Design and characterization of AmLi neutron sources for the LZ experiment

In this paper we describe the development, testing, and characterization of three low-emission rate AmLi neutron sources. The sources are used to calibrate the nuclear recoil response of the LUX-ZEPLIN (LZ) dark matter experiment. The sources' neutron emission rate was measured using $^{3}$He proportional tubes. The sources' gamma emissions were characterized using a high-purity germanium (HPGe) detector. Source-validated GEANT4 Monte Carlo simulations allowed to calibrate the Ge and neutron detector responses.Comment: 20 pages, 13 figures, 4 tables, revised manuscripts after accommodating the reviewer's comment

First divertor physics studies in Wendelstein 7-X

The Wendelstein 7-X (W7-X) optimized stellarator fusion experiment, which went into operation in 2015, has been operating since 2017 with an un-cooled modular graphite divertor. This allowed first divertor physics studies to be performed at pulse energies up to 80 MJ, as opposed to 4 MJ in the first operation phase, where five inboard limiters were installed instead of a divertor. This, and a number of other upgrades to the device capabilities, allowed extension into regimes of higher plasma density, heating power, and performance overall, e.g. setting a new stellarator world record triple product. The paper focuses on the first physics studies of how the island divertor works. The plasma heat loads arrive to a very high degree on the divertor plates, with only minor heat loads seen on other components, in particular baffle structures built in to aid neutral compression. The strike line shapes and locations change significantly from one magnetic configuration to another, in very much the same way that codes had predicted they would. Strike-line widths are as large as 10 cm, and the wetted areas also large, up to about 1.5 m(2), which bodes well for future operation phases. Peak local heat loads onto the divertor were in general benign and project below the 10 MW m(-2) limit of the future water-cooled divertor when operated with 10 MW of heating power, with the exception of low-density attached operation in the high-iota configuration. The most notable result was the complete (in all 10 divertor units) heat-flux detachment obtained at high-density operation in hydrogen

Conceptual Design of a Scintillator-Based Fast-Ion Loss Detector for the Wendelstein 7-X Stellarator

A conceptual design of a scintillator-based fast-ion loss detector (FILD) has been developed for the Wendelstein 7-X stellarator (W7-X). Simulations using the Monte Carlo codes ASCOT5 and BEAMS3D have been performed to calculate the expected flux of neutral beam injection (NBI)-generated fast hydrogen ions onto the conceptual detector probe head. These fast-ion loss fluxes have been calculated for several magnetic field configurations as well as probe insertion positions. At the maximum insertion position, both co- and counter-going losses with high incident pitch angles are observed; however, at retracted positions, only co-going fast ions reach the probe head. The FILDSIM code has been used to optimize the geometry of the detector entrance and collimating elements to achieve a wide velocity space coverage as well as a high velocity-space resolution. A synthetic FILD signal is calculated for the expected loss distribution via forward modeling using the instrument response function. The synthetic signal is found to largely retain the velocity space features of the loss distribution.EUROfusion Consortium 10.13039/100018708-European Union via the Euratom Research and Training Programme (Grant Number: 101052200–EUROfusion) 10.13039/501100004837-Ministerio de Ciencia e Innovación (Grant Number: FJC-2019-041092-I