Passive Spectroscopy Research Articles

ChemCam passive reflectance spectroscopy of surface materials at the Curiosity landing site, Mars

The spectrometers on the Mars Science Laboratory (MSL) ChemCam instrument were used in passive mode to record visible/near-infrared (400–840nm) radiance from the martian surface. Using the onboard ChemCam calibration targets’ housing as a reflectance standard, we developed methods to collect, calibrate, and reduce radiance observations to relative reflectance. Such measurements accurately reproduce the known reflectance spectra of other calibration targets on the rover, and represent the highest spatial resolution (0.65mrad) and spectral sampling (<1nm) visible/near-infrared reflectance spectra from a landed platform on Mars. Relative reflectance spectra of surface rocks and soils match those from orbital observations and multispectral data from the MSL Mastcam camera. Preliminary analyses of the band depths, spectral slopes, and reflectance ratios of the more than 2000 spectra taken during the first year of MSL operations demonstrate at least six spectral classes of materials distinguished by variations in ferrous and ferric components. Initial comparisons of ChemCam spectra to laboratory spectra of minerals and Mars analog materials demonstrate similarities with palagonitic soils and indications of orthopyroxene in some dark rocks. Magnesium-rich “raised ridges” tend to exhibit distinct near-infrared slopes. The ferric absorption downturn typically found for martian materials at <600nm is greatly subdued in brushed rocks and drill tailings, consistent with their more ferrous nature. Calcium-sulfate veins exhibit the highest relative reflectances observed, but are still relatively red owing to the effects of residual dust. Such dust is overall less prominent on rocks sampled within the “blast zone” immediately surrounding the landing site. These samples were likely affected by the landing thrusters, which partially removed the ubiquitous dust coatings. Increased dust coatings on the calibration targets during the first year of the mission were documented by the ChemCam passive measurements as well. Ongoing efforts to model and correct for this dust component should improve calibration of the relative reflectance spectra. This will be useful as additional measurements are acquired during the rover’s future examinations of hematite-, sulfate-, and phyllosilicate-bearing materials near the base of Mt. Sharp that are spectrally active in the 400–840nm region.

THE BLACK HOLE BINARY V4641 SAGITARII: ACTIVITY IN QUIESCENCE AND IMPROVED MASS DETERMINATIONS

We examine ~10 years of photometric data and find that the black hole X-ray binary V4641 Sgr has two optical states, passive and active, during X-ray quiescence. The passive state is dominated by ellipsoidal variations and is stable in the shape and variability of the light curve. The active state is brighter and more variable. Emission during the active state varies over the course of the orbital period and is redder than the companion star. These optical/infrared states last for weeks or months. V4641 Sgr spends approximately 85% of X-ray quiescence in the passive state and 15% in the active. We analyze passive colors and spectroscopy of V4641 Sgr and show that they are consistent with a reddened B9III star (with E(B-V) = 0.37 +/- 0.19) with little or no contribution from the accretion disk. We use X-ray observations with an updated ephemeris to place an upper limit on the duration of an X-ray eclipse of <8.3 deg in phase (~1.6 hours). High resolution spectroscopy yields a greatly improved measurement of the rotational velocity of the companion star of V_rot_sin(i) = 100.9 +/- 0.8 km s^-1. We fit ellipsoidal models to the passive state data and find an inclination angle of i = 72.3 +/- 4.1 deg, a mass ratio of Q = 2.2 +/- 0.2, and component masses for the system of M_BH = 6.4 +/- 0.6 M_sun and M_2 = 2.9 +/- 0.4 M_sun. Using these values we calculate an updated distance to V4641 Sgr of 6.2 +/- 0.7 kpc.

Determination of isotopic ratios of uranium samples using passive gamma spectroscopy with multiple detectors

Uranium samples of various enrichments have been passively counted on the University of Texas detector gamma–gamma coincidence system. By observing gamma rays emitted from 235U and its daughters compared to gamma rays emitted by 238U daughters and comparing the data to standards of known enrichments, a technique has been developed to take a uranium sample of unknown enrichment and passively count it to determine its uranium isotopic concentration. Because the gamma rays from 235U are generally in the low-energy regime, there is a strong susceptibility to background interferences, especially from the Compton background produced from higher energy gamma rays. Other interferences, such as those from the decay series of uranium also exist for 235U gamma rays. In this light, we have collected data using list-mode to produce two-dimensional gamma–gamma coincidence spectra, which allows us to gate the low-energy gamma rays from 235U with gamma rays that are in coincidence. In doing this, much of the low energy interferences are reduced, and one can analyze the 235U gamma rays with high precision. Because of the high density of uranium, self-shielding has significant effects especially in the low-energy regime. To correct for this attenuation the detector system has been modeled by MCNP and self-shielding factors have been calculated across the energy spectrum. A big advantage to this method is the capability of performing this analysis with small (<1 g) samples in a non-destructive and relatively inexpensive manner. If necessary, this analysis can be performed within 24 h if an urgent nuclear forensics scenario arises.

