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Michael Schuler, Seth Whitsitt, Louis-Paul Henry, Subir Sachdev, Andreas M Läuchli
The low-energy spectra of many body systems on a torus, of finite size L, are well understood in magnetically ordered and gapped topological phases. However, the spectra at quantum critical points separating such phases are largely unexplored for (2+1)D systems. Using a combination of analytical and numerical techniques, we accurately calculate and analyze the low-energy torus spectrum at an Ising critical point which provides a universal fingerprint of the underlying quantum field theory, with the energy levels given by universal numbers times 1/L...
November 18, 2016: Physical Review Letters
T Nishizawa, M D Nornberg, D J Den Hartog, D Craig
The upgraded spectrometer used for charge exchange recombination spectroscopy on the Madison Symmetric Torus resolves emission fluctuations up to 400 kHz. The transimpedance amplifier's cutoff frequency was increased based upon simulations comparing the change in the measured photon counts for time-dynamic signals. We modeled each signal-processing stage of the diagnostic and scanned the filtering frequency to quantify the uncertainty in the photon counting rate. This modeling showed that uncertainties can be calculated based on assuming each amplification stage is a Poisson process and by calibrating the photon counting rate with a DC light source to address additional variation...
November 2016: Review of Scientific Instruments
P D VanMeter, P Franz, L M Reusch, J S Sarff, D J Den Hartog
The Soft X-Ray (SXR) tomography system on the Madison Symmetric Torus uses four cameras to determine the emissivity structure of the plasma. This structure should directly correspond to the structure of the magnetic field; however, there is an apparent phase difference between the emissivity reconstructions and magnetic field reconstructions when using a cylindrical approximation. The difference between the phase of the dominant rotating helical mode of the magnetic field and the motion of the brightest line of sight for each SXR camera is dependent on both the camera viewing angle and the plasma conditions...
November 2016: Review of Scientific Instruments
YooSung Kim, Yue-Jiang Shi, Jeong-Hun Yang, SeongCheol Kim, Young-Gi Kim, Jeong-Jeung Dang, Seongmoo Yang, Jungmin Jo, Soo-Ghee Oh, Kyoung-Jae Chung, Y S Hwang
No abstract text is available yet for this article.
November 2016: Review of Scientific Instruments
Wenzhe Mao, Peng Yuan, Jian Zheng, Weixing Ding, Hong Li, Tao Lan, Adi Liu, Wandong Liu, Jinlin Xie
A compact and lightweight support platform has been used as a holder for the interferometer system on the Keda Torus eXperiment (KTX), which is a reversed field pinch device. The vibration caused by the interaction between the time-varying magnetic field and the induced current driven in the metal optical components has been measured and, following comparison with the mechanical vibration of the KTX device and the refraction effect of the ambient turbulent air flow, has been identified as the primary vibration source in this case...
November 2016: Review of Scientific Instruments
Drew Elliott, Derek Sutherland, Umair Siddiqui, Earl Scime, Chris Everson, Kyle Morgan, Aaron Hossack, Brian Nelson, Tom Jarboe
Two-photon laser-induced fluorescence measurements were performed on the helicity injected torus (HIT-SI3) device to determine the density and temperature of the background neutral deuterium population. Measurements were taken in 2 ms long pulsed plasmas after the inductive helicity injectors were turned off. Attempts to measure neutrals during the main phase of the plasma were unsuccessful, likely due to the density of neutrals being below the detection threshold of the diagnostic. An unexpectedly low density of atomic deuterium was measured in the afterglow; roughly 100 times lower than the theoretical prediction of 10(17) m(-3)...
November 2016: Review of Scientific Instruments
M Nocente, D Rigamonti, V Perseo, M Tardocchi, G Boltruczyk, A Broslawski, A Cremona, G Croci, M Gosk, V Kiptily, S Korolczuk, M Mazzocco, A Muraro, E Strano, I Zychor, G Gorini
Gamma-ray spectroscopy measurements at MHz counting rates have been carried out, for the first time, with a compact spectrometer based on a LaBr3 scintillator and silicon photomultipliers. The instrument, which is also insensitive to magnetic fields, has been developed in view of the upgrade of the gamma-ray camera diagnostic for α particle measurements in deuterium-tritium plasmas of the Joint European Torus. Spectra were measured up to 2.9 MHz with a projected energy resolution of 3%-4% in the 3-5 MeV range, of interest for fast ion physics studies in fusion plasmas...
