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  • 1
    Electronic Resource
    Electronic Resource
    The LIDAR Thomson scattering diagnostic on JET (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1451-1456 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: By combining the time-of-flight or LIDAR principle with a Thomson backscatter diagnostic, spatial profiles of the electron temperature and density are measured in a magnetically confined fusion plasma. This technique was realized for the first time on the JET tokamak. A ruby laser (3-J pulse energy, 300-ps pulse duration, 0.5-Hz repetition rate) together with a 700-MHz bandwidth detection and registration system yields a spatial resolution of about 12 cm. A spectrometer with six channels in the wavelength range 400–800 nm gives a dynamic range of the temperature measurements of 0.3–20 keV. The stray light problem in the backscatter geometry is overcome by spectral discrimination and gating of the photomultipliers. A ruby filter in the spectral channel containing the laser wavelength allows calibration of the vignetting along the line of sight by means of Raman scattering, enabling the measurement of density profiles. The low level of background signal due to the short integration time for a single spatial point yields low statistical errors (ΔTe /Te ≈6%, Δne /ne ≈4% at Te =6 keV, ne =3×1019 m−3 ). Goodness-of-fit tests indicate that the systematic errors are within the same limits. The system is described and examples of measurements are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139686
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  • 2
    Electronic Resource
    Electronic Resource
    A laser diode as a light source for calibrating the time base of a streak camera (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 3338-3339 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The dc operation of some laser diodes produces high-frequency amplitude modulation of the laser output in the GHz frequency range. This phenomenon provides a simple and inexpensive method for checking the sweep linearity of a fast-gated streak camera.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144304
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  • 3
    Electronic Resource
    Electronic Resource
    A high-resolution Lidar–Thomson scattering diagnostic for JET : Eighth topical conference on high−temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2843-2845 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A LIDAR–Thomson scattering system with better than 5 cm spatial resolution to resolve edge electron temperature and density gradients in H-mode operation in JET is needed. A dynamic range in measurable electron temperature of 0.1–1.5 keV and a minimum detectable electron density of 1019/m3 are required. To achieve these levels of performance, it is planned to use a modified section of the existing JET LIDAR–Thomson scattering system. A new detection system, consisting of a streak camera and an intensifier unit, will be used. Spectral dispersion is to be performed by a three-channel edge filter spectrometer. Recording and digitization of the scattered signal will be performed by a CCD camera read out by a personal computer. The system is described and results of experiments to determine the minimum visible light levels using a commercial streak camera, intensifier unit, and CCD camera and a pulsed laser diode light source are briefly presented. In addition, simulations of expected signal-to-noise ratio performance are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141801
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  • 4
    Electronic Resource
    Electronic Resource
    A new method for estimating and identifying systematic error in Thomson scattering diagnostics : Eight topical conference on high-temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2849-2851 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method has been developed to identify and estimate systematic error in the calibration of Thomson scattering systems. The basis of the technique is an iterative recalculation of electron temperature using successively more self-consistent calibrations. A computational method was developed to calculate from a large dataset a calibration correction factor for each channel. The correction factor was then applied and the fitting routine rerun on the whole dataset with the new calibration factors. The resulting frequency distribution of chi-squared values was close to the theoretical distribution while the calculated electron temperatures were changed by only 1 to 2%. The technique succeeded in identifying and quantifying errors in a dataset known to be of poor quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141803
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  • 5
    Electronic Resource
    Electronic Resource
    A self-calibration technique for a Thomson scattering system : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 725-727 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A self-calibration technique, based on the use of two lasers of different wavelengths is described. Such a scheme is essential in the presence of inaccessible optical components, as found on large present day machines. In these devices spectral characteristics may change with time, posing a problem for the calibration of a Thomson scattering diagnostic. From a combination of the scattered spectra generated by the two lasers on the same plasma, the temperature and the unknown, slowly varying spectral transmission of the different channels can be determined. A visible wavelength scattering system on a high-temperature plasma is assumed with laser wavelengths of 800 and 530 nm. Details of the analysis procedure and the results of fitting for the unknown spectral calibrations are presented. A statistical analysis of the error in the fitted calibration curve is included. A practical solution, with reference to ITER, is proposed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147686
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  • 6
    Electronic Resource
    Electronic Resource
