摘要:

Since the beginning of magnetic fusion research, reducing the impurity level in experiments has been strongly correlated with successful achievement of high performance plasmas. One of the most important examples of this was the recognition that the use of tungsten as a plasma facing material and the associated high radiative losses were responsible for the poor performance of the ORMAK and PLT tokamaks. Tungsten was replaced with graphite and the central plasma temperature in PLT increased a factor of ten. The magnetic fusion program is now planning on constructing an ignited fusion experiment. One of the major design issues is the reduction of the peak heat loads on the plasma facing components. It appears that the carefully controlled introduction of impurities can lead to a solution of the problem. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51323

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

X‐ray spectra of 2l‐nl′ transitions with 3≤n≤12 in the row five transition metals zirconium (Z=40), niobium (Z=41), molybdenum (Z=42) and palladium (Z=46) from charge states around neonlike have been observed from Alcator C‐Mod plasmas. Accurate wavelengths (±.2 mA˚) have been determined by comparison with neighboring argon, chlorine and sulphur lines with well known wavelengths. Line identifications have been made by comparison toabinitioatomic structure calculations, using a fully relativistic, parametric potential code. For neonlike ions, calculated wavelengths and oscillator strengths are tabulated for 2p‐nd transitions in Y (Z=39), Tc (Z=43), Ru (Z=44) and Rh (Z=45) with n=6 and 7. The magnitude of the configuration interaction between the (2p5)1/26d3/2J=1 level and the (2p5)3/27d5/2J=1 levels is demonstrated as a function of atomic number for successive neonlike ions. Measured spectra of selected transitions in the aluminum‐, magnesium‐, sodium‐ and fluorinelike isosequences are also shown. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51329

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Research on TEXT from inception of operation in 1980 to its end in 1995 resulted in major contributions to the general advance of both plasma physics and atomic physics that has been made using tokamaks. In some experiments, spectroscopy was applied to understand the physics of transport. These experiments identified the role of turbulence in particle transport and made significant progress toward identifying the source of the turbulence. TEXT was also an excellent platform for the generation of atomic data for investigation of atomic structure and electron‐ion collisions. The atomic physics applications have increased the availability of atomic data and the accuracy of the atomic database. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51314

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The EUV spectral region contains a wealth of plasma diagnostics for stellar coronae (Te∼5×105to 2×107K). Of particular importance for understanding coronal structure are the observable emission lines of highly ionized iron (Fe VIII—XXIV), which allow the determination of electron temperatures (and the detailed temperature distributions) and electron densities. Comparison of continuum emission and lines from other elements with the iron lines provides diagnostics for relative abundances in the stellar atmospheres. Recent work in both solar and stellar coronal physics has greatly changed our picture of the corona, with EUV spectroscopy providing critical pieces of the puzzle. Here we discuss some important new spectral diagnostic results, examining in particular the quality of the theoretical atomic physics used in the data interpretation. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51322

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

One of the dominant forms of astronomical line emission in the 6 A˚ to 18 A˚ spectral region is line emission produced byn=n′ ton=2 transitions in Fe16+to Fe23+(i.e., FeL‐shell n‐2 line emission). Using the Lawrence Livermore National Laboratory electron beam ion trap (EBIT) facility, we have carried out a number of measurements designed to address astrophysical issues concerning FeL‐shell line emission. Desired ions are produced and trapped using the nearly monoenergetic electron beam of EBIT Trapped ions are collisionally excited and the resulting X‐ray line emission detected using Bragg crystal spectrometers. We have recently completed a line survey of FeL‐shell 3‐2 line emission. The line survey will allow a more reliable accounting of line blending in astronomical spectra. We have now begun a series of broadband, high resolution line ratio measurements. These measurements are designed to benchmark atomic calculations used in astronomical plasma emission codes and also for comparison with X‐ray spectral observations of astronomical objects. Initial measurements have been carried out in Fe23+. Preliminary results agree with distorted wave calculations to within 20 percent and better. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51341

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This paper describes the various types of ionization equilibrium applicable to the modeling of astrophysical plasmas, particularly collisional ionization and photoionization equilibrium. Modern astrophysical studies rely heavily on atomic data for derivation of physical parameters from observations, as well as for theoretical modeling. I will describe the current state of atomic data for two areas: (1) Abundances and absorption‐line oscillator strengths; (2) Hot plasma ionization and emission. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51324

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We review results of the first demonstration of large soft‐x‐ray amplification in a discharge‐created plasma. A fast compressive capillary discharge was utilized to create elongated plasma columns with length‐to‐diameter ratios in excess of 500:1 having the required density and temperature for soft‐x‐ray amplification by collisional excitation of Ne‐like ions. The most recent measurements, conducted in capillary discharges up to 20 cm in length, have yielded an amplification of ∼exp(14) in the 46.9 nm line of Ne‐like argon. The dependence of the laser line intensity with discharge parameters and the dynamics of the capillary discharge plasma column under lasing conditions are reported. Prospects for laser operation at shorter wavelengths are discussed. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51325

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The observation of multiple Xe 2p‐vacancy production occurring in plasma channels generated with subpicosecond 248 nm radiation can be put in correspondence with multiple electron processes involved in ion‐atom collisions. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51326

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report the generation of both incoherent and coherent short‐wavelength radiation which results from the unique interaction of an intense laser pulse with atomic clusters. The atomic clusters are produced by a pulsed gas jet. In the higher intensity regime (1015–1017W/cm2) the laser pulse ionizes and heats the atomic cluster resulting in a novel plasma with ∼1 keV electron temperatures. This plasma strongly emits incoherent x‐rays in the 20–500 A˚ wavelength range. Using laser pulses at intensities of 1014W/cm2, high order harmonics are created which, when compared to single atom gases, yield a higher appearance intensity for a given harmonic order, stronger non‐linear dependence of harmonic signal on laser intensity, higher‐order harmonics, and reduced saturation of the harmonic signal at high laser intensity. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51327

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This paper reviews the recent developments in the measurement of absolute partial cross sections for the ionization and dissociative ionization of molecules and free radicals of interest to low‐temperature processing plasmas. In addition to a discussion of selected recent results, this paper will highlight experimental challenges such as the need to develop techniques for the production of unstable target species such as free radicals and the influence of discrimination effects arising from the formation of energetic fragment ions on the measurement of dissociative ionization cross sections. Lastly, an attempt is made to relate measured molecular ionization cross sections to realistic plasma applications. As an example, we will discuss a collision‐induced decomposition scheme of the Si‐organic molecule tetramethylsilane (TMS), which is used in plasma deposition applications, based on recently measured partial ionization cross sections. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.51338

出版商:AIP    

年代:1996

数据来源: AIP