Suprathermal ion studies in ECRH and NBI phases of the TJ-II stellarator

The goal of this work is to study the empirical behaviour of suprathermal ions in the electron cyclotron resonance heating (ECRH) and neutral-beam injection (NBI) phases of the TJ-II stellarator. Our approach combines passive emission spectroscopy, which detects confined suprathermal ions with energies up to hundreds of electronvolts, and a luminescent probe operated as a multichannel fast-ion energy spectrometer using pulse height analysis, which detects suprathermal ions with energies ⩾1 keV that escape from the plasma. We will present data taken from density and power scans of TJ-II ECRH plasmas and the spatial and time response of suprathermal protons and impurities in both scenarios. The comparative behaviour between the suprathermal ions present in the plasma and those escaping ions may shed some light on the physical mechanisms responsible for the generation and confinement of these ions.

Spectroscopic measurements of Be erosion at JET ILW and interpretation with ERO modelling

Beryllium (Be) erosion has been studied in dedicated limiter discharges in JET with the recently installed ITER-like wall [1]. Passive spectroscopy [2] in the vicinity of the solid Be limiter is used for measurement of the Be physical sputtering as the main erosion mechanism. To consider the 3D configuration of plasma parameters and the electromagnetic field, the actual limiter shape and the local transport affecting the fraction of Be coming into the observation volume, a detailed modelling with the ERO code has been applied to interpret the experimental data. The observed dependence of BeI and BeII line intensities on plasma parameters during the density scan and various line ratios are used to validate the model and the underlying data including the recently introduced assumptions for Be physical sputtering, the very same which were used before for ITER predictive modelling [3].

The ChemCam Instrument Suite on the Mars Science Laboratory (MSL) Rover: Science Objectives and Mast Unit Description

ChemCam is a remote sensing instrument suite on board the “Curiosity” rover (NASA) that uses Laser-Induced Breakdown Spectroscopy (LIBS) to provide the elemental composition of soils and rocks at the surface of Mars from a distance of 1.3 to 7 m, and a telescopic imager to return high resolution context and micro-images at distances greater than 1.16 m. We describe five analytical capabilities: rock classification, quantitative composition, depth profiling, context imaging, and passive spectroscopy. They serve as a toolbox to address most of the science questions at Gale crater. ChemCam consists of a Mast-Unit (laser, telescope, camera, and electronics) and a Body-Unit (spectrometers, digital processing unit, and optical demultiplexer), which are connected by an optical fiber and an electrical interface. We then report on the development, integration, and testing of the Mast-Unit, and summarize some key characteristics of ChemCam. This confirmed that nominal or better than nominal performances were achieved for critical parameters, in particular power density (>1 GW/cm2). The analysis spot diameter varies from 350 μm at 2 m to 550 μm at 7 m distance. For remote imaging, the camera field of view is 20 mrad for 1024×1024 pixels. Field tests demonstrated that the resolution (∼90 μrad) made it possible to identify laser shots on a wide variety of images. This is sufficient for visualizing laser shot pits and textures of rocks and soils. An auto-exposure capability optimizes the dynamical range of the images. Dedicated hardware and software focus the telescope, with precision that is appropriate for the LIBS and imaging depths-of-field. The light emitted by the plasma is collected and sent to the Body-Unit via a 6 m optical fiber. The companion to this paper (Wiens et al. this issue) reports on the development of the Body-Unit, on the analysis of the emitted light, and on the good match between instrument performance and science specifications.

