摘要:

AbstractThe probe‐current densitiesjand their firstj' and secondjderivatives with respect to the probe potentials in magnetized plasmas of the toroidal device “Blaamann” have been measured. For analysis of data a kinetic probe theory was used. The comparison of measured and calculatedjandj' shows that electron energy distributions in the plasmas are close to Maxwellian and allows us to calculate electron temperatures and densities. Application of the Langmuir probe theory for unmagnetized plasmas for investigated conditions gives too high electron temperatures (up to 30–40%) and too low densities (with factor from 3 to 10). The measured and calculatedjhave more complicated structure (they may have additional maximums) than in the case of unmagnetized plasmas. The possibility of direct probe measurements of ion energy distributions in the magnetized plasma is di

ISSN:0863-1042    

DOI:10.1002/ctpp.19980380105

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe plasma layer in front of an emissive probe was studied with a particle‐in‐cell code including a Fokker‐Planck model of Coulomb collisions. The results are compared with a 1‐D analytic model and an experiment performed in a gas discharge plasma. At the wall in front of a strongly emitting probe a space charge double layer is formed which limits the emission current. Under floating conditions the potential in the double layer decreases towards the wall, reaches a minimum, and then rises again. The potential drop between the sheath edge and the minimum potential is limited by the development of the double layer. The rise of the potential just in front of the wall is of the order of a fewkTwall.Therefore, the floating potential of an emissive probe lies (in a hydrogen plasma) up to 0.7kTebelow the presheath potential and is not, as is often assumed, at the plasma potential. An analytic model for the floating potential measured by an emissive probe was found to be in good agreement with measurements in an Ar

ISSN:0863-1042    

DOI:10.1002/ctpp.19980380106

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractMeasurements with a single Langmuir probe are in principle a simple electrostatic problem. The probe, the plasma, the power supply and the vacuum vessel form a closed electric circuit. If all resistivities except the sheath resistance in front of the probe can be neglected the measured nonlinearI – Vcharacteristic allows for an evaluation of density and temperature of the plasma. For a complete analysis we have at least to discuss the influence of all other possible resistivities and therefore we must know the exact way, where and how the current path inside the plasma is closed. Dedicated measurements for the flush mounted target plate probes at ASDEX Upgrade as well as theoretical models show that the sheath resistance at the return area has to be accounted for whereas the parallel Spitzer resistivity can be neglected under most circumstance

ISSN:0863-1042    

DOI:10.1002/ctpp.19980380107

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractA problem of a flush‐mounted probe in a fully ionized magnetized plasma (such as SOL plasma) is treated analytically and numerically for arbitrary probe size. The model describes the structure of electric field and particle fluxes, as well as the transport processes, in a plasma zone disturbed by the probe. The I‐V characteristics and the structure of return current to the electrode are derived on this ba

ISSN:0863-1042    

DOI:10.1002/ctpp.19980380108

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractAn analytical model has been developed to estimate the collecting area of a “gapped” single Langmuir probe flush to a local limiter, when the probe characteristic dimension perpendicular to the magnetic field direction is comparable to the ion Larmor radius. The problem has been solved for angles between the magnetic field direction and the probe surface between 12° and 42°, and for square and circular probe cross‐sections. A numerical model, adopting a Montecarlo type approach, has also been developed in order to generalize the solution. Both models also estimate the dependence of the collecting area on the sheath thickness. The models are in good agreement and have been applied to the probes used on the RFX exp

ISSN:0863-1042    

DOI:10.1002/ctpp.19980380109

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractA strong anomaly of the single Langmuir probe characteristics has been observed in detached recombining plasmas, where the conventional analysis of the probe characteristics gives us a considerably high electron temperature compared with the value determined with the spectroscopic methods. We discuss the reason why such characteristics are obtained in terms of the temperature gradient along the magnetic field associated with the parallel electron transport. Moreover, the validity of the probe measurements in the detached recombining plasmas by using multiple electrodes is also discussed.

ISSN:0863-1042    

DOI:10.1002/ctpp.19980380110

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractI‐Vcharacteristics showing high densities and low temperatures are difficult to understand in standard Langmuir probe theory because such a plasma would be highly resistive and would drop more voltage than observed unless the current path were very short. A short current path implies large cross‐field currents, producing largejxBforces. It is shown within the framework of linearized magnetohydrodynamics that this force may be balanced by interaction with the neutrals or by convective accelerations. It is neither appropriate nor necessary to include anomalous diffusivity. The strength of these mechanisms is estimated to be larger than that of classical viscosity and is able to explain theI‐Vcharacteristics observed. With some additional assumptions, it is possible to tentatively relate the results of the linear theory to the level of the electron saturation current and explain a number of trends which have been observed. Analytical expressions for the slope of theI‐Vcharacteristics at floating potential of strip probes have been found and numerical calculations carried out for rectangular

ISSN:0863-1042    

DOI:10.1002/ctpp.19980380111

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractIn this paper, the array of Langmuir probes at the COMPASS‐D divertor and the analysis and interpretation of the probe data are described. The divertor probe system consists of 39 graphite single Langmuir probes embedded in the divertor target. The probe array is being used to investigate the properties of the divertor plasma on COMPASS‐D single‐null X‐point discharges; its high spatial and temporal resolutions allow a detailed study of a variety of fast phenomena such as fluctuations and ELMs. Results on these topics are also pr

ISSN:0863-1042    

DOI:10.1002/ctpp.19980380112

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe behaviour of edge plasma in STP‐3M Reversed Field Pinch is investigated by using a probe with triple electrode. It can be scanned from the boundary of the confined plasma to 122 mm outside and simultaneously measure three signals, such as floating potential, and ion and electron saturation currents. Measurements of the edge plasma far from the confined region made clear that energetic ions are emitted from the core plasma to the outside. The energetic ions are accompanied with the clumps of electrons. Furthermore, measurements by using the probes with three electrodes show that these ions go through energetic electrons in the limiter shadow. These energetic electrons flowing the edge region drive the inversed current to the main current driving in the core regio

ISSN:0863-1042    

DOI:10.1002/ctpp.19980380113

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThis paper presents an overview of the advance in probe design and measurements made at JET during the MkIIa divertor experimental campaign. In addition to the fixed probe system, new probes have been implemented specifically to investigate the effect of plasma resistivity on probe derived electron temperatures and to measure turbulence in the SOL.

ISSN:0863-1042    

DOI:10.1002/ctpp.19980380114

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY