AN OPTICAL PUMPING SCHEME FOR EUV LASERS IN TWO COUPLED MEDIA USING A QUASI-CONTINUUM EMITTED BY RARE-EARTH ELEMENTS

Dans la présente étude on propose l'utilisation de bandes étroites de rayonnement quasi-continu émis par les éléments de terres rares dans le domaine 60-100Å, afin d'effectuer le pompage optique d'ions chargés produits indépendamment au sein d'un milieu couplé. Les transitions laser se situeraient daus le domaine XUV (λ > 300Å). Le milieu de pompage proposé consiste en une étincelle sous vide à faible inductance et à courant élevé. Les ions des éléments du Lanthane au Dysprosium possédant une sous - couche 4dk ouverte, émettent dans l'étincelle un très grand nombre de raies correspondant aux transitions 4p64dk - 4p54dk+1 et 4dk-4dk-14f, à l'intérieur d'une bande de 2 a 4 Å de large. Par ailleurs, les degrés d'ionisation relativement bas d'éléments de faible Z du milieu laser seront obtenus à l'aide de fils explosants enrobés. Ce dernier type de source devrait permettre l'obtention de plasmas présentant un vaste domaine de densité à des températures relativement basses, afin de pouvoir minimiser les processus de transfert collisionnel ainsi que l'élargissement Doppler des raies considérées. On propose en particulier un schéma faisant appel à la bande émise par le Cérium, centrée à 89Å, afin de réaliser le pompage vers les niveaux 2p54p de Si V. Les transitions laser 4p → 3s prédites doivent apparaître dans la région 300-400Å.The present work proposes the use of narrrow bands of quasi-continuum radiation emitted by rare earth elements in the 60 - 100 Å range, in order to optically pump charged ions obtained separately in a coupled medium. The lasing transitions would be in the XUV range (λ > 300 Å). The proposed pumping medium is a low-inductance high-current vacuum spark. Ions of the elements Lanthanum to Dysprosium having an open 4dk sub-shell, emit a very large number of lines belonging to the 4p64dk - 4p54dk+1 and 4dk-4dk-14f transitions, within a 2 to 4 Å width band. Relatively low ionization states of low Z elements in the lasing medium are produced by means of an embedded exploding wire (EEW). The EEW source will enable to obtain plasmas having a wide range of densities and relatively low temperatures - thus minimizing both collisional transfer processes and Doppler broadening of the lines of interest. A scheme, using a Cerium band centered at 89Å to pump the 2p54p levels of SiV is proposed. The lasing 4p → 3s transitions will be emitted in the 300 - 400 Å region

ANALYSIS OF QUASI-CONTINUUM BANDS AND LINE SPECTRA OF HIGHLY IONIZED W and Au

Dans la présente étude, on montre que l'étroite bande de rayonnement quasi-continu émise entre 40 et 100 Å par le plasma d'éléments lourds (Z > 50) dans des conditions fort différentes (plasma créé par laser, étincelle sous vide, ou Tokamak) provient du mélange d'un grand nombre de raies correspondant aux transitions Ɗn=0, n=4. Les calculs des faisceaux de transitions non résolues (UTA) montrent, en effet, que pour près de vingt degrés d'ionisation consécutifs, les transitions de résonance sont émises dans un domaine très étroit de longueurs d'onde. Les calculs, présentés ici pour le cas de l'or et du tungstène ont été effectués à l'aide de nouvelles formules UTA qui incluent les effets de mélange de configurations. Cette étude permet l'extension des résultats obtenus précédemment pour les terres rares.The spectra of heavy elements (Z > 50) observed in laser-produced plasmas, vacuum sparks and Tokamaks are characterized by a strong quasi-continuum band emitted in the 40-100 Å range. This band originates from the blending of a great number of lines emitted in the Ɗ n=0, n=4 transitions. Indeed, the Unresolved Transition Array (UTA) computations show that for about twenty adjacent ionization States, the mean wavelength of the main resonance transitions remains in a very small wavelength range. The results of these computations are given here for tungsten and gold. The computations rely on new UTA formulae which include the effect of configuration mixing. This work extends the previous results obtained for the rare-earths spectra

SPACE RESOLVED MEASUREMENTS OF THE EMISSION OF INTERMEDIATE AND HIGH IONIZATION STATES OBTAINED FROM VACUUM SPARK PLASMAS USING XUV MULTILAYER MIRRORS AND A RbAP CRYSTAL

On détermine l'étendue spatiale des régions émettant les raies spectrales des degrés d'ionisation intermédiaires (tels que ceux de la séquence de NeI) et élevés (séquence de Li I) des éléments . Ti, V, Fe, Co et Ni au sein d'une étincelle sous vide à faible inductance et à courant élevé, en utilisant des miroirs à couches multiples ou à l'aide d'un cristal RbAP. Les spectres ont été enregistrés dans le domaine 10 à 30 Å. La conclusion principale de cette étude est que la région d'émission des degrés d'ionisation intermédiaires est de l'ordre de 200 microns, tandis que les états d'ionisation extrêmes sont formés dans le plasma ponctuel produit par striction.The spatial extent of the regions from which lines of the intermediate, NeI-like and high Li I-like ionization states of Ti, V, Fe, Co, and Ni, are emitted in a low inductance high-current vacuum spark plasma, has been determined using multilayer mirrors and a RbAP crystal. The spectra have been recorded in the 10-30 Å range. The main conclusion of the present work is that the intermediate ionization states are emitted from an extended plasma region, of the order of 200 microns, while the highly ionized states are formed, as it has been previously stated, in the minute plasma pinch

