23 research outputs found
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 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