Will SPARC demonstrate a fusion gain Q above 1 before 31 December 2027?
deadline 2027-12-31
confidence medium
tier 4 evidence
13%Asturna estimate
Resolution criterion
Yes if CFS announces, and a paper or scientific presentation documents, a SPARC discharge with fusion power greater than the injected heating power.
Verified starting state
SPARC targets Q of roughly 11 and 140 MW on 10-second discharges, with a public target of scientific breakeven in 2027. First plasma had not occurred as of 17 September 2026. Ramping up to deuterium-tritium typically takes more than a year of campaign.
What pushes it up
- CFS continues to hold a stated public target of achieving scientific breakeven in 2027 [tier 1].
- Substantial funding continues to support acceleration of SPARC construction and commissioning [tier 4].
What pushes it down
- First plasma had still not occurred as of 17 September 2026, leaving barely 15 months until the deadline [tier 1].
- Ramping up a tokamak from first plasma to deuterium-tritium campaigns typically requires more than a year of operational testing and commissioning [tier 1].
- Achieving Q > 1 and publishing or presenting documentation before 31 December 2027 leaves virtually no buffer for any hardware, cryogenic, or tritium handling delays [tier 1].
What would move this number most
The exact date of first plasma and how rapidly CFS can commission heating systems and obtain tritium authorization to initiate full DT discharges.
How this number is built
| Deadline | 2027-12-31 |
| Base rate | 15% |
| Best evidence | tier 4 · 1 article(s) used |
| Independent runs | 12 · 14 (spread 2 pts) |
| Confidence | medium |
| Evidence cap | not triggered |
| Last revised | 2026-10-10 12:48 |
| Model | gemini-3.7-flash |
Sources consulted
Probability history
2026-10-10 12:48 13% 1 article(s) on file · gemini-3.7-flash
- What pushes it up. CFS continues to hold a stated public target of achieving scientific breakeven in 2027 [tier 1].
- What pushes it up. Substantial funding continues to support acceleration of SPARC construction and commissioning [tier 4].
- What pushes it down. First plasma had still not occurred as of 17 September 2026, leaving barely 15 months until the deadline [tier 1].
- What pushes it down. Ramping up a tokamak from first plasma to deuterium-tritium campaigns typically requires more than a year of operational testing and commissioning [tier 1].
- What pushes it down. Achieving Q > 1 and publishing or presenting documentation before 31 December 2027 leaves virtually no buffer for any hardware, cryogenic, or tritium handling delays [tier 1].
- What would move this number most. The exact date of first plasma and how rapidly CFS can commission heating systems and obtain tritium authorization to initiate full DT discharges.
2026-10-07 09:19 15% 1 article(s) on file · openai/gpt-oss-20b (Groq)
- What pushes it up. Funding injection of $1B may accelerate development and bring SPARC closer to its ambitious Q~11 target [tier 4]
- What pushes it up. Public target of scientific breakeven in 2027 indicates strong commitment and realistic planning [tier 1]
- What pushes it down. No first plasma achieved as of 17 Sep 2026; ramping to D‑T typically requires more than a year of campaign [tier 1]
- What pushes it down. Historical precedent shows few new devices reach Q>1 within the first few years of operation, making the target optimistic [tier 1]
- What would move this number most. Whether SPARC will achieve first plasma and D‑T discharges before 31 Dec 2027
2026-09-22 00:34 14% 1 article(s) on file · gemini-3-flash-preview
Reasons not recorded for this revision (detailed history has only been kept since recently).