摘要:

Experimental details of operation and plasma flow are presented for bucket ion sources having magnetic flux that bridges the source between the regions of electron injection and ion extraction. The basic goal is to increase the atomic fraction of hydrogen and deuterium by 15% and yet retain an ion‐flux‐density uniformity over the extraction region to within ±7%. A rod structure containing permanent magnets produces a known bridging flux filter across a well‐defined region. This provides an experimental apparatus useful for the study of the effect of magnetic flux on the source plasma flow. The parameters of filter position, filter strength, filter orientation, arc power, and gas pressure are related to species fractions, profile uniformity, and electrical efficiency. The option of having the bridging flux without a rod structure is presented, and experimental results of sources thought to contain this field configuration are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1139083

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A dc negative ion facility has been built to study both the mechanisms controlling H−production in multipole volume sources and the design of accelerators for negative ion beams. After a 7.5‐cm movement of the extraction aperture position within the ion source, the arc current and source gas pressure were optimized, and an H−current of 10 mA was extracted from a 0.5‐cm2circular aperture in a 30‐s pulse from a 100‐A, 90‐V discharge run at 18.8 mT. This is the first operation of such sources to provide a quasi‐dc current of 20 mA cm−2. The installation of an octupole electron trap in the beam forming electrode has lowered the electron current extracted simultaneously with the H−beam by approximately a factor of 4, and this has led to a low H−beam divergence. The application of a small bias voltage of up to 2 V between the beam forming electrode and the anode has reduced this electron current still further (by more than a factor of 10) while maintaining the extracted ion current. It is now possible to extract ion currents from such a source/accelerator configuration that are larger than the accompanying electron current.

ISSN:0034-6748    

DOI:10.1063/1.1139084

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A 30‐kV triode accelerator has been constructed to test the design and operating characteristics of accelerators for negative hydrogen ion beams. Incorporating both a quadrupole electron trap and an octupole electron suppressor, the accelerator has been used to extract, accelerate, and focus H−ion beams of up to current densities of 20 mA cm−2. The results suggest that this accelerator design is capable of focusing across a wide range of ion current densities (0–20 mA cm−2) and acceleration voltages (15–30 kV) using the variation of a single‐gap potential to achieve the required focusing. Applying a bias voltage of up to 2 V between the beam forming electrode and the anode of the source suppresses electrons and has allowed accelerator power efficiencies of over 73% to be obtained for all ion current densities up to 20 mA cm−2so far extracted. Initial evidence that the extracted and accelerated negative ion beam may be undergoing self‐focusing is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1139085

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A high‐power radio‐frequency plasma source was built and tested for an antenna frequency of 2.45 MHz. A puff valve fed hydrogen gas into a plasma chamber made from 4‐in.‐diam Pyrex tubing. A helical antenna was wound directly around this chamber. The plasma source was surrounded by a magnetic bucket which used a longitudinal line‐cusp geometry. For 20 kW of rf input power, the peak electron density was 2.0×1019m−3, the electron temperature was 2.0 eV, the ion temperature was 0.9 eV, and the atomic hydrogen density was 4.4×1019m−3. For 90 kW of rf input power, the peak electron density was 8.9×1019m−3, the electron temperature was 2.5 eV, the ion temperature was 3.0 eV, and the atomic hydrogen density was 2.3×1019m−3. The plasma source had a typical current efficiency of 6 A/kW. A theoretical model for the plasma loading resistance was developed.

ISSN:0034-6748    

DOI:10.1063/1.1139086

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The boundary plasma of the Alcator C tokamak exhibits poloidal asymmetries in plasma parameters. In order to investigate this phenomenon, an array of 80 closely spaced Langmuir probes has been built to directly sample this plasma region. This specially developed, densely packed probe array (DENSEPACK) is unique in that it provides a simultaneous, time‐dependent, two‐dimensional mapping (minor radiusr, poloidal angle &thgr;) of plasma density, electron temperature, and floating potential over nearly the full 360° poloidal extent of the boundary plasma in this circular cross‐section tokamak. The construction and operation of the DENSEPACK probe array, as well as support hardware and software systems needed to handle the large volume of data generated by this array, are described in this paper.

ISSN:0034-6748    

DOI:10.1063/1.1139087

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Investigations of the effects of rf on plasma potential measurements with electron emitting probes and methods for interpreting data are presented. Techniques correspond to the floating and inflection point methods of single‐emitting and differential emitting probes, respectively. A simple method of measurement of plasma potential fluctuations is given which makes use of time‐averaged emitting probeI–Vcharacteristics.

ISSN:0034-6748    

DOI:10.1063/1.1139088

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Modulated grid Faraday cup plasma analyzers are a very useful tool for makinginsitumeasurements of space plasmas. One of their great attributes is that their simplicity permits their angular response function to be calculated theoretically. In this paper we derive an expression for this response function by computing the trajectories of the charged particles inside the cup. We use the Voyager plasma science (PLS) experiment as a specific example. Two approximations to the ‘‘rigorous’’ response function useful for data analysis are discussed. The theoretical formulas were tested by multisensor analysis of solar wind data. The tests indicate that the formulas represent the true cup response function for all angles of incidence with a maximum error of only a few percent.

ISSN:0034-6748    

DOI:10.1063/1.1139089

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

We report the development of a new diagnostic capable of measuring plasma ion distributions as a function of all three velocity–space coordinates. The diagnostic makes use of laser‐induced fluorescence (LIF) and computer‐assisted image reconstruction techniques. LIF yields high‐resolution, nonperturbing measurements of one‐dimensional distributions that are integrated in two directions through three‐dimensional velocity space. Computer tomography allows for the unambiguous determination of the complete ion velocity distribution. In addition to a description of the diagnostic, examples of recovered distributions obtained from experiments are given, and the effects of the major steps in the data processing are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1139090

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A multichannel radiation bolometer has been developed for the Tokamak Chauffage Alfve´n (TCA) tokamak. It has 16 equally spaced chords that view the plasma through a narrow horizontal slit. Almost an entire vertical plasma cross section can be observed. The bolometer operates on the basis of a semiconducting element which serves as a temperature‐dependent resistance. A new electronic circuit has been developed which takes advantage of the semiconductor characteristics of the detector by using feedback techniques. Measurements made with this instrument are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1139091

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An ultrafast x‐ray framing camera is being developed at Lawrence Livermore National Laboratory to be used as a diagnostic instrument in laser experiments. The framing camera is designed to provide temporal resolution of 50 ps and spatial resolution of 30 &mgr; at the image plane. The unique design incorporates the x‐ray photocathode directly into a suspended‐strip transmission line. The photocathode is gated using a high‐voltage (−5 kV) pulse of short duration generated with a photoconductive switch. The photoelectrons are extracted through an unbiased microchannel plate and are directly detected with a charge‐coupled device in the electron‐bombardment mode. We report on current progress in the fabrication, characterization, and integration of the various components of the instrument.

ISSN:0034-6748    

DOI:10.1063/1.1139092

出版商:AIP    

年代:1986

数据来源: AIP