摘要:

The simulation of volume produced negative ions from a plasma is by far more complicated than the extraction of positive ions, while in experiments the only difficulty seemes to be connected with the power of the electrons, which are extracted at the same time. The reason for this complication in simple minded simulations is the infinite space charge, which builds up in the turning point of the positive ions in the extraction aperture for the negative ions. Smearing out the energy of the positive ions seems to help, however, this is mostly not justified by experiments, showing a low ion energy, especially in the region between the magnetic filter and the extraction hole. This difficulty may be overcome by using experience from virtual cathode formation in magnetically focused, decelerated electron beams. The decelerated electrons behave similarly to the reflected positive ions and are forming a virtual cathode in the reflection zone. From the analysis of the electron deceleration experiment, a simple power law is deduced to describe the decreasing electron current by the local potential. In turn, this power law may also be applied to the positive ion current, resulting in simulations without space charge singularity, even in the case of monoenergetic ions. As a first step towards the numerical simulation of negative ion extraction, a linear model has been made, using this power law. The transition from a Boltzmann distribution for the plasma electrons to a truncated one for the extracted beam electrons is considered as well, parallel to Langmuir’s treatment of a thermal diode for electrons. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148713

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The plasma lens is investigated for focusing of a proton beam of energy 5 MeV, current 10 mA, and pulse duration 30 &mgr;s, obtained on the accelerator “Ural-5” with radio-frequency quadrupole (RFQ) radial-phase focusing. The parameters of the plasma flow produced by a coaxial plasma gun are the following: plasma density1011–1015 cm−3,temperature 1–3 eV, velocity107 cm/s,and time duration 500 &mgr;s. The magnetic-field value of a short coil is 500–1000 Oe. The focusing coefficient is ten times the compression at the length of 30 cm obtained. The dependence of ion-beam size upon various parameters of the plasma lens is investigated. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148639

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

At the “Laboratorio Nazionale del Sud” two different ion sources are under development: SERSE (a superconducting electron cyclotron resonance ion source to be coupled to the superconducting cyclotron) and MIDAS (a microwave discharge ion source for recoils ionization). In most cases, for these kinds of sources, the coupling system remains empirical, and the exact description of the waves absorbed from the plasma is poorly known. In the following paper an analysis of power transfer characteristics between an arbitrary power source and load impedances is presented. Particular attention is paid to the matching systems. Herein is presented a 2.45 Ghz microwave line for the MIDAS ion source and a proposal for a matching system that can be used in SERSE when it will be driven by three frequencies: 10, 14, and 18 Ghz. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148640

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In recent years new processes of ion-plasma technology of thin-film coating in which rather dense mono-kinetic ion flows on processable substrates are used have been developed. In the processing of optical film coating, e.g., ion beams of argon, oxygen, and other heavy gases with a cross section of up to 100 mm in diameter, with a current density of up to 2 mA/cm2and energy 50–70 eV are required. Such beams are difficult for receiving in “classical” ion sources because of restriction on ion space charge. The new approach to resolve this problem consists of the application of decelerating the ions. In this method a broad ion beam is formed in an ion source of known type with the ion energy 500–1000 eV, and then the ions are decelerated in a specially developed ion decelerator. Devices on breaking of ion—ion decelerators based on the discharge with closed electron drift in crossed EXE fields were proposed and technological decelerators of ions, intended for processing of substrates with a diameter of up to 100 mm, were developed. The properties of the system consisting of an ion source and an ion decelerator, were investigated. It was shown that the researched system effectively produces ion beams with above-mentioned parameters. But in case of submission of breaking potential on DE, positive in relation to the output electrode of a source, potential of a beam also grows. The increase of the beam potential causes the reduction of the axial component of the ions’ velocity and preservation of their transversal velocity component constant. The divergency of a beam thus increases, and the ion current density on DE falls. Essential influence of a decelerating degree is shown at deep (more than 50&percent;) decelerating of ions on the ion current density distribution and on the plasma potential of the beam body. Probe measurements of the local plasma properties and ion beam parameters in the space of ion beam transportation were done and show that the change of the beam potential is observed in wide area of the beam, and only 30&percent;–40&percent; of the potential drop is concentrated in a short layer near DE. The analysis of balances of currents of ions and electrons in the investigated system are brought forward for cases, when no special means were used for the ion beam space charge compensation and when on the source output there a neutralizer in kind of a heated filament was applied. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148750