The ChemCam Instrument Suite on the Mars Science Laboratory (MSL) Rover: Body Unit and Combined System Tests

The ChemCam instrument suite on the Mars Science Laboratory (MSL) rover Curiosity provides remote compositional information using the first laser-induced breakdown spectrometer (LIBS) on a planetary mission, and provides sample texture and morphology data using a remote micro-imager (RMI). Overall, ChemCam supports MSL with five capabilities: remote classification of rock and soil characteristics; quantitative elemental compositions including light elements like hydrogen and some elements to which LIBS is uniquely sensitive (e.g., Li, Be, Rb, Sr, Ba); remote removal of surface dust and depth profiling through surface coatings; context imaging; and passive spectroscopy over the 240–905 nm range. ChemCam is built in two sections: The mast unit, consisting of a laser, telescope, RMI, and associated electronics, resides on the rover’s mast, and is described in a companion paper. ChemCam’s body unit, which is mounted in the body of the rover, comprises an optical demultiplexer, three spectrometers, detectors, their coolers, and associated electronics and data handling logic. Additional instrument components include a 6 m optical fiber which transfers the LIBS light from the telescope to the body unit, and a set of onboard calibration targets. ChemCam was integrated and tested at Los Alamos National Laboratory where it also underwent LIBS calibration with 69 geological standards prior to integration with the rover. Post-integration testing used coordinated mast and instrument commands, including LIBS line scans on rock targets during system-level thermal-vacuum tests. In this paper we describe the body unit, optical fiber, and calibration targets, and the assembly, testing, and verification of the instrument prior to launch.

Beams, brightness, and background: Using active spectroscopy techniques for precision measurements in fusion plasma research

The use of an injected neutral beam—either a dedicated diagnostic beam or the main heating beams—to localize and enhance plasma spectroscopic measurements can be exploited for a number of key physics issues in magnetic confinement fusion research, yielding detailed profile information on thermal and fast ion parameters, the radial electric field, plasma current density, and turbulent transport. The ability to make these measurements has played a significant role in much of our recent progress in the scientific understanding of fusion plasmas. The measurements can utilize emission from excited state transitions either from plasma ions or from the beam atoms themselves. The primary requirement is that the beam “probe” interacts with the plasma in a known fashion. Advantages of active spectroscopy include high spatial resolution due to the enhanced localization of the emission and the use of appropriate imaging optics, background rejection through the appropriate modulation and timing of the beam and emission collection/detection system, and the ability of the beam to populate emitter states that are either nonexistent or too dim to utilize effectively in the case of standard or passive spectroscopy. In addition, some active techniques offer the diagnostician unique information because of the specific quantum physics responsible for the emission. This paper will describe the general principles behind a successful active spectroscopic measurement, emphasize specific techniques that facilitate the measurements and include several successful examples of their implementation, briefly touching on some of the more important physics results. It concludes with a few remarks about the relevance and requirements of active spectroscopic techniques for future burning plasma experiments.

3D vector tomography using vector spherical harmonics decomposition

The article presents the reconstruction method of the flow fields from vector tomography passive ion Doppler spectroscopy in a plasma experiment. The method is based on series expansion in terms of vector spherical harmonics for volumetric, divergent-free vector fields and intended for three-dimensional diagnostic in the spherical tokamak devices. An inversion of spectral experimental data is known in tomography as an inversion of vectorial ray transform. The relation of the vectorial ray transform with Doppler spectroscopy measurements are given in Balandin and Ono (2001, 2003) [7,8]. The effectiveness of the proposed method is tested on a range of model 3D divergent-free vector fields.

Microwave discharge in a finite length vessel

A microwave surface-wave discharge at low pressure in a finite length vessel is experimentally investigated. Argon plasma is created in a dielectric capillary with length of 15 mm, the tube being an extension of an open-ended coaxial structure. Microwave power at frequency 2.45 GHz is coupled into the source applicator at power levels 6-15 W. The plasma column increases with the power applied and standing wave mode is realized when its length is equal to the capillary length. The electron temperature and plasma density are obtained simultaneously by passive optical emission spectroscopy using the line-ratio method. The surface waves phase-diagram shows that their wavelengths are much lower than the free-space wavelength. The input impedance of the plasma column - modelled as a lossy transmission line - has resonance behaviour when its length is equal to λg/2 or λg (λg being the surface waves wavelength). The results obtained for the plasma parameters, the surface waves wavelength and the vessel length show correlation to the power reflected, absorbed and radiated from the plasma column. The radiation pattern of the column shows that the main lobe is nearly perpendicular to the capillary axis.

Referenced passive spectroscopy using dual frequency combs

A referenced passive spectroscopy scheme using infrared frequency combs is presented. We perform a noise analysis and compare the results with a classical Fourier transform spectrometer. Experimental results are shown and great agreement with theory is obtained.

