R. L. Boivin

Sandia National Laboratories, Albuquerque, New Mexico, United States

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Publications (189)166.62 Total impact

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    ABSTRACT: The DIII-D tokamak magnetic diagnostic system [E. J. Strait, Rev. Sci. Instrum. 77, 023502 (2006)] has been upgraded to significantly expand the measurement of the plasma response to intrinsic and applied non-axisymmetric “3D” fields. The placement and design of 101 additional sensors allow resolution of toroidal mode numbers 1 ≤ n ≤ 3, and poloidal wavelengths smaller than MARS-F, IPEC, and VMEC magnetohydrodynamic model predictions. Small 3D perturbations, relative to the equilibrium field (10−5 < δB/B0 < 10−4), require sub-millimeter fabrication and installation tolerances. This high precision is achieved using electrical discharge machined components, and alignment techniques employing rotary laser levels and a coordinate measurement machine. A 16-bit data acquisition system is used in conjunction with analog signal-processing to recover non-axisymmetric perturbations. Co-located radial and poloidal field measurements allow up to 14.2 cm spatial resolution of poloidal structures (plasma poloidal circumference is ∼500 cm). The function of the new system is verified by comparing the rotating tearing mode structure, measured by 14 BP fluctuation sensors, with that measured by the upgraded BR saddle loop sensors after the mode locks to the vessel wall. The result is a nearly identical 2/1 helical eigenstructure in both cases.
    Review of Scientific Instruments 01/2014; 85(8):083503-083503-8. · 1.60 Impact Factor
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    ABSTRACT: A dispersion interferometer based on the second-harmonic generation of a carbon dioxide laser in orientation-patterned gallium arsenide has been developed for measuring electron density in plasmas. The interferometer includes two nonlinear optical crystals placed on opposite sides of the plasma. This instrument has been used to measure electron line densities in a pulsed radio-frequency generated argon plasma. A simple phase-extraction technique based on combining measurements from two successive pulses of the plasma has been used. The noise-equivalent line density was measured to be 1.7 × 10(17) m(-2) in a detection bandwidth of 950 kHz. One of the orientation-patterned crystals produced 13 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 13 W of peak power. Two crystals arranged sequentially produced 58 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 37 W of peak power.
    The Review of scientific instruments 09/2013; 84(9):093502. · 1.52 Impact Factor
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    ABSTRACT: One of the systems planned for the measurement of electron density in ITER is a multi-channel tangentially viewing combined interferometer-polarimeter (TIP). This work discusses the current status of the design, including a preliminary optical table layout, calibration options, error sources, and performance projections based on a CO2/CO laser system. In the current design, two-color interferometry is carried out at 10.59 μm and 5.42 μm and a separate polarimetry measurement of the plasma induced Faraday effect, utilizing the rotating wave technique, is made at 10.59 μm. The inclusion of polarimetry provides an independent measure of the electron density and can also be used to correct the conventional two-color interferometer for fringe skips at all densities, up to and beyond the Greenwald limit. The system features five chords with independent first mirrors to reduce risks associated with deposition, erosion, etc., and a common first wall hole to minimize penetration sizes. Simulations of performance for a projected ITER baseline discharge show the diagnostic will function as well as, or better than, comparable existing systems for feedback density control. Calculations also show that finite temperature effects will be significant in ITER even for moderate temperature plasmas and can lead to a significant underestimate of electron density. A secondary role TIP will fulfill is that of a density fluctuation diagnostic; using a toroidal Alfvén eigenmode as an example, simulations show TIP will be extremely robust in this capacity and potentially able to resolve coherent mode fluctuations with perturbed densities as low as δn∕n ≈ 10(-5).
    The Review of scientific instruments 04/2013; 84(4):043501. · 1.52 Impact Factor
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    ABSTRACT: This paper describes a generally applicable technique for simultaneously measuring offset and gain of 64 analog fiber optic data links used for the DIII-D fixed Langmuir probes by embedding a reference voltage waveform in the optical transmitted signal before every tokamak shot. The calibrated data channels allow calibration of the power supply control fiber optic links as well. The array of fiber optic links and the embedded calibration system described here makes possible the use of superior modern data acquisition electronics in the control room.
    The Review of scientific instruments 10/2012; 83(10):10D710. · 1.52 Impact Factor
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    ABSTRACT: A new set of magnetic sensors has been designed to diagnose the 3D plasma response due to applied resonant magnetic perturbations (RMPs). The system will also allow for detailed investigation of locked modes and the effects of error fields. This upgrade adds more than 100 co-located radial and poloidal field sensors positioned on the high and low field sides of the tokamak. The sensors are arranged in toroidal and poloidal arrays. Their dimensions and spacing are determined using MARS-F and IPEC model predictions to maximize sensitivity to expected 3D field perturbations. Irregular toroidal spacing is used to minimize the condition numbers for simultaneous recovery of toroidal mode numbers n<=4. A subset of closely spaced sensors will also be installed to measure short wavelength MHD such as ELM precursors and TAEs.
    10/2012;
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    ABSTRACT: The advent of the recent spatial resolution upgrade to the edge Thomson scattering diagnostic at DIII-D allows re-examination of methods for measuring electron density and temperature scale lengths. The modified hyperbolic tangent fit is widely used, however, this function is clearly inappropriate in some situations such as when density profiles are distorted by applied resonant magnetic perturbations (RMPs). In these cases, a flattening of the density profile is observed at or near the separatrix while the RMP is applied. However, no similar structure is observed in the temperature profile so far. Furthermore, the tanh fit is based on a diffusive model and recently observed differences between the tanh fit and measured profiles using newly available high spatial resolution data are revealing more subtle transport processes at the mm scale.
    10/2012;
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    ABSTRACT: The quality of plasma produced in a magnetic confinement fusion device is influenced to a large extent by the neutral gas surrounding the plasma. The plasma is fueled by the ionization of neutrals, and charge exchange interactions between edge neutrals and plasma ions are a sink of energy and momentum. Here we describe a diagnostic capable of measuring the spatial distribution of neutral gas in a magnetically confined fusion plasma. A high intensity (5 MW/cm(2)), narrow bandwidth (0.1 cm(-1)) laser is injected into a hydrogen plasma to excite the Lyman β transition via the simultaneous absorption of two 205 nm photons. The absorption rate, determined by measurement of subsequent Balmer α emission, is proportional to the number of particles with a given velocity. Calibration is performed in situ by filling the chamber to a known pressure of neutral krypton and exciting a transition close in wavelength to that used in hydrogen. We present details of the calibration procedure, including a technique for identifying saturation broadening, measurements of the neutral density profile in a hydrogen helicon plasma, and discuss the application of the diagnostic to plasmas in the DIII-D tokamak.
    The Review of scientific instruments 10/2012; 83(10):10D701. · 1.52 Impact Factor
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    ABSTRACT: A new pair of in situ reciprocating Mach probes termed swing probes has been deployed on the DIII-D centerpost for the 2012 experimental campaign. When not deployed, the entire assembly is housed in a <5 cm space underneath the centerpost tiles. This design is unique in that the probe swings vertically through the edge plasma, taking measurements along a 180° arc with a 20 cm radius. The motion is powered by actuator coils that interact with the tokamak's magnetic field. Two electrodes maintain a Mach-pair orientation throughout the swing and provide measurements of saturation current, electron temperature, and parallel flow speeds up to the separatrix.
    The Review of scientific instruments 10/2012; 83(10):10D723. · 1.52 Impact Factor
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    ABSTRACT: Validation of models of pedestal structure is an important part of predicting pedestal height and performance in future tokamaks. The Thomson scattering diagnostic at DIII-D has been upgraded in support of validating these models. Spatial and temporal resolution, as well as signal to noise ratio, have all been specifically enhanced in the pedestal region. This region is now diagnosed by 20 view-chords with a spacing of 6 mm and a scattering length of just under 5 mm sampled at a nominal rate of 250 Hz. When mapped to the outboard midplane, this corresponds to ∼3 mm spacing. These measurements are being used to test critical gradient models, in which pedestal gradients increase in time until a threshold is reached. This paper will describe the specifications of the upgrade and present initial results of the system.
    The Review of scientific instruments 10/2012; 83(10):10E343. · 1.52 Impact Factor
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    ABSTRACT: As part of the FY2011 DOE Joint Research Target on Pedestal Physics, tests are being performed on DIII-D for gyrokinetic modes that have been proposed as physics mechanisms for controlling the H-mode pedestal structure. These modes include kinetic ballooning modes (KBM), candidates for limiting the total pedestal pressure gradient, ion temperature gradient modes (ITGM), candidates for limiting the Ti gradient at the pedestal top and electron temperature gradient modes (ETGM), candidates for limiting the Te gradient both in the pedestal and on top of the pedestal. The theoretical control parameters for these modes are αMHD for KBM, ηe for ETGM and ηi for ITGM. Experiments are being performed in DIII-D to determine if measured values of these parameters are close to the theoretical threshold values for the linear onset of these modes.
