beams depend on the possibility to precisely manipulate the trajectories of the ions or, more generally, to control their phase-space distribution. We show that the combination of a laser-cooled ion source and time-dependent acceleration fields gives new possibilities to perform precise phase-space control. We demonstrate reduction of the longitudinal energy spread and realization of a lens with control over its focal length and sign, as well as the sign of the spherical aberrations. This creates new possibilities to correct for the spherical and chromatic aberrations which are presently limiting the spatial resolution.

Multiaperture ion beam extraction from gas-dynamic electron cyclotron resonance source of multicharged ions

Electron cyclotron resonance ion source with quasi-gas-dynamic regime of plasma confinement (ReGIS), constructed at the Institute of Applied Physics, Russia, provides opportunities for extracting intense and high-brightness multicharged ion beams. Despite the short plasma lifetime in a magnetic trap of a ReGIS, the degree of multiple ionization may be significantly enhanced by the increase in power and frequency of the applied microwave radiation. The present work is focused on studying the intense beam quality of this source by the pepper-pot method. A single beamlet emittance measured by the pepper-pot method was found to be approximately 70 pi mm mrad, and the total extracted beam current obtained at 14 kV extraction voltage was approximately 25 mA. The results of the numerical simulations of ion beam extraction are found to be in good agreement with experimental data.

Enhanced optical cooling system test in an electron storage ring

We are proposing an experiment to test the new idea of enhanced optical cooling (EOC) in an electron storage ring. This experiment will confirm new fundamental processes in beam physics and will demonstrate new unique possibilities with this cooling technique. It will open important applications of EOC in nuclear physics, elementary particle physics, and in light sources based on high brightness electron and ion beams.

Ion beams and their applications in high-resolution probe formation

The most critical demand for high-brightness ion beams emerged from the realm of industrial applications of focused ion beams and it was met by using liquid metal ion source technology. Although recognized as a successful technology, liquid metal ion sources have major limitations in view of beam species. Noncontaminating ion beam species with beam brightness comparable to liquid metal ion source, i.e., /spl sim/10/sup 6/ A cm/sup -2/ sr/sup -1/ and energy spread of /spl sim/1 eV will be ideal for many cutting-edge applications including ion beam milling, mask repair, and imaging studies. This paper attempts to bring out the essential points in the development of high-resolution probe forming beams. With this specific objective in view, this study is based on an analysis of point sources and then a variety of other sources, under the general classification of "broad" source (primarily plasma sources), are discussed. Several sources in this category including a Penning-type source, a multicusp source, and new-generation high-charged state sources seem to have merits for circumventing the limitations of liquid metal ion sources, although further research is needed to improve the beam brightness and advance the state-of-the art.

Neutralized transport experiment

Experimental details on providing active neutralization of high brightness ion beam have been demonstrated for Heavy Ion Fusion program. A K + beam was extracted from a variable–perveance injector and transported through 2.4 m long quadrupole lattice for final focusing. Neutralization was provided by a localized cathode arc plasma plug and a RF volume plasma system. Effects of beam perveance, emittance, convergence focusing angle, and axial focusing position on neutralization have been investigated. Good agreement has been observed with theory and experiment throughout the study.

High-resolution primary ion beam probe for SIMS

High-brightness negative ion beams, especially O − beams, from a compact gaseous plasma source are studied to evaluate the suitability for high-resolution SIMS. Ion-optical calculations are made using the beam parameters from the new source. Results suggest that sub-100 nm spot with O − beam current of 10 pA is achievable. Beam focusing, the resulting beam current distributions at the target and the expected instrumental performance are discussed.

Formation of intense focused ion and atomic beams

Abstract Series of injectors of focused neutralized ion and atomic beams with beam energy ranging from 5 to 40 keV, equivalent beam current of 1–20 A, angular divergence of beam ∼10 −2 rad, equivalent current density in focus of beam more than 1 A/cm 2 , pulse duration of 0.1–100 ms is developed in Budker Institute of Nuclear Physics. A specific approach to the formation of high brightness ion beams is used in these injectors. The low transverse ion temperature of the plasma emitter is achieved by the use of plasma emitter formed by the collisionlessly expanding plasma jet. Ion beams are extracted from the plasma emitter by precise multi-aperture four-electrode ion optics systems. Two methods of beam focusing have been tested and successfully applied. In the first one the formed ion beam is focused by a magnetic lens and charge-exchanged into atoms in a pulse gas target. The second method is based on geometrical focusing of the beam by spherically bent electrodes of an ion optics system. To profit better use of the nonuniform plasma jet, the developed ion optics systems with geometrical beam focusing have gaps extending with radius which provides optimal beam formation from the enlarged surface.

Study of energy broadening of high-brightness ion beams from a surface plasma Penning source and its relevance in ion projection lithography

The energy spread ΔE (Full Width at Half Maximum of the energy distribution) of negative hydrogen ion (H−) beams has been measured for angular beam intensities (IΩ) over a range of about 40 to 100 mA/sr. An IΩ23 dependence of the energy spread is observed. This trend supports the mechanism of energy broadening due to potential energy relaxation. The observed energy spread of ≲ 3 eV at IΩ of about 40 mA/sr projects a favorable scenario toward the demand of a future production-line ion projection lithography system. The maximum value of IΩΔE2 = 4 mA/sr eV2 suggests the possibility of H− beams for ion microscopy and surface analysis applications also. The H− ion source is currently operated in pulsed mode (maximum duty of 1%-- 1 ms, 10 Hz); cw operation can be achieved by improving the cooling system of the electrodes.

Gas breakdown effects in the generation and transport of light ion beams for fusion

The efficiency of delivering an ion beam to an inertial confinement fusion target depends on the ability to control the breakdown of both unintended (in the ‘‘vacuum’’ diode region) and intended (in the transport region) gas. The desorption and breakdown of anode-surface contaminants in an ion diode complicates the generation of a pure, high-brightness ion beam. Beyond the accelerator, the gas in the reactor vessel must provide excellent charge neutralization and specified current neutralization to permit the beam transport and focusing to a <1 cm radius, spherical target. Two schemes, in which controlling gas breakdown is essential, are ‘‘ballistic’’ and ‘‘self-pinched’’ ion transport. Results are discussed from hybrid particle-fluid simulations of anode contaminant desorption and ion beam transport.

Production of very low energy and high brightness ion beam

In order to produce high brightness beam at energies below 100 eV, the effects of high deceleration voltage in a triode extraction system and plasma potential have been studied. Although the application of high deceleration voltage caused beam spreading, beam brightness was increased at least up to accel–decel ratio of 80. It is found that the reduction of sheath potential of the source plasma caused the increase in beam brightness under high deceleration voltage condition. In particular, it is desirable to reduce sheath potential at the energy below 50 eV because this potential is comparable to external applied acceleration voltage.