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Nuclear fusion in all its forms

Nuclear fusion: start-ups are moving in!

On September 6th, 2022 |
4 min reading time
Pierre Henriquet
Pierre Henriquet
Doctor in Nuclear Physics and Columnist at Polytechnique Insights
Key takeaways
  • Nuclear fusion is a so-called “decarbonised” energy, which consists of fusing two hydrogen isotopes to produce helium. Since the process is not combustion, there are no CO2 emissions from the reaction.
  • The tokamak is a technology that allows plasma to be confined by magnetic fields where nuclear fusion can take place.
  • The ITER (International Thermonuclear Experimental Reactor) project, currently under construction in Cadarache (France), is part of the 2nd generation of tokamak prototypes.
  • Numerous start-ups are moving into the sector. Investment in this type of energy is no longer limited to the public, and the technical advances are looking promising for the future.

Con­sid­ered by some as a poten­tial solu­tion to human­i­ty’s future ener­gy prob­lems, con­trol­ling ther­monu­clear fusion has been the dream of researchers (and research lab­o­ra­to­ries) since the 1950s. Over the past 70 years, enor­mous progress has been made in mas­ter­ing this ener­gy source – the same process­es by which all the stars in the uni­verse are pow­ered (includ­ing our Sun). As impres­sive as this progress is, it is clear that indus­tri­al appli­ca­tions of this research are still lack­ing. “Nuclear fusion is 30 years away… and has been for 50 years now,” we often hear. In recent years, how­ev­er, the pri­vate sec­tor has begun to show inter­est in the field. Where are these projects at? Here is a quick rundown.

Exam­ple of a nuclear fusion generator.

Major international projects

When one thinks of civil­ian ener­gy pro­duc­tion by ther­monu­clear fusion, the first project that comes to mind is ITER (Inter­na­tion­al Ther­monu­clear Exper­i­men­tal Reac­tor). This colos­sal sci­en­tif­ic, tech­ni­cal and indus­tri­al project, cur­rent­ly under con­struc­tion in Cadarache (France), is part of the 2nd gen­er­a­tion of toka­mak pro­to­types. The toka­mak is a tech­nol­o­gy that allows a plas­ma (a “soup” of light atom­ic nuclei heat­ed to at least sev­er­al tens of mil­lions of degrees) to be con­fined, using mag­net­ic fields, in a vast toroidal cas­ing in which nuclear fusion can take place.

Dia­gram of the final inte­gra­tion of the ITER toka­mak prototype.

The first gen­er­a­tion of this type of reac­tor pro­duced very inter­est­ing results in the 1990s. In 1997, the British exper­i­men­tal reac­tor JET (Joint Euro­pean Torus) achieved both a record plas­ma tem­per­a­ture (of 320 mil­lion degrees) and a record ampli­fi­ca­tion thresh­old (of η = 0.7). This means that for every 1,000 joules of input ener­gy, 700 joules of fusion reac­tions are produced.

The objec­tive is obvi­ous­ly to recov­er more ener­gy from these reac­tions than was fed into them (η > 1). In absolute terms, if we con­sid­er the var­i­ous loss­es and tech­ni­cal lim­i­ta­tions at all stages of the process, a pro­duc­tion yield of at least 10 (i.e. recov­er­ing 10 times more ener­gy than that inject­ed) would have to be achieved to start indus­tri­al pro­duc­tion for this type of reac­tor. How­ev­er, this effi­cien­cy depends (among oth­er things) on the vol­ume of the reac­tor. This is why ITER, an inter­na­tion­al project result­ing from the col­lab­o­ra­tion of 35 coun­tries, will be much larg­er than JET (the vac­u­um cham­ber will be 6.20 m wide and 6.80 m high for a plas­ma vol­ume of 840 m3). Its objec­tive is not – and it is impor­tant to remem­ber this – to pro­duce ener­gy indus­tri­al­ly but rather to prove that an effi­cien­cy of 10 can be achieved.

The toroidal toka­mak prin­ci­ple is not the only pos­si­ble design for a so-called nuclear fusion “mag­net­ic con­fine­ment reac­tor”. Oth­er con­fig­u­ra­tions are also being stud­ied and are pro­duc­ing very inter­est­ing results. In Ger­many, anoth­er avenue is being explored: the Wen­del­stein 7‑X stel­lara­tor. The prin­ci­ple of the stel­lara­tor is still to con­fine the burn­ing plas­ma by means of an intense mag­net­ic field. These sys­tems are much more com­plex to build (requir­ing deformed mag­net­ic field coils) but much sim­pler to use once the plas­ma has been confined.

Anoth­er impor­tant route to nuclear fusion is being explored: iner­tial con­fine­ment. Here, instead of a mag­net­ic field to con­tain the plas­ma, puls­es (elec­tric or laser) are used to com­press a ball of fuel to pres­sures and tem­per­a­tures that allow nuclear reac­tions to be ini­ti­at­ed. Unlike mag­net­ic con­fine­ment, which uses low-den­si­ty plas­mas but very long reac­tion times (cur­rent­ly of the order of a minute), iner­tial con­fine­ment works on the oppo­site prin­ci­ple: obtain­ing extreme­ly high den­si­ties dur­ing very short times (of the order of a nanosec­ond or even less).

Z‑Machine, San­dia Lab­o­ra­to­ries – New Mexico.

Small private projects

Since 2015, the pri­vate sec­tor has also become very inter­est­ed (and increas­ing­ly so) in the field of con­trolled nuclear fusion for sev­er­al rea­sons. The first is cli­mate change. Indeed, nuclear fusion is a “decar­bonised” ener­gy. The fusion of two hydro­gen iso­topes (deu­teri­um and tri­tium) pro­duces heli­um, a reac­tion that does not gen­er­ate any com­bus­tion or CO2 emis­sions. It is there­fore a cli­mate-friend­ly. The oth­er rea­son is tech­no­log­i­cal. The ITER project promis­es clean ener­gy pro­duc­tion, some­thing that pri­vate projects are bank­ing on. In addi­tion, new mate­ri­als and tech­nolo­gies (super­con­duct­ing tapes, lasers, cal­cu­la­tion algo­rithms, etc.) allows for small exper­i­men­tal reac­tors at low­er cost. Final­ly, of course, the promise of a risky invest­ment, but extreme­ly prof­itable if suc­cess­ful, attracts investors and com­pa­nies, often backed up by invest­ment funds, bene­fac­tors (Bill Gates, Jeff Bezos) and some pub­lic funding.

Pri­vate invest­ment in nuclear fusion from 2000 to 2020 ©Greg de Temmerman

There are now more than 30 pri­vate­ly held merg­er com­pa­nies in the world, accord­ing to an Octo­ber sur­vey by the Fusion Indus­try Asso­ci­a­tion (FIA) in Wash­ing­ton, DC, which rep­re­sents com­pa­nies in the sec­tor. The 18 com­pa­nies, report­ing fund­ing, say they have attract­ed more than $2.4bn in total – almost entire­ly from pri­vate investment.

In the absence of research teams as impor­tant as those involved in pub­lic projects, size often needs to be replaced with smarts, and nov­el tech­niques need to be tried out. Again, this is a high-risk tac­tic, but the rewards can be extreme­ly high if suc­cess­ful. Here, we can cite Gen­er­al Fusion with its con­cept of a pis­ton-cov­ered sphere into which a deu­teri­um-tri­tium mix­ture is inject­ed before the pis­tons pro­duce a shock wave that com­press­es the plas­ma and pro­duces the pres­sure and tem­per­a­ture con­di­tions nec­es­sary for fusion.

Anoth­er com­pa­ny, CFS (Com­mon­weath Fusion Sys­tems) is rely­ing on the devel­op­ment of new high-tem­per­a­ture super­con­duct­ing mag­nets to build SPARC, a com­pact toka­mak with an expect­ed effi­cien­cy of up to 2. CFS announced in Sep­tem­ber 2021 that their new super high tem­per­a­ture mag­net had reached an inten­si­ty of 20 Tes­las. Con­struc­tion is expect­ed to be com­plet­ed in 2025. Final­ly, Helion Ener­gy, rather than seek­ing to pro­duce elec­tric­i­ty by turn­ing tur­bines using the heat gen­er­at­ed by the reac­tion at the heart of a toka­mak, is propos­ing to pro­duce this elec­tric­i­ty direct­ly by induc­tion in elec­tri­cal coils that sur­round the reactor.

Final­ly, First Light Fusion is a com­pa­ny that came out of Oxford Uni­ver­si­ty in the UK. It is pur­su­ing a dif­fer­ent strat­e­gy: the iner­tial con­fine­ment dis­cussed above. Here, the fusion plas­ma is not held by mag­net­ic fields. Instead, a shock wave com­press­es it to the immense den­si­ties need­ed for fusion. But at First Light, the com­pres­sion shock wave is not cre­at­ed by ener­gy-hun­gry lasers, but by using an elec­tro­mag­net­ic pis­tol that fires a pro­jec­tile into a tar­get con­tain­ing the hydro­gen iso­topes. The com­pa­ny is keep­ing the details of the process secret, but said that to achieve fusion, it will have to fire this pro­jec­tile at 50km per sec­ond – twice as fast as is typ­i­cal­ly applied in cur­rent shock wave experiments.

Will these pri­vate com­pa­nies, which are ven­tur­ing into one of the most advanced areas of sci­ence and tech­nol­o­gy, suc­ceed where the largest inter­na­tion­al col­lab­o­ra­tions are advanc­ing only in baby steps? Noth­ing is less cer­tain, but the next few decades are sure to be very interesting.

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