In situ calibration of neutron activation system on the large helical device

In situ calibration of the neutron activation system on the Large Helical Device (LHD) was performed by using an intense ²⁵²Cf neutron source. To simulate a ring-shaped neutron source, we installed a railway inside the LHD vacuum vessel and made a train loaded with the ²⁵²Cf source run along a typical magnetic axis position. Three activation capsules loaded with thirty pieces of indium foils stacked with total mass of approximately 18 g were prepared. Each capsule was irradiated over 15 h while the train was circulating. The activation response coefficient (9.4 ± 1.2) × 10^-8 of ¹¹⁵In(n, n')^115mIn reaction obtained from the experiment is in good agreement with results from three-dimensional neutron transport calculations using the Monte Carlo neutron transport simulation code 6. The activation response coefficients of 2.45 MeV birth neutron and secondary 14.1 MeV neutron from deuterium plasma were evaluated from the activation response coefficient obtained in this calibration experiment with results from three-dimensional neutron calculations using the Monte Carlo neutron transport simulation code 6.

Probabilistic n/γ discrimination with robustness against outliers for use in neutron profile monitors

A method to stochastically discriminate neutron and γ-ray signals measured with a stilbene organic scintillator is proposed. Each pulse signal was stochastically categorized into two groups: neutron and γ-ray. In previous work, the Expectation Maximization (EM) algorithm was used with the assumption that the measured data followed a Gaussian mixture distribution. It was shown that probabilistic discrimination between these groups is possible. Moreover, by setting the initial parameters for the Gaussian mixture distribution with a k-means algorithm, the possibility of automatic discrimination was demonstrated. In this study, the Student's t-mixture distribution was used as a probabilistic distribution with the EM algorithm to improve the robustness against the effect of outliers caused by pileup of the signals. To validate the proposed method, the figures of merit (FOMs) were compared for the EM algorithm assuming a t-mixture distribution and a Gaussian mixture distribution. The t-mixture distribution resulted in an improvement of the FOMs compared with the Gaussian mixture distribution. The proposed data processing technique is a promising tool not only for neutron and γ-ray discrimination in fusion experiments but also in other fields, for example, homeland security, cancer therapy with high energy particles, nuclear reactor decommissioning, pattern recognition, and so on.

Suppression of Trapped Energetic Ions Driven Resistive Interchange Modes with Electron Cyclotron Heating in a Helical Plasma

The resistive interchange mode destabilized by the resonant interaction with the trapped energetic ions is fully suppressed when the injected power of electron cyclotron heating exceeds a certain threshold. It is shown for the first time that the complete stabilization of the energetic-particle-driven mode without relaxing the energetic particle (EP) pressure gradient is possible by reducing the radial width of the eigenmodes δ_{w}, especially when δ_{w} narrows to a small enough value relative to the finite orbit width of EP.

Novel pre-therapeutic scoring system using patient and haematological data to predict facial palsy prognosis

OBJECTIVES

We describe a novel scoring system, the facial Palsy Prognosis Prediction score (PPP score), which we test for reliability in predicting pre-therapeutic prognosis of facial palsy. We aimed to use readily available patient data that all clinicians have access to before starting treatment.

DESIGN

Multicenter case series with chart review.

SETTING

Three tertiary care hospitals.

PARTICIPANTS

We obtained haematological and demographic data from 468 facial palsy patients who were treated between 2010 and 2014 in three tertiary care hospitals. Patients were categorised as having Bell's palsy or Ramsey Hunt's palsy.

MAIN OUTCOME MEASURES

We compared the data of recovered and unrecovered patients. PPP scores consisted of combinatorial threshold values of continuous patient data (eg platelet count) and categorical variables (eg gender) that best predicted recovery. We created separate PPP scores for Bell's palsy patients (PPP-B) and for Ramsey Hunt's palsy patients (PPP-H).

