Search

Millimeter-sized CD foils fielded close (order mm) to inertial confinement fusion (ICF) implosions have been proposed as a game-changer for improving energy resolution and allowing time-resolution in neutron spectrum measurements using the magnetic recoil technique. This paper presents results from initial experiments testing this concept for direct drive ICF at the OMEGA Laser Facility. While the foils are shown to produce reasonable signals, inferred spectral broadening is seen to be high (∼5 keV) and signal levels are low (by ∼20%) compared to expectation. Before this type of foil is used for precision experiments, the foil mount must be improved, oxygen uptake in the foils must be better characterized, and impact of uncontrolled foil motion prior to detection must be investigated.

Rotational spectroscopy has been used for decades for virtually unambiguous identification of gas phase molecular species, but it has rarely been used for the quantitative analysis of molecular concentrations. Challenges have included the nontrivial reconstruction of integrated line strengths from modulated spectra, the correlation of pressure-dependent line shape and strength with partial pressure, and the multiple standing wave interferences and modulation-induced line shape asymmetries that sensitively depend on source-chamber-detector alignment. Here, we introduce a quantitative analysis methodology that overcomes these challenges, reproducibly and accurately recovering gas molecule concentrations using a calibration procedure with a reference gas and a conversion based on calculated line strengths. The technique uses frequency-modulated rotational spectroscopy and recovers the integrated line strength from a Voigt line shape that spans the Doppler- and pressure-broadened regimes. Gas concentrations were accurately quantified to within the experimental error over more than three orders of magnitude, as confirmed by the cross calibration between CO and N2O and by the accurate recovery of the natural abundances of four N2O isotopologues. With this methodology, concentrations of hundreds of molecular species may be quantitatively measured down to the femtomolar regime using only a single calibration curve and the readily available libraries of calculated integrated line strengths, demonstrating the power of this technique for the quantitative gas-phase detection, identification, and quantification.

International audience; Numerical simulations are critical in improving the capabilities of microwave diagnostics. In this work, the 2D finite-difference time-domain full-wave code REFMUL was applied to broadband turbulent plasmas using the conventional reflectometry setup. Simulations were performed with O-mode waves, fixed frequency probing, and I/Q detection. The plasma density, determining O-mode propagation , was modeled as the sum of a slab background plasma with a fluctuating component following a Kolmogorov-like amplitude k-spectrum. The density turbulence level δn e /n e was scanned over several orders of magnitude for simulated plasma flows of constant plasma velocity in either the radial or the poloidal direction. Simulations show trends, such as spectral broadening of the complex A(t)e iϕ(t) signals and increasing fluctuations in A(t) and ϕ(t) with increasing δn e /n e , that are similar for both plasma flow directions. These together with possibilities to reconstruct a poloidal wavenumber spectrum are discussed in view of extending the measuring capabilities. The onset of non-linear effects associated with phase runaway, as previously observed with other 1D and 2D codes, as well as radial Doppler effects is also observed and discussed. https://doi.

A sensitive and versatile sensor for the detection of traces of atoms or molecules in air based on the emission spectroscopy of glow discharge in air has been developed and studied. The advantages of this sensor compared to other well-known methods are that it renders the use of ultrahigh vacuum or cryogenic temperatures superfluous. The sensor is insensitive to the presence of water vapor (for example, in exhaled air) because of the absence of strong water lines in the visible spectral range. It has a high spectral selectivity limited only by Doppler broadening of the emission lines. The high selectivity of the sensor combined with a wide spectral range allows the detection of many toxic impurities, which can be present in air. Moreover, the spectral range used covers almost all biomarkers in exhaled air, making the proposed sensor extremely interesting for medical applications. To our knowledge, the proposed method is the first based on a glow discharge in air.

