摘要:

In order to study beam optics of NIRS‐ECR ion source used in the HIMAC project, the EGUN code has been modified to make it capable of modeling ion extraction from a plasma. Two versions of the modified code are worked out with two different methods in which 1D and 2D sheath theories are used, respectively. Convergence problem of the strong nonlinear self‐consistent equations is investigated. Simulations on NIRS‐ECR ion source and HYPER‐ECR ion source are presented in this paper, exhibiting an agreement with the experiment results.

ISSN:0034-6748    

DOI:10.1063/1.1144935

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A two dimensional electrostatic particle simulation was done to study the extraction of positive (negative) ions from a volume plasma source. The simulation model is a rectangular system which consists of an extraction grid (left wall), a plasma grid, and a grounded wall (right wall). Upper and lower boundaries are connected by the periodic boundary condition. Full dynamics of charged particles are followed. Positive (negative) ions are extracted from the plasma region through a slit in the plasma grid to the extraction grid. Electrons are reflected by the magnetic filter and confined in the region to the right of the magnetic filter. Simulation results are compared with the Child–Langumuir law where the extracted ion current is proportional to the three‐halves power of the potential of the extraction grid. In the case of the positive ion extraction, simulation results agree quite well with the Child–Langumuir law. Whereas, in the case of the negative ion extraction, simulation results agree with the law only for the lower value of extraction grid potential.

ISSN:0034-6748    

DOI:10.1063/1.1144936

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Ion beam formation at low energy (∼1 keV or so) is more difficult to accomplish than at high energy because of beam blowup by space‐charge forces in the uncompensated region within the extractor, an effect which is yet more pronounced for heavy ions and for high beam current density. For the same reasons, the extracted ion beam is more strongly subject to space charge blowup than higher energy beams if it is not space‐charge neutralized to a high degree. A version of vacuum arc ion source with an extractor that produces low‐energy metal ion beams at relatively high current (∼0.5–10 kV at up to ∼100 mA) using a multi‐aperture, accel–decel extractor configuration has been created. The experimentally observed beam extraction characteristics of this source is compared with those predicted using theaxcel−inpcode, and the implied downstream beam transport with theoretical expectations. It is concluded that the low‐energy extractor performance is in reasonable agreement with the code, and that good downstream space charge neutralization is obtained. Here, the code and the experimental results are described, and the features that contribute to good low‐energy performance are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144937

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

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.

ISSN:0034-6748    

DOI:10.1063/1.1144938

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

After the ion beams are extracted from ion sources, it is necessary to transport the beams to the experimental areas or to the accelerating installations. Low‐energy beam transport systems usually consist of some axially symmetrical electrostatic focusing and accelerating lenses as well as quadrupoles and dipoles. Here, we discuss the calculation methods for the beam transport in electrostatic lens systems and describe a computer program for this use.

ISSN:0034-6748    

DOI:10.1063/1.1144939

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Some expressions of the variation of the beam divergence caused by apertures in each electrode versus the electric field intensity ratio for the extraction system with four and five electrodes are given. When the electric field intensity ratio is changed from 0.8 to 3.2 for a four‐electrode system, the divergence caused by an aperture in the third electrode is always divergent and slightly increases with the electric field intensity ratio. The divergence caused by an aperture in the second electrode increases linearly with the electric field intensity ratio and varies from divergence through the zero point to convergence. When the beam perveance is matched, the beam divergence formed by the ion emission boundary will cancel out the role of the second and third electrodes. Thus, the beam divergence caused by the ion emission boundary decreases with increases in the electric field intensity ratio and varies from convergence through the zero point to divergence. On one hand, the perveance ratio increases as the electric field intensity ratio increases, and on the other hand, the perveance of the plane diode, at a certain beam energy, will evidently decrease as the electric field intensity ratio increases. Therefore, the beam current only falls slightly with an increase in the electric field intensity ratio at a certain beam energy. When the beam divergence in each electrode aperture is smaller, the optimum electric field intensity ratio only decreases from 1.76 to 1.47. For an extraction system with five electrodes, the beam current is changed by changing the voltage across the extraction gap, and then the beam is accelerated to the given energy by the voltage across the third gap. Moreover, the beam current can be kept constant by adjusting the voltage across the extraction gap; in this case, the beam energy is changed by changing the voltage across the third gap.

ISSN:0034-6748    

DOI:10.1063/1.1144940

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In technology intense (propagation without space‐charge neutralization is impossible) ion beams of low energy (<1 keV) are often used. In this energy range neutralization as a result of ambient gas ionization immediately by ions is not effective. Different channels of electron appearing have been investigated by authors experimentally and theoretically with different modes of neutralization. Detail probe measurements of electron temperature and energy distribution, electron and ion densities, plasma potential have been carried out. On the basis of the experimental results a self‐consistent theoretical model has been developed. The electron temperature and plasma potential are calculated from self‐consistent energy and particle balance equations. The energy distribution of plasma electrons is found using the Fokker–Planck equation. All theoretical results are given in comparison with experimental data.

ISSN:0034-6748    

DOI:10.1063/1.1144941

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The addition of electrons in both rf plasma and ion beam extracted from a rf ion source enhanced the source’s performance and beam optics. The increase of plasma intensity increases the charge state of the extracted ions. The mixing of electrons with the ions within the ion beam decreases the space charge effect on beam expansion.

ISSN:0034-6748    

DOI:10.1063/1.1144942

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This paper provides arguments to choose electrostatic low‐energy beam transport (LEBT) over the magnetic LEBT for the SSC linac. We will outline the rules to design the electrostatic LEBTs with examples of SSC LEBTs.

ISSN:0034-6748    

DOI:10.1063/1.1144943

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We are developing a new type of microbeam system, intentionally utilizing the process of acceleration, accompanied with the beam contraction effect (conservation of normalized emittance). This device will enable one to produce microbeams for any ion species, less than 0.1 &mgr;m in diameter. A tentative design of lens system (ion energy=100 kV), composed of an entrance aperture lens and an einzel lens, will be described, and it will be discussed why the spherical aberration can be depressed much lower than the usual nonaccelerating lenses. The chromatic aberration due to the fluctuation of the acceleration voltage can be avoided in principle. Hence the only source of this type of aberration is the energy spread of the ion beam from the ion source. The maximum performance of this microbeam system may be obtained when the energy increasing ratio is large enough so that the incident beam energy is kept as low as possible. For investigating these points a hydrogen ion source of special design has been tested. It was found that the intrinsic energy spread can be made considerably low (∼0.5 eV) and a narrow parallel ion beam of several tens eV, which is nearly perfectly neutralized in space charge, can be obtained.

ISSN:0034-6748    

DOI:10.1063/1.1144944

出版商:AIP    

年代:1994

数据来源: AIP