This article describes the design and performance of a multi-point (200) high repetition rate (4×50 Hz) Thomson scattering diagnostic installed on the Large Helical Device. A unique feature of this system is its oblique back scattering configuration, which enables us to observe the entire plasma region along a major radius on the midplane under a severely restricted port constraint. High throughput collection optics using a mosaic mirror of 1.5 m×1.8 m area yield high quality data even with 0.5 J pulse energy delivered from 50 Hz repetition rate Nd: yttrium–aluminum–garnet lasers. High repetition and high spatial resolution (2–4 cm) of the system enable us to study island evolution in the plasma.

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Design and performance of the Thomson scattering diagnostic on LHD

A transport code (TRANSP) is used to simulate future deuterium-tritium (DT) experiments in TFTR. The simulations are derived from 14 TFTR DD discharges, and the modelling of one supershot is discussed in detail to indicate the degree of accuracy of the TRANSP modelling. Fusion energy yields and alpha particle parameters are calculated, including profiles of the alpha slowing down time, the alpha average energy, and the Alfven speed and frequency. Two types of simulation are discussed. The main emphasis is on the DT equivalent, where an equal mix of D and T is substituted for the D in the initial target plasma, and for the D0 in the neutral beam injection, but the other measured beam and plasma parameters are unchanged. This simulation does not assume that alpha heating will enhance the plasma parameters or that confinement will increase with the addition of tritium. The maximum relative fusion yield calculated for these simulations is QDT ~ 0.3, and the maximum alpha contribution to the central toroidal β is βα(0) ~ 0.5%. The stability of toroidicity induced Alfven eigenmodes (TAE) and kinetic ballooning modes (KBM) is discussed. The TAE mode is predicted to become unstable for some of the simulations, particularly after the termination of neutral beam injection. In the second type of simulation, empirical supershot scaling relations are used to project the performance at the maximum expected beam power. The MHD stability of the simulations is discussed

/pdf/simulations-of-deuterium-tritium-experiments-in-tftr-3eid0g99gb.pdf

Simulations of deuterium-tritium experiments in TFTR

In recent years, the method of incoherent Thomson scattering has been applied to make measurements of electron properties of glow discharges used for industrial applications. These plasmas have electron density of the order of and electron temperature of a few eV. This paper reviews the recent progress in this research area. Details of the experimental systems are given and examples of measurements made in several different types of glow discharges are presented. A method in which Thomson scattering is combined with Rayleigh scattering to provide direct measurements of the neutral density is also described and an example of measurements is given. The electron velocity and energy distribution functions are also an important property of these plasmas, and the extent to which Thomson scattering can measure the distribution function is discussed. Future trends for Thomson scattering in glow discharges are also discussed.

https://iopscience.iop.org/article/10.1088/0741-3335/40/7/002/pdf

Diagnostics of low-density glow discharge plasmas using Thomson scattering

In order to get precise local electron density information from chordal interferometric measurements of a tokamak plasma, a self-consistent and reliable inversion method is necessary. In this paper, an asymmetric Abel-inversion method is introduced. This method includes flexible boundary conditions, application to a noncircular geometry, and estimation of the plasma in the scrape-off layer. The advantages of this method are demonstrated by comparison with other methods. This inversion method is applied to a parametric study which includes dependence on the Shafranov shift and elongation of the profile.

https://iopscience.iop.org/article/10.1088/0741-3335/31/13/007/pdf

A new asymmetric Abel-inversion method for plasma interferometry in tokamaks

The largest superconducting fusion machine, Large Helical Device (LHD), is now under construction in Japan and will begin operation in 1997. Design and construction of related R&D programs are now being carried out. The major radius of this machine is 3.9 m and the magnetic field on the plasma center is 3 T. The NbTi superconducting conductors are used in both helical coils and poloidal coils to produce this field. This will be upgraded in the second phase a using superfluid coil cooling technique. A negative ion source is being successfully developed for the NBI heating of LHD. This paper describes the present status and progress in its experimental planning and theoretical analysis on LHD, and the design and construction of LHD torus, heating, and diagnostics equipments.

Large Helical Device (LHD) program

The TFTR Thomson scattering system has been operational since January 1984. The diagnostic uses two ruby lasers and two spectrometer‐detector systems to provide profiles at two times in a discharge. The two scattering lines consist of 76 spatial channels which span the 200‐cm vacuum vessel along a major radius. The detectors are gated, intensified CCD arrays with single photoelectron sensitivity. Te(R) and Ne(R) profiles are presented.

TFTR Thomson scattering system

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.

Multichannel Thomson scattering systems with high spatial resolution (invited)

A system is under construction which will make use of the laser and collection optics of an existing multichannel Thomson scattering system on the tokamak fusion test reactor (TFTR). A scanning sampling mechanism will divert signal from a 10‐cm segment of the radial‐beam path to a spectrometer–detector system which is optimized for low temperatures and densities. In the absence of stray laser light and background plasma light the system will be capable of measuring temperatures down to 3–5 eV at 1–3×1011 cm−3 minimum densities.

TFTR edge 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).

The JFT-2M TV 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.

D. Dimock

Papers

TFTR Thomson scattering system

Multichannel Thomson scattering systems with high spatial resolution (invited)

TFTR edge Thomson scattering system

The JFT-2M TV Thomson scattering system

Alignment of TFTR Thomson scattering system