Fig. 1. Diagram of temperature and pressure control system for multi-pass gas cell

Fig. 2. Heating film drive circuit

Fig. 3. PT1000 temperature collection circuit

Fig. 4. Proportional valve control circuit

Fