Prof. Prabhat Ranjan CEO and Co-founder of a nuclear fusion company called ASPL Fusion. He is former Vice Chancellor of D Y Patil International University, Akurdi, Pune
The Prototype Fast Breeder Reactor went critical at Kalpakkam in April. It is a good moment to ask what we actually mean when we say “thorium” — because it is not one technology but at least six distinct engineering routes, and all of them are answers to the same question: how does India get more U-233, sooner?
On the many roads from monazite sand to megawatt-hours — and where a fusion-driven neutron source fits in.
On 6 April 2026, the Prototype Fast Breeder Reactor at Kalpakkam attained first criticality. For those of us who have spent our working lives around India’s nuclear and plasma programmes, it was a moment to sit with quietly. Construction began in 2004. First operation was once planned for 2010. The reactor is now running, and India has formally entered the second stage of the programme Homi Bhabha sketched in 1954.
I want to use that milestone to ask a question we do not ask often enough: when we say “thorium,” what exactly do we mean?
On 19 June 2026 Realta Fusion drew real current straight from a fusion plasma, no turbine involved. Prof. Prabhat Ranjan on direct energy conversion versus the steam turbine — what it changes for deuterium–tritium, why it is a magnetic-mirror story, and where it points for advanced, low-neutron fuels.
On 19 June 2026, Realta Fusion, working with the University of Wisconsin–Madison, drew a few amperes of current at around a hundred volts from charged particles streaming out of the ends of their WHAM mirror device — enough, in their own words, to light a few bulbs. It is worth pausing on how modest that sounds, and how significant it actually is.
This was the first time a private fusion company has converted the kinetic energy of a fusion-relevant plasma directly into electricity, without first turning it into heat. The team has been careful to say what it is not: it is neither net-electric production nor large-scale conversion of fusion-born power. That restraint is exactly why the result deserves attention. A real current in a real circuit is a physical fact, not a press release.
I want to use the occasion to discuss something the fusion community does not talk about often enough — the rather nineteenth-century machine sitting at the heart of almost every twenty-first-century power plant we propose to build.
In his previous blog, Prof. Ranjan argued that America’s new fusion roadmap marks a change of posture — the state stepping back from building the first power plant and instead building the shared infrastructure that lets private companies build it. Here he asks the natural follow-up for India: not what our public institutions should build, but what they should open. A surprising share of what a private fusion industry needs already sits inside the Department of Atomic Energy.
In my last essay I argued that the deepest lesson of America’s new fusion roadmap is a change of posture — the state stepping back from building the first power plant, and instead building the shared infrastructure that lets private companies build it. That argument invites an obvious question for India: if our public institutions are to enable a private fusion industry, what exactly should they build?
After some months of looking closely, I think the more urgent question is what they should open. A great deal of what India needs already exists, scattered across the units of the Department of Atomic Energy. The fastest and cheapest way to accelerate fusion here is not a greenfield campaign of new institutes; it is to upgrade, repurpose, and — above all — open a defined slice of the capability the DAE has spent six decades building.
I do not write this from the outside. I carried out my own doctoral fusion research at Berkeley; spent nine years as a scientist at the Saha Institute of Nuclear Physics, where I worked on India’s first tokamak, commissioned in 1987; and later led the ADITYA tokamak at the Institute for Plasma Research, along with the operation and control group of its SST-1 superconducting tokamak. Several of the units I describe below I have worked inside, and I have watched this establishment’s plasma capability grow from a single small tokamak into a national programme. What follows is, in part, an argument that India underestimates what it already owns.
A platform, not a building
The American roadmap calls its shared infrastructure the Tritium-Blanket Development Platform — a distributed network of test stands and loops, public and private, that any developer can draw on because no single company can justify building them alone. India can assemble an equivalent almost entirely from assets it already holds. The right unit of thinking is not a new national laboratory but a platform — a coordinated set of shared user facilities, each anchored in an existing DAE unit and opened, under clear rules, to vetted private developers. Let me walk through fusion’s hardest gaps and where, in the DAE, each could be addressed.
In June 2026 the US Department of Energy published a fusion roadmap that quietly hands the lead to its private sector. Prof. Ranjan draws the real lessons for India — the public-to-private shift, the partnership mechanisms worth copying, the lanes where India can genuinely lead, and the case for a roadmap of our own.
In June 2026, the United States Department of Energy published its Fusion Science and Technology Roadmap. It is, on the surface, a domestic planning document — a list of facilities, milestones, and gaps that one nation intends to close over the next decade. But read carefully, it is something more interesting: the clearest articulation yet of how a great scientific power intends to hand the lead in an emerging energy technology to its private sector, while keeping its public institutions firmly in the game.
For those of us trying to build a credible private fusion enterprise on Indian soil, this document repays close study. Not because we should copy it — our circumstances are different — but because it surfaces, in plain language, the choices every nation now faces. I want to set down what I take to be the real lessons for India, and where I think our own path must diverge.
The strategic shift hidden in three words
The Roadmap organises everything around three verbs: Build, Innovate, Grow. Underneath the alliteration sits a genuine change of posture. For seventy years, the American public programme — like every national fusion programme, including our own — assumed that the state would design and construct the first power plant. The 2021 National Academies report said as much.
The DOE strategy in one line: the state builds shared capability so that companies can build reactors.
The new Roadmap quietly retires that assumption. It now treats the private sector as the builder of first-of-a-kind machines, with the public programme repositioned to do something narrower and arguably more valuable: close the common scientific and technical gaps that no single company can justify paying for on its own. To make this concrete, DOE created a stand-alone Office of Fusion in late 2025 and restructured its science programme around it.
This is the lesson India should absorb first. The question is no longer “when will the Department of Atomic Energy build a fusion reactor?” It is “what must our public institutions build so that Indian companies can build reactors?” That is a different — and in my view, far more answerable — question.
Public money belongs where private money cannot go
The most useful part of the American document is its honesty about where public investment is decisive. It identifies six challenge areas — structural materials, plasma-facing components, confinement, the fuel cycle, breeder blankets, and whole-plant engineering — and is candid that several of these are bounded by physics and metallurgy, not by money. Materials qualification under fusion neutrons, and closing the tritium fuel cycle, take wall-clock time that capital cannot compress. No amount of venture funding shortens an irradiation campaign.
The American answer is to pool these burdens. Shared neutron sources, blanket and tritium test platforms, and a network of test stands are to be funded publicly and made accessible to all developers, because the cost of duplicating them is ruinous and the knowledge they generate is largely non-proprietary.
India already has the raw ingredients for exactly this model — and, in some respects, a head start. The Institute for Plasma Research, BARC’s irradiation and tritium-handling facilities, and our materials laboratories are national assets that took decades to build. The strategic act now is to deliberately open a defined slice of that capability to qualified private players, with clear rules of access. This is precisely the logic behind incubating a private company within IPR’s ecosystem — a path our own work is pursuing, and which I believe should become routine rather than exceptional. The American roadmap gives that instinct an external endorsement.
Learn the mechanisms, not just the intent
Good intentions about public–private partnership are common; workable instruments are rare. Here the Americans have done the hard design work, and we should study their toolkit rather than reinvent it.
Four instruments, four bargains — the same rupee deployed against four different kinds of risk.
They run four distinct instruments side by side, each with a different bargain. The Milestone Program pays private companies only for achieving defined technical and business milestones — a model borrowed deliberately from NASA’s commercial cargo programme. INFUSE issues small vouchers that buy private companies access to national-laboratory expertise. The FIRE Collaboratives fund universities and laboratories to close specific gaps that industry has flagged. A newer instrument, Fusion BRIDGE, co-finances the construction of shared facilities with state governments, philanthropy, and industry together.
India does not lack funding vehicles — between the Anusandhan National Research Foundation, the Technology Development Board, and the architecture now being enabled by recent legislation, the pieces exist. What we lack is the discipline of differentiated instruments matched to differentiated risks: one for milestone-based capital, one for expertise access, one for shared infrastructure. The American experience suggests this differentiation is not bureaucratic neatness; it is what allows the same rupee to be used four different ways for four different problems.
At INEF 2026 I realised how little the fission and fusion communities still talk to each other. Yet a fusion device is, before it is ever a power plant, an intense source of fast neutrons — and that surplus can breed U-233 from India’s thorium, burn long-lived waste, and drive a sub-critical hybrid that never goes critical. Fission problems with a fusion answer.
The Neutron Bridge — Part 1 | Prof. Prabhat Ranjan
I spent two days at the India Nuclear Energy Forum at IIT Bombay this May, and I came away with one impression more strongly than any other. The people who build and run our fission plants — some of the most capable nuclear engineers anywhere — have, for entirely understandable reasons, not been watching what has happened in fusion over the last five or six years. And the fusion community, equally guilty, has rarely bothered to explain itself in terms a reactor physicist would find useful.
That is a shame, because the two fields are closer to needing each other than either side seems to realise. I want to use this note to close a little of that gap, written deliberately for colleagues who think in cross-sections and neutron budgets rather than press releases.
What changed in fusion while you were busy keeping the grid running
For most of our careers, “fusion” meant one thing: a very large tokamak, decades away, funded by governments. ITER is real and important, but it shaped a perception that fusion is monolithic and remote. That perception is now out of date in two specific ways.
First, the magnet problem has largely been solved by materials, not by scale. High-temperature superconductors — REBCO tapes in particular — let us reach the field strengths that used to require enormous low-temperature magnets, in machines a fraction of the size. A high field at a small radius changes the entire economic argument, because confinement and reaction rate scale steeply with field. This is why the credible new private programmes are an order of magnitude smaller than ITER and still expect meaningful performance.
Second, and more relevant to this audience, the field has rediscovered configurations the fission community would find refreshingly simple. I work on the axisymmetric magnetic mirror — the Gas Dynamic Trap lineage from Budker Institute in Novosibirsk, recently validated by the WHAM experiment at Wisconsin and its commercial successor. A linear mirror is not a closed toroidal device. It is, conceptually, a long straight magnetic bottle. It is easier to build, easier to maintain, and — crucially — it is an excellent neutron source even when its energy gain is modest. Hold that last point; it is the whole argument.
