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Title: Pellet-Injector Technology—Brief History and Key Developments in the Last 25 Years

Abstract

High-speed injection of solid fuel was first proposed in 1954 as a possible solution to the problem of transporting fresh fuel across the confining magnetic fields into the plasma of a fusion reactor. While it took a few decades, the use of cryogenic pellets (typically H2 and D2) on fusion experiments became common place; most tokamaks and stellarators are now equipped with a pellet injector(s). These devices operate at low temperatures (~10 to 20 K) and most often use a simple light gas gun to accelerate macroscopic-size pellets (~0.4- to 6-mm diameter) to speeds of ~100 to 1000 m/s. Before the advantages of pellet injection from the magnetic high-field side (HFS) of a tokamak were recognized in 1997, development focused on increasing the pellet speed to achieve deeper plasma penetration and higher fueling efficiency. The HFS injection technique typically dictates slower pellets (~100 to 300 m/s) to survive transport through the curved guide tubes that route the pellets to the plasma from the inside wall of the device. Two other key operating parameters for plasma fueling are the pellet-injection repetition rate and time duration—a single pellet is adequate for some experiments and a steady-state injection rate of up to ~50more » Hz is appropriate for others. In addition to plasma fueling, cryogenic pellets have often been used for particle transport and impurity studies in fusion experiments (most often with neon pellets). During the past two decades, a few new applications for cryogenic pellets have been developed and used successfully in plasma experiments: (1) one for edge-localized mode mitigation, (2) one for plasma disruption mitigation (requires large pellets that are shattered before injection into the plasma), and (3) another in which pure argon pellets are used to trigger runaway electrons in the plasma for scientific studies. Here in this paper, a brief history and the key developments in this technology during the past 25 years are presented and discussed.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1460225
Grant/Contract Number:  
AC05-00OR22725; FC02-04ER54698
Resource Type:
Accepted Manuscript
Journal Name:
Fusion Science and Technology
Additional Journal Information:
Journal Volume: 73; Journal Issue: 4; Journal ID: ISSN 1536-1055
Publisher:
American Nuclear Society
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Cryogenic pellet; plasma fueling; disruption mitigation; ELM mitigation; runaway electrons

Citation Formats

Combs, Stephen Kirk, and Baylor, Larry R. Pellet-Injector Technology—Brief History and Key Developments in the Last 25 Years. United States: N. p., 2018. Web. doi:10.1080/15361055.2017.1421367.
Combs, Stephen Kirk, & Baylor, Larry R. Pellet-Injector Technology—Brief History and Key Developments in the Last 25 Years. United States. https://doi.org/10.1080/15361055.2017.1421367
Combs, Stephen Kirk, and Baylor, Larry R. Wed . "Pellet-Injector Technology—Brief History and Key Developments in the Last 25 Years". United States. https://doi.org/10.1080/15361055.2017.1421367. https://www.osti.gov/servlets/purl/1460225.
@article{osti_1460225,
title = {Pellet-Injector Technology—Brief History and Key Developments in the Last 25 Years},
author = {Combs, Stephen Kirk and Baylor, Larry R.},
abstractNote = {High-speed injection of solid fuel was first proposed in 1954 as a possible solution to the problem of transporting fresh fuel across the confining magnetic fields into the plasma of a fusion reactor. While it took a few decades, the use of cryogenic pellets (typically H2 and D2) on fusion experiments became common place; most tokamaks and stellarators are now equipped with a pellet injector(s). These devices operate at low temperatures (~10 to 20 K) and most often use a simple light gas gun to accelerate macroscopic-size pellets (~0.4- to 6-mm diameter) to speeds of ~100 to 1000 m/s. Before the advantages of pellet injection from the magnetic high-field side (HFS) of a tokamak were recognized in 1997, development focused on increasing the pellet speed to achieve deeper plasma penetration and higher fueling efficiency. The HFS injection technique typically dictates slower pellets (~100 to 300 m/s) to survive transport through the curved guide tubes that route the pellets to the plasma from the inside wall of the device. Two other key operating parameters for plasma fueling are the pellet-injection repetition rate and time duration—a single pellet is adequate for some experiments and a steady-state injection rate of up to ~50 Hz is appropriate for others. In addition to plasma fueling, cryogenic pellets have often been used for particle transport and impurity studies in fusion experiments (most often with neon pellets). During the past two decades, a few new applications for cryogenic pellets have been developed and used successfully in plasma experiments: (1) one for edge-localized mode mitigation, (2) one for plasma disruption mitigation (requires large pellets that are shattered before injection into the plasma), and (3) another in which pure argon pellets are used to trigger runaway electrons in the plasma for scientific studies. Here in this paper, a brief history and the key developments in this technology during the past 25 years are presented and discussed.},
doi = {10.1080/15361055.2017.1421367},
journal = {Fusion Science and Technology},
number = 4,
volume = 73,
place = {United States},
year = {Wed Feb 21 00:00:00 EST 2018},
month = {Wed Feb 21 00:00:00 EST 2018}
}

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Works referencing / citing this record:

Design of a shattered pellet injection system on J-TEXT tokamak
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The role of kinetic instabilities in formation of the runaway electron current after argon injection in DIII-D
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