L. K. Huang

Soft X-ray bands of highly ionized tungsten, gold and lead emitted by the TEXT tokamak plasma☆

Spectra of highly ionized tungsten, gold and lead emitted from the TEXT tokamak have been recorded in the 20–70 A range by means of a grazing incidence, time-resolving spectrograph. The narrow and bright emission bands centered around 40, 45 and 50 A in Pb, Au and W respectively, and bands of lesser intensities at lower wavelenghts, are emitted by a very large number of superimposed lines originating from transitions of the type 4d104fn−4d94fn+1, 4d104fn−4d94fn5p and 4fn−4fn−15l (l=d, g). The isoelectronic analysis shows that at the electron temperatures prevailing in the present experiment, Te≈800 eV, there are no contributions to the bands from ions having a 4p64dn ground state. This, together with the experimental measurement of the electron temperature profile, indicates that the heavy ion impurity distribution in the tokamak plasma is very close to ionization equilibrium.

Scanning polarimeter for measurement of the poloidal magnetic field in a tokamak

The internal magnetic field in a magnetically confined plasma may be deduced from the analysis of circular polarization of spectral lines emitted by the plasma. The theory of the measurement and a detailed design of a polarimeter constructed to measure the poloidal field profile in the Texas Experimental Tokamak (TEXT) are presented. The instrument measures the difference between left‐hand and right‐hand circularly polarized line profiles, a quantity directly proportional to the magnetic field component in the direction of observation. The high throughput of the Fabry–Perot interferometer employed in this design, combined with efficient light‐collecting optics and lock‐in detection of the polarization signal, allows measurement of the fractional circular polarization of the magnetic dipole line Ti xvii 3834 A with an accuracy on the order of 10−3. The line‐of‐sight averaged poloidal field is determined with uncertainty as small as 50 G. The line emission used in the present measurement is not well localiz...

Laboratory test of a LSM‐based narrow bandpass and high throughput camera for Tokamak plasma imaging between 100 and 200 Å

A narrow‐bandpass (∼7 A) and high‐throughput (f/5.5) extreme ultraviolet (XUV) camera using layered synthetic microstructure (LSM) coated optics has been built and tested at the Johns Hopkins University laboratory in order to image tokamak plasma emission between 100 and 200 A. The LSM camera was tested with a Penning ionization discharge emission source. The test measures the spectral bandpass, the spatial resolution, and the relative photosensitivities. The XUV camera will be used to measure the O vi 150 A line brightness on the Phaedrus‐T tokamak with a tangential view to investigate the impurity transport.

Measured conversion efficiencies of P45, paraterphenyl, tetraphenyl butadiene, and sodium salicylate phosphors in the soft-x-ray wavelength range

The measured conversion efficiencies at 9.89, 23.6, 44.7, and 160 Å of P45 phosphor screens, as well as those of paraterphenyl, tetraphenyl butadiene, and sodium salicylate at 9.89, 44.7, and 67.6 Å, are presented. The conversion efficiency is defined as the ratio of photoelectrons ejected from the photocathode of a visible detector, which are excited by the scintillated photons that are emitted from the phosphor in a solid angle of 2π, to the number of soft-x-ray photons incident on the phosphor. The effect of the phosphors thickness on the conversion efficiency was studied. The P45 phosphor converts the soft-x-ray photon (10-200 Å) into an order of magnitude more visible photons than the low-Z phosphors. The P45 phosphor screen used in conjunction with a photomultiplier tube offers a soft-x-ray photodetector with a conversion efficiency that ranges from 0.5 at 160 Å to 12 at 9.89 Å and a high electronic gain.

A soft x‐ray multilayer mirror scanning monochromator for magnetically confined fusion plasmas

A high throughput scanning soft x‐ray monochromator that uses a flat multilayer mirror in a near normal incidence configuration was built and tested in the Plasma Spectroscopy laboratory at Johns Hopkins University and operated on the DIII‐D tokamak. Depending upon the mirror used, the monochromator covers the range 10–170 A, with a resolution of 0.25 to 10.8 A. The instrument was photometrically calibrated between 10 and 45 A. Spectra from DIII‐D were obtained under a variety of discharge conditions over the entire range of the instrument. This paper describes the monochromator, the photometric calibration, and presents initial results.

Narrow bandpass layered synthetic microstructure‐based pinhole camera to image a tokamak plasma in H‐like carbon emission at 34 Å

The layered synthetic microstructure (LSM) technology has made two‐dimensional soft x‐ray imaging of a tokamak plasma in a single impurity spectral line emission feasible. The curved LSM is used both as an optical filter, with a bandpass in the range of interest on the order of 1.5 A, and as a focusing optic. A detailed design of a narrow bandpass curved LSM‐based pinhole camera, which will image the the region from the scrape‐off layer 26 cm into the plasma in the DIII‐D tokamak plasma in C vi Lyman α emission at 34 A, will be presented.

Plasma imaging in the XUV wavelength range (175 Å) using curved layered-synthetic-microstructure coated surfaces

A recently constructed calibration facility utilizing a Manson soft x-ray line source in the wavelength range of 8 - 114 angstroms and a Penning ionization discharge (PID) in the 100 - 350 angstroms range, has been used to map the reflectivity across a curved layered synthetic microstructure (LSM) coated surface. This calibrated mirror was also used to image the Al III emission ((lambda) equals 170 - 175 angstroms) from the PID.

A polarimeter for localized continuous measurement of the poloidal magnetic field in a tokamak

A polarimeter for the circular polarization of Zeeman‐split spectral line emissions has been developed to measure the poloidal magnetic field in tokamak plasmas. The Li I 6708 A line originating from a monoenergetic lithium beam provided a localized spectral source. In the polarimeter, interference filters of narrow bandpass were set at the peak wavelength of the circular polarization, enabling the measurement to be continuous and sensitive.

A feasibility study of an XUV spectroscopic measurement of electron density and temperature fluctuations in tokamak plasma center (abstract)

With the advent of layered synthetic microstructure (LSM) technology, high‐reflectivity narrow‐band XUV filters, and LSM coated gratings become available, thus making possible normal‐incidence high‐throughput devices in the 10–200 A range. Therefore it may become feasible to measure rapid (τ∼10−6 s) fluctuations of the electron density and temperature in the hot central region of the tokamak plasma, by measuring fluctuations on the L‐shell charge‐state line emissions. We present and discuss the linear dependence of correlated line intensity fluctuations on local Te and ne. Various configurations for the proposed measurements are presented and evaluated.

Use of narrow bandpass optical filters in Zeeman polarimetry for poloidal field measurements on the Texas Experimental Tokamak (abstract)

Very narrow bandpass optical fibers have been used in Zeeman polarimetry of Li I 6708 A line emission from a monoenergetic lithium beam as a spectral source makes the measurement well localized. Initial experimental results for measurements of q0 will be presented.