摘要:

A C+60ion beam was extracted from a hollow cathode ion source (model 911A). The mass spectra of 6 keV C60and its fragments have been measured. Only those clusters with an even number of C atoms were observed and the largest one was C84. The result shows that the fragment ion beam has an exponential distribution, which is similar to that of C+60–H2(He) collision experiments. We also have extracted C‐cluster negative‐ion beams from a Middleton 860 sputtering source. With a graphite cathode, we have observed many cluster ions which were not previously reported. For a C60/C70cathode, we have obtained a stable C−60ion beam with current of about 1 nA. The spectra of the negative ions are complicated due to the existence of the Cs–Cnclusters.

ISSN:0034-6748    

DOI:10.1063/1.1144976

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A compact atomic‐beam type of polarized ion source, under construction at Kyushu University, is described. Newly developed permanent sextupole magnets are used and their operational characteristics are measured precisely and analyzed. In order to optimize the strong magnetic field electron impact ionizer performances, a computer code has been developed which simulates the trajectories in the ionizing volume of the electrons and the positive ions produced. A method of optimizing the radio‐frequency unit is proposed. This polarized ion source will be used for a variety of research, especially for the polarized fuel fusion reaction study.

ISSN:0034-6748    

DOI:10.1063/1.1144977

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This project developed an automated controller based on an artificial neural network and evaluated its applicability in a real‐time environment. This capability was developed within the context of a small angle negative ion source on the Discharge Test Stand at Los Alamos. The controller processes information obtained from the beam current wave form, developing a figure of merit (fom) to determine the ion source operating conditions. The fom is composed of the magnitude of the beam current, the stability of operation, and the quietness of the beam. Using no knowledge of operating conditions, the controller begins by making of rough scan of the four‐dimensional operating surface. This surface uses as independent variables the anode and cathode temperatures, the hydrogen flow rate, and the arc voltage. The dependent variable is the fom described above. Once the rough approximation of the surface has been determined, the network formulates a model from which it determines the best operating point. The controller takes the ion source to that operating point for a reality check. As real data is fed in, the model of the operating surface is updated until the neural network’s model agrees with reality. The controller then uses a gradient ascent method to optimize the operation of the ion source. Initial tests of the controller indicate that it is remarkably capable. It has optimized the operation of the ion source on six different occasions bringing the beam to excellent quality and stability.

ISSN:0034-6748    

DOI:10.1063/1.1144978

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

This paper reviews the results obtained in this laboratory in experimental studies of volume H−ion sources. Two techniques are discussed, emission spectroscopy and vacuum ultraviolet laser absorption spectroscopy. Time‐resolved detection of Balmer‐alpha emission has been used to study the excited‐state hydrogen atom population. Vacuum ultraviolet laser absorption spectroscopy has been used to measure the ground electronic state atomic and molecular hydrogen populations. The Balmer‐alpha emission exhibits a modulation in the intensity at a frequency of twice the exciting rf radiation. On the other hand, the laser absorption measurements show that the density of ground‐state hydrogen atoms does not vary significantly with the phase of the exciting rf. Measurements of the vibrational population summed over all rotational states give a vibrational temperature of 6200 K. However, there is no evidence of the ‘‘plateau’’ predicted in the distribution forv≥5.

ISSN:0034-6748    

DOI:10.1063/1.1144979

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A description of methods is given which are used in computer programs for the simulation of extraction systems for ion sources. Specific equations which are important for ion beam extraction will be given. The need of specialized programs will be pointed out with the help of examples.

ISSN:0034-6748    

DOI:10.1063/1.1144980

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A particle simulation code has been developed to study ion optics and the effect of charge‐exchange‐induced grid erosion in electron bombardment ion thrusters. The code is based on the particle‐in‐cell method to simulate the beam extraction and ion optics and a Monte Carlo method to calculate the charge exchange collisions between fast beam ions and neutral particles. The space charge effects for both fast beam ions and slow charge exchange ions are included. Both two‐ and three‐dimensional versions of this code have been developed for both two‐grid and three‐grid systems. The two‐dimensional model provides a qualitative description of the details of the ion flow and the charge exchange collisions. The three‐dimensional version has successfully predicted the experimentally observed erosion pattern in which the maximum erosion occurs at the geometric centers of accelerator grid apertures.

ISSN:0034-6748    

DOI:10.1063/1.1144981

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Several types of collision processes (such as stripping of negative ions and neutrals and ionization of gas molecules and atoms by negative ions) have been introduced in a simulation code of the extraction, acceleration, and transport of negative ions. The energy spectra of neutral atoms formed in the accelerator, for various values of the pressure in the transport region, have been computed. It will be shown that most of the neutrals are formed in the neighborhood of the thick extraction electrode. The effect of these neutrals on the charge‐state distribution in the beam and the effect of the positive ion formation in the transport region on the ion trajectories will be discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144931

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The characteristics of a 30 mA, 35 kV H−beam from a volume source have been determined using emittance measurements. A low energy‐beam transport (LEBT) system consisting of six electrostatic quadrupole lenses and a short (about 5 cm long) single‐stage einzel lens is designed with the aim of transporting the beam over a distance of about 30 cm and focusing a clean, matched beam into a radio‐frequency quadrupole accelerator of the Superconducting Super Collider. The system parameters are chosen on the basis of simulation of beam dynamics. The emittance growth in the LEBT section is within a factor of about 1.5 and this satisfies the requirement of the emittance budget. The LEBT system is designed to be mechanically rugged.

ISSN:0034-6748    

DOI:10.1063/1.1144932

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The static and dynamic characteristics of a high‐current plasma lens (PL) with the two‐component quasineutral plasma medium formed by a wide‐aperture pulse periodical ion beam and secondary ion–electron emission, with the features of focusing and control of a well‐formed low‐divergent multiaperture ion beam by this lens are investigated experimentally in a wide energy range. It is shown that a careful selection of magnetic field geometry, the fixing electrode number, and the external potential distribution on them, according to theoretical plasmaoptics principles, allow a radial electrical profile in a volume of PL to be modified in a given way. This enables the reduction of the spherical aberration of the beam which is being focused. Experimentally and theoretically it is shown that the controlled introduction of spherical aberrations makes it possible to control a radial beam profile on a target and, in particular, to make it homogeneous. The results of low‐energy metal ion beams focused and controlled by PL are obtained. Lens collective processes caused by a principally unremovable magnetic field radial gradient in the ion beam focusing direction are investigated and it is shown that lens electron leakages are connected with these turbulent noises.

ISSN:0034-6748    

DOI:10.1063/1.1144933

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The extraction of ion beams from ECR ion sources is investigated. It is shown that for high magnetic fields within the extraction region, as in the CAPRICE‐type ECR, all different charge states have to be simulated simultaneously to achieve the correct space charge distribution of the extracted ion beam. The change of the longitudinal velocity distribution for different charge states is taken into account. Beam emittance measurements made 280 mm behind the extraction system will be compared with the results of the simulation. Two possible extraction systems which should have influence on the beam characteristics are investigated.

ISSN:0034-6748    

DOI:10.1063/1.1144934

出版商:AIP    

年代:1994

数据来源: AIP