A high-resolution quartz ultraviolet spectrometer based on a single compact 16-channel multianode photomultiplier tube (MAPMT) has been developed and tested on coaxial helicity injection and ohmic transformer current drive plasmas generated on the Helicity Injected Torus at the University of Washington. The use of the compact MAPMT allows a simple design with high light collection and high resolution for an ion Doppler shift diagnostic. The high quality and low cost of the design make it uniquely attractive for university scale plasma experiments. The Doppler shift of impurity ion emission lines from two chords of equal impact parameter but of opposite rotational sense is used to determine chord-averaged toroidal flow velocity. The width of the Doppler broadening is used to calculate the ion temperature. A detailed description of the ion Doppler spectrometer measurement system and some typical results are presented.

This work reports dual-mode operation of a broadly tunable CO2-laser/microwave-sideband spectrometer employing a Cheo waveguide modulator and a CO2 laser that can operate on hot and sequence band lines as well as low- and high-J regular band lines. The spectrometer has a broadband scanning mode at Doppler-limited resolution for spectral searching and assignment, and a narrow-band sub-Doppler mode for precision measurements. In broadband mode, a 6.7–18.5 GHz (∼0.4 cm−1) window can be covered for each sideband in a single microwave sweep with a tracking Fabry–Perot etalon filter under computer control. In sub-Doppler mode, saturation-dip spectra are obtained at sub-MHz resolution with absolute frequency measurement accuracy of the order of ±200 kHz. The instrumental performance is demonstrated via spectra of the C–O stretching fundamental vibrational band of methanol. Doppler-limited broadband scans have been recorded with good signal-to-noise ratio in both the low- and high-J regions of the 9.6-μm-CO2 lase...

A mid-infrared tunable diode laser molecular-beam spectrometer for the purpose of trace gas sensing and the study of van der Waals complexes is described. The spectrometer employs a Herriott multipass cell with up to 72 passes. The sample gas is injected parallel to the optical axis through a hole at the center of the far mirror. The molecular absorption is Doppler split, resulting from the laser beam propagating parallel and antiparallel to the molecular-beam expansion. The axial expansion leads to narrower line widths and increased sensitivity, compared to the traditional vertical injection method, as a result of selective sampling of the central part of the molecular expansion with reduced Doppler broadening and longer residence time of the molecular sample in the laser beam. The molecular expansion leads also to selective signal enhancement of low-J transitions, as demonstrated for the ν3 antisymmetric stretch vibration of CO2. A microwave horn antenna was implemented into the spectrometer to enable m...

A generalized least-square method with Tikonov–Miller regularization and non-negativity constraints has been developed for deconvoluting two-dimensional coincidence Doppler broadening spectroscopy (CDBS) spectra. A projected Newton algorithm is employed to solve the generalized least-square problem. The algorithm has been tested on Monte Carlo generated spectra to find the best regularization parameters for different simulated experimental conditions. Good retrieval of the underlying positron–electron momentum distributions in the low momentum region is demonstrated. The algorithm has been successfully used to deconvolute experimental CDBS data from aluminum.

A Johann-type x-ray crystal spectrometer has been designed using a ray tracing calculation and constructed for ion temperature measurement in the plasma center of a large helical device (LHD) using Doppler broadening of a He-like resonance line of ArXVII, TiXXI, CrXXIII, or FeXXV. Four curved quartz (2020), (2023), (3140), and (2243) crystals are set in a quadrangular rotary crystal holder for measuring the x-ray line from such four different elements. Each of the crystals can be externally selected through a computer network. The curved crystals with a radius of 3 m are fabricated by gluing thin quartz (0.7 mmt) on an accurately ground cylindrical blue glass plate. The curvature of the crystals was checked by scanning a sharp pin along the crystal surface. As a result, an excellent agreement with the designed cylindrical curvature was obtained with an accuracy of 1 μm. A secular change of the curved crystal surface structure was found by measuring the curvature of the curved crystal fabricated 15 years e...