November 2016: Review of Scientific Instruments
E Parke, W X Ding, J Duff, D L Brower
Measuring high-frequency fluctuations (above tearing mode frequencies) is important for diagnosing instabilities and transport phenomena. The Madison Symmetric Torus interferometer-polarimeter system has been upgraded to utilize improved planar-diode mixer technology. The new mixers reduce phase noise and allow more sensitive measurements of fluctuations at high frequency. Typical polarimeter rms phase noise values of 0.05°-0.07° are obtained with 400 kHz bandwidth. The low phase noise enables the resolution of fluctuations up to 250 kHz for polarimetry and 600 kHz for interferometry...
November 2016: Review of Scientific Instruments
M Rebai, L Giacomelli, A Milocco, M Nocente, D Rigamonti, M Tardocchi, F Camera, C Cazzaniga, Z J Chen, T F Du, T S Fan, A Giaz, Z M Hu, T Marchi, X Y Peng, G Gorini
A Single-crystal Diamond (SD) detector prototype was installed at Joint European Torus (JET) in 2013 and the achieved results have shown its spectroscopic capability of measuring 2.5 MeV neutrons from deuterium plasmas. This paper presents measurements of the SD response function to monoenergetic neutrons, which is a key point for the development of a neutron spectrometer based on SDs and compares them with Monte Carlo simulations. The analysis procedure allows for a good reconstruction of the experimental results...
November 2016: Review of Scientific Instruments
Zichao Li, Hong Li, Cui Tu, Jintong Hu, Wei You, Bing Luo, Mingsheng Tan, Yolbarsop Adil, Yanqi Wu, Biao Shen, Bingjia Xiao, Ping Zhang, Wenzhe Mao, Hai Wang, Xiaohui Wen, Haiyang Zhou, Jinlin Xie, Tao Lan, Adi Liu, Weixing Ding, Chijin Xiao, Wandong Liu
In a reversed field pinch device, the conductive shell is placed as close as possible to the plasma so as to balance the plasma during discharge. Plasma instabilities such as the resistive wall mode and certain tearing modes, which restrain the plasma high parameter operation, respond closely with conditions in the wall, in essence the eddy current present. Also, the effect of eddy currents induced by the external coils cannot be ignored when active control is applied to control instabilities. One diagnostic tool, an eddy current probe array, detects the eddy current in the composite shell...
November 2016: Review of Scientific Instruments
W J Capecchi, J K Anderson, P J Bonofiglo, J Kim, S Sears
The neutron emissivity profile in the Madison Symmetric Torus is being reconstructed through the use of a collimated neutron detector. A scintillator-photomultiplier tube (PMT) system is employed to detect the fusion neutrons with the plasma viewing volume defined by a 55 cm deep, 5 cm diameter aperture. Effective detection of neutrons from the viewing volume is achieved through neutron moderation using 1300 lbs of high density polyethylene shielding, which modeling predicts attenuates the penetrating flux by a factor of 10(4) or more...
November 2016: Review of Scientific Instruments
P Beiersdorfer, E W Magee, N Hell, G V Brown
We describe a crystal spectrometer implemented on the Livermore electron beam ion traps that employ two spherically bent quartz crystals and a cryogenically cooled back-illuminated charge-coupled device detector to measure x rays with a nominal resolving power of λ/Δλ ≥ 10 000. Its focusing properties allow us to record x rays either with the plane of dispersion perpendicular or parallel to the electron beam and, thus, to preferentially select one of the two linear x-ray polarization components. Moreover, by choice of dispersion plane and focussing conditions, we use the instrument either to image the distribution of the ions within the 2 cm long trap region, or to concentrate x rays of a given energy to a point on the detector, which optimizes the signal-to-noise ratio...
November 2016: Review of Scientific Instruments
Jolien Dendooven, Eduardo Solano, Matthias M Minjauw, Kevin Van de Kerckhove, Alessandro Coati, Emiliano Fonda, Giuseppe Portale, Yves Garreau, Christophe Detavernier
We report the design of a mobile setup for synchrotron based in situ studies during atomic layer processing. The system was designed to facilitate in situ grazing incidence small angle x-ray scattering (GISAXS), x-ray fluorescence (XRF), and x-ray absorption spectroscopy measurements at synchrotron facilities. The setup consists of a compact high vacuum pump-type reactor for atomic layer deposition (ALD). The presence of a remote radio frequency plasma source enables in situ experiments during both thermal as well as plasma-enhanced ALD...
November 2016: Review of Scientific Instruments
A Muraro, L Giacomelli, M Nocente, M Rebai, D Rigamonti, F Belli, P Calvani, J Figueiredo, M Girolami, G Gorini, G Grosso, A Murari, S Popovichev, D M Trucchi, M Tardocchi
A prototype Single crystal Diamond Detector (SDD) was installed at the Joint European Torus (JET) in 2013 along an oblique line of sight and demonstrated the possibility to carry out neutron spectroscopy measurements with good energy resolution and detector stability in discharges heated by neutral beam injection and radio-frequency waves. Starting from these positive results, within the Vertical Neutron Spectrometer project of the Joint European Torus, we have developed a pixelated instrument consisting of a matrix of 12 independent SDDs, called the Diamond Vertical Neutron Spectrometer (DVNS), which boosts the detection efficiency of a single SDD by an order of magnitude...
