摘要:

The generation of an electron beam by a hollow cathode gun in a cusp magnetic field is discussed. Such a gun is proposed for an electron cooling device without toroids. In a section with a homogeneous magnetic field, this beam experiences a disturbance region near the axis where the electron temperature becomes higher. The main purpose of the article is to define conditions for generating the beam so as to restrict the extent of this region as much as possible. It is shown that a state with a virtual cathode in the vicinity of the zero magnetic field point is the most suitable for this aim. The experimental and essential analytical results are presented. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147949

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A nonperturbing probe that utilizes a focused ion beam has been developed to measure the position and profile of a tightly bunched charged particle beam (CPB). The ions are injected across the path of the CPB and are deflected by the electromagnetic field of the CPB. Deflected ions are detected by a gated microchannel plate detector and video camera. From the magnitude of the deflections, one can determine the position, radial profile, and in some cases, the axial length of the CPB. Ion parameters can be adjusted to tailor the probe to a wide range of CPB parameters, from submicron, ps bunches to millimeter-sized, quasicontinuous beams. We present the theory of operation of the probe, provide a number of numerical examples to illustrate its capabilities, and describe a proof-of-principle version of the probe that we built and successfully tested at SLAC. The experimental results obtained with this prototype version have shown the ion probe diagnostic to be feasible, reliable, and well understood by the theory and models. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147626

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The optimization results of the ion-optics system in a neutral beam injector are considered which is developed for application of beam emission spectroscopy in the TEXTOR tokamak. The injector is capable to deliver a neutral beam of at least 1 A in hydrogen and deuterium at 50 keV for a pulse length of 5 s into the plasma. The simulation results with theAXCELcode for grids of 4 mm thickness are discussed. The ion current of 2 A extracted by a multihole grid system at a current density of120 mA/cm2is generated by a rf driven ion source. The beamlet half angular divergence is below 0.6° for the optimized four-electrode ion optics system. The estimated temperature rise of the inertially cooled molybdenum grids with 150 holes and 58&percent; transparency is max. 270 K and the related degradation in beam quality by thermal grid expansion is acceptable. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147627

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An experimental setup for the production of pulsed supersonic He beams to be used for plasma edge diagnosis in fusion devices is described. A compromise between compact design, low cost, and good quality of the probe beams has been met. The main characteristics of the generated beams, such as pulse shape, absolute flux intensity, and velocity distribution, differ in general from those expected for ideal beam performance and have been determined and optimized experimentally. A first test of this He beam source at the TJ-I UP Torsatron in Madrid is also reported. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147628

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The design, fabrication, and characterization of a 2.3 kJ plasma focus device with negative inner electrode are discussed. The purpose of the design was to initiate research in and study of plasma dynamics, nuclear reactions, and neutron emission mechanisms at the university. Also the device will be used to teach and demonstrate plasma phenomena at the postgraduate level and to perform experiments with inverted polarity to examine different operating regimes with nonstandard gases. It is hoped that in the long run the research work will help find a solution to the polarity riddle of plasma focus devices. When the system was operated with spectrographic argon as the filling gas, the best focus was obtained at a pressure range of 0.1–1.25 Torr. With nitrogen as the filling gas, the best focus was obtained at pressures between 0.1 and 1.25 Torr. Air gave the best focus at a pressure range of 0.5–1.5 Torr. The observed good focus action is attributed to the small inner electrode length (this reduces the amount of anode material ablated into the current sheath) and tapering of the inner electrode. Positivez-directed electrons contribute to the temperature and further ionization of the plasma gas during focusing. The performance of the device compares quite well with other known devices. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148390

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A semiconductor detector is applied for measurement of high energy end loss ions (E⩾15 keV) from a tandem mirror. Its energy sensitivity to protons calibrated by using a monochromatic ion source is found to be the same as that to electrons. The semiconductor detector is installed on an end wall of the GAMMA 10 tandem mirror and high energy end loss ions are observed with the detector when ions in the confinement region are strongly heated by ion cyclotron waves. Counts of high energy end loss ions are closely related with a diamagnetic signal representing ion heating. The energy of the end loss ions spreads with time and attains to 50–60 keV. Time behavior of the ion count suggests that unknown loss processes other than classical Coulomb scattering are relevant to ion end loss. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147629

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have utilized neural networks for fast evaluation of tomographic data on the MT-1M tokamak. The networks have proven useful in providing the parameters of a nonlinear fit to experimental data, producing results in a fraction of the time required for performing the nonlinear fit. Time required for training the networks makes the method worth applying only if a substantial amount of data are to be evaluated. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147630

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A pellet injector of the repeating pneumatic pipe-gun type has been designed for plasma fueling applications. Its use reduces the time for pellet formation by anin situtechnique from 2 to 3 min to 2–10 s. The basic idea of the proposed approach to pellet formation is to melt prefrozen solid fuel and to admit it through a porous unit into a barrel for refreezing. The injector provides for a continuous injection of an unlimited number of pellets. Over 250 hydrogen and deuterium pellets of 3 mm diameter and 3–10 mm in length were accelerated to 1.2 km/s at a rate of 1 pellet per 10–34 s by manually controlled injector operation. An automatically controlled multishot pellet injector(>10barrels) is capable of providing a continuous and reliable fueling of large fusion devices such as the large helical device and the International Thermonuclear Experimental Reactor (ITER). ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147631

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A combined atomic force microscope (AFM) and scanning near-field optical microscope (SNOM) has been constructed to obtain images under liquids. In this combined AFM-SNOM an inverted ac mode configuration is used where the AFM cantilever is driven by exciting acoustic modes of the liquid cell. Optical images of latex spheres on a cantilever have been obtained under perfluorononane, butanol, and water with a lateral resolution of 100 nm. Fluorescence images of latex spheres have been obtained under perfluorononane. The ability to image under liquids opens up a wide range of applications of near field optical microscopy in chemistry and biology. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147937

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new ultrahigh vacuum (UHV) scanning tunneling microscope design has been developed and optimized forin situinvestigations of thin-film growth. The basic concept of the microscope is to retract the sample by means of the coarse positioning motor under an angle of 30° with respect to the piezotube scanner. This geometric arrangement allows normal film deposition and excludes any interaction between the evaporation beam and the tip. The instrument has the capability of regaining a particular microscopic location on the sample surface with an accuracy of less than 100 nm posterior to a sample displacement of more than 20 mm. Sequences of images of a spot during homoepitaxial growth of Cr on a Cr(100) single-crystal substrate have been obtained. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147951

出版商:AIP    

年代:1997

数据来源: AIP