K. M. Young

Tokamak Fusion Test Reactor x‐ray imaging diagnostic

An array of 64 silicon surface‐barrier diodes on a circular arc view Tokamak Fusion Test Reactor (TFTR) plasmas through a slot aperture to provide poloidal imaging of x‐ray emission in the 200 eV–15 keV range. Information is inferred on magnetohydrodynamic (MHD) instabilities, disruptions, radiation, impurity transport, electron temperature, and electron thermal conductivity. Spatial resolution is 2.5 cm. Movable absorber foil arrays provide energy selection. Preamplifier–amplifier pairs have gains of 0.05–100 V/μA. Two outputs are provided with (1) 40‐, 80‐, and 300‐Hz and (2) 40‐, 80‐, and 600‐kHz filtering. The signals are digitized at rates up to 500 kHz and stored in 128K (total system) memory. Foils, gains, and filters are selectable from the control room by a computer.

Periscope-camera system for visible and infrared imaging diagnostics on TFTR

An optical diagnostic consisting of a periscope which relays images of the torus interior to an array of cameras is used on the Tokamak Fusion Test Reactor (TFTR) to view plasma discharge phenomena and inspect the vacuum vessel internal structures in both the visible and near‐infrared wavelength regions. Three periscopes view through 20‐cm‐diam fused‐silica windows which are spaced around the torus midplane to provide a viewing coverage of approximately 75% of the vacuum vessel internal surface area. The periscopes have u2009f/8 optics and motor‐driven controls for focusing, magnification selection (5°, 20°, and 60° field of view), elevation and azimuth setting, mast rotation, filter selection, iris aperture, and viewing port selection. The four viewing ports on each periscope are equipped with multiple imaging devices which include: (1) an inspection eyepiece, (2) standard (RCA TC2900) and fast (RETICON) framing rate television cameras, (3) a PtSi CCD infrared imaging camera, (4) a 35‐mm Nikon F3 still camer...

Tokamak Fusion Test Reactor horizontal high‐resolution Bragg x‐ray spectrometer

A bent quartz‐crystal spectrometer of the Johann type with a spectral resolution of λ/Δλ= 10000–25000 is used on the Tokamak Fusion Test Reactor (TFTR) to determine central plasma parameters from the spectra of helium‐like and lithium‐like metal impurity ions (Ti, Cr, Fe, and Ni). The spectra are observed along a central radial chord and are recorded by a position‐sensitive multiwire proportional counter with a spatial resolution of 250 μ. Standard delay‐line time‐difference readout is employed. The data are histogrammed and stored in 64 K of memory providing 128 time groups of 512‐channel spectra. The central ion temperature and the toroidal plasma rotation are inferred from the Doppler broadening and Doppler shift of the Kα lines. The central electron temperature, the distribution of ionization states, and dielectronic recombination rates are obtained from satellite‐to‐resonance line ratios. The performance of the spectrometer is demonstrated by measurements of the Tiu2009xxi Kα radiation.

Tokamak Fusion Test Reactor prototype x‐ray pulse‐height analyzer diagnostic

The x‐ray pulse‐height analysis (PHA) diagnostic uses a liquid‐nitrogen cooled array of 5 Si(Li) and one HpGe detectors to do time‐resolved (5–100 ms) x‐ray spectroscopy of the central horizontal chord of the Tokamak Fusion Test Reactor (TFTR) plasmas in the 1–50‐keV range. Central electron temperature Te and concentration of medium and low‐Z impurities are derived from the spectra. Remotely selectable absorber‐foil arrays provide selection of the energy range. Fixed and movable aperture arrays allow approximate equalization of count rates in different energy bands and extend dynamic range. Amplifier pulse shapes are approximately triangular. Main amplifier peaking time is 4 μs yielding 230‐eV FWHM at 5.9 keV. Pileup inspection times are selectable at 0.13, 0.4, or 0.9 μs. Throughput is up to 42 kHz. The PHA has been used to study temperature and impurities over a wide range of TFTR operational parameters. Dramatic variations in metal impurities with density, plasma current, and major radius have been obs...

Vertical high-resolution Bragg x-ray spectrometer for the tokamak fusion test reactor

A Bragg x‐ray spectrometer of high spectral resolution (λ/Δλ=10u2009000–20u2009000) which accommodates three crystals and position‐sensitive detectors in the Johann configuration has been installed in the diagnostic basement of the tokamak fusion test reactor (TFTR) for the measurement of radial ion temperature profiles. The ion temperature is derived from the Doppler broadening of Kα‐resonance lines of metal impurity ions, e.g., Ti, Cr, Fe, and Ni, in the helium‐like and hydrogen‐like charge states. The x‐ray diffraction plane is almost perpendicular to the magnetic axis, but slightly tilted by an angle of 3.8°, which makes it possible to measure poloidal and toroidal plasma rotation velocities of vΘ>5×103 m/s and vΦ>1×105 m/s, from the Doppler shift of spectral lines. Results obtained from the observation of TiXXl Kα‐line spectra with a 220‐silicon crystal of a 2d spacing of 3.8400 A and a curvature radius of 11.05 m are reported.

