摘要:

Studies of the production, transport, and radiative losses of impurities in present‐day tokamak divertors provide input necessary for the design of future burning‐ plasma machines. Several types of information rely on detailed analysis of emission profiles. These include ion temperatures, ion flows along field lines, and impurity production mechanisms. Temperatures and flows are determined from Doppler broadening and shifts by comparing measured line shapes to theoretical profiles that include the nonlinear Zeeman/Paschen‐Back effect. The two major production mechanisms for atomic carbon are physical and chemical sputtering. These processes can be distinguished by comparing atomic and molecular fluxes, which requires modeling the band emissions of CD and C2. They can also be differentiated from measurements of effective temperatures of C I (best profile fits to thermal distributions). Careful inspection of profiles that give high effective temperatures reveals that they are not actually Gaussian but have asymmetries and shifts that can be correlated to energy distributions expected for physical sputtering. Examples of all these applications are discussed in this review. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1525431

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Characterizing edge plasmas is an important issue for a better control of the plasma wall interaction, and the recycling of thermonuclear fuel. We use line profiles emitted by hydrogen isotopes, helium and impurity ions, as a non intrusive probe for diagnosing the density and temperature of edge particles. An analysis of line wings of D&agr; has been performed with the aim of investigating the dynamics of edge particles. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1525432

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Zeeman spectroscopy is a valuable tool both for diagnostic purposes, and for more fundamental studies of atomic and molecular processes in the boundary region of magnetically confined fusion plasmas (B≃ 1 to 10 T). The method works well when the Zeeman (Paschen‐Back) effect plays an important, or dominant, ro⁁le in relation to other broadening mechanisms (Doppler, Stark, resonant excitation transfer) in determining the spectral line shape. For impurity species identification and temperature determination, Zeeman spectroscopy has advantages over charge‐exchange recombination spectroscopy from highly excited radiator states, since spectral features practically unique to the species under investigation are analysed. It also provides useful information on probable mechanisms of line production (e.g. sputtering mechanisms, electron impact‐induced dissociative excitation from molecules in the edge plasma), and on the temperature evolution of lower charge states in the process of convection inwards or diffusion outwards from the hotter plasma interior. Where different physical processes are responsible for different sections of the line profile — especially in the case of hydrogen isotopes — Zeeman spectroscopy can provide a set of characteristic temperatures for each section. The method is introduced in both passive and active spectroscopy, and general principles of the Zeeman effect are discussed with special reference to re´gimes of interest for the tokamak. Relevant physical processes (sputtering mechanisms, electron impact‐induced dissociative excitation from molecules in the edge plasma, and ion‐atom collisional heating mechanisms) are illustrated by sample spectra. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1525433

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Plasmas in edge regions of tokamaks can be very optically thick to hydrogen lines. Strong line radiation introduces a non‐local coupling between different regions of the plasma and can significantly affect the ionization and energy balance. These effects can be very important, but they are not included in current edge plasma simulations. We report here on progress in self‐consistently including the effects of a magnetic field, line radiation and plasma transport in modeling tokamak edge plasmas. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1525434

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

In previous theoretical investigations we found that two‐photon Doppler‐free laser‐induced fluorescence (TPDF‐LIF) in the Lyman‐&agr; line of the hydrogen isotopes may provide a diagnostic for magnetically confined fusion plasmas, in particular for the determination of the deuterium/tritium density ratio. The results obtained in these investigations were based on a quasi‐stationary treatment of TPDF‐LIF. So far, however, 243‐nm laser radiation with sufficient intensity has only been generated as pulsed radiation with pulse lengths not much longer than the decay time of the fluorescence. Moreover, under suitable conditions short‐pulse excitation may be more efficient than quasi‐stationary excitation. For both reasons we have extended our treatment to include pulsed TPDF‐LIF. Numerical calculations for representative plasma parameters show that up to about twice as many fluorescence photons as with quasi‐stationary operation can be obtained with suitable laser pulse lengths and intensities. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1525435

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

The far wings of intense D&agr;lines measured at the edge of the Tore Supra Tokamak are found to exhibit a power‐law behavior. The characteristic exponent is not far from two. Since the low density rules out thermal Stark broadening, we discuss non thermal effects which may arise from the edge plasma drift‐wave turbulence. We suggest that both the Stark and the Doppler profile could be affected by the turbulence. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1525436

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

A Stark line shape code has been coupled to a collisional‐radiative model and to an analytical model for the merging into the continuum of the Balmer lines. The coupled codes have been used for temperature and density diagnostics of detached plasmas. In contrast with the occupation probability and the lowering of the continuum edge approaches, the analytical line merging model used here consists in the use of Lorentzian profiles for highly excited Balmer transitions of deuterium. In addition, high‐n helium lines (1s2p‐1snl) up ton=12 observed in the JET divertor have been preliminary analyzed. The intensities of these experimental helium lines decrease more rapidly with the upper state nlthan the intensities calculated with state populations at local thermodynamic equilibrium (LTE). © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1525437

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Measurements of the spectrum ofFe24+in the 1.845 Å to 1.885 Å range obtained on the EBIT‐I electron beam ion trap at Lawrence Livermore National Laboratory were used for determining the radiative lifetime of the 1s2p1P1excited state. The spectrum contains electric dipole forbidden transitions at 1.855Å (“x”) and 1.868Å (“z”) whose lineshape is well represented by a Gaussian line profile and is assumed to be due primarily to Doppler and instrumental broadening. The Gaussian contribution is assumed to be the same for all lines in the spectrum. This assumption simplifies the problem when considering a more complex combination of broadening mechanisms. For allowed transitions such as 1s2p1P1→ 1s21S0, “w”, at 1.850 Å we assume a Voigt profile. In the simplest case this combines both natural (Lorentzian) and Doppler (Gaussian) broadening effects which contribute to the width of the spectral line. With the Gaussian contribution determined from lines “x” and “z”, deconvolving the Gaussian from the Voigt profile gives the natural line width. This then is directly related to the radiative lifetime of the 1s2p1P1excited level. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1525438

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Opto‐galvanic spectra of the Doppler‐broadened line profiles of H&agr;have been obtained in the cathode fall of a low pressure gas discharge in order to determine the local electric field strength by comparison with calculated Stark‐profiles. Small but significant differences between the experimental and the theoretical profiles caused us to i) repeat the calculations with a second computer code to check the consistency of the respective results and ii) to repeat the measurements with deuterium instead of hydrogen to look for a possible influence of the hyper‐ fine‐structure. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1525439

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

The aim of this paper is to discuss in detail the schemes for electric field measurements in low density plasmas via Stark‐splitting of the first two hydrogen resonance lines. Beyond it, we have proved by experiment that advanced UV‐laser spectrometers, especially developed for two‐photon spectroscopy of plasmas, are well suited for this purpose. As a first demonstration at low electric fields, simple opto‐galvanic detection was chosen for measuring the Stark‐splitting of the Doppler‐free 1S‐2S and 1S‐3S/D two‐photon transition of atomic hydrogen produced by thermal dissociation in a small reference cell. In addition, we have performed measurements in a hollow cathode discharge which provides higher electric fields in its cathode fall region and the 1S‐2S spectrum was detected spatially resolved by means of an opto‐galvanic signal and polarization spectroscopy as well. Finally, another detection scheme, namely two‐photon induced Balmer‐&agr; fluorescence applied as sheet diagnostic will be described. © 2002 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1525440

出版商:AIP    

年代:1902

数据来源: AIP