The neutron-rich edge of the nuclear landscape: Experiment and theory.

This review concentrates on the specific properties and characteristics of damage structures generated with high-energy ions in the electronic energy loss regime. Irradiation experiments with so-called swift heavy ions (SHI) find applications in many different fields, with examples presented in ion-track nanotechnology, radiation hardness analysis of functional materials, and laboratory tests of cosmic radiation. The basics of the SHI-solid interaction are described with special attention to processes in the electronic subsystem. The broad spectrum of damage phenomena is exemplified for various materials and material classes, along with a description of typical characterization techniques. The review also presents state-of-the-art modeling efforts that try to account for the complexity of the coupled processes of the electronic and atomic subsystems. Finally, the relevance of SHI phenomena for effects induced by fission fragments in nuclear fuels and how this knowledge can be applied to better estimate damage risks in nuclear materials is discussed.

Fundamental phenomena and applications of swift heavy ion irradiations

In this review, we describe the experimental facilities and methods which make it possible to produce and measure the properties of the extreme neutron rich nuclei. We then develop the theoretical framework that will accompany us along the review; the shell-model approach with large scale configuration interaction (mixing) SM-CI, with special emphasis in the competition between the spherical mean field and the nuclear correlations (mainly pairing and quadrupole-quadrupole). The symmetry properties of the latter are treated in detail as they will show to be of great heuristic value. We explore in detail the Islands of Inversion (IoI) at N=20 and N=28. We make a side excursion into the heavier Calcium and Potassium isotopes, to discuss current issues on shell evolution and new magic numbers far from stability. We visit the N=40 Island of Inversion. We discuss the doubly magic nucleus 78Ni, its shape coexistence and the prospect of a new IoI at N=50 below Z=28. We examine the N=70 and N=82 neutron closures approaching the neutron drip line.

/pdf/the-neutron-rich-edge-of-the-nuclear-landscape-experiment-3tzj3nijpn.pdf

The Neutron-Rich Edge of the Nuclear Landscape. Experiment and Theory.

An array of powerful neutrino-beam experiments will study the fundamental properties of neutrinos with unprecedented precision in the coming years. Along with their primary neutrinophysics motivations, there has been growing recognition that these experiments can carry out a rich program of searches for new, light, weakly-coupled particles that are part of a dark sector. In this white paper, we review the diverse theoretical motivations for dark sectors and the capabilities of neutrino beam experiments to probe a wide range of models and signatures. We also examine the potential obstacles that could limit these prospects and identify concrete steps needed to realize an impactful dark sector search program in this and coming decades. Submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021)

/pdf/dark-sector-studies-with-neutrino-beams-1vzj2dxf.pdf

Dark Sector Studies with Neutrino Beams

Abstract For stable and efficient fusion energy production using a tokamak reactor, it is essential to maintain a high-pressure hydrogenic plasma without plasma disruption. Therefore, it is necessary to actively control the tokamak based on the observed plasma state, to manoeuvre high-pressure plasma while avoiding tearing instability, the leading cause of disruptions. This presents an obstacle-avoidance problem for which artificial intelligence based on reinforcement learning has recently shown remarkable performance 1–4 . However, the obstacle here, the tearing instability, is difficult to forecast and is highly prone to terminating plasma operations, especially in the ITER baseline scenario. Previously, we developed a multimodal dynamic model that estimates the likelihood of future tearing instability based on signals from multiple diagnostics and actuators 5 . Here we harness this dynamic model as a training environment for reinforcement-learning artificial intelligence, facilitating automated instability prevention. We demonstrate artificial intelligence control to lower the possibility of disruptive tearing instabilities in DIII-D 6 , the largest magnetic fusion facility in the United States. The controller maintained the tearing likelihood under a given threshold, even under relatively unfavourable conditions of low safety factor and low torque. In particular, it allowed the plasma to actively track the stable path within the time-varying operational space while maintaining H-mode performance, which was challenging with traditional preprogrammed control. This controller paves the path to developing stable high-performance operational scenarios for future use in ITER. 

