Monday, October 25, 2021

Nuclear Fusion: How Close Really?

Environmental & Science Education, STEM, Nature of Science, History of Science

Ed Hessler

Our sun is a fusion engine. So are all of our stars.--Rivka Galchen (The New Yorker, October 8, 2021) 

This started as a single entry, a video on fusion (and subsequent confusion) by a scientist. In the meantime I read an article by a non-scientist that looked more at the engineering side and decided to add it so it is longer than usual. The contrast between the science and the engineering provides a perspective on the nature of science and engineering. It is divided into two parts.


Nuclear fusion power, if based on the media reports, are far more glowing than the results. 

This is the claim made in a new video (12m 49s) on nuclear fusion by Sabine Hossenfelder has a new video (12m 49s) in which she talks about "Nuclear (Con)fusion." She discusses how close we are to seeing it as an effective way to provide energy. 

According to her analysis "the research (appears) more promising than it really is." Hossenfelder focuses on "its most important aspect, how much energy goes into a fusion reactor, and how much comes out," i.e., the energy gain." This is a ratio between energy out over what goes in. In this ratio Q, as it is known, must reach 1 to break even.

To comment you must be a member of her blog. It is also posted on YouTube (you have a choice) for general comments. Eventually, I think, you'll find it useful to review both, i.e., comments from blog readers and comments from a more general audience.

The visual talk and the script go hand-in-hand because Hossenfelder sometimes uses animations and illustrations.


Coincidentally, writer Rivka Galchen has a New Yorker essay (October 8, 2021) on fusion energy--the perspective is largely from the engineering side. So far, as Dr. Hossenfelder noted above,  the promise has never been fulfilled. Galchen put it this way, quoting the White Queen in Through the Looking Glass: The rule is, jam to-morrow and jam yesterday – but never jam to-day."

There have been successes and two boxes can be checked: creating plasmas "hotter than the center of the sun" and creating "Containers that could hold those making 'bottles' out of strong magnetic fields" In addition experimental fusion device have been built in laboratories.

Galchen covers the attempts to contain plasmas, the ups and downs and downs of a fusion researcher's life, the sun as a fusion engine, what fission is, its false messiahs, shysters, and cranks, funding cycles, demonstration plants under construction or planned, and the essay is sprinkled throughout with comments on the nature (and allure) of  engineering.                                                                                                                                                                         Here I focus on more recent, perhaps promising, events, research, development and renewal of interest as well as hope.

But first a brief comment on plasma. It is one of the fundamental states of matter--plasma is the most abundant form of ordinary matter in the universe, a cloud of charged particles, their behavior dominated by electric and magnetic fields, according to the Wiki entry.

In 2009 Dennis Whyte who directs the Plasma Science and Fusion Center at MIT passed a colleague while walking in the hall, an encounter that restored "his interest in fusion.". His colleague was holding "'a bundle of what looked like the spoolings of a cassette tape.'" It was instead "a relatively new material: ribbons of high temperature superconductor  (H.T.S.). Superconductors are materials that offer little to no resistance to the flow of electricity; for this reason, they make ideally efficient electromagnets, and magnets are the key components of tokamaks--fusion devices shaped like doughnuts.

Whyte figures prominently in this story and his interest in fusion energy began in high school.  Galchen reports he knew from fifth grade "he wanted to be a scientist, and in the eleventh grade he wrote a term paper on that wild idea which often appeared in science fiction--near-boundless energy generated by the fusing of two atoms, as happens in stars." Whyte told Galchen "I remember getting that paper back, and my teacher saying, 'Great job, but it's too complicated.'" He also told her that at one point he "almost retired" due primarily to its economics.

H.T.S. "opened up new possibilities...could make a much more effective magnet than had ever existed, resulting in a significantly smaller and cheaper fusion devices. 'Everytime you double a magnetic field, the volume of the plasma required to produce the same amount of power goes down by a factor of sixteen,' Whyte explained." By a factor of commonly means either multiplied or divided by, depending on whether it is expressed as an increase or decrease.

So Whyte asked graduate students in his engineering-design class to use this new material to design "a compact fusion-power plant...enough to power a small city." It was what is called a '"good enough'" machine. Its key feature was that "the use of H.T.S. magnets made it about the size of a conventional power plant--a tenth the size of ITER. ITER is "an enormous fusion device being built in southern France by an international collaboration. ...The schedule is for ITER to demonstrate net fusion energy in 2035, i.e., more energy out than in. 

Whyte has a dual interest in giving such practical problems to students."'I've always wanted to expose my students  not only to the science questions but also to the technology questions."

H.T.S. is fragile material and "it remained to be seen seen if it could even be made into a hardy magnet, and, if it could, how well that magnet would endure bombardment by charged particles. Plus, H.T,S, was not yet commercially  available at sufficient scale and performance. ... 'But those were engineering barriers, not scientific barriers. That class really changed my mind about where we were in fusion."'

Following two classes of graduate students, some of them formed a group to continue working on the problem Whyte presented. Since then it has sputtered and spurted on in various shapes and forms. In 2018, two years after MIT's experimental fusion device was shut down, a "seven-person private fusion company was formed known as Commonwealth Fusion Systems (C.F.S.).  It now (2021) employs about 300 people."

A crucial magnet test occurred in September--three years under development. It reached its performance goal. "Soon after the demonstration," writes Galchen, "Paul Dabbar, the former Under-Secretary for Science and a visiting fellow at Columbia University's Center on Global Energy policy, declared in an op-ed for The Hill that 'the fusion age was upon us.'"

Galchen calls attention remaining to some of the formidable hurdles to even "demonstrating a fusion devices that gives out considerably more energy than it takes to run. ...before fusion will turn on the lights in your kitchen (and I'd add keep them on day in and day out.)." Some of these challenges include whether "these fusion devices (will) sustain plasmas for sufficient periods of time? Will their daunting fuel-cycle issues (recycle its own fuel), and manage their exhaust, and will the stresses of the extreme conditions destroy the devices themselves?" 

According to Galchen "fusion scientists often speak of waiting for a 'Kitty Hawk moment,' though they argue about what would constitute one. Only in retrospect do we view the Wright brothers' Flyer as the essential breakthrough in manned flight. Hot-air balloons had already achieved flight, of a kind; gliders were around, too, although...a catapult or leap" was required for take off. And what is meant by flight anyhow? Of one of the Wright brothers' "flights that lasted less than a A. P. reporter said of that event, 'Fifty-seven seconds, hey? If it had been fifty-seven minutes, then it might have been a news item."

And then she writes, fittingly, "Will there come a time when there is jam today, and the day after, and the day after that?" The big question.


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