Public Abstract

DE-SC0024523: An Inductively-Coupled Ion Source For The DIII-D Neutral Beam Heating System

Award Status: Active

Institution: North Carolina State University, Raleigh, NC
UEI: U3NVH931QJJ3
DUNS: 042092122

Most Recent Award Date: 08/08/2024
Number of Support Periods: 2
PM: Lanctot, Matthew

Current Budget Period: 09/01/2024 - 08/31/2025
Current Project Period: 09/01/2023 - 08/31/2025
PI: Laggner, Florian

Supplement Budget Period: N/A

Public Abstract

An Inductively-Coupled Ion Source For The DIII-D Neutral Beam Heating System Florian M. Laggner, North Carolina State University (Principal Investigator) Amanda Lietz, North Carolina State University (Co-Investigator) Steven Shannon, North Carolina State University (Co-Investigator) This research activity aims to develop a prototype radio frequency (RF), inductively coupled plasma (ICP) positive ion source for the DIII-D National Fusion Facility neutral beam injection (NBI) system. The goal is to build capabilities that will inform critical design choices and ultimately deliver a full-scale prototype RF ICP positive ion source that provides a uniform positive ion density at the ion extraction area for 10 s, which translates to at least 85 A of positive ion current to the accelerator. A successful completion of the project will demonstrate the feasibility of deploying a RF ICP positive ion source on DIII-D, which will reduce maintenance needs and enable the envisioned power rise from 16 to 24 MW of total injected NBI power. With this substantial power upgrade, DIII-D will be able to push towards regimes and power densities that are relevant for plasma scenarios in a Fusion Pilot Plant. One major limitation of the present NBI system is the Common Long Pulse Source (CLPS) ‘arc chamber’, which produces positive hydrogenic ions through thermionic emission-limited arcs between tungsten filaments. Higher NBI power requires higher arc voltage to increase the arc current and, thereby, the extractable positive ion current. Unfortunately, at present arc currents, a main failure mode of the CLPS arc chambers are electrical shorts, which are expected to become even more frequent when increasing the arc voltage. To eliminate the NBI power limitation and failure modes of the arc chambers, we propose to design a RF ICP positive ion source, which offers reduced failure rate, maintenance, and cost due to the absence of filament insulator gaskets that can electrically short out. We aim to demonstrate a RF ICP positive ion source design that is fully compatible with the present DIII-D NBI accelerator, i.e., a ‘drop-in’ exchange of the CLPS arc chamber will be possible. We will deploy new solid state RF power generators, novel multi-strap RF antenna designs and optimized Faraday shields that ultimately target a cost reduction per production unit. Modeling and simulation of ICP ion sources will create a new capability to fundamentally understand the source performance, guide the RF ICP positive ion source design and optimize the operation parameters. Our design considerations for RF ICP sources include frequency selection, inductive coil design, impedance matching design, and incorporation of a Faraday shield. Our research project has two phases. First, we will establish a reduced-scale test setup that matches the positive ion flux at the ion extraction area to inform the full-scale prototype design and to demonstrate a multi-strap single turn antenna to avoid turn-to-turn arcing and compare its performance to a conventional multi-turn antenna. State-of-the-art, Hybrid Plasma Equipment Model (HPEM) simulations will be performed and validated against experimental data from the reduced-scale test setup to inform critical design decisions and optimize the uniformity of the ion flux across the ion extraction area. In the second project phase, we will finalize the design of a full-scale RF ICP positive ion source prototype, manufacture the components, assemble them and demonstrate operation at nominal design parameters.

An Inductively-Coupled Ion Source For The DIII-D Neutral Beam Heating System
Florian M. Laggner, North Carolina State University (Principal Investigator)
Amanda Lietz, North Carolina State University (Co-Investigator)
Steven Shannon, North Carolina State University (Co-Investigator)

This research activity aims to develop a prototype radio frequency (RF), inductively coupled plasma (ICP) positive ion source for the DIII-D National Fusion Facility neutral beam injection (NBI) system. The goal is to build capabilities that will inform critical design choices and ultimately deliver a full-scale prototype RF ICP positive ion source that provides a uniform positive ion density at the ion extraction area for 10 s, which translates to at least 85 A of positive ion current to the accelerator. A successful completion of the project will demonstrate the feasibility of deploying a RF ICP positive ion source on DIII-D, which will reduce maintenance needs and enable the envisioned power rise from 16 to 24 MW of total injected NBI power. With this substantial power upgrade, DIII-D will be able to push towards regimes and power densities that are relevant for plasma scenarios in a Fusion Pilot Plant.

One major limitation of the present NBI system is the Common Long Pulse Source (CLPS) ‘arc chamber’, which produces positive hydrogenic ions through thermionic emission-limited arcs between tungsten filaments. Higher NBI power requires higher arc voltage to increase the arc current and, thereby, the extractable positive ion current. Unfortunately, at present arc currents, a main failure mode of the CLPS arc chambers are electrical shorts, which are expected to become even more frequent when increasing the arc voltage. To eliminate the NBI power limitation and failure modes of the arc chambers, we propose to design a RF ICP positive ion source, which offers reduced failure rate, maintenance, and cost due to the absence of filament insulator gaskets that can electrically short out. We aim to demonstrate a RF ICP positive ion source design that is fully compatible with the present DIII-D NBI accelerator, i.e., a ‘drop-in’ exchange of the CLPS arc chamber will be possible. We will deploy new solid state RF power generators, novel multi-strap RF antenna designs and optimized Faraday shields that ultimately target a cost reduction per production unit. Modeling and simulation of ICP ion sources will create a new capability to fundamentally understand the source performance, guide the RF ICP positive ion source design and optimize the operation parameters.

Our design considerations for RF ICP sources include frequency selection, inductive coil design, impedance matching design, and incorporation of a Faraday shield. Our research project has two phases. First, we will establish a reduced-scale test setup that matches the positive ion flux at the ion extraction area to inform the full-scale prototype design and to demonstrate a multi-strap single turn antenna to avoid turn-to-turn arcing and compare its performance to a conventional multi-turn antenna. State-of-the-art, Hybrid Plasma Equipment Model (HPEM) simulations will be performed and validated against experimental data from the reduced-scale test setup to inform critical design decisions and optimize the uniformity of the ion flux across the ion extraction area. In the second project phase, we will finalize the design of a full-scale RF ICP positive ion source prototype, manufacture the components, assemble them and demonstrate operation at nominal design parameters.