Electron temperature profiles at densities above the electron cyclotron emission (ECE) cutoff are measured at the W7-AS stellarator by a novel diagnostic based on black body emission and Bernstein-extraordinary-ordinary mode conversion of electron Bernstein waves (EBWs). The radiation is collected along a special oblique line of sight by an antenna with gaussian optics. This was optimized for maximal conversion efficiency and minimal Doppler broadening by means of EBW ray tracing calculations in full stellarator geometry. The elliptical O-mode polarization detected along the oblique line of sight is changed into a linear polarization by a broadband quarter wave shifter, namely an elliptical waveguide. The signal is spectrum analyzed by an heterodyne radiometer and temperature profiles are derived from spectra by means of ray tracing. The diagnostic was applied to measurements of edge-localized modes to illustrate its advantages in terms of spatial and temporal resolution. Moreover, for the first time, the heat wave propagation method for the determination of local heat transport coefficients was extended beyond the ECE cutoff density by combining EBW emission measurements at the first harmonic (f=66–78 GHz) with modulated EBW heating at the second harmonic (140 GHz).

A high dispersion, multichannel, visible spectrometer has been developed for the ISTTOK tokamak, aiming at measuring the evolution of both the edge ion temperature and plasma poloidal velocity, by analysis of a CIII spectral line. It is based on a double monochromator configuration with two high ruling densities (2700 l/mm) and 1 m focal length concave diffraction gratings, a commercial double microchannel plate image intensifier, a fast (f/#=1) relay lens built with two high diameter condensers in a back-to-back configuration, and a 2048 element photodiode charge coupled device optical multichannel analyzer. Laboratory tests have shown that a high dispersion has been achieved (≈1.65 A/mm), while keeping good temporal resolution (5 ms). Typical values measured for ion temperature (from Doppler broadening) were Ti≅25 eV while for poloidal velocity (from Doppler shift) vθ≅6 km/s.

This article reports on γ-ray diagnosis of ICRF-accelerated 4He ions and fusion α particles used in the JET tokamak. This diagnostic based on the analysis of γ rays emitted in nuclear reaction 9Be(α,nγ)12C. The results of the first observation of the 4.44-MeV γ-radiation due to the reaction 9Be(α,nγ)12C in JET deuterium–tritium experiment (DTE1) are presented. Gamma-ray spectra have been recorded with collimated spectrometer, and the γ-ray emission radial profiles measured with the JET neutron/gamma profile monitor. Doppler broadening effects which could be used for the ICRF-accelerated 4He-ion diagnosis with high energy resolution γ-ray detectors are discussed. Capabilities of the γ-ray measurements in next step D–T devices are discussed.

In this article, the recent installed multiposition Thomson scattering (TS) of the TJ-II stellarator is presented. Light from a pulsed ruby laser is scattered by the free electrons of the plasma and led to a spectrometer for spectral analysis. The Doppler broadened spectrum of the scattered light is analyzed with a spectrometer in the Littrow configuration, detected with a GaAsP image intensifier and recorded with two intensified charged coupled device cameras. Values of the electron temperature (T-e) in the range of 50 eV up to 4 keV can be measured at 160 spatial elements of 2.25 mm along a chord of 360 mm. First results show that the observational error for T-e is close to the expected error of similar to 10% at an electron density (n(e)) of 1 X 10(19) m(-3) using a laser energy of 8 J. (C) 1999 American Institute of Physics. [S0034-6748(99)64101-6].

A new electro-optically modulated optical solid-state (MOSS) interferometer has been constructed for the measurement of the low order spectral moments of line emission from optically thin radiant media. The instrument, which is based on the principle of the Fourier transform spectrometer, is rugged, compact, and inexpensive and offers a number of advantages over conventional grating based spectrometers. Most importantly, by employing electro-optical path-length modulation techniques, the spectral information is obtained using a single photomultiplier tube. Specifically, the zeroth moment (brightness) is given by the average signal level, the first moment (shift) by the modulation phase and the second moment (line width) by the modulation amplitude. In applications such as Zeeman spectroscopy and motional Stark effect (MSE), polarization modulation can be used to effect a modulation of the center frequency and/or coherence of the light which is then measured by the MOSS spectrometer. This article describes...