    11/2011;
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    ABSTRACT: The density profile of hydrogenic neutrals in the edge of DIII-D plays an important role in the problems of momentum transport, pedestal formation, and plasma-wall interaction, but an accurate measurement has proven difficult. A two-photon absorption laser induced fluorescence (TALIF) diagnostic is under construction and is intended to provide temporally and spatially resolved neutral density measurements in the pedestal region. This three-level TALIF scheme offers the advantages of direct excitation of ground state atoms, emission in the visible portion of the spectrum, a high degree of spatial localization, and the potential for a Doppler-free measurement. The large background of Dα emission, the principal challenge of the measurement, can be overcome by the focusing of a high power (1 MW) UV laser. Calculations of the SNR show that densities of 10^15 m-3 or lower can be measured with a spatial resolution of 0.3 mm. We present design details of the proposed laser system, calculations of the expected performance in DIII-D and in a helicon source plasma, and measurements of the HI profile in the helicon plasma.
    11/2011;
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    ABSTRACT: Various spatial heterodyne polarization interferometers for spectrally-resolved optical imaging of edge and core parameters in high temperature magnetized plasmas are described. Applications for such “coherence imaging” (CI) systems include imaging motional Stark effect and Zeeman effect polarimetry for determination of the magnetic field pitch angle, and passive and active (charge exchange recombination spectroscopy - CXRS) Doppler imaging of plasma temperature and flow. In this paper we describe spatial heterodyne coherence imaging systems and present first results of Doppler flow imaging in the DIII-D divertor.Instruments have been installed for imaging flows in the divertor and scrape-off-layer in the DIII-D tokamak and also for Doppler imaging on the H-1 heliac [1]. In the former case, single snapshot interferometric images of the plasma in CII 514nm, and CIII 465nm emission have been demodulated to obtain flow and ion temperature projections in both the scrape-off-layer and divertor. Flow field amplitudes in the divertor are found to be broad agreement with UEDGE modeling [2], and point the way towards experiments that address important divertor transport issues in future (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    Beiträge aus der Plasmaphysik 03/2011; 51(2‐3):194 - 200.
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    ABSTRACT: The radial diffusion coefficient for confined counter-passing MeV ions is evaluated in a new way, using measurements of escaping D-D fusion products. A class of passing ions near the plasma centre is measured whose orbits could eventually diffuse across their passing/trapped boundary, resulting in unconfined trapped orbits which can be detected at the plasma wall. The analysis indicates that the passing MeV ion diffusion coefficient D is smaller than ≈0.1 m2/s, which is small compared to the thermal diffusivities of ≈1 m2/s for these plasmas. The same experiment and analysis should be applicable to alpha particles in D-T plasmas.
    Nuclear Fusion 01/2011; 31(12):2219. · 2.73 Impact Factor
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    ABSTRACT: A detailed comparison between the observed and expected loss of alpha-like MeV fusion products in TFTR is presented. The D-D fusion products (mainly the 1 MeV triton) were measured with a 2-D imaging scintillation detector. The expected first-orbit loss was calculated with a simple Lorentz orbit code. In almost all cases the measured loss was consistent with the expected first-orbit loss model. Exceptions are noted for small major radius plasmas and during strong MHD activity.
    Nuclear Fusion 01/2011; 30(8):1551. · 2.73 Impact Factor
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    ABSTRACT: Two-dimensional (2D) imaging of electron temperature perturbations provides a powerful constraint for validating theoretical models describing magnetohydrodynamic plasma behavior. In observation of Alfvén wave induced temperature fluctuations, electron cyclotron emission imaging provides unambiguous determination of the 2D eigenmode structure. This has provided support for nonperturbative eigenmode solvers which predict symmetry breaking due to poloidal flows in the fast ion population. It is shown that for Alfvén eigenmodes, and in cases where convective flows or saturated perturbations lead to nonaxisymmetric equilibria, electron plasma displacements oriented parallel to a gradient in mean temperature are well defined. Furthermore, during highly dynamic behavior, such as the sawtooth crash, highly resolved 2D temperature behaviors yield valuable insight. In particular, addressing the role of adiabatic heating on time scales much shorter than the resistive diffusion time through the additional diagnosis of local electron density allows progress to be made toward a comprehensive understanding of fast reconnection in tokamak plasmas.
