D. Dimock

Multichannel Thomson scattering systems with high spatial resolution (invited)

Thomson scattering systems capable of providing snapshot profiles of electron temperature and density with high spatial resolution (>50 points) have become routine diagnostics on the Princeton large torus (PLT), Princeton divertor experiment (PDX), and tokamak fusion test reactor (TFTR) tokamaks. The design parameters of these systems are compared. Particular attention is given to describing those new components and techniques which have contributed most to improved data quality and reliability in the ten‐year evolution of these systems. Examples of recent TFTR Te(R) and ne(R) profiles are presented.

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  f/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...

A compact Thomson scattering system

We have made and installed a multipulse Nd:YAG Thomson scattering system for measuring electron temperature and density profiles in the throat of the divertor of the Alcator C-Mod machine. The observing head is located in the vacuum vessel in a re-entrant chamber. It is optically fast and very compact. A system for providing feedback to maintain the laser beam alignment is a part of the observing head assembly. The head is designed to minimize eddy currents, and have a very rigid adjustable mounting to resist the forces generated by the eddy currents during plasma disruptions. A four wavelength polychromator using 25 element avalanche photodiode arrays for spatial resolution has been designed and built for this system. Two of these polychromators and a single observing head will provide 50 spatial resolution elements.

The JFT-2M TV Thomson Scattering System

It is the purpose of this report to present a detailed description of the TV Thomson scattering system on the JFT-2M tokamak, produced through the collaboration of the Princeton Plasma Physics Laboratory (PPPL), and the JFT-2M group of the Japan Atomic Energy Research Institute (JAERI).

Alignment of TFTR Thomson scattering system

A technique is described for maintaining the highly precise alignment needed for accurate density profile measurements with the TFTR Thomson scattering system. The method uses the transverse coherence of the fiber bundles in the collection optics to encode the alignment information in the spatial distribution of the scattered light signal. A scheme for decoding this information is demonstrated and the limitations of this technique are discussed.

A large aperture laser triggered intensified charge coupled device using second-harmonic laser light triggering

For application to a ruby laser Thomson scattering system, we have developed a laser triggered intensified charge coupled device (CCD) with 80 mm aperture, two stages of intensification, and 80 ns gating. To improve the dynamic range, the CCD is cooled and read out slowly (1 s). To obtain a good extinction ratio (>1.1×107), the zoom electrode of the first intensifier is gated using a ∼10 kV laser triggered spark gap. The stability of this spark gap has been greatly improved by frequency doubling the laser trigger light.

The PBX-M Thomson scattering system

The PBX‐M Thomson scattering system is reviewed after its first 9 months of operation. The system measures Te(R) and ne(R) at 55 radial points on the horizontal midplane with a spatial resolution of ≤1.1 cm. The scattered light is collected by a Bouwers concentric mirror system and imaged onto 12‐m‐long fiber bundles. A composite entrance slit is used to optimize the system performance. The synchronization between the scattered light and detector gate is done via a laser‐triggered spark gap. A penetration in the indentation coil allows the (ruby) laser beam to be dumped away from the plasma chamber. Other aspects of the system will be discussed.

Angular dependence of transmissivity in a high-pass optical filter for Thomson scattering measurement

The angular dependence of a high-pass optical filter for Thomson scattering is measured. Increasing the angle of incidence decreases the transmittance on the long-wavelength side in the experimental curve (the wavelength of 80% transmissivity shifts from 690 nm to 620 nm, as the angle of incidence goes from normal incidence to 45 degrees).

Levitation and Stabilization of a Single Particle by Use of Negative Feedback

An optical sensing and electrical feedback system is described which will damp out the orbital motion of a particle levitated in a three‐phase electric field. This eliminates the necessity of introducing a background gas for this purpose.

Temperature Compensation of Sine-Drive Monochromators*

It is shown that the effects of thermal expansion of the grating and sine drive in a monochromator can be made to cancel exactly by proper mounting of the drive screw, and by choosing the material of the drive arm such that its thermal coefficient of expansion just equals the sum of the coefficients of the grating and drive screw.