A new fast scan submillimeter spectroscopic technique (FASSST) has been developed which uses a voltage tunable backward wave oscillator (BWO) as a primary source of radiation, but which uses fast scan (∼105 Doppler limited resolution elements/s) and optical calibration methods rather than the more traditional phase or frequency lock techniques. Among its attributes are (1) absolute frequency calibration to ∼1/10 of a Doppler limited gaseous absorption linewidth (

A pulsed Na atomic beam source developed for spectroscopic diagnosis of a high-power ion diode is described. The goal is to produce a ∼1012-cm−3-density Na atomic beam that can be injected into the diode acceleration gap to measure electric and magnetic fields from the Stark and Zeeman effects through laser-induced fluorescence or absorption spectroscopy. A ∼10 ns full width at half-maximum (FWHM), 1.06 μm, 0.6 J/cm2 laser incident through a glass slide heats a Na-bearing thin film, creating a plasma that generates a sodium vapor plume. A ∼1 μs FWHM dye laser beam tuned to 5890 A is used for absorption measurement of the Na I resonant doublet by viewing parallel to the film surface. The dye laser light is coupled through a fiber to a spectrograph with a time-integrated charge-coupled-device camera. A two-dimensional mapping of the Na vapor density is obtained through absorption measurements at different spatial locations. Time-of-flight and Doppler broadening of the absorption with ∼0.1 A spectral resolut...

The width of the energy distribution of fusion-produced neutrons is often used as an indication of the temperature of the reacting ions. The Doppler broadening of the neutron energy is due to the center-of-mass velocity of reacting ion pairs and is characterized by the ion temperature for a Maxwellian distribution of ions with zero collective velocity. If there is bulk fluid motion or turbulence characterized by a velocity on the order of the ion thermal speed, a significant additional broadening may be introduced. Suggestions of this phenomenon have been observed for two classes of laser targets. The first is a “gas bag” target, in which a deuterated hydrocarbon gas is contained in a thin spherical membrane and illuminated uniformly. The second target is an ICF capsule with a deuterated plastic inner layer. In both cases, measured neutron energy distributions were wider than expected from theoretical ion temperatures and if interpreted as indicative of the ion temperature, are inconsistent with the neutron yields observed.

We have completed the upgrade and calibration of the ion dynamics spectrometer (IDS), a high-speed Doppler duo spectrometer which measures ion flow and temperature in the MST reversed-field pinch. This paper describes an in situ calibration of the diagnostic’s phase and frequency response. A single clock was employed to generate both a digital test signal and a digitizer trigger thus avoiding frequency drift and providing a highly resolved measurement over the system bandwidth. Additionally, we review the measurement of the spectrometer instrument function and absolute intensity response. This calibration and subsequent performance demonstrate the IDS to be one of the fastest, highest throughput diagnostics of its kind. Typical measurements are presented.

A coolable gas cell for the measurement of mid‐infrared spectra of gases at cryogenic temperatures as low as 77 K is described. The design of the cell allows it to be operated in collisional cooling (or diffusive trapping) mode to generate significant nonequilibrium pressures of monomer vapor for gases which would normally have vanishingly small vapor pressure at low temperatures. Fourier transform infrared spectra of carbon dioxide (CO2), nitrogen dioxide (NO2), and methyl silane (CH3SiH3) vapors cooled by collisions with helium gas at 77 K are reported. Sufficiently high concentrations of monomer gas may be produced at low total pressure conditions (

A conventional visible spectrometer system has been applied to velocity fluctuation measurements in plasmas. By measuring the number of photons, the effect of quantum noise is subtracted, and real velocity fluctuations are obtained. The first measurements in a reversed‐field‐pinch plasma show finite velocity fluctuations of about 1.7×103 m/s when the system views off‐center chords. When it views the central chord, finite fluctuations are not found. These results impose an upper limit to spurious Doppler broadening, which could arise from fast and large vibrations of cold plasma. The effect of the spurious Doppler broadening is found to be small.

