Tokamaks and Spheromaks

1. Tokamaks and Spheromaks Kevin Blondino 5 November 2012 “We say that we will put the sun into a box. The idea is pretty. The problem is, we don’t know how to make the box.” -- Pierre-Gilles de Gennes

2. Summary of Fusion • Fusion of light nuclei into heavier ones releases energy. • Most popular candidate for reaction is the D-T cycle. Others include D-D and D-3He. • Overwhelming majority hypothesize that magnetic confinement is the way to go. • Lawson criterion is to be met for fusion to be a viable energy source.

3. What is a Tokamak? • The confinement of plasma as a torus using external magnetic fields. • Field lines are required to move around the torus in a helical shape, generated by a toroidal and poloidal field. • Most popular candidate for thermonuclear fusion. • Russian acronym for “toroidal chamber with magnetic coils.”

4. The overall goal is to produce a magnetic field that follows around the torus while also wraping around it.

5. History of the Tokamak • Invented in the 1950’s by Igor Tamm and Andrei Sakharov in the Kurchatov Institute. • Introduced to the public in 1968, with results that demolished competition from every other design. • Still the most developed for fusion: ITER, NSTX, Pegasus Toroidal Experiment, and many more.

6. What is a Spheromak? • Confinement of plasma through self-induced magnetic field • The current due to the flow of plasma creates a magnetic field, which in turn, confines it. • Less popular candidate for fusion • Considered a compact toroid • Name is the arrangement of plasma, not the device that generates it

8. History of the Spheromak • Initially developed to study magnetohydrodynamical waves in astrophysical plasma in 1959 by Hannes Alfvén (Alfvén waves). • ZETA machine provided boom in design ideas, including the spheromak. • By the 1980’s, tokamaks surpassed confinement times by orders of magnitude. • SSX and SSPX in 1994

9. Pros • Tokamak: • Highly scalable • Relatively simple to control and model • Spheromak: • Much less upkeep power required • Generally smaller • No complicated magnets required

10. Cons • Tokamak: • Large power requirement due to “brute force” method • Cryogenics required for superconducting magnets • Spheromak: • Hard to scale up • Plasma behavior is complex and hard(er) to predict and control

11. General Problems with Fusion • High energy neutrons could be damaging • Turbulence! – something not quite understood • Some hypothesize that there is some underlying quantum mechanical effect that has not been taken into account or not yet discovered that causes it. • Sputtering – when higher mass particles are mixed into the fuel, lowering its temperature. • “…squeezing a balloon – the air will always attempt to pop out somewhere else.”

12. KSTAR • Korea Superconducting Tokamak Advanced Research at the National Fusion Research Institute in Daejon, South Korea. • Completed in 2007; first plasma in July 2008 • Features fully superconducting magnets • Uses hydrogen and deuterium fuels (D-D cycle), but not deuterium-tritium

14. ITER • International Thermonuclear Experimental Reactor being built in southern France; will be the largest and most powerful tokamak • EU, India, Japan, China, Russia, South Korea, and the US is funding and running • Designed to produce 500 MW output for 50 MW input • First plasma production scheduled for 2020 • DEMO, the successor to ITER, will be the first power plant scheduled to make fusion energy in 2033.

15. SSPX • Sustained Spheromak Physics Experiment at Lawrence Livermore National Lab • Completed in 1999 • One of the only spheromaks actively researching fusion

17. References • http://plasma.physics.swarthmore.edu/ssx/ • http://en.wikipedia.org/wiki/Tokomak • http://en.wikipedia.org/wiki/Spheromak • http://www.iter.org/ • https://www.llnl.gov/str/Hill.html