    Physics of Plasmas 01/2011; 18(5). · 2.38 Impact Factor
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    ABSTRACT: ITER will explore a plasma parameter envelope currently not available in tokamaks. This will require a set of diagnostics that can follow this envelope. To implement these diagnostics in a reliable and robust way requires development of current techniques in many areas to make them applicable to ITER: they need to be operable in the ITER environment and satisfy the physics and engineering requirements. In some cases, the exploitation of new techniques will be required. While much work has been carried out in this area, significant further work remains to bring the system to implementation.
    01/2011;
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    ABSTRACT: A new diagnostic system based on two-photon absorption laser-induced fluorescence (TALIF) has been developed to measure neutral hydrogen density in the edge of fusion plasmas. 205 nm photons from a frequency tripled dye laser are injected co-propagating into the plasma chamber where they excite the 1s-3D transition in neutral hydrogen. The 3D state then decays emitting light at 656 nm. The emission intensity is directly proportional to the ground state hydrogen density. With the tabulated atomic absorption rates for hydrogen and krypton, TALIF measurements of krypton gas provide an absolute calibration. Here we present the technical details and measured performance of the TALIF system (laser line width, pulse length, pulse energy, RMS stability) and TALIF measurements of room temperature krypton gas. The krypton measurements are compared to expectations and the measured line widths are analyzed in terms of Doppler and saturation broadening. We also present TALIF measurements of the radial profiles of the absolute neutral hydrogen and neutral temperature in a helicon plasma source as a function of source parameters.
    IEEE International Conference on Plasma Science 01/2011;
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    ABSTRACT: A new electron cyclotron emission imaging diagnostic has been commissioned on the DIII-D tokamak. Dual detector arrays provide simultaneous two-dimensional images of Te fluctuations over radially distinct and reconfigurable regions, each with both vertical and radial zoom capability. A total of 320 (20 vertical×16 radial) channels are available. First data from this diagnostic demonstrate the acquisition of coherent electron temperature fluctuations as low as 0.1% with excellent clarity and spatial resolution. Details of the diagnostic features and capabilities are presented.
    Review of Scientific Instruments 10/2010; 81(10):10D928-10D928-4. · 1.60 Impact Factor
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    ABSTRACT: This article describes the results of spatial heterodyne Doppler "coherence imaging" of carbon ion flows in the divertor region of the DIII-D tokamak. Spatially encoded interferometric projections of doubly ionized carbon emission at 465 nm have been demodulated and tomographically inverted to obtain the spatial distribution of the carbon ion parallel flow and emissivity. The operating principles of the new instruments are described, and the link between measured properties and line integrals of the flow field are established. An iterative simultaneous arithmetic reconstruction procedure is applied to invert the interferometric phase shift projections, and the reconstructed parallel flow field amplitudes are found to be in reasonable agreement with UEDGE modeling.
    The Review of scientific instruments 10/2010; 81(10):10E528. · 1.52 Impact Factor
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    ABSTRACT: A tangential viewing, 10.59 microm CO(2) laser polarimeter for electron density measurements based on plasma induced Faraday rotation has been installed on DIII-D. The system uses colinear right- and left-hand circularly polarized beams with a difference frequency of 40 MHz to generate the necessary signal for heterodyne phase detection. The high-resolution phase information required to adequately resolve degree level polarization rotation is obtained using an all-digital "real-time" phase demodulation scheme based on modern digital signal processing techniques. Initial application of the system to DIII-D disruption mitigation experiments utilizing "massive gas jet" injection exhibits reliable operation and excellent agreement with CO(2) interferometer measurements; interestingly, the obtained Faraday rotation angles are in the range of those expected in ITER plasmas.
    The Review of scientific instruments 11/2008; 79(10):10E719. · 1.52 Impact Factor

Publication Stats

1k Citations
166.62 Total Impact Points

Institutions

  • 2012
    • Sandia National Laboratories
      Albuquerque, New Mexico, United States
  • 2003–2012
    • General Atomics
      San Diego, California, United States
  • 1990–2011
    • Princeton University
      • Princeton Plasma Physics Laboratory
      Princeton, NJ, United States
  • 2010
    • Australian National University
      • Plasma Research Laboratory (PRL)
      Canberra, Australian Capital Territory, Australia
  • 1991–2003
    • Massachusetts Institute of Technology
      • Plasma Science and Fusion Center (PSFC)
      Cambridge, MA, United States