ISSN:0863-1042    

DOI:10.1002/ctpp.19960360102

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

ISSN:0863-1042    

DOI:10.1002/ctpp.19960360103

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe First Workshop on Electrical Probes in Magnetized Plasmas was held in Berlin, Germany, on June 13–15, 1994. Some highlights of the 17 talks are presented here. Although at the time probes were considered to be a reliable method to measure electron temperature, data was presented indicating very low values of the sheath power transmission factor, which can perhaps best be explained by systematic errors in the temperature measurement. A valuable framework for discussing the electron saturation current was provided by a model of current collection based on 100% recycling. Unfortunately, experimental results on the current ratio as a function of angle and the path of the return current were presented which could not be explained within the model. More successful was a model to explain the nonsaturation observed in the ion current as the result of growth of the Debye sheath. Two designs of ion sensitive probes were discussed, without coming to a full understanding of their operation. It was demonstrated that probes swept at very high frequencies can show new phenomena, whereas the averaging required for probes swept slower than the frequency of plasma fluctuations can distort the dat

ISSN:0863-1042    

DOI:10.1002/ctpp.19960360104

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe general form of Bohm's condition for sheath formation (λD→ 0) and its relation to the plasma sheath transition is discussed both in the frames of a hydrodynamic and of a kinetic ion analysis. The sheath condition is usually fulfilled in the marginal (equality) form. Previous results for special problems are summariz

ISSN:0863-1042    

DOI:10.1002/ctpp.19960360105

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractIn this paper, the new fixed Langmuir probe systems developed for the Mark I pumped divertor phase of JET are described along with the plans for the new Mark II divertor probe systems. The system installed in Mark I consisted of 22 limiter probes plus 149 divertor probe tips configurable as 149 single Langmuir probes or as 39 triple probes plus 32 single probes. A VME based data acquisition system was developed which acquired data from all probes simultaneously at a rate of 5KHz (342 channels). The concept of the “hands‐off” intelligent probe system and its realisation are described. In contrast to previous probe designs, after one year of operation, the pyrolitic graphite probe tips showed very little sign of erosion. Possible reasons for this important advance are presented. Plans for a “pop‐up” probe system in the new Mark II divertor are outlined which will be used to expose less robust pin‐plate probes to the plasma which would not survive permanent exposure. It is hoped that pin‐plate probes will allow the elimination of the effects of plasma resistivity from the interpretation of single probe

ISSN:0863-1042    

DOI:10.1002/ctpp.19960360106

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractIn this paper, results from the array of fixed Langmuir probes in the JET Mark I divertor are presented. During low density discharges there is good agreement between single and triple probes. At higher density, near the onset of divertor detachment, very low values of the electron to ion saturation current (even<1) are observed which results in an overestimation of the electron temperature, particularly by the triple probe. Alternative methods of probe interpretation are applied and comparisons carried out with independent measurements. The consistency of probe measurements during H‐mode discharges are also briefly discusse

ISSN:0863-1042    

DOI:10.1002/ctpp.19960360107

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractAn array of sixteen flush‐mounted probes has been installed in the upper, outboard divertor plate of the TdeV tokamak, giving a radial resolution of 3.3mmat the strike point. It has become apparent, in the case of grazing angles of incidence of the magnetic field with the plate, that the finite size of both the probe sheath and the sheath of the surrounding plate are the dominant factors which determine the effective probe area for charge collection. We can modify these sheaths by biasing the probes with respect to the plate, and the plate with respect to the vacuum vessel, with very illustrative results. A model, based on sheath expansion, has been developed which can be used to calculate the electron density. The model has been tested experimentally by comparing the results obtained from a flush probe and a standard cylindrical probe which were operated simultaneously in the same plasm

ISSN:0863-1042    

DOI:10.1002/ctpp.19960360108

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractDue to the high heat flux in the divertor region of present day tokamaks, the use of thermally robust flush mounted Langmuir probes becomes more and more important. We will present a model for the analysis of theI‐V‐characteristics yielded by such probes, discuss some of their special features and their suitability as triple probes. It will become evident that flush mounted probes can be used as well as domed probes to determine the plasma parameters in front of the target pla

ISSN:0863-1042    

DOI:10.1002/ctpp.19960360109

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractIn a plasma with a strong electron temperature gradient along magnetic field lines the electron velocity distribution near a target may deviate appreciably from a Maxwellian: due to their long mean free path electrons from the hot region transport their energy non locally into the colder region thus forming a non Maxwellian tail in the velocity distribution. The sheath potential (well below the electron saturation current) is determined by this high energy tail of the electron distribution. The probe characteristic of an electric probe near or below the floating point thus measures the “temperature” of the high energy tail, not of the bulk electron distribution. Therefore an overestimation of the electron temperatures by the probe measurements may occur.This effect is studied numerically using a 1d kinetic particle code. Plasma streams through the computation area to an absorbing target representing the pin of a probe. The electron temperature gradient is produced by the energy transfer condition of the target sheath. From the floating sheath potential drop an effective temperature of transmitted electrons may be derived. This effective electron temperature is different from the temperature at the sheath edge. It renders the temperature of electrons upstream of the sheath by about a mean free path length λ = 10λeswhere λesis the mean free path length for thermal electrons at the sheat

ISSN:0863-1042    

DOI:10.1002/ctpp.19960360110

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe effect of secondary electron emission and sputtered impurity ions on the sheath potential drop has been studied. An analytical model has been developed which allows a self‐consistent description of the above mentioned effects. In the analysis different materials (two kinds of graphite and tungsten) have been compared and a considerable dependence of the potential drop on the material choice has been observed. It is shown that the most of energy coming from the plasma to the target is carried by electrons because of both the decrease of potential drop caused by SEE and the enhancement of electron current to the plate caused by sputterin

ISSN:0863-1042    

DOI:10.1002/ctpp.19960360111

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY