ANS is committed to advancing, fostering, and promoting the development and application of nuclear sciences and technologies to benefit society.
Explore the many uses for nuclear science and its impact on energy, the environment, healthcare, food, and more.
Division Spotlight
Reactor Physics
The division's objectives are to promote the advancement of knowledge and understanding of the fundamental physical phenomena characterizing nuclear reactors and other nuclear systems. The division encourages research and disseminates information through meetings and publications. Areas of technical interest include nuclear data, particle interactions and transport, reactor and nuclear systems analysis, methods, design, validation and operating experience and standards. The Wigner Award heads the awards program.
Meeting Spotlight
International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2025)
April 27–30, 2025
Denver, CO|The Westin Denver Downtown
Standards Program
The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
Latest Magazine Issues
Apr 2025
Jan 2025
Latest Journal Issues
Nuclear Science and Engineering
June 2025
Nuclear Technology
Fusion Science and Technology
May 2025
Latest News
Dragonfly, a Pu-fueled drone heading to Titan, gets key NASA approval
Curiosity landed on Mars sporting a radioisotope thermoelectric generator (RTG) in 2012, and a second NASA rover, Perseverance, landed in 2021. Both are still rolling across the red planet in the name of science. Another exploratory craft with a similar plutonium-238–fueled RTG but a very different mission—to fly between multiple test sites on Titan, Saturn’s largest moon—recently got one step closer to deployment.
On April 25, NASA and the Johns Hopkins University Applied Physics Laboratory (APL) announced that the Dragonfly mission to Saturn’s icy moon passed its critical design review. “Passing this mission milestone means that Dragonfly’s mission design, fabrication, integration, and test plans are all approved, and the mission can now turn its attention to the construction of the spacecraft itself,” according to NASA.
Erik L. Vold, Tak Kuen Mau, Robert W. Conn
Fusion Science and Technology | Volume 12 | Number 2 | September 1987 | Pages 197-229
Fusion Reactors | doi.org/10.13182/FST87-A11963780
Articles are hosted by Taylor and Francis Online.
A flexible time-dependent, zero-dimensional plasma burn code with radial profiles was developed and employed to study the fractional power operation and the thermal burn control options for an International Tokamak Reactor (INTOR)-sized tokamak reactor. The code includes alpha thermalization and a time-dependent transport loss that can be represented by any one of several currently popular scaling laws for energy confinement time.
Ignition parameters were found to vary widely in density-temperature (n-T) space for the range of scaling laws examined. Critical ignition issues were found to include the extent of confinement time degradation by alpha heating, the effect of auxiliary heating on confinement, and as expected, the ratio of ion to electron transport power loss. Ignition will probably not occur in an INTOR tokamak if all of the alpha power degrades confinement. Applied to a compact tokamak, a simple model showed that ignition would be marginally likely. If only the auxiliary heating degrades confinement, the ignited operating region shows the interesting characteristic of the plasma temperature increasing in response to a decrease in auxiliary power due to the resulting greater decrease in transport losses. If ion confinement is neoclassic (τi/τe large), the ignition criteria are shown to be much more optimistic than for anomalous ion loss, even when the total transport loss is governed by a specific scaling law.
Feedback control of the auxiliary power and ion fuel sources are shown to provide thermal stability for operating points near the low-density, high-temperature portion of the ignition curve. A potential problem will arise if the ignition curve falls below the regions of (n-T) space where the desired reactor net electric power results. Then, net reactor output power occurs in a thermally unstable operating region, and the ignition conditions may need to be “spoiled,” displacing the ignition curve upward in (n-T) space for stable marginally ignited operation. Mechanisms to stabilize this region are investigated, including a “soft beta” limit, auxiliary feedback, impurity radiation, divertor mode variation, varying ion to electron confinement times, and various means of increasing transport power losses. The soft beta limit is unambiguously stabilizing. Confinement degradation by a small fraction (∼15%) of the alpha power would also provide passive thermal stability. Confinement degraded proportionally to plasma temperature, rather than to input power, is shown to marginally provide thermal stability near the ignition curve. In the case of confinement time degraded by auxiliary heating, thermal stability in operating regions well above the ignition curve can be maintained by active feedback of the auxiliary power systems, but very reliable feedback control will be required to avoid thermal runaway.
It is concluded that the problem of thermal control and fractional power operation of a tokamak reactor with ignited plasma is far from trivial. Several possible approaches have been examined for thermally stable operation in the ignited regime. Many of these approaches effectively degrade confinement so that the desired operating point becomes marginally ignited. If ignition is not achieved, thermal stability is achieved in a driven subignited reactor mode. These approaches must be evaluated further and with more refined empirical estimates for the energy confinement scaling in order to reduce the present uncertainty in this area.
