Fusion Exhaust Gas Analysis
Quadrupole residual gas analyzers (RGAs) are common in fusion labs, but they are not built to resolve the most important light-isotope conflicts in DT and D-3He work. BSI's compact FT-ICR mass spectrometer targets those mass 3 and mass 4 separations directly, delivering R > 10,000 where a standard RGA manages only R ≈ 4–10.
The isotope-resolution layer
FT-ICR resolution scales favorably at low mass — exactly the regime where fusion exhaust and fuel-accounting questions become hard. Think of it as the high-resolution isotope layer of the diagnostic stack, not a replacement for every vacuum gauge.
R > 10,000
At m/z 3–4, enough to separate He-3/HD, He-4/D2, and HT/D2 — well beyond the single-digit resolving power of a quadrupole RGA at these masses.
0.5–50 pmol
Picomole-level quantification for trace hydrogen-isotope and helium-species accounting in exhaust and breeding-loop gas.
Room Temp
A permanent-magnet design removes cryogenics. The tabletop instrument fits on a lab bench or in a diagnostics rack near the machine.
The technical challenge
A quadrupole RGA is a practical vacuum diagnostic, but the hardest fusion questions are not about detecting a nominal mass peak. DT fuel ratio, tritium accountability, helium ash, and D-3He research all require separating species that sit extremely close together in mass. At m/z 3, He-3, HD, and T overlap; at m/z 4, He-4, D2, and HT crowd together. The resolving power needed runs into the hundreds or thousands — far beyond the R ≈ 4–10 a typical RGA delivers at mass 4.
| Nominal m/z | Species A | Mass (Da) | Species B | Mass (Da) | Δm (Da) | R required | RGA? |
|---|---|---|---|---|---|---|---|
| 3 | He-3 | 3.0160 | HD | 3.0219 | 0.0059 | 511 | No |
| 3 | T | 3.0161 | He-3 | 3.0160 | 0.0001 | 30,160 | No |
| 4 | He-4 | 4.0026 | D2 | 4.0282 | 0.0256 | 157 | No |
| 4 | HT | 4.0239 | D2 | 4.0282 | 0.0043 | 936 | No |
| 5 | DT | 5.0300 | HD2 | 5.0376 | 0.0076 | 662 | No |
| 6 | T2 | 6.0322 | D3+ | 6.0423 | 0.0101 | 597 | No |
R required = m / Δm at 10% valley definition. A standard quadrupole RGA achieves R ≈ 4–10 at mass 4 — below every pair above. BSI's FT-ICR clears them all at R > 10,000. See the full analysis on the low-mass spectrometry page.
Where it fits
DT fuel ratio, tritium accountability, helium ash, and D-3He research require separating species that sit extremely close together in mass — not just detecting a nominal peak. That is beyond a quadrupole RGA's resolving power.
At m/z 3, He-3, HD, and T overlap so peak assignment becomes unreliable. At m/z 4 and nearby channels, He-4, D2, DT, and HT-related species add ambiguity. RGAs often deliver single-digit resolving power at these masses.
FT-ICR resolution scales favorably at low mass. BSI's compact instrument targets R > 10,000 at mass 3 and 4 — exactly where fusion exhaust and fuel-accounting questions become difficult.
It is the high-resolution isotope layer, not a replacement for every pressure gauge or vacuum monitor. It is most relevant when the decision depends on isotope identity, fuel ratio, tritium accountability, helium ash, or D-3He campaign analysis.
Not a general purchasing office seeking a commodity RGA. The fit is a diagnostics engineer, tritium-systems lead, fuel-cycle team, or lab manager who already knows mass 3 and 4 ambiguity is limiting operational data quality.
Yes. RGAs remain useful for routine vacuum monitoring. The FT-ICR adds the isotope-resolution capability they lack, so both coexist in the same diagnostic suite.
Data for decisions
| Capability | Quadrupole RGA | BSI FT-ICR |
|---|---|---|
| Resolving power at m/z 3–4 | Often about R 4–10 | R > 10,000 |
| He-3 / HD / T distinction | Not reliable | Designed for separation |
| He-4 / D2 / DT ambiguity | Often unresolved | High-resolution low-mass analysis |
| Trace sensitivity | Limited at low m/z | Calibrated 0.5–50 pmol |
| Size | Small vacuum instrument | Compact tabletop FT-ICR, room temperature |
| Cost class | Lower | $180k+ preorder |
Frequently asked questions
Yes. Any DT campaign that depends on accurate hydrogen-isotope and helium-species accounting needs more resolution than a basic RGA can provide. The FT-ICR resolves HT (4.0239 Da) from D2 (4.0282 Da) and DT (5.0300 Da) from HD2 (5.0376 Da), which is what tritium accountability requires.
No. RGAs remain useful for routine vacuum monitoring and total-pressure work. BSI's FT-ICR is for the isotope-resolution layer that RGAs cannot provide — the two are complementary.
Private fusion teams and national labs face the same measurement physics as they move toward DT campaigns, tritium handling, or D-3He fuel-cycle research. The mass 3 and mass 4 ambiguity is identical regardless of reactor concept.
BlankSlate Innovation, a Texas Tech University spinoff with peer-reviewed published research. For the fusion-specific use case, see our FT-ICR fusion diagnostics page; for the underlying resolution physics, the low-mass spectrometry page.
Next step
If your fusion program is using an RGA for mass 3 or mass 4 decisions, ask BSI whether FT-ICR resolution belongs in your diagnostic stack.