To meet experimental requirements, the J-TEXT electron cyclotron emission (ECE) diagnostic is being upgraded. The front end antenna and transmission line have been modified and a new 8-channel W-band detecting unit has been developed. The improved ECE system will extend the frequency range from 94.5-124.5 GHz to 80.5-124.5 GHz. This will enable the system to cover the most plasma in the radius direction for BT = 1.8–2.2 T, and it even can cover almost the whole plasma range ρ = − 0.8–0.9 (minus means the high field side) at BT = 1.8 T. A new auxiliary channel bank with 8 narrow band, tunable yttrium iron garnet filters is planned to add to the ECE system. Due to observations along a major radius, perpendicular to BT, and relatively low electron temperature, Doppler and relativistic broadening are minimal and thus high spatial resolution measurements can be made at variable locations with these tunable channels.

We report the calibration of the Orion High-Resolution X-ray (OHREX) imaging crystal spectrometer at the EBIT-I electron beam ion trap at Livermore. Two such instruments, dubbed OHREX-1 and OHREX-2, are fielded for plasma diagnostics at the Orion laser facility in the United Kingdom. The OHREX spectrometer can simultaneously house two spherically bent crystals with a radius of curvature of r = 67.2 cm. The focusing properties of the spectrometer allow both for larger distance to the source due to the increase in collected light and for observation of extended sources. OHREX is designed to cover a 2.5°–3° spectral range at Bragg angles around 51.3°. The typically high resolving powers at these large Bragg angles are ideally suited for line shape diagnostics. For instance, the nominal resolving power of the instrument (>10 000) is much higher than the effective resolving power associated with the Doppler broadening due to the temperature of the trapped ions in EBIT-I. The effective resolving power is only around 3000 at typical EBIT-I conditions, which nevertheless is sufficient to set up and test the instrument’s spectral characteristics. We have calibrated the spectral range for a number of crystals using well known reference lines in the first and second order and derived the ion temperatures from these lines. We have also made use of the 50 μm size of the EBIT-I source width to characterize the spatial focusing of the spectrometer.

Saturation broadening is an obstacle in using laser‐induced fluorescence as a plasma diagnostic. The Doppler‐broadened line shape ideally yields the ion velocity distribution function, but at high laser power, saturation of the optical transition leads to additional undesirable line broadening. We test three different prescriptions for plasma experimentalists to avoid saturation broadening while maintaining a strong signal. Based on experiments in an argon plasma, and a semiclassical atomic physics simulation, we have identified the prescription that is the easiest to use and the least sensitive to the spatial profile of the laser beam. This procedure is to measure the laser intensity that leads to saturation on the peak of the spectral line, and then to reduce the intensity to 20% of the saturation level.

With the recent advances in layered synthetic microstructure (LSM) technology, it is now possible to build a simple, high‐throughput, near‐normal incidence soft x‐ray spectrometer as a diagnostic for magnetically confined plasmas. Such spectrometers could be used for radiative power loss measurements from intrinsic impurities, an impurity concentration monitor, or ion temperature measurements from Doppler broadening of high charge‐state metallic impurities. LSMs have been developed as either flat or curved multilayer mirrors (MLMs) or as coatings for conventional gratings. Flat multilayer mirrors can have near‐normal incidence reflectivities greater than 50% throughout the entire soft x‐ray region with bandpasses that can be less than 4 A. Coated gratings are being developed that will combine the high soft x‐ray reflectivity of the LSM with the high resolution of the grating. Specific applications of LSMs as dispersive elements will be discussed. As an example, LSM‐based low‐resolution spectra of both a laboratory and tokamak plasma will be presented.