Emission in the 50-80 A region from highly ionized silver in PLT tokamak plasmas

The spectrum of silver emitted by Princeton Large Torus (PLT) tokamak plasmas has been recorded in the 25 to 150 A region by a multichannel time-resolving grazing-incidence spectrometer. Silver atoms have been introduced in the tokamak plasma using the laser blow-off technique. For the first time, lines emitted within the 3p-3d transitions of Ag XXIX, Ag XXX, and Ag XXXI ions, between 50 and 80 A, have been identified

Spectra in the 60 )angstrom) to 345 )angstrom) wavelength region of elements injected into the PLT tokamak

High resolution spectra of the elements Fe, Ni, Zn, Ge, Se, and Mo injected into the PLT tokamak were recorded by the 2-meter Schwob-Fraenkel soft X-ray multichannel spectrometer (SOXMOS). Spectra were recorded every 50 ms during the time before and after injection. The spectral lines of the injected element were very strong in the spectrum recorded immedately after injection, and the transition in the injected element were easily distinguished from the transitions in te intrinsic elements (C, O, Ti, Cr, Fe, and Ni). An accurate wavelength scale was established using well-known reference transitions in the intrinsic elements. The spectra recorded just prior to injection were substracted from the spectra recorded after injection, and the resulting spectrum was composed almost entirely of transitions from the injected element. A large number of ..delta..n + 0 transitions between the ground and the first excited configurations in the Li I through K I isoelectronic sequences of the injected elements were identified in the wavelength region 60 )angstrom) to 345 )angstrom). 33 refs., 5 figs., 1 tab

HIGH RESOLUTION MULTICHANNEL XUV SPECTROMETER WITH A 3-PICOSECOND TIME-RESOLUTION FOR LASER-PRODUCED PLASMAS DIAGNOSTICS

Nous décrivons la réalisation d'un nouveau spectrographe XUV à résolution temporelle dont les performances espérées sont une résolution spectrale de 0.1 Å et temporelle de 3 ps . Cet instrument est constitué d'un spectromètre Schwob-Fraenkel modifié, couplé à une nouvelle caméra électronique à balayage de fente ultra-rapide.A new XUV spectrometer designed to have a time-resolution of 3 ps and a spectral resolution of 0.1 Å is described. It is basically a modified version of a Schwob-Fraenkel spectrometer, which is coupled to a new ultrafast electronic streak camera

SOFT X-RAY SPECTROSCOPY ON THE TFR TOKAMAK

The 2m-grating radius, extreme grazing incidence (1.5°) Schwob-Fraenkel spectrograph was developed at the Racah Institute of Physics (under CEA contract) more than 10 years ago. The first results (using photographie plates) on the TFR tokamak permitted the indentification of the spectrum of highly ionised Mo ions in the 5-50 Å spectral region /1/. Subsequently, the system was modified by J.L. Schwob into a duochromator, using two channeltron electron multipliers independently movable along the Rowland circle. It was thus possible to obtain radial profiles of the emissivities of the strongest lines of the H-and He-like isoelectronic sequences of light impurities in the 18-42 Å spectral range /2/. Recently, the duochromator has been converted into a multichannel spectrometer by equipping it with a microchannelplate (MCP) detector again movable along the Rowland circle. The detector consists of a MgF2 coated, funneled MCP, associated with a phosphor screen image intensifier and coupled by a flexible fiber optic conduit to a 1024 element photodiode array (controlled and read-out by a commercially available PAR-1461 EGG Princeton Applied Research optical multichannel analyser system). The first of this type of detector was developed at Princeton for the PLT and TFTR tokamaks and was described by Schwob et al /3/. An identical system has been installed on TFR, using a 20 µm entrance slit and a 600 groove mm-1 Jobin-Yvon holographic grating. This instrument has been routinely used during the last year of TFR operation to monitor spectra of both intrinsic impurities (C, O, Cr, Fe, and Ni, with traces of Mn, Cl, and S) and purposely injected impurity elements in the 10-330 Å spectral range. The spectrometer has been used in both the spectrographic and the polychromator modes. In the former mode, spectra of highly-ionized, unstudied, heavy elements (injected either by the laser blow-off technique or as gaseous elements) have been obtained /4,5/. In the latter utilization (in which selected individual pixels are read-out as function of time) line radiance evolutions of several different Fe ions have been simultaneously obtained on a single discharge. This has allowed the impurity transport to be modelled /6/ even though the system was not absolutely calibrated, since different ionization degrees have different time evolutions

XUV SPECTROSCOPY IN JET

The 2m extreme grazing incidence XW Schwob-Fraenkel spectrometer has been described in detail [1]. Its use on the TFR tokamak is presented in a parallel paper [2]. The instrument installed on JET differs in that it has two microchannel plates scanning independently two portions of the spectral range from 10 to 335Å. A full scan takes 164 ms, due to the low number of photons. 127 spectra may be taken during a 20s tokamak discharge. The calculated and measured spectral resolution (FWHM) with a 600g/mm Bausch and Lomb grating and 20 µm entrance slit is shown in Fig. 1 for detector positions, y, between 200 and 390 mm (corresponding wavelengths of the central pixels are 85 and 310 Å, respectively)