Flow measurements and modelling in helical RFX-mod equilibria

In the reversed field pinch experiment RFX-mod, plasma currents larger than 1 MA show a spontaneous transition from an axisymmetric to a helical configuration, where electron internal transport barriers (eITB) are observed in the proximity of the maximum of the q safety factor. 3D MHD simulations predict a helical flow pattern associated with the helical deformation of the magnetic flux surfaces. This paper reports the recent experimental findings on plasma flow in these helical regimes. Passive spectroscopy measurements of carbon and boron line Doppler shift allow the reconstruction of the m = 1 component of the velocity pattern associated with the helical equilibrium in a poloidal cross-section. The helical plasma flow is observed to form a m = 1 convective cell creating a localized sheared flow outside the region of strong electron temperature gradients characterizing the eITB. The experimental pattern is compared with the results of 3D MHD simulations (by means of the SpeCyl code). While the code predicts a flow shear peaking in the proximity of the null of the magnetic shear, where the safety factor is maximum, experimentally the maximum flow shear is found to be more external, leaving as a still open question the role played by the flow shear for the thermal barrier formation in RFX-mod helical plasmas.

Global observations of thermospheric temperature and nitric oxide from MIPAS spectra at 5.3μm

[1] We present vertically resolved thermospheric temperatures and NO abundances in terms of volume mixing ratio retrieved simultaneously from spectrally resolved 5.3 μm emissions recorded by the Michelson Interferometer for Passive Atmospheric Spectroscopy (MIPAS) in its upper atmospheric observation mode during 2005–2009. These measurements are unique since they represent the first global observations of temperature and NO for both day and night conditions taken from space. A retrieval scheme has been developed which accounts for vibrational, rotational and spin-orbit non-LTE distributions of NO. Retrieved polar temperature and NO profiles have a vertical resolution of 5–10 km for high Ap values, and degrade to 10–20 km for low Ap conditions. Though retrieved NO abundances depend strongly on the atomic oxygen profile used in the non-LTE modeling, observations can be compared to model results in a consistent manner by applying a simple correction. Apart from this, total retrieval errors are dominated by instrumental noise. The typical single measurement precision of temperature and NO abundances are 5–40 K and 10–30%, respectively, for high Ap values, increasing to 30–70 K for Tk and 20–50% for NO VMR for low Ap conditions. Temperature and NO profiles observed under auroral conditions are rather insensitive to smoothing errors related to the mapping of a priori profile shapes. However, for extra-polar and low Ap conditions, a potential systematic bias in the retrieved nighttime temperature and NO profiles related to smoothing errors has been identified from a comparison to Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) simulations. We have constructed a solar minimum monthly climatology of thermospheric temperature and NO from MIPAS observations taken during 2008–2009. MIPAS temperature distributions agree well, on average, with the Mass Spectrometer and Incoherent Scatter radar model (NRLMSISE-00), but some systematic differences exist. MIPAS temperatures are generally colder than NRLMSISE-00 in the polar middle thermosphere (mainly in the summer polar region) by up to 40 K; and are warmer than NRLMSISE-00 in the lower thermosphere around 120–125 km by 10–40 K. Thermospheric NO daytime distributions agree well with the Nitric Oxide Empirical Model (NOEM), based on Student Nitric Oxide Explorer (SNOE) observations. A comparison of MIPAS NO number density with the previous climatology for the declining phases of the solar cycle based on HALOE and SME data shows that MIPAS is generally larger with values ranging from 10 to 40%, except in the auroral region and at the equatorial latitudes above 130 km where the MIPAS/HALOE+SME ratio varies from 1.6 to 2. Day-night differences in MIPAS NO show daytime enhancements of up to 140% in the tropical and midlatitudes middle thermosphere. In the lower thermosphere, the diurnal amplitude is smaller and NO concentrations are generally higher during night by about 10–30%, particularly in the auroral regions.

Observation of Anomalous Ion Heating by Broadband Drift-Wave Turbulence

Using laser induced fluorescence and passive spectroscopy on a magnetically confined low-temperature plasma, anomalous ion heating is observed which exceeds collisional heating from the electrons by a factor of up to five. Direct wave heating due to the 2.45GHz microwave as well as stochastic heating by large-amplitude fluctuations could be ruled out as explanations. Good quantitative agreement is found when comparing the missing power in the ion species with heating power due to the dissipation of drift-wave turbulence. This turbulent energy transfer into the ion channel could have important consequences for the interpretation of transport in fusion plasmas.

