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Jun 2012

Volume 83, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 83, 061101 (2012); http://dx.doi.org/10.1063/1.4720102 (35 pages)

Marcel Lucas and Elisa Riedo

Versatility from combining scanning probe microscopy with optical spectroscopy. Scanning probe microscopy can characterize (top, left to right) mechanical properties, topography, transport properties and chemical composition of the sample. Optical spectroscopy (bottom, left to right) can probe chemical composition, crystal structure, and deformation, and map them in hyperspectral images.

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back to top Nuclear Physics, Fusion and Plasmas

A linear helicon plasma device with controllable magnetic field gradient

Kshitish K. Barada, P. K. Chattopadhyay, J. Ghosh, Sunil Kumar, and Y. C. Saxena

Rev. Sci. Instrum. 83, 063501 (2012); http://dx.doi.org/10.1063/1.4723816 (6 pages) | Cited 2 times

Online Publication Date: 1 June 2012

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Current free double layers (CFDLs) are localized potential structures having spatial dimensions – Debye lengths and potential drops of more than local electron temperature across them. CFDLs do not need a current for them to be sustained and hence they differ from the current driven double layers. Helicon antenna produced plasmas in an expanded chamber along with an expanding magnetic field have shown the existence of CFDL near the expansion region. A helicon plasma device has been designed, fabricated, and installed in the Institute for Plasma Research, India to study the role of maximum magnetic field gradient as well as its location with respect to the geometrical expansion region of the chamber in CFDL formation. The special feature of this machine consisting of two chambers of different radii is its capability of producing different magnetic field gradients near the physical boundary between the two chambers either by changing current in one particular coil in the direction opposite to that in other coils and/or by varying the position of this particular coil. Although, the machine is primarily designed for CFDL experiments, it is also capable of carrying out many basic plasma physics experiments such as wave propagation, wave coupling, and plasma instabilities in a varying magnetic field topology. In this paper, we will present the details of the machine construction, its specialties, and some preliminary results about the production and characterization of helicon plasma in this machine.
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52.75.-d Plasma devices
52.25.Fi Transport properties
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Magnetic bucket for rotating unmagnetized plasma

Noam Katz, Cami Collins, John Wallace, Mike Clark, David Weisberg, Jon Jara-Almonte, Ingrid Reese, Carl Wahl, and Cary Forest

Rev. Sci. Instrum. 83, 063502 (2012); http://dx.doi.org/10.1063/1.4723820 (6 pages)

Online Publication Date: 1 June 2012

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A new experiment is described which generates flow in unmagnetized plasma. Confinement is provided by a cage of permanent magnets, arranged to form an axisymmetric, high-order, multipolar magnetic field. This field configuration—sometimes called a “magnetic bucket”—has a vanishingly small field in the core of the experiment. Toroidal rotation is driven by J × B forces applied in the magnetized edge. The cross-field current that is required for this forcing flows from anodes to thermionic cathodes, which are inserted between the magnet rings. The rotation at the edge reaches 3 km/s and is viscously coupled to the unmagnetized core plasma. We describe the conditions necessary for rotation, as well as a 0-dimensional power balance used to understand plasma confinement in the experiment.
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52.55.Lf Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps
52.30.-q Plasma dynamics and flow
52.25.Fi Transport properties

Surface analysis using a new plasma assisted desorption/ionisation source for mass spectrometry in ambient air

A. Bowfield, D. A. Barrett, M. R. Alexander, C. A. Ortori, F. M. Rutten, T. L. Salter, I. S. Gilmore, and J. W. Bradley

Rev. Sci. Instrum. 83, 063503 (2012); http://dx.doi.org/10.1063/1.4729120 (7 pages) | Cited 1 time

Online Publication Date: 12 June 2012

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The authors report on a modified micro-plasma assisted desorption/ionisation (PADI) device which creates plasma through the breakdown of ambient air rather than utilising an independent noble gas flow. This new micro-PADI device is used as an ion source for ambient mass spectrometry to analyse species released from the surfaces of polytetrafluoroethylene, and generic ibuprofen and paracetamol tablets through remote activation of the surface by the plasma. The mass spectra from these surfaces compare favourably to those produced by a PADI device constructed using an earlier design and confirm that the new ion source is an effective device which can be used to achieve ambient mass spectrometry with improved spatial resolution.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
52.75.-d Plasma devices

Calibration of the neutron detectors for the cluster fusion experiment on the Texas Petawatt Laser

W. Bang, H. J. Quevedo, G. Dyer, J. Rougk, I. Kim, M. McCormick, A. C. Bernstein, and T. Ditmire

Rev. Sci. Instrum. 83, 063504 (2012); http://dx.doi.org/10.1063/1.4729121 (7 pages) | Cited 2 times