Our objective is to diagnose primarily Ar z-pinch plasmas with 1019

A Ba+ beam is generated in a thermal contact–ionization plasma source made of a rhenium‐foil cylinder 5 mm in diameter inserted into a tungsten cylinder for protection. The source can be heated up to about 3000 K. The maximum current of Ba+ already attained is 200 μA. The beam can be accelerated to 40 keV. The Ba+ beam is passed through a Li‐vapor cell and neutralized by a charge‐exchange reaction with Li atoms. A 100 μA/e Ba beam has already been obtained. The next subject is to measure the increase of energy spread of the beam passing through the Li cell by collisions with vapor atoms. An optical system has been developed for measuring it by the Doppler broadening of spectral lines emitted by Ba and Ba+ beam particles. Results of optical measurement are presented. The production of slow energy components has been observed. They are attributable to the head‐on collision of Ba beam particles with a Na atom and with a K atom as impurities in the Li vapor cell. Because of the head‐on collision, the energy s...

The results of spectral measurements in the D iii–D divertor region, carried out using a high‐resolution spectrometer and a survey spectrograph developed at the TRINITI Laboratory, Russia are presented in this report. Observations were made along a vertical chord passing through the X point and intersecting the divertor floor at the major radius of the V1 ports. The high‐resolution spectrometer is designed for simultaneous measurements along eight spatial chords with a time resolution of 7 ms. Each of the eight spectra is dispersed over 512 pixels on an intensified charge coupled device (CCD) detector. 768 frames of data are recorded directly to RAM memory of a PC computer during every discharge. High optical throughput is achieved simultaneously with high spectral resolution; the instrument has an f/number of 3 and a spectral resolution of 0.025 nm. The spectrometer can also operate in survey mode, recording a spectral region of 13 nm with 0.1‐nm resolution. Using Doppler broadening of spectral lines, th...

A 1‐m normal incidence spectrometer has been modified for use as a diagnostic of ion diode plasmas. To improve instrumental sensitivity, an elliptical mirror images an anode surface plasma onto the entrance slit of an f/10 normal incidence spectrometer. The detector is a time‐resolving copper iodide coated microchannel plate stripline framing camera with 60‐μm resolution, limiting instrumental resolution to 1 A with a 600 l/mm grating in first order. Reflectivity of optics and photoelectron efficiency limit the spectral range from 400 to 2000 A. With a 600‐l/mm grating the detector spans a 600‐A range. Applications of the instrument may include ion source divergence measurements from Doppler broadening, electric field measurements from Stark splittings or shifts, electron temperature from mean ionization state, and magnetic field measurements on high‐power Z pinches from Zeeman splitting.

Vacuum ultraviolet spectra of emissions released from tungsten ions at lower ionization stages were measured in the Large Helical Device (LHD) in the wavelength range of 500-2200 Å using a 3 m normal incidence spectrometer. Tungsten ions were distributed in the LHD plasma by injecting a pellet consisting of a small piece of tungsten metal and polyethylene tube. Many lines having different wavelengths from intrinsic impurity ions were observed just after the tungsten pellet injection. Doppler broadening of a tungsten candidate line was successfully measured and the ion temperature was obtained.

A high-resolution grazing-incidence grating spectrometer has been implemented on the Livermore electron beam ion traps for performing very high-resolution measurements in the soft x-ray and extreme ultraviolet region spanning from below 10 Å to above 300 Å. The instrument operates without an entrance slit and focuses the light emitted by highly charged ions located in the roughly 50 μm wide electron beam onto a cryogenically cooled back-illuminated charge-coupled device detector. The measured line widths are below 0.025 Å above 100 Å, and the resolving power appears to be limited by the source size and Doppler broadening of the trapped ions. Comparisons with spectra obtained with existing grating spectrometers show an order of magnitude improvement in spectral resolution.