    Window transmission monitoring and cleaning schemes used with the Light Detection and Ranging Thomson scattering diagnostic on the JET tokamak (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3077-3078 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Light Detection and Ranging Thomson scattering diagnostic on the JET tokamak makes routine measurements of the plasma electron temperature and density profiles. During JET operations the windows used for scattered light collection gradually become coated with deposits due to the plasma erosion of the wall. The consequent loss in transmission can affect the electron density and also the electron temperature measurement. This paper describes both the method adopted to monitor the change in transmission due to the gradual build up of deposits and the application of laser window cleaning to counteract it. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145534
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  • 7
    Electronic Resource
    Electronic Resource
    300 ps ruby laser using stimulated Brillouin scattering pulse compression (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2460-2463 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Using the stimulated Brillouin scattering phase conjugation and pulse compression technique, a conventional long pulse ruby laser was successfully converted to give 300 ps pulses at 1 J energy level. The technique allows the use of smaller amplifiers than required in a conventional short pulse laser which in turn leads to operation at increased repetition rate. The completed laser when operated at 1.5 Hz produces stable output parameters. Each laser pulse is characterized by a sharp rise and a measured pre-pulse level of less than 10−6 of the main pulse, making it suitable for LIDAR Thomson scattering measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144703
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  • 8
    Electronic Resource
    Electronic Resource
    Recent developments in LIDAR Thomson scattering measurements on JET (invited) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 471-475 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The LIDAR Thomson scattering technique uses the time of flight of a short laser pulse to spatially resolve measurements of electron temperature (Te) and density (ne) in a plasma. The technique was pioneered at JET and the first profiles were obtained in 1986. The initial system used a 3 J, 0.5 Hz, 300 ps ruby laser and microchannel-plate photomultiplier detectors to make Te and ne profile measurements with ∼10 cm spatial resolution. Since then we have sought to improve both the spatial resolution and frequency of measurement during a JET pulse. It has proved possible to develop a 4 Hz version of the ruby laser and to enhance the rate of cycling of detection and digitizing to match. The main LIDAR system has now been upgraded to 4 Hz and first JET profiles obtained with the new system are presented. For a LIDAR system, the spatial resolution δL along the laser path is given by δL=(c/2)(τ2L+τ2D)1/2, where c is the velocity of light, τL the laser pulse width, and τD the detection system response time. Over a limited spatial extent it is possible to improve spatial resolution by using a streak camera detection system. We have successfully improved the spatial resolution by a factor of 2 by setting up a streak camera detection system in parallel with the main photomultiplier system.The much shorter response time of the streak camera gave ∼5 cm resolution over a 75 cm segment of the ∼2 m plasma diameter. This system was used to examine profile details in the outer part of the JET plasma. Results from this high-resolution LIDAR detection system will be presented. Building on the improved spatial resolution obtained with the streak camera technique, we have now designed and installed a new LIDAR scattering system to diagnose the divertor region of the JET plasma. The laser for the new system is again ruby but uses a different principle to obtain short pulses. We have demonstrated with colleagues from the Troitsk Institute the conversion, using SBS pulse compression, of a standard 25 ns ruby laser into a 300 ps system suitable for LIDAR applications. The main components of the JET Divertor LIDAR system are also described. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146321
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  • 9
    Electronic Resource
    Electronic Resource
    Proposal to measure the q profile on JET by Thomson scattering : Eighth topical conference on high−temperature plasma diagnostics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 2926-2928 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The existing single point Thomson scattering apparatus on JET has been modified to allow measurements of local magnetic fields. Multiviewing access will be provided by axicone optics, giving a scattering angle of about 4°, and should provide an accuracy of better than 10% in measuring Bpol over most of the plasma radius. A Fabry–Perot spectrometer will detect the scattered spectra, modulated at the electron gyrofrequency, using a gated image intensifier and a cooled CCD camera. The location of an interference partial fringe will give the magnetic field vector at a particular position in the plasma. From the locus of such partial fringes, the q profile may be determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141778
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  • 10
    Electronic Resource
    Electronic Resource
    First results from Thomson scattering on JET (abstract) (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1070-1070 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Single Point Thomson Scattering System uses a multipulse ruby laser to measure Te and ne up to twenty times during a JET plasma pulse. The scattering volume is on the equatorial plane and, between plasma pulses, can be relocated to any one of seven specific points on a major radius. The collection system employs multimirror arrays and a triple prism spectrometer is used to eliminate stray laser light and disperse the scattered light. Novel features include two optoelectronic feedback systems which maintain alignment within the laser input and the collection systems. Sensitive components are located outside the biological shield, and those inside are compatible with remote handling procedures. The entire diagnostic can be remotely controlled via the JET computer system. Initial results from the diagnostic are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138222
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