Online Publication Date: 13 June 2012

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Three types of neutron detectors (plastic scintillation detectors, indium activation detectors, and CR-39 track detectors) were calibrated for the measurement of 2.45 MeV DD fusion neutron yields from the deuterium cluster fusion experiment on the Texas Petawatt Laser. A Cf-252 neutron source and 2.45 MeV fusion neutrons generated from laser-cluster interaction were used as neutron sources. The scintillation detectors were calibrated such that they can detect up to 108 DD fusion neutrons per shot in current mode under high electromagnetic pulse environments. Indium activation detectors successfully measured neutron yields as low as 104 per shot and up to 1011 neutrons. The use of a Cf-252 neutron source allowed cross calibration of CR-39 and indium activation detectors at high neutron yields (∼1011). The CR-39 detectors provided consistent measurements of the total neutron yield of Cf-252 when a modified detection efficiency of 4.6×10−4 was used. The combined use of all three detectors allowed for a detection range of 104 to 1011 neutrons per shot.
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29.40.-n Radiation detectors
06.20.fb Standards and calibration
29.25.Dz Neutron sources

Soft x-ray tomography for real-time applications: present status at Tore Supra and possible future developments

D. Mazon, D. Vezinet, D. Pacella, D. Moreau, L. Gabelieri, A. Romano, P. Malard, J. Mlynar, R. Masset, and P. Lotte

Rev. Sci. Instrum. 83, 063505 (2012); http://dx.doi.org/10.1063/1.4730044 (14 pages)

Online Publication Date: 21 June 2012

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This paper is focused on the soft x-ray (SXR) tomography system setup at Tore Supra (DTOMOX) and the recent developments made to automatically get precise information about plasma features from inverted data. The first part describes the main aspects of the tomographic inversion optimization process. Several observations are made using this new tool and a set of shape factors is defined to help characterizing the emissivity field in a real-time perspective. The second part presents a detailed off-line analysis comparing the positions of the magnetic axis obtained from a magnetic equilibrium solver, and the maximum of the reconstructed emissivity field for ohmic and heated pulses. A systematic discrepancy of about 5 cm is found in both cases and it is shown that this discrepancy increases during sawtooth crashes. Finally, evidence of radially localized tungsten accumulation with an in–out asymmetry during a lower hybrid current drive pulse is provided to illustrate the DTOMOX capabilities for a precise observation of local phenomena.
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52.55.Fa Tokamaks, spherical tokamaks
52.70.La X-ray and γ-ray measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Nr Plasma heating by DC fields; ohmic heating, arcs

Source characterization and modeling development for monoenergetic-proton radiography experiments on OMEGA

M. J.-E. Manuel, A. B. Zylstra, H. G. Rinderknecht, D. T. Casey, M. J. Rosenberg, N. Sinenian, C. K. Li, J. A. Frenje, F. H. Séguin, and R. D. Petrasso

Rev. Sci. Instrum. 83, 063506 (2012); http://dx.doi.org/10.1063/1.4730336 (9 pages) | Cited 4 times

Online Publication Date: 22 June 2012

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A monoenergetic proton source has been characterized and a modeling tool developed for proton radiography experiments at the OMEGA [T. R. Boehly et al., Opt. Comm. 133, 495 (1997)]10.1016/S0030-4018(96)00325-2 laser facility. Multiple diagnostics were fielded to measure global isotropy levels in proton fluence and images of the proton source itself provided information on local uniformity relevant to proton radiography experiments. Global fluence uniformity was assessed by multiple yield diagnostics and deviations were calculated to be ∼16% and ∼26% of the mean for DD and D3He fusion protons, respectively. From individual fluence images, it was found that the angular frequencies of ≳50 rad−1 contributed less than a few percent to local nonuniformity levels. A model was constructed using the Geant4 [S. Agostinelli et al., Nuc. Inst. Meth. A 506, 250 (2003)]10.1016/S0168-9002(03)01368-8 framework to simulate proton radiography experiments. The simulation implements realistic source parameters and various target geometries. The model was benchmarked with the radiographs of cold-matter targets to within experimental accuracy. To validate the use of this code, the cold-matter approximation for the scattering of fusion protons in plasma is discussed using a typical laser-foil experiment as an example case. It is shown that an analytic cold-matter approximation is accurate to within ≲10% of the analytic plasma model in the example scenario.
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52.50.Dg Plasma sources
52.65.-y Plasma simulation
52.70.La X-ray and γ-ray measurements
02.60.Gf Algorithms for functional approximation

A new method for determining the plasma electron density using three-color interferometer

Hiroyuki Arakawa, Yasunori Kawano, and Kiyoshi Itami

Rev. Sci. Instrum. 83, 063507 (2012); http://dx.doi.org/10.1063/1.4731651 (7 pages) | Cited 1 time

Online Publication Date: 28 June 2012

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A new method for determining the plasma electron density using the fractional fringes on three-color interferometer is proposed. Integrated phase shift on each interferometer is derived without using the temporal history of the fractional fringes. The dependence on the fringe resolution and the electrical noise are simulated on the wavelengths of CO2 laser. Short-time integrations of the fractional fringes enhance the reliability of this method.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
42.60.-v Laser optical systems: design and operation
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
07.60.Ly Interferometers
52.25.-b Plasma properties
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