Archived - MIT Fusion Reactor and Facilities

[Brian McDermott]

Today I got a tour of MIT's fusion facilities. It was very informative and I learned a lot.

The last picture you see is of a grad student standing in front of the enourmous concrete shield for the Alcator C tokamak device. I am 5'8" and it extends at least another 20 feet over my head. The vacuum chamber is within this concrete structure. The grad student I talked to said the concrete was more for protecting the chamber from dings and bumps than from protecting the staff from the neutron flux. The whole thing was then placed into a large room with concrete walls and blast doors 3 feet thick. Currently, the chamber is open to air, and there is actually a man with a vacuum cleaner inside that small opening that the person is standing next to.

Their typical fusion production is 10^14 neutrons total in a 2 second "shot." The peak magnetic field is 8 Tesla, at many Mega Amperes, and about 1-10keV thermal energy. They use an alternator and flywheel to dump many megawatts into the device in a "shot," and there is a 15 minute cool off and regeneration period between shots.

It is interesting to note that the grad student I talked to said that the whole program is "all about money." He said that the tokamak's job was to not produce energy viable fusion per say, rather to explore the properties of plasmas and create useful technologies based on the findings. He also compared using the tokamak to monster truck racing in that you experience all these extreme conditions during operation. It really is just a big group of scientists and grad students having fun and dinking around with plasmas, just on a much bigger scale than fusors.

The first picture is of one side of the Alcator control room (immediately adjacent to the device itself). The second picture is of the unfinished Levitated Dipole Device (LDX, it was too big to fit the whole thing in the camera's viwefinder), and the third picture is of a smaller, nonfusion tokamak built by grad students.

All the vacuum systems are turbopumped and can reach pressures of 10^-7 Torr. In the levitated dipole, they backfill with deuterium to between 10^-5 and 10^-6 Torr. The LDX is slated to have its first plasma in two weeks, but there was a lot of joking about how things never seem to be on schedule.

This visit landed me a few new friends and an invitation to come and watch some experiments in the future. They were certainly impressed with the amateur fusion effort and it came as news to me that MIT had an IEC device of their own. I'm going to try and find out more on this at a later date.

We all sit here and editorialize the tokamak, but when you actually go to look at one and it's associated equipment, it's pretty cool indeed.

[MARK-HARRISS]

Thanks for sharing that Brian, very informative pics..... I wish I had that third device and maybe a shed to stick it in......and direct connection to the local power station and.........

Mark H

[Brian McDermott]

The whole power supply assembly took up a two-story gym-sized room and was bigger than the tokamak itself! The first picture here doesn't do justice to the sheer size of the thing! The power requirements are many times larger than the amount of power used by the city of Cambridge at any given time.

The second picture is of the klystron assembly for heating the plasma, which occupied a large catwalk.

The torus is secured by 36 enourmous steel bolts. Coincidentally, these are the same bolts that NASA uses to hold the space shuttle to the ground while the engines build up to full thrust. Except NASA only uses 2 bolts! Why the need for such retention?

It turns out that the plasma can undergo disruption and collapse rather quickly. If this occurs, a prodigious amount of energy is dumped into the vacuum chamber itself, and that energy is enough to torque the torus into oblivion, resulting in an expensive pile of twisted metal. It needs those bolts to protect the machine from damage during disruptions. One day, they ran an entire session of disruption experiments, simply to study the mechanism behind it. The bolts did their job and protected the machine.

With the LDX device, they are currently leak hunting. They lowest pressure they can get at the present time is about 10^-4 torr. That means that many unfortunate graduate students are going to have many sleepless nights running the helium leak detector and passing the gas stream over every single flange, fitting and weld and fixing leaks.

One of the things I like about MIT is that the line between theory and engineering is often blurred. The physicists are down on the floor tinkering with things just as much as the technicians are. Everybody knows the quirks of the equipment and how to utilize them in a way that is not detrimental to the experiment.

It should be noted that the MIT tokamak is not one big Manhattan Project-style experiment working to make fusion energy possible. Rather, it is more like one of those big astronomical observatories. You simply sign up for a shot date, set up your experiment, collect your data, and let the next guy take his turn.

[Richard Hester]

They've been working on Alcator in some form or other for years. I did my thesis work almost 20 years ago at the Magnet lab, right next to the world's most powerful continuous magnet at the time (200kGauss). Alcator was in the next room. The flywheel pulse power system was also around at that time. There are a lot of concrete cells for paltry 50kG magnets. The cells are blast protection in case cooling to a magnet fails, and the coil melts down. The combination of steam and magnetic field pressure is a double whammy... The magnets are wound with sheet copper with cooling channels etched in. Francis Bitter (the lab was named after him) invented that type of solenoid for generating intense continuous magnetic fields.

[Richard Hull]

Brian,

I have decided to archive this mainly due to the nice images and their relationship to much talked about subject matter elsewhere in other forums. Leave the images right here.

Nice info.

I knew all of this that you reported, of course.

Robert Hirsch told me that all he inherited when taking over the entire AEC fusion effort was a bunch of labs playing with plasmas, doing plasma diagnostics that just sorta' never ended.

Once he forced them to look at the Tokomak, against their will at first, they now had a mission focused at "making fusion power" or so he and the AEC thought. Unfortunately, that very mission devolved back to plasma diagnostics once it was obvious that the tokomak was not going to be the power machine hoped for.

The big difference was they were now in the large and could dream up more new directions to keep the bloated projects going and so here we are today..........Still playing with plasmas that can't be confined, hoping against all hope that we will find the magic bullet. It reminds me of the sad bunch of magnetic perpetual motion machine propellar heads, straining like a gear box thinking that just one more magnet or maybe just a bit more field in an extant magnet will make their motor self-pertuating.

So they are learning, but nothing that will lead to power fusion. What they learn may have other apps and will definitely make a gang o' them grad students Phd's and fill pages in a lot of scientific journals in future.

By the way, those neutron numbers were impressive and match what a fission reactor at full power can do, but two seconds might as well be 2 usec. If you can't do it 24-7, you might as well have not done it at all, so far as the utilities, the bean counters and the power consuming couch potatoes in America are concerned.

Richard Hull

[3l]

Hi Brian:

I rather like your pictures.
MIT is still at it after all these years?
Amazing!
My visit was in 1978.
Pretty much the same as I remember it.
Glad to see they have kept the paint up.
I never had conceived that years later I would be matching their output... with a Tesla coil linac.
Oh BTW the linac is continious....as long as the juice flows ya gets neutrons.
My whole setup will fit in a 20 x 20 concrete shed.

Happy Fusoring!
Larry Leins
Fusor Tech