Space Charge Lens Research Articles

ASSESSMENT OF THE POSSIBILITY OF MODERNIZING A SPACE CHARGE LENS FOR FOCUSING BEAMS OF NEGATIVE HYDROGEN IONS DUE TO CONFINEMENT OF POSITIVE BACKGROUND IONS BY AN ALTERNATING ELECTRIC FIELD

The work is devoted to considering the possibility of improving the focusing properties of a space charge lens due to charge retention of positive ions by an electric field that varies both in time and along the axis of the system. Numerical calculations of motion trajectories of positive argon ion during interaction with an alternating electric field with oscillation frequencies in the range of 1...8 MHz and amplitude in the range of 1.5...6 kV were carried out. A significant increase in the residence time of positive argon ion in the overcompensated beam of negative hydrogen ions is shown, which indicates the possibility of significant influencing focusing charge in the lens for focusing beams of negative hydrogen ions.

Self-consistent PIC simulations of ultimate space charge compensation with electron lenses

Further progress of fundamental particle physics requires high intensity and high brightness of accelerated proton and ion beams. This goal is essential for the FAIR hadron beams at GSI, for the neutrino production at the facilities such as Fermilab and JPARC, and for the Large Hadron Collider luminosity at CERN. One of the most formidable obstacles toward that goal is the beam's own space charge, whose forces cause beam emittance growth, losses and lifetime degradation. Typically, such effects become intolerable when the space charge tune-shift parameter Δ QSC exceeds ∼ - (0.25–0.5). To reduce these detrimental effects, it was suggested to use electron lenses to compensate the space charge forces. This paper reports on detailed particle-in-cell space charge and electron lens compensation simulations for extremely intense proton bunches whose space charge tune-shift parameter exceeds -1.0. Different scenarios were evaluated based on reduction in the emittance growth and particle loss at a 4σ aperture. We investigate phenomena and issues related to the focusing lattice errors, importance of the transverse and longitudinal matching of the electron beam profiles to the proton ones, and vary the strength and the number of the electron lenses distributed around a circular machine to optimize the reduction of harmful space charge effects.

Space Charge Lenses for Intensive Ion Beams Formation

Space Charge Lenses for Intensive Ion Beams Formation

Gabor lenses for capture and energy selection of laser driven ion beams in cancer treatment

AbstractThe application of laser accelerated ion beams in Hadron therapy requires ion beam optics with unique features. It has been shown that due to the spectral and spatial distribution of laser accelerated protons a lens based focusing system has advantages over aperture collimated beam formation. We present a compact ion optical system with therapy applications, based on Gabor space charge lenses for collecting, focusing and energy filtering the laser produced proton beam. For a full therapy solution, a scenario based on three space charge lenses is presented. In this very compact beam line an aperture is foreseen for energy selection.

Space charge lenses for particle beams

Space charge lenses provide strong cylinder symmetric focusing for low-energy high-perveance particle beams using a stable space charge cloud. They need drastically reduced magnetic and electrostatic field strength compared with conventional systems and are superior for a degree of lens filling above 17%. They can theoretically provide linear transformation in phase space and reduce beam aberrations and space charge forces. The density distribution of the enclosed space charge is given by the transverse and longitudinal enclosures of the cloud. By the use of self-consistent simulations of the space charge cloud, the focusing properties of space charge lenses in the presented design can be forecasted with sufficient quality. The presented simulations show that the theoretical values can be reached locally. The results of our investigations on the beam transport in a high-current test injector equipped with space charge lenses, including emittance measurements, will be presented and discussed. They show that significant improvements of lens operation have been reached by the reduction of the residual gas pressure and a careful design of the external fields using numerical simulation techniques to calculate the local density distributions. Comparisons of the experimental results with the beam transport simulations show good agreement concerning both focusing strength and linearity of phase space transformation. For the lens design used, the observed degree of lens filling is at least 38% of the theoretical value and more than twice the threshold value.