November 2016: Review of Scientific Instruments
R G L Vann, K J Brunner, R Ellis, G Taylor, D A Thomas
The Synthetic Aperture Microwave Imaging (SAMI) system is a novel diagnostic consisting of an array of 8 independently phased antennas. At any one time, SAMI operates at one of the 16 frequencies in the range 10-34.5 GHz. The imaging beam is steered in software post-shot to create a picture of the entire emission surface. In SAMI's active probing mode of operation, the plasma edge is illuminated with a monochromatic source and SAMI reconstructs an image of the Doppler back-scattered (DBS) signal. By assuming that density fluctuations are extended along magnetic field lines, and knowing that the strongest back-scattered signals are directed perpendicular to the density fluctuations, SAMI's 2-D DBS imaging capability can be used to measure the pitch of the edge magnetic field...
November 2016: Review of Scientific Instruments
F Bedoya, J P Allain, R Kaita, C H Skinner, L Buzi, B E Koel
A novel Plasma Facing Components (PFCs) diagnostic, the Materials Analysis Particle Probe (MAPP), has been recently commissioned in the National Spherical Torus Experiment Upgrade (NSTX-U). MAPP is currently monitoring the chemical evolution of the PFCs in the NSTX-U lower divertor at 107 cm from the tokamak axis on a day-to-day basis. In this work, we summarize the methodology that was adopted to obtain qualitative and quantitative descriptions of the samples chemistry. Using this methodology, we were able to describe all the features in all our spectra to within a standard deviation of ±0...
November 2016: Review of Scientific Instruments
C M Jacobson, M T Borchardt, D J Den Hartog, A F Falkowski, L A Morton, M A Thomas
The Thomson scattering diagnostic on the Madison Symmetric Torus (MST) records excessive levels of stray Nd:YAG laser light. Stray light saturates the 1064 nm spectral channel in all polychromators, which prevents absolute electron density measurements via Rayleigh scattering calibration. Furthermore, stray light contaminates adjacent spectral channels for r/a ≥ 0.75, which renders the diagnostic unable to make electron temperature measurements at these radii. In situ measurements of stray light levels during a vacuum vessel vent are used to identify stray light sources and strategies for reduction of stray light levels...
November 2016: Review of Scientific Instruments
A H Seltzman, J K Anderson, A M DuBois, A Almagri, C B Forest
A pulse height analyzing x-ray tomography system has been developed to detect x-rays from electron Bernstein wave heated electrons in the Madison symmetric torus reversed field pinch (RFP). Cadmium zinc telluride detectors are arranged in a parallel beam array with two orthogonal multi-chord detectors that may be used for tomography. In addition a repositionable 16 channel fan beam camera with a 55° field of view is used to augment data collected with the Hard X-ray array. The chord integrated signals identify target emission from RF heated electrons striking a limiter located 12° toroidally away from the RF injection port...
November 2016: Review of Scientific Instruments
G Nemtsev, V Amosov, S Meshchaninov, S Popovichev, R Rodionov
We present the results of analysis of triton burn-up process using the data from diamond detector. Neutron monitor based on CVD diamond was installed in JET torus hall close to the plasma center. We measure the part of 14 MeV neutrons in scenarios where plasma current varies in a range of 1-3 MA. In this experiment diamond neutron monitor was also able to detect strong gamma bursts produced by runaway electrons arising during the disruptions. We can conclude that CVD diamond detector will contribute to the study of fast particles confinement and help predict the disruption events in future tokamaks...
November 2016: Review of Scientific Instruments
D Liu, W W Heidbrink, K Tritz, E D Fredrickson, G Z Hao, Y B Zhu
A compact and multi-view solid state neutral particle analyzer (SSNPA) diagnostic based on silicon photodiode arrays has been successfully tested on the National Spherical Torus Experiment-Upgrade. The SSNPA diagnostic provides spatially, temporally, and pitch-angle resolved measurements of fast-ion distribution by detecting fast neutral flux resulting from the charge exchange (CX) reactions. The system consists of three 16-channel subsystems: t-SSNPA viewing the plasma mid-radius and neutral beam (NB) line #2 tangentially, r-SSNPA viewing the plasma core and NB line #1 radially, and p-SSNPA with no intersection with any NB lines...
November 2016: Review of Scientific Instruments
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