Transport and losses of fusion-born alpha particles in the presence of tearing modes using the new Toroidal Accelerated P Article Simulator (TAPAS)

The transport and losses of fusion-born alpha particles is studied in the presence of a single-helicity tearing mode, characterized by (m=2,n=1). The analysis is performed by means of the recently developed Toroidal Accelerated PArticle Simulator (TAPAS). Although such modes have been usually believed to result only in a local flattening of the radial profiles, it is shown that the density profile can exhibit a global modification leading to significant losses of alpha particles. This is due to the fact that, although the magnetic field does not exhibit any chaotic behaviour, the trajectories of alpha particles do, as revealed by their Poincaré maps. Such result is in qualitative agreement with past observations and simulations of energetic particles generated by neutral beam injection in TFTR, DIII-D and AUG tokamaks. In-depth analysis is carried out to characterize the impact of the tearing mode on the transport and losses of fusion-born alpha-particles with a realistic density profile. The impact of the amplitude is evidenced. Moreover, the effect of the island rotation frequency is assessed based on a detailed analysis of the linear resonances in phase-space, in agreement with the simulation results. Finally, the probability density function of the exit time has been computed and the transport of alpha particles has been found to be anomalous.

Theoretical study of the Alfven Eigenmode stability in CFETR steady state discharges

The aim of this study is to analyze the stability of Alfven Eigenmodes (AE) in the China Fusion Engineering Test Reactor (CFETR) plasma for steady state operations. The analysis is done using the gyro-fluid code FAR3d including the effect of the acoustic modes, EP Finite Larmor radius damping effects and multiple energetic particle populations. Two high poloidal β scenarios are studied with respect to the location of the internal transport barrier (ITB) at r/a ≈ 0.45 (case A) and r/a ≈ 0.6 (case B). Both operation scenarios show a narrow TAE gap between the inner-middle plasma region and a wide EAE gap all along the plasma radius. The AE stability of CFETR plasmas improves if the ITB is located inwards, case A, showing AEs with lower growth rates with respect to the case B. The AEs growth rate is smaller in the case A because the modes are located in the inner-middle plasma region where the stabilizing effect of the magnetic shear is stronger with respect to the case B. Multiple EP populations effects (NBI driven EP + alpha articles) are negligible for the case A, although the simulations for the case B show a stabilizing effect of the NBI EP on the n=1 BAE caused by alpha particles during the thermalization process. If the FLR damping effects are included in the simulations, the growth rate of the EAE/NAE decreases up to 70 %, particularly for n > 3 toroidal families. Low n AEs (n<6) show the largest growth rates. On the other hand, high n modes (n=6 to 15) are triggered in the frequency range of the NAE, strongly damped by the FLR effects.

Activities in Divertor Reflector and Linear Plates Using WCLL and HCPB Breeding Blanket Concepts

In fusion devices, such as European Demonstration Fusion Power Reactor (EU DEMO), primary neutrons can cause material activation due to the interaction between the source particles and the targeting material. Subsequently, the reactor’s inner components become activated. For safety and safe performance purposes, it is necessary to evaluate neutron-induced activities. Activities results from divertor reflector and liner plates are presented in this work. The purpose of liner shielding plates is to protect the vacuum vessel and magnet coils from neutrons. As for reflector plates, the function is to shield the cooling components under plasma-facing components from alpha particles, thermal effects, and impurities. Plates are made of Eurofer with a 3 mm layer of tungsten, while the water is used for cooling purposes. The calculations were performed using two EU DEMO MCNP (Monte Carlo N-Particles) models with different breeding blanket configurations: helium-cooled pebble bed (HCPB) and water-cooled lithium lead (WCLL). The TENDL–2017 nuclear data library has been used for activation reactions cross-sections and nuclear reactions. Activation calculations were performed using the FISPACT-II code at the end of irradiation for cooling times of 0 s–1000 years. Radionuclide analysis of divertor liner and reflector plates is also presented in this paper. The main radionuclides, with at least 1% contribution to the total value of activation characteristics, were identified for the previously mentioned cooling times.

Study of the influence of MoO3 concentration on the chemical structure, physical properties, and radiation absorption prowess of alumino lead borate glasses