The deeper shift is one of intent. A generation of fusion programmes asked only one question: when do we put electricity on the grid? The newer programmes ask a different one first: what is fusion good for before it is a power plant? And the honest answer is that a fusion device is, first and foremost, a controllable, intense source of fast neutrons. That reframing is what should interest you.
Why a fusion neutron is different
A deuterium–tritium reaction releases 17.6 MeV, of which 14.1 MeV leaves as a neutron. Compare that with the roughly 2 MeV average of a fission neutron. The factor of seven in energy is not a curiosity — it opens reaction channels that are simply closed to a thermal or even a fast fission spectrum.
The fusion neutron is born about seven times more energetic than a fission neutron, clearing the thresholds for neutron multiplication and hard-spectrum fission that a reactor spectrum cannot.
At 14 MeV you get neutron multiplication almost for free. Inelastic and (n,2n) channels in beryllium and lead mean a blanket can return more neutrons than it receives. That surplus is the resource. In a critical reactor every neutron is spoken for — you live or die by the six-factor formula and you have almost no margin to spend neutrons on anything that does not sustain the chain. A fusion source hands you a neutron budget you do not have to balance against criticality.
What you choose to do with that surplus — breed fuel that has eluded our thorium programme for decades, burn the waste that fills our repositories, and generate power without the assembly ever going critical — is exactly where our two fields meet.
What does India need to do, together, to be ready to build, supply, and benefit from fusion reactors? The Dutch fusion community asks itself that question once a year, in one room, for one day. After the SHANTI Act and PFBR criticality, India needs to start asking it too.
Earlier this month, on 8 May 2026, the Dutch fusion community gathered at DIFFER in Eindhoven for the third edition of Dutch Fusion Day. Around two hundred participants — from VDL on the established-industry side to Somni Solutions on the start-up side, together with TU/e, DIFFER and BigScienceNL as conveners — spent the day asking a single, very practical question: what does the Netherlands need to do, together, to be ready to build, supply, and benefit from fusion reactors?
The framing on the event’s own retrospective page is striking in its bluntness.
I read that line several times. It is, I think, exactly the sentence India’s fusion community needs to internalise — and the reason I believe we should now have an India Fusion Day.
The Netherlands does not have a tokamak the size of SST-1. It does not have an ITER-class fabrication base. What it has is DIFFER, a strong materials and plasma-wall-interactions community at Eindhoven, a handful of serious startups, and an industrial machine-building culture — VDL, ASML’s suppliers, semiconductor precision shops — that is now being courted by Proxima Fusion in Germany, Renaissance Fusion in France, UKFE’s STEP programme in Britain, and IFMIF-DONES in Spain.
What the Dutch organisers did with Dutch Fusion Day is simply this: they put the buyers and the sellers in the same room for one day a year. That is the entire formula — one day, one venue, a tight programme, public materials, and a room engineered for partnership conversations rather than press releases. It works because it is small enough to be honest. Two hundred people cannot do a ribbon-cutting; they can only do business.
When I look at where India is today, I am convinced we have crossed a threshold that justifies — and frankly requires — a convening of the same kind. The SHANTI Act 2025 came into force this December. The IPR fusion roadmap is published. PFBR achieved first criticality at Kalpakkam in April. A real private fusion ecosystem is now visible. This is no longer a community of three labs and one diaspora WhatsApp group. It is a sector. And sectors need a forum.
What would such a forum actually look like in India? What would it do, who would host it, and why must it happen now rather than after SST-Bharat is built? Those are the questions I want to answer next.
For most failure modes that actually matter in modern manufacturing, X-rays cannot see the problem. Neutrons can. After sixty years as a tool of national laboratories, that capability is finally about to become available to Indian industry on commercial terms.
The probe Indian industry has been doing without — Prabhat Ranjan
A friend who runs R&D at a major Indian cell manufacturer told me recently about a warranty problem. Their cells were failing in the field at rates substantially higher than the equivalent imported product. The chemistry was the same. The form factor was the same. The production line was new. They had spent eight months and a great deal of money on X-ray CT, electrochemical impedance, and accelerated cycling, and they still did not know why the failures were happening.
Their problem was that the failure was almost certainly hidden inside the sealed cell can — a gas pocket, perhaps, or a region where the electrolyte had not wet the separator uniformly, or a local lithium plating event during fast charging. A determined X-ray physicist will tell you that phase-contrast and high-resolution micro-CT can sometimes coax these features out under ideal geometry and unlimited time. But the lithium, the electrolyte, and the gas are nearly invisible to electron-density imaging, and the steel-and-aluminium can is exactly what X-rays do see. The contrast you need is buried in the noise. You can occasionally win that fight on a single cell in a research lab; you cannot win it on a sampling cadence that keeps up with a production line. Neutrons give you the same answer in one exposure, with stark and unambiguous contrast, because the physics is working for you instead of against you.
Thirty years of neutron radiography literature would have given them the answer in a day. They knew this. They could not access it. The nearest commercial neutron-imaging facility was in Switzerland.
