THE FIGHT FOR FU­SION

How Toka­mak En­ergy com­pares to other nu­clear fu­sion projects…

Focus-Science and Technology - - NUCLEAR FUSION - Philip Ball is a sci­ence writer and pre­sen­ter of Sci­ence Sto­ries on BBC Ra­dio 4. His lat­est book is Be­yond Weird (£17.99, Bod­ley Head).

“Un­like fis­sion, fu­sion can be switched off in an in­stant. It’s a lot safer”

2 su­per­con­duc­tors (HTSs) to cre­ate the mag­netic fields in their ma­chine. These ma­te­ri­als, dis­cov­ered in the 1980s, can su­per­con­duct at higher tem­per­a­tures than or­di­nary su­per­con­duc­tors and so can be rel­a­tively eas­ily cooled us­ing liq­uid ni­tro­gen. Cru­cially, they can also carry big­ger cur­rents and so gen­er­ate stronger mag­netic fields. King­ham thinks that us­ing HTSs for nu­clear fu­sion mag­nets could be their ‘killer app’.

“There’s a grow­ing recog­ni­tion that HTS mag­nets are a boost to fu­sion,” says Toka­mak’s se­nior com­mer­cial man­ager Dr Ross Mor­gan, point­ing out that Com­mon­wealth Fu­sion Sys­tems, a spinout com­pany from the MIT Plasma Sci­ence and Fu­sion Cen­ter in the US, also con­sid­ers this to be the key en­abling tech­nol­ogy. If it’s to work, the ma­te­ri­als will need to be made in large quan­ti­ties, and right now there are few sup­pli­ers – one rea­son why us­ing HTSs is much more fea­si­ble for smaller ma­chines. If HTSs be­came a cen­tral com­po­nent of fu­sion re­ac­tors, they would surely be mass-pro­duced, mak­ing them cheaper.

This is only one of the many en­gi­neer­ing chal­lenges that must be solved if mini-toka­maks are to be­come to­mor­row’s power sources. Toka­mak En­ergy also places its faith in an un­usual toka­mak shape: spheres, rather than the usual cylin­dri­cal de­vices favoured by the big­ger projects such as ITER and JET. Spher­i­cal toka­maks have “sig­nif­i­cant physics ad­van­tages but greater en­gi­neer­ing chal­lenges,” says King­ham.

This is a view that’s echoed by Chris War­rick, the com­mu­ni­ca­tions man­ager at the UK Atomic En­ergy Au­thor­ity (UKAEA) in Cul­ham. “We have known for decades that more com­pact, ‘spher­i­cal’ toka­maks have great po­ten­tial,” he says. “They are in­her­ently more ef­fi­cient than con­ven­tional toka­maks, re­quir­ing less mag­netic field to con­fine the plasma of fu­els.” The UKAEA has been de­vel­op­ing its own small spher­i­cal toka­mak, called the Mega Amp Spher­i­cal Toka­mak (MAST), since the late 1990s. But War­rick adds that they have draw­backs too, es­pe­cially the chal­lenges of re­mov­ing the tremen­dous amount of heat from the re­ac­tor, be­cause it is more in­tensely con­cen­trated in the com­pact de­sign.

POW­ER­ING THE FU­TURE

Toka­mak En­ergy is just one of the small play­ers in this game. In the United States alone there has been

over $1bn of pri­vate ven­ture cap­i­tal put into fu­sion projects, and there are now about 25 such com­pa­nies world­wide. One is AGNI En­ergy, a Wash­ing­ton-based start-up pur­su­ing an un­con­ven­tional ver­sion of scaled-down fu­sion in which a beam of high-en­ergy deu­terium atoms is fired at a tar­get of lithium and tri­tium. How­ever, the com­pany’s CEO Troy Dana says it is not seek­ing to use nu­clear fu­sion for power gen­er­a­tion. “We have iden­ti­fied com­mer­cial ap­pli­ca­tions for our de­vice that do not re­quire net en­ergy gain,” he says. The com­pany hopes to have a proof of con­cept de­vice op­er­at­ing by mid-2019.

Mean­while, Gen­eral Fu­sion, based in Burn­aby, Canada, is aim­ing to de­velop the world’s first com­mer­cial fu­sion power plant us­ing a new tech­nique called ‘mag­ne­tised tar­get fu­sion’. This, ex­plains CEO Christofer Mowry, com­bines as­pects of the mag­netic con­fine­ment of plasma in a toka­mak with the al­ter­na­tive ap­proach to fu­sion called ‘in­er­tial con­fine­ment’, in which lasers are used to cause sud­den, high com­pres­sion of the fuel to trig­ger fu­sion. In the Gen­eral Fu­sion de­vice it hap­pens in a pulsed man­ner, rather like the com­pres­sion cy­cles of an in­ter­nal com­bus­tion en­gine. Mowry ar­gues that the big­ger fu­sion projects aren’t try­ing to make cost-ef­fec­tive, com­mer­cially vi­able forms of fu­sion – which, he says, is pre­cisely why the smaller pri­vate en­ter­prises can com­ple­ment those ef­forts.

If small-scale com­mer­cial nu­clear fu­sion re­ac­tors were to be­come a re­al­ity, it wouldn’t just trans­form the way we make en­ergy, it would also al­ter the whole in­fra­struc­ture. Un­like fis­sion, fu­sion can be switched off in an in­stant. “In a fu­sion re­ac­tor at any one time, you have only a few sec­onds’ worth of fuel, whereas in a fis­sion re­ac­tor you have 25 years’ worth,” says King­ham. “It’s in­her­ently a lot safer.”

That means fu­sion re­ac­tors wouldn’t need to be far from cen­tres of pop­u­la­tion or in­dus­try. It’s pos­si­ble to imag­ine towns or com­pa­nies hav­ing their own ded­i­cated ma­chines, mak­ing en­ergy gen­er­a­tion much more dis­trib­uted and lo­cal.

But will the lit­tle guys re­ally achieve where the gi­ants have so far failed? “They [the larger projects] were rather taken aback five years ago when we started to look se­ri­ous,” says King­ham. Ac­cord­ing to Mor­gan, the abil­ity of start-ups to build small de­vices rapidly – in three to four months – is cru­cial. It means they can learn quickly and build that knowl­edge into the next gen­er­a­tion. In con­trast, says King­ham, the large-scale projects “tend to be quite risk-averse and con­ven­tional.”

Toka­mak En­ergy says that they hope to have a prac­ti­cal de­vice that achieves in­dus­trial-scale heat by around 2025, which could be­come com­mer­cialised by 2030. That’s am­bi­tious. But as King­ham says, “to make progress, we’ve got to have bold plans.”

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