Fast multichannel electron temperature diagnostic for TFTR using x‐ray imaging

The TFTR x‐ray imaging system (XIS) is an array of 64‐Si surface barrier diodes which image the plasma poloidally. Special absorber foils have been installed to permit measurement of electron temperature Te with <100‐μs time resolution along 10–30 chords. The technique uses the ratio of x‐ray fluxes transmitted through two different foils, which depend mainly on Te. Simulations show that strong line radiation can change this ratio. To correct for these effects, special beryllium–scandium filters are employed to select the line‐free region between 2 and 4.5 keV. Separate filter pairs allow correction for strong L line radiation as well as Ti or Ni Kα emission. The Te determination is based on simulations. Comparison of results with Te values from the electron–cyclotron emission and x‐ray pulse height analysis diagnostics is presented.

TFTR vertical x‐ray imaging system

A vertically viewing x‐ray imaging system (XIS) has been designed to complement the existing 64‐channel horizontal system on the tokamak fusion test reactor (TFTR) and enhance measurements of soft x‐ray emissivity, plasma (major) radial position, and magnetohydrodynamic (MHD) phenomena. System parameters have been selected to provide adequate signal strength and spatial resolution while permitting a substantial size and cost reduction with respect to the horizontal system. The compact, helium filled x‐ray camera employs four eight‐channel silicon detector modules and views the plasma through a 3‐mil‐thick beryllium window, providing 6‐cm position resolution at the center. An x‐ray absorber foil changer permits energy selection to match the horizontal XIS. Lead and hydrogenous shielding reduce noise from thermonuclear neutrons and associated gamma rays.

An overview of ITER diagnostics (invited)

The requirements for plasma measurements for operating and controlling the ITER device have now been determined. Initial criteria for the measurement quality have been set, and the diagnostics that might be expected to achieve these criteria have been chosen. The design of the first set of diagnostics to achieve these goals is now well under way. The design effort is concentrating on the components that interact most strongly with the other ITER systems, particularly the vacuum vessel, blankets, divertor modules, cryostat, and shield wall. The relevant details of the ITER device and facility design and specific examples of diagnostic design to provide the necessary measurements are described. These designs have to take account of the issues associated with very high 14 MeV neutron fluxes and fluences, nuclear heating, high heat loads, and high mechanical forces that can arise during disruptions. The design work is supported by an extensive research and development program, which to date has concentrated o...

Measurements with vertically viewing charge exchange analyzers during ion cyclotron range of frequencies heating in TFTR

The utility of charge exchange neutral particle analyzers for studying energetic ion distributions in high‐temperature plasmas has been demonstrated in a variety of tokamak experiments. Power deposition profiles have been estimated in the Princeton large torus (PLT) from particle measurements as a function of energy and angle during heating in the ion cyclotron range of frequencies (ICRF) and extensive studies of this heating mode are planned for the upcoming operational period in the tokamak fusion test reactor (TFTR). Unlike the horizontally scanning analyzer on PLT, the TFTR system consists of vertical sightlines intersecting a poloidal cross section of the plasma. A bounce‐averaged Fokker–Planck program, which includes a quasilinear operator to calculate ICRF‐generated energetic ions, is used to simulate the charge exchange flux expected during fundamental hydrogen heating. These sightlines also cross the trajectory of a diagnostic neutral beam (DNB), and it may be possible to observe the fast ion tai...

Physics Guidelines for the Compact Ignition Tokamak

The goal of the Compact Ignition Tokamak (CIT)d program is to provide a cost-effective route to the production of a burning deuterium-tritium plasma, so that alpha-particle effects may be studied. A key issue to be studied in the CIT is whether alpha power behaves like other power sources in affecting tokamak plasma confinement. The program is managed by the Princeton Physics Laboratory and includes broad community involvement. Guidelines for the preliminary design effort have been provided by the Ignition Technical Oversight Committee in discussion with the tokamak community. The reference design is a tokamak with a high filed (10 T), high current (10 MA), poloidal divertor, and liquid-nitrogen-cooled coils. It is a small, high-power-density device of the type proposed by Bruno Coppi (MIT). It has a major radius of 1.23 m, a minor radius of 0.43 m, and plasma elipticity of 1.8. This paper reviews the aims of the program and the basis for the physics guidelines. The role of the CIT in the longer-term tokamak program is briefly discussed. 23 refs., 9 figs., 1 tab.