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The three-dimensional particle orbit simulation is carried out to analyze the plasma generation in a bucket-type ion source. The characteristics of ion source plasma is analyzed when the filament current is changed. When the filament current is increased, the electron is trapped by the magnetic field made by a filament current, and makes less contribution to the plasma discharge. In this study, the filament configurations are studied in viewpoints of efficiency of discharge, where electron emission is examined by tracing electron orbits from and near the filaments. The uniformity of plasma distribution is also studied due to the filament configuration and current.©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148641

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Presented is a report on the development of an electron-beam ion source (EBIS) for the relativistic heavy ion collider at Brookhaven National Laboratory (BNL) which requires operating with a 10 A electron beam. This is approximately an order of magnitude higher current than in any existing EBIS device. A test stand is presently being designed and constructed where EBIS components will be tested. It will be reported in a separate paper at this conference. The design of the 10 A electron gun, drift tubes, and electron collector requires extensive computer simulations. Calculations have been performed at Novosibirsk and BNL using two different programs,SAMandEGUN. Results of these simulations will be presented. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148714

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

It is a known fact that in electron cyclotron resonance ion sources, plasma impurities play a role in the formation of the ion charge state distribution (CSD). Writing the balance equations for the ion densities in a matrix form allows us to calculate CSD easily for plasmas containing an arbitrary number of elements, taking into account electron ionization, radiative recombination, charge exchange between ions, and ion flowing out of the magnetic trap. Moreover, by defining two global quantities—S0andSc—representative of charge exchange, the stationary case can be reduced to the resolution of only one nonlinear equation forS0andSc.Therefore plasma equilibria even with several species of impurity ions (carbon, oxygen, hydrogen, etc.) can be easily described and solved in this model. The application to the special case of no ion flow is discussed, to study a case similar to thermodynamic equilibrium. An additional factorexp{&mgr;˜ i4/3},whereiis the charge state, is shown to be necessary to fit the CSD. The relationship between the ionization temperature as it appears from the CSD and the electron temperature is given. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148644

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

When measuring the rf emission spectra of an electron cyclotron resonance plasma by a shielded antenna under different discharge conditions, a parametric decay of electron cyclotron waves was detected. Above a certain threshold of the launched microwave power, the pump wave at&ohgr;0/2&pgr;=9.733 GHzdecays into two different wave modes following the condition&ohgr;2=&ohgr;0±&ohgr;1,where&ohgr;1is in the ion cyclotron resonance frequency range. Thus heating of ions is possible. Light ions are preferably heated. We consider this mechanism a possible candidate for explaining the isotope anomaly detected by A. Drentje &etal; [Rev. Sci. Instrum.67, 3 (1996)], which indicates that the heavier isotope of the same ion species is preferentially enriched in the discharge, whereas the lighter one is more easily transported out of the plasma. Experimental results are discussed with respect to this hypothesis. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148715

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The results of numerical simulation of highly charged ion production in the electron cyclotron resonance ion source (ECRIS) during the afterglow of the pulsed operation mode are presented in this article. The influence of the short neutral flux injected into the plasma on the parameters of afterglow is studied. It is shown that a pulse of neutral atoms reduces the duration and increases the amplitude of afterglow. The free expansion of laser ablation plasma was experimentally studied to find the ways for neutral flux production. AQ-switchedYAG:Nd+3laser of 60 mJ focused onto the surface of a Zn target was used for this purpose. A neutral density up to1013cm−3at a distance of 5 cm from the target was obtained. The plasma pulse duration is 10 &mgr;s, the ionization degree in the flux is about 5&percent;, and the velocity of neutrals is in the range of106cm/s. These parameters of the neutral flux are quite enough to test the afterglow enhancement as well as for the load of metal or solid elements into the ECRIS. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148645

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Effects of cesium related reactions are investigated using a simulation code forH−ion sources. Effects begin to appear when cesium density is1011 cm−3,but are still small and become large when the cesium density is greater than1012 cm−3.TheH−density decreases due to electron detachment. Decreasing the plasma potential by cesium seeding results in 12&percent; smallerH−density. The minimum of the plasma potential shown experimentally by Bacal is found to correspond to a cesium coverage of 50&percent; with the use of Langmuir adsorption isotherm. Surface production is effective only when the cesium density is around1011 cm−3.For cesium density greater than1012 cm−3,the effect of the cesium related volume reaction becomes larger. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148646

出版商:AIP    

年代:1998

数据来源: AIP