Low-energy beam transport using space-charge lenses

Space-charge lenses (SCL) of the Gabor type provide strong cylinder symmetric focusing for low-energy ion beams using a confined nonneutral plasma [1]. They need modest magnetic and electrostatic field strength and provide a short installation length when compared to conventional LEBT—lenses like quadrupoles and magnetic solenoids. The density distribution of the enclosed space charge within the Gabor lens is given by the confinement in transverse and longitudinal directions [2]. In the case of a positive ion beam, the space charge of the confined electron cloud may cause an overcompensation of the ion beam space-charge force and consequently focuses the beam. To investigate the capabilities of an SCL double-lens system for ion beam into an RFQ, a test injector was installed at IAP and put into operation successfully. Furthermore, to study the focusing capabilities of this lens at beam energies up to 500 keV, a high-field Gabor lens was built and installed downstream of the RFQ. Experimental results of the beam injection into the RFQ are presented as well as those of these first bunched beam-focusing tests with the 110 A keV He + beam.

Space-Charge Lens for Focusing Negative Ion Beams by Means of an Additional Electron Ionizer

A space-charge lens created at the Institute of Physics, National Academy of Sciences of Ukraine, to focus negative ion beams using an additional electron ionizer is investigated. In the previous version of the lens, in which the gas was ionized by the ion beam itself, the focal power was quite high (the focal length was ƒ ≤ 20 cm) but the gas pressure was too great (P ∼ 10−3 torr), which resulted in significant charge-exchange losses of the beam ions. The experimental and theoretical study reported here shows that the use of a 100-eV electron beam as an auxiliary ionizer allows the working pressure in the lens to be significantly reduced. As a result, a simple, inexpensive, and efficient lens has been developed that can be used in systems for transportation of negative ion beams.

Space charge lens for focusing negative ion beam: Theory and experiment

Detailed researches the of space charge lens for focusing negative ion beam are performed for the cases when positive space charge forming is done either by the beam itself, or by special flow of electrons. Numerical simulations of space charge fields and beam ion trajectories are accomplished, and results of the calculations are compared with experimental data. It is shown both theoretically and experimentally that in the proposed device electric field strength reaches a value of ∼100 V/cm, thus providing a focal length of <20 cm.

Space-charge lens for focusing a negative-ion beam

Space-charge lens for focusing a negative-ion beam

Space-charge lens for focusing negative ion beam

The idea of a space-charge lens for focusing intensive negative hydrogen ion beams is presented. Estimations of focal length of the lens are performed independent of parameters of the beam and gaseous medium. The effectiveness of the focusing H− ion beam with current up to ∼30 mA and energy of ∼10 keV by means of such a lens is demonstrated experimentally. Measured values of focal length are in good agreement with calculated ones.

Space charge lens for focusing negative-ion beams

A space charge lens is proposed to focus intense beams of negative hydrogen ions. The focal length of the lens is determined as a function of the parameters of the beam and the gas medium. It is demonstrated experimentally that the lens efficiently focuses H-ion beams with currents of up to ∼30 mA and energies of ∼10 keV. The measured focal lengths are in good agreement with the calculated ones.

PREVAIL Alpha system: Status and design considerations

An overview is given of the PREVAIL Alpha system program, a joint project of IBM and Nikon to develop a production-level electron project lithography system. The Alpha system program is based on the successful completion of an initial feasibility phase conducted by the IBM/Nikon alliance team and on the PREVAIL proof of concept results reported at EIPBN 1999. The electron beam column and associated electronics and software are under development at IBM’s Semiconductor R&D Center in East Fishkill, New York, while the high speed, high precision stages for both reticle and wafer as well as the overall systems architecture are being developed at Nikon’s facilities. A key architectural objective is the combination of leading edge stepper technology with state-of-the-art PREVAIL electron optics. The design of the electron optics is based on carefully balancing geometric aberrations and Coulomb interactions for optimum resolution at the required high beam current. Cornerstones of the design are the high emittance gun and the curvilinear variable axis lens concept developed for PREVAIL. Design considerations of the Alpha column are emphasized including a detailed treatment of space-charge lens aberrations.

Modeling and design of space charge lenses/aberration correctors for focused ion beam systems

Spherical and chromatic aberrations of electrostatic lenses with negative space charge in axial area are studied. A ‘‘toroidal subbeam’’ algorithm has been developed to model the evolution of the current and charge density distributions of intense charged particle beams taking into account space charge and initial thermal velocity effects. Optimized designs are presented which prove that negative spherical and chromatic aberration coefficients can be achieved for a space charge lens using an electron gun to produce the space charge cloud.

Application of group theory on the nonlinear transport system following ion source

The transfer group theory is used to study the nonlinear transport system that follows the ion source. The properties of the transfer group and the method of computing the phase-space contours, distribution functions, and moments of ion beams are studied. It is shown that the nonlinear element can be used to compensate for the aberration. As an example, a method of improving the quality of the beam extracted from an ion source by means of a nonlinear space-charge lens is discussed.

Self-sustaining space-charge lens

The self-sustaining space-charge lens focuses the ion beams, which travel through the lens, by means of the electron cloud supported by the cold-cathode Penning discharge. Its focusing power mainly depends on the electron density in the electron cloud which can be determined by the rf method. In this article the structure and performance of this type of lens are reported. The relations between the focal length of the lens and external conditions are discussed.

Focusing Properties of Short Space-Charge Lenses

The electron densities in a short space-charge lens are measured with the radiofrequency method under different applied magnetic inductions and voltages, and relations between the focusing power of the lens and the external electromagnetic fields are investigated.

A linear ion optics model for extraction from a plasma ion source

A linear ion optics model for ion extraction from a plasma ion source is presented, based on the paraxial equations which account for lens effects, space charge and finite source ion temperature. This model is applied to three- and four-electrode extraction systems with circular apertures. The results are compared with experimental data and numerical calculations in the literature. It is shown that the improved calculations of space charge effects and lens effects allow better agreement to be obtained than in earlier linear optics models. A principal result is that the model presented here describes the dependence of the optimum perveance on the aspect ratio in a manner similar to the nonlinear optics theory.

Progress in Space Charge Lens Development

A number of space charge lens electrode geometries have been studied for use at very high beam currents at low energy, and for precision optics at MeV energies. One such lens mounted very near a Duo-plasmatron extractor delivered a 30-keV beam of H+ ions through an analyzing magnet at a current of 175 mA for a period of six hours. Another produced a focal spot of diameter 0.2 mm when a 1-cm diameter beam of 1.2-MeV protons was focussed 90 cm from the lens. This paper also describes observations on self-sustaining discharge in the lenses. A very interesting rotation of the lens optic axis about the geometric axis at a frequency near the drift frequency occurs when the vacuum is spoiled by electrode outgassing.

Space charge lens for high current ion beams

A space charge or plasma lens consists of an axial electron trap produced with biased ring electrodes and an axial magnetic field to inhibit radial motion of electrons. It is useful for high current ion beams because it does not remove the neutralizing electrons from the beam. In this paper the design of the space charge trap is discussed qualitatively, the focal length is derived for a simple geometry, and a space charge lens in use in a 400 keV−25 mA deuteron beam transport system is described.

Use of Space Charge in Electron Optics

The electron optical properties of a cylindrical space charge cloud are derived. The possibility of achieving a system free from either spherical or chromatic aberration by combining a space charge lens with a space charge free converging lens is examined. It is concluded that the achromatization of a thin electric or magnetic lens is possible only if the resultant action of the combination is divergent. The correction of the spherical aberration of a high quality lens, such as an electron microscope objective, is shown to be impossible on account of electron interaction effects.