The present study established a glass system with composition of 55B2O3 -30Pb3O4-(15 - x) Al2O3- xMoO3, where x: (0≤x≤5 mol %) by melt quenching conventional method. The structure of the synthesized samples was examined by XRD and FT-IR techniques. It is found that the molybdenum acts as a modifier and enhances the change between BO3 and BO4 structural units. Increasing MoO3 in the sample improved the glass network compactness and enhanced the coherence of the glass network and the structure stiffening. Some physical parameters were studied with increasing MoO3 content in the samples such as Ri, ri, rp, dB-B average coordination number, number of bonds, field strength of (Mo+3), the floppy modes, the cross-linking density and effective coordination number and found to be enhanced. Increasing MoO3 dopingconcentration from 0 – 5 mol % produced corresponding increase in fast neutron effective removal cross section ΣR from 0.07127 – 0.10825 cm-1, total cross section for thermal neutrons σT from 68.35875 – 105.7526 cm-1, and an increment in the cold neutron scattering cross section. Furthermore, the influence of MoO3 doping in the glasses is such that the stopping powers (Sp) and ranges RCSDA /Rp of electrons, proton, alpha particles, and carbon ion follows the trend: (Sp)BPAM-G1 > (Sp)BPAM-G2 > (Sp)BPAM-G3 >(Sp)BPAM-G4 > (Sp)BPAM-G5, and(RCSDA /Rp)BPAM-G1 > (RCSDA /Rp)BPAM-G2 > (RCSDA /Rp)BPAM-G3 > (RCSDA /Rp)BPAM-G4 > ((RCSDA /Rp)BPAM-G5 respectively. On the other hand, the doping produced no noticeable differences in the equivalent atomic number and the exposure buildup factor of the glasses.

Single source-based energy and efficiency calibration method for the assessment of an alpha imaging detector

An alpha imaging detector acquires a two-dimensional distribution of a sample that emits alpha particles. For the quantitative analysis of the image of an alpha-emitting sample, the individual energies of the alpha particles must be identified, which can be achieved using the spectrometric method after detector calibration. In this study, an energy and efficiency calibration method was investigated to assess an alpha imaging detector. The calibration was performed using a single standard source of Am-241 based on the energy loss characteristic of an alpha particle. The feasibility of the calibration method was evaluated using another source, Ac-225. The calibrated alpha imaging detector was evaluated in terms of energy resolution and detection efficiency, and the alpha imaging detector was found to be efficiently calibrated using a single standard source. The calibrated alpha imaging detector appears promising for the quantitative analysis of samples that emit alpha particles.

Assessment of shutdown dose rates in the ITER Collective Thomson Scattering system and in equatorial port plug 12

The ITER Collective Thomson Scattering (CTS) system will be the main diagnostic responsible for measuring the velocity distribution function of fusion-born alpha particles in the plasma. As the CTS diagnostic is integrated in the equatorial port plug 12 (drawer 3), with direct apertures to the port interspace where maintenance hands-on operation will be carried out, it is essential to assess the shutdown dose rates (SDDR) in these maintenance areas. In this work, the D1S-UNED3.1.4 Monte-Carlo transport code, based on the implementation of the direct-one-step methodology in MCNP5 v1.60, was used to estimate the dose rate level 12 days (106 s) after shutdown in the port interspace. The results show that the CTS system does not contribute significantly to the SDDR in the area where hands-on maintenance is foreseen with contribution to dose rates less than 1 µSv/h. This is consistent with previous estimates, although with the most recent model of the CTS design there is a slight increase of the SDDR values. This deviation can be attributed to design changes and improved shielding modelling and/or most importantly, to statistical fluctuations of the D1S simulations. From a neutronics point of view, the increase in the SDDR falls within the range of the statistical fluctuations, and the design is still compliant with the radiation safety ALARA principle aiming at minimizing radiation doses, and there is no requirement for further design optimizations.

A Solar Source of Alfvénic Magnetic Field Switchbacks: In Situ Remnants of Magnetic Funnels on Supergranulation Scales

One of the striking observations from the Parker Solar Probe (PSP) spacecraft is the prevalence in the inner heliosphere of large amplitude, Alfvénic magnetic field reversals termed switchbacks. These δ B R / B ∼  ( 1 ) fluctuations occur over a range of timescales and in patches separated by intervals of quiet, radial magnetic field. We use measurements from PSP to demonstrate that patches of switchbacks are localized within the extensions of plasma structures originating at the base of the corona. These structures are characterized by an increase in alpha particle abundance, Mach number, plasma β and pressure, and by depletions in the magnetic field magnitude and electron temperature. These intervals are in pressure balance, implying stationary spatial structure, and the field depressions are consistent with overexpanded flux tubes. The structures are asymmetric in Carrington longitude with a steeper leading edge and a small (∼1°) edge of hotter plasma and enhanced magnetic field fluctuations. Some structures contain suprathermal ions to ∼85 keV that we argue are the energetic tail of the solar wind alpha population. The structures are separated in longitude by angular scales associated with supergranulation. This suggests that these switchbacks originate near the leading edge of the diverging magnetic field funnels associated with the network magnetic field—the primary wind sources. We propose an origin of the magnetic field switchbacks, hot plasma and suprathermals, alpha particles in interchange reconnection events just above the solar transition region and our measurements represent the extended regions of a turbulent outflow exhaust.