Core Impurity Transport Studies from Different Diagnostic Approaches in LHD

Impurity transport has been studied in the Large Helical Device (LHD) with different diagnostic approaches based on an active method that combine carbon pellet injection with visible bremsstrahlung measurement and three passive methods for radial profile measurements of Ar and Fe Kα X-ray lines, Zeff, and extreme ultraviolet (EUV, ≤500 Å) impurity line emissions, in addition to usual passive spectroscopy. The existence of an inward convective velocity is confirmed in the edge region (ρ > 0.6) using the active method, whereas no convection is required in the core region (ρ < 0.6). The electron density dependence is weak for the diffusion coefficient (typically D = 0.15 to 0.25 m2/s) for densities of 1 to 5 × 1013 cm-3 but is strong for the inward convective velocity, which varies in the range of V(a) = −0.2 to −1.5 m/s. The inward V in helium plasmas (−0.4 m/s at ρ = 0.8 and the central density, ne ~ 4.0 × 1013 cm−3) is nearly half that in hydrogen plasmas (−0.7 m/s). This difference suggests a charge state dependence of fuel ions predicted by the neoclassical theory. Radial profiles of impurity transport coefficients of argon and iron have been studied using spatially resolved soft X-ray pulse-height analyzers. The impurity transport has also been studied in extremely high density discharges achieved by H2 pellet injection based on the passive spectroscopy and Zeff profile measurement. A flat Zeff profile is obtained at ne = 2.5 × 1014 cm−3 with values of 1.1 ≤ Zeff ≤ 1.2, suggesting no existence of impurity accumulation and radially constant impurity partial pressure. Finally, radial profiles of impurity lines in the EUV range are analyzed with the transport coefficients.

Modelling of passive spectroscopy in the ITER divertor: the first hydrogen Balmer lines

The first lines of the hydrogen Balmer series are investigated in ITER divertor conditions using a line shape code and a plasma edge transport code. It is shown that most of the emissivity originates from a localized, cold and dense region close to the divertor target plates, where the plasma is in the recombining regime. We simulate the signal obtained by pointing a spectrometer at this zone. The physical processes which contribute to the spectral line formation are examined, with a special emphasis on the Stark effect, photon absorption and stimulated emission. It is shown that, even though the Stark effect is significant, local information on the Doppler atomic temperature can be obtained from a fitting analysis of the Dα spectral line shape.

Probing the edge ion temperature by passive Doppler spectroscopy in the TJ-II stellarator

We report on the measurement of the edge ion temperature in TJ-II plasmas, heated by electron cyclotron waves and neutral beam injection, using passive spectroscopy of impurity ions in low ionization stages. The measurements, which provide both temporal and some spatial resolution, offer some advantages over more intrusive or more sophisticated methods. The capabilities and limitations of this approach are illustrated by showing typical results obtained under conditions of interest for fusion plasmas.

Rapid petroleum potential assessment of Bantumilli marginal oil field using infrasonic passive differential spectroscopy

Rapid petroleum potential assessment of Bantumilli marginal oil field using infrasonic passive differential spectroscopy

Is the future of seismic passive?

Ernst D. (Paul) Rode, Hatem Nasr and Monzer Makhous introduce their work on the possibilities of passive seismic, particularly infrasonic passive differential spectroscopy, as a supporting technology for reflection seismic and other methods. A separate article follows with a case study of the techniques used in India.

The spatial distribution of the reactive iodine species IO from simultaneous active and passive DOAS observations

Abstract. We present investigations of the reactive iodine species (RIS) IO, OIO and I2 in a coastal region from a field campaign simultaneously employing active long path differential optical absorption spectroscopy (LP-DOAS) as well as passive multi-axis differential optical absorption spectroscopy (MAX-DOAS). The campaign took place at the Martin Ryan Institute (MRI) in Carna, County Galway at the Irish West Coast about 6 km south-east of the atmospheric research station Mace Head in summer 2007. In order to study the horizontal distribution of the trace gases of interest, we established two almost parallel active LP-DOAS light paths, the shorter of 1034 m length just crossing the intertidal area, whereas the longer one of 3946 m length also crossed open water during periods of low tide. In addition we operated two passive Mini-MAX-DOAS instruments with the same viewing direction. While neither OIO nor I2 could be unambiguously identified with any of the instruments, IO could be detected with active as well as passive DOAS. The IO column densities seen at both active LP-DOAS light paths are almost the same. Thus it can be concluded that coastal IO is almost exclusively located in the intertidal area, where we detected mixing ratios of up to 29±8.8 ppt (equivalent to pmol/mol). Nucleation events with particle concentrations of 106 cm−3 particles were observed each day correlating with high IO mixing ratios. Therefore we feel that our detected IO concentrations confirm the results of model studies, which state that in order to explain such particle bursts, IO mixing ratios of 50 to 100 ppt in so called "hot-spots" are required.