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Nuclear Energy Conference & Expo (NECX)
September 8–11, 2025
Atlanta, GA|Atlanta Marriott Marquis
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Fusion Science and Technology
August 2025
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The newest era of workforce development at ANS
As most attendees of this year’s ANS Annual Conference left breakfast in the Grand Ballroom of the Chicago Downtown Marriott to sit in on presentations covering everything from career pathways in fusion to recently digitized archival nuclear films, 40 of them made their way to the hotel’s fifth floor to take part in the second offering of Nuclear 101, a newly designed certification course that seeks to give professionals who are in or adjacent to the industry an in-depth understanding of the essentials of nuclear energy and engineering from some of the field’s leading experts.
Stanley K. Borowski, Y-K. Martin Peng, Terry Kammash
Fusion Science and Technology | Volume 6 | Number 1 | July 1984 | Pages 7-29
Technical Paper | Plasma Heating System | doi.org/10.13182/FST84-A23116
Articles are hosted by Taylor and Francis Online.
Auxiliary radio-frequency (rf) heating of electrons before and during the current rise phase of a large tokamak, such as the Fusion Engineering Device (FED) [R0 = 4.8 m, a = 1.3 m, σ = 1.6, B(R0) = 3.62 T], is examined as a means of reducing both the initiation loop voltage and resistive flux expenditure during startup. Prior to current initiation, 1 to 2 MW of electron cyclotron resonance heating power at ∼90 GHz is used to create a small volume of high conductivity plasma (Te ≃ 100 eV, ne ≃ 1019 m−3) near the upper hybrid resonance (UHR) region. This plasma conditioning, referred to as preheating, permits a small radius (a0 ≃ 0.2 to 0.4 m) current channel to be established with a relatively low initial loop voltage (≤25 V as opposed to ∼100 V without rf assist). During the subsequent plasma expansion and current rise phase, a combination of rf heating (up to 5 MW) and linear current ramping leads to a substantial savings in volt-seconds by (a) minimizing the resistive flux consumption and (b) producing broad current density profiles. (With such broad profiles, the internal flux requirements are maintained at or near the flat profile limit.) To study the “preheating” phase, a near classical particle and energy transport model is developed to estimate the electron heating efficiency in a currentless toroidal plasma. The model assumes that preferential electron heating at the UHR leads to the formation of an ambipolar sheath potential between the neutral plasma and the conducting vacuum vessel and limiter. The ambipolar electron field (EAMB) enables the plasma to neutralize itself via poloidal EAMB × B drift. This form of effective rotational transform “short circuits” the vertical charge separation and improves particle confinement. The benefits of this effective electrostatic confinement are tempered, however, by the possibility of significant secondary electron emission from the limiters and vessel wall. A comparison of theoretical estimates and experimental preheating data from the Impurity Study Experiment-B tokamak shows reasonably good agreement and provides some confidence in the preheating power estimates obtained for the FED. Using FED preheating parameters as initial conditions, a single fluid zero-dimensional tokamak model is then used to study the time evolution of the plasma temperature, voltage, and flux requirements during the expanding radius current startup phase. The sensitivity of these parameters to variations in the initial minor radius, oxygen impurity content, and the electron preheating level is also analyzed and discussed.