Target development for a compact liquid lithium neutron source

Stemmley, Steven A.

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https://hdl.handle.net/2142/113983 Copy

Description

Title

Target development for a compact liquid lithium neutron source

Author(s)

Stemmley, Steven A.

Issue Date

2021-12-06

Director of Research (if dissertation) or Advisor (if thesis)

Ruzic, David N

Committee Member(s)

Andruczuk, Daniel

Department of Study

Nuclear, Plasma, & Rad Engr

Discipline

Nuclear, Plasma, Radiolgc Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Lithium
• Plasma
• Neutron
• Fusion
• Thermoelectric Magnetohydrodynamics

Abstract

As fusion devices tend toward higher densities and temperatures, more robust plasma facing components will need to be developed, especially when they start producing neutrons. Many of the current materials, like refractory metals, will melt and ablate under the intense heat loads of these devices and will undergo degradation in the intense neutron field. Recently, many researchers have begun to look at liquid metal components to remedy some of the issues. Liquid lithium seems to be a prime candidate as its chemical and nuclear properties aid in plasma performance and control. Previously, at the University of Illinois Urbana-Champaign (UIUC), a plasma facing component for use with liquid lithium has been developed, called the Liquid Metal Infused Trench (LiMIT) concept. LiMIT utilizes thermoelectric magnetohydrodynamics (TEMHD) to passively drive flow through a set of metal trenches. This concept has been previously tested in devices around the world such as HT-7, Magnum PSI, and EAST with heat fluxes up to several MW m−2. Recently, this concept has been adapted for use as an ion beam target for neutron generation. This thesis focuses on the design, modeling, and experimentation of a miniaturized LiMIT-like target for neutron production. COMSOL models and proof of concept experiments have shown that 5 cm s−1 flow is achievable without a top heat flux. With surface heating due to an ion beam, it should be able to achieve upwards of 100 cm s−1 and handle 10 MW m−2 without significant evaporation losses. This target was placed under a 100 kV deuterium ion beam, to determine its heat flux handling and neutron output. It is thought by having flowing liquid lithium, the target surface will stay clean allowing the deutrons to potentially produce near 14 MeV neutrons from the D-7Li reaction. When characterized, the ion beam was found to have a large D2+ fraction (∼70%) and an ion current near 17 μA. A d-stilbene detector was used to measure the fast neutron output and the energy spectrum. It was predicted through a finite difference and Monte Carlo model that the detector should expect about 160 and 63 neutrons per second incident on the surface for D-D and D-7Li neutrons, respectively. Unfortunately, no D-7Li neutrons were detected, however, D-D neutrons were measured. The maximum measured amount was about 80 counts per second at a distance of 16.5 cm. Due to an equipment malfunction, the beam was upgraded to produce near 100 μA of ion current. Still, no D-7Li neutrons were detected. The highest measurement rate at the increased current from D-D neutrons was about 1100 counts per second with a detector distance 22.5 cm away from the target. It was found that the surface condition, primarily the impurity layers on the surface, impacted the neutron production rate. As time went on during the irradiation experiments, the neutron output declined with increasing impurity build up. Overall, a small LiMIT-style target was designed, built, and tested as a high heat flux target for high energy neutron production. With greater ion beam energy and current, this compact neutron generation method could be utilized for small scale testing of fusion reactor materials. This type of testing could enable the creation of better, neutron-damage resistant materials for future large-scale fusion reactors.

Graduation Semester

2021-12

Type of Resource

Thesis

Permalink

http://hdl.handle.net/2142/113983

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Copyright 2021 Steven Stemmley

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