RESULTS

The PPP-B score included age (≥65 years), gender (male) and neutrophil-to-lymphocyte ratio (≥2.9). The PPP-H score included age (≥50 years), monocyte rate (≥6.0%), mean corpuscular volume (≥95 fl) and platelet count (≤200 000 /μL). Patient recovery rate significantly decreased with increasing PPP scores (both PPP-B and PPP-H) in a step-wise manner. PPP scores (ie PPP-B score and PPP-H score) ≥2 were associated with worse than average prognosis.

CONCLUSIONS

Palsy Prognosis Prediction scores are useful for predicting prognosis of facial palsy before beginning treatment.

Scintillator-based fast ion loss measurements in the EAST

A new scintillator-based fast ion loss detector (FILD) has been installed on Experimental Advanced Superconducting Tokamak (EAST) to investigate the fast ion loss behavior in high performance plasma with neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH). A two dimensional 40 mm × 40 mm scintillator-coated (ZnS:Ag) stainless plate is mounted in the front of the detector, capturing the escaping fast ions. Photons from the scintillator plate are imaged with a Phantom V2010 CCD camera. The lost fast ions can be measured with the pitch angle from 60° to 120° and the gyroradius from 10 mm to 180 mm. This paper will describe the details of FILD diagnostic on EAST and describe preliminary measurements during NBI and ICRH heating.

2D spatial profile measurements of potential fluctuation with heavy ion beam probe on the Large Helical Device

Two-dimensional spatial profiles of potential fluctuation were measured with the heavy ion beam probe (HIBP) in the Large Helical Device (LHD). For 2D spatial profile measurements, the probe beam energy has to be changed, which requires the adjustment of many deflectors in the beam transport line to optimize the beam trajectory, since the transport line of LHD-HIBP system is long. The automatic beam adjustment system was developed, which allows us to adjust the beam trajectory easily. By analyzing coherence between potential fluctuation and magnetic probe signal, the noise level of the mode power spectrum of the potential fluctuation can be reduced. By using this method, the 2D spatial profile of potential fluctuation profile was successfully obtained.

Faraday-cup-type lost fast ion detector on Heliotron J

A Faraday-cup type lost-fast ion probe (FLIP) has been designed and installed in Heliotron J for the purpose of the studies of interaction between fast ions and MHD instabilities. The FLIP can measure the co-going fast ions whose energy is in the range of 1.7-42.5 keV (proton) and pitch angle of 90^∘-140^∘, especially for fast ions having the injection energy of neutral beam injection (NBI). The FLIP successfully measured the re-entering passing ions and trapped lost-fast ions caused by fast-ion-driven energetic particle modes in NBI heated plasmas.

Development of fast neutron pinhole camera using nuclear emulsion for neutron emission profile measurement in KSTAR

We have developed a compact fast neutron camera based on a stack of nuclear emulsion plates and a pinhole collimator. The camera was installed at J-port of Korea superconducting tokamak advanced research at National Fusion Research Institute, Republic of Korea. Fast neutron images agreed better with calculated ones based on Monte Carlo neutron simulation using the uniform distribution of Deuterium-Deuterium (DD) neutron source in a torus of 40 cm radius.

Triton burnup measurements in KSTAR using a neutron activation system

Measurements of the time-integrated triton burnup for deuterium plasma in Korea Superconducting Tokamak Advanced Research (KSTAR) have been performed following the simultaneous detection of the d-d and d-t neutrons. The d-d neutrons were measured using a ³He proportional counter, fission chamber, and activated indium sample, whereas the d-t neutrons were detected using activated silicon and copper samples. The triton burnup ratio from KSTAR discharges is found to be in the range 0.01%-0.50% depending on the plasma conditions. The measured burnup ratio is compared with the prompt loss fraction of tritons calculated with the Lorentz orbit code and the classical slowing-down time. The burnup ratio is found to increase as plasma current and classical slowing-down time increase.