Avoiding fusion plasma tearing instability with deep reinforcement learning

The RAON is the name of the heavy ion accelerator facility under construction in Korea that includes the In-flight Fragment (IF) and Isotope Separation On-Line (ISOL) facilities to support cutting-edge research in various science fields. The superconducting linac is the driver for the IF facility that can accelerate beams from proton to uranium with 200 MeV/u, 400 kW (for uranium beam). A 70-MeV, 1-mA H− cyclotron is the driver for the ISOL facility and is followed by a post-accelerator consisting of s superconducting linac that can accelerate rare-isotope (RI) beams and deliver them to experimental halls. These facilities provide high-intensity stable ion and rare isotope (RI) beams for domestic and international users. In this paper, design and prototyping efforts for the RAON accelerator systems are presented.

Design of the RAON accelerator systems

Nuclear fusion is one of the most attractive alternatives to carbon-dependent energy sources1. Harnessing energy from nuclear fusion in a large reactor scale, however, still presents many scientific challenges despite the many years of research and steady advances in magnetic confinement approaches. State-of-the-art magnetic fusion devices cannot yet achieve a sustainable fusion performance, which requires a high temperature above 100 million kelvin and sufficient control of instabilities to ensure steady-state operation on the order of tens of seconds2,3. Here we report experiments at the Korea Superconducting Tokamak Advanced Research4 device producing a plasma fusion regime that satisfies most of the above requirements: thanks to abundant fast ions stabilizing the core plasma turbulence, we generate plasmas at a temperature of 100 million kelvin lasting up to 20 seconds without plasma edge instabilities or impurity accumulation. A low plasma density combined with a moderate input power for operation is key to establishing this regime by preserving a high fraction of fast ions. This regime is rarely subject to disruption and can be sustained reliably even without a sophisticated control, and thus represents a promising path towards commercial fusion reactors. A magnetic confinement regime established at the Korea Superconducting Tokamak Advanced Research device enables the generation of plasmas over 108 kelvin for 20 seconds with the aid of fast ions without plasma edge instabilities or impurity accumulation. 

/pdf/a-sustained-high-temperature-fusion-plasma-regime-1h0hw989.pdf

A sustained high-temperature fusion plasma regime facilitated by fast ions

While the peeling–ballooning mode is known to be stabilized by strong plasma shaping in a high-confinement mode (H-mode), a significant difference is found in the roles of elongation and triangularity. The elongation mainly stabilizes the high- n ballooning branch, while the triangularity of the low- n peeling one with some destabilization of the high- n ballooning one, where n is the toroidal mode number. This difference is conjectured mainly due to the magnetic shear effect which is substantially enhanced in a high triangularity regime, giving a destabilization on the ballooning branch, while a stabilization on the peeling one. An important consequence of these different roles of the two shape parameters is that they should work together to stabilize simultaneously both branches of the PBM, implying the necessity of synergy between them for the large pedestal height enhancement.

Different roles of elongation and triangularity in the H-mode pedestal height enhancement through strong plasma shaping

In plasmas with strong shape and large pedestal width, like DIII-D high poloidal-beta discharges, the eigenvalue spectrum of the peeling ballooning mode (PBM) is shown to shift to the very low-n regime near one, where n is the toroidal mode number. This peeling-type eigenvalue spectrum has a further shift to n = 1, thus being smoothly connected to the n = 1 external kink mode (EKM), as the normalized beta (βN) increases. Once this connection occurs, the mode takes a mixture form of the PBM and EKM with its mode structure varying from the PBM-like to the EKM-like one as βN increases. The mode stability also becomes sensitive to both the local pedestal gradient and global βN, thus allowing an anti-correlation between the two driving forces. These results appear to provide a qualitative explanation of the two unexpected features observed in the DIII-D high poloidal-beta discharges, that is, the dominance of the n = 1 mode in the edge-localized-modes and the negative correlation between the pedestal height and the internal transport barrier strength.

https://pubs.aip.org/aip/pop/article-pdf/doi/10.1063/5.0149685/17913733/050702_1_5.0149685.pdf

Close coupling of the peeling ballooning and external kink modes in high poloidal-beta discharges with strong shape and large pedestal width

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Papers

Design of the RAON accelerator systems

A sustained high-temperature fusion plasma regime facilitated by fast ions

Different roles of elongation and triangularity in the H-mode pedestal height enhancement through strong plasma shaping

Close coupling of the peeling ballooning and external kink modes in high poloidal-beta discharges with strong shape and large pedestal width