A 32/64-channel charge exchange recombination spectroscopy (CXRS) diagnostic system is developed on the HL-2A tokamak (R = 1.65 m, a = 0.4 m), monitoring plasma ion temperature and toroidal rotation velocity simultaneously. A high throughput spectrometer (F/2.8) and a pitch-controlled fiber bundle enable the temporal resolution of the system up to 400 Hz. The observation geometry and an optimized optic system enable the highest radial resolution up to ∼1 cm at the plasma edge. The CXRS system monitors the carbon line emission (C VI, n = 8 7, 529.06 nm) whose Doppler broadening and Doppler shift provide ion temperature and plasma rotation velocity during the neutral beam injection. The composite CX spectral data are analyzed by the atomic data and analysis structure charge exchange spectroscopy fitting (ADAS CXSFIT) code. First experimental results are shown for the case of HL-2A plasmas with sawtooth oscillations, electron cyclotron resonance heating, and edge transport barrier during the high-confinement mode (H-mode).

In many situations it is necessary to analyze spectral line shapes where the data contain significant amounts of noise or statistical fluctuations. Our visible spectroscopy measurements exploring ion diode physics on the PBFA II accelerator typically result in noisy spectra because the harsh environment limits the number of photons collected. The spectral line profiles include contributions from Doppler (Ti∼1–3 keV), Stark (ne∼1017 cm−3), and instrument broadening, as well as from Stark shifting (E∼3–10 MV/cm) and Zeeman splitting (B∼2–10 T). We extract a range of parameters (e.g., ion temperature from Doppler broadening) that fit the data by determining a range of fits that are consistent with the uncertainty due to the noise in the data. The range of fits is generated by a Monte Carlo technique. This method effectively distinguishes between actual spectral features and artifacts due to noise. It provides not only estimates of physical parameters, but also their uncertainties. We evaluated the technique ...

In DIII‐D, visible spectroscopic measurements of the He ii 468.6 nm and C vi 529.2 nm Doppler broadened spectral lines, resulting from charge exchange recombination interactions between beam neutral atoms and plasma ions, are performed to determine ion temperatures, and toroidal and poloidal rotation velocities. The diagnostics system comprises 32 viewing chords spanning a typical minor radius of 63 cm across the midplane, of which 16 spatial chords span 11 cm of the plasma edge just within the separatrix. A temporal resolution of 260 μs per time slice can be obtained as a result of using MCP phosphors with short decay times and fast camera readout electronics. Results from this system will be used in radial electric field comparisons with theory at the L–H transition and ion transport analysis.

A five‐spectrometer array has been designed to provide high‐wavelength resolution x‐ray spectra from the Alcator C‐Mod plasma. Each independently scannable von Hamos type spectrometer consists of a variable entrance slit, quartz crystal, and position sensitive proportional counter, and has 3 cm spatial resolution with a resolving power of 4000. The wavelength range of each spectrometer is from 2.8 to 4.0 A, which covers the complete Rydberg series of helium‐ and hydrogen‐like argon. Wavelengths are remotely selectable, with 120 mA covered at any one setting. The array will provide single shot ion temperature profiles by measuring the Doppler broadening of the resonance lines of argon. Five proportional counters have been fabricated and all five spectrometers have been constructed. Calibration spectra using cadmium and scandium anode sources have been obtained, and measured performance characteristics are presented.

Doppler backscattering (DBS) is a plasma diagnostic used in tokamaks and other magnetic confinement devices to measure the fluctuation level of intermediate wavenumber (k(θ)ρ(s) ~ 1) density fluctuations and the lab frame propagation velocity of turbulence. Here, a synthetic DBS diagnostic is described, which has been used for comparisons between measurements in the DIII-D tokamak and predictions from nonlinear gyrokinetic simulations. To estimate the wavenumber range to which a Gaussian beam would be sensitive, a ray tracing code and a 2D finite difference, time domain full wave code are used. Experimental density profiles and magnetic geometry are used along with the experimental antenna and beam characteristics. An example of the effect of the synthetic diagnostic on the output of a nonlinear gyrokinetic simulation is presented.

Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian function associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. These measurements are used to gain a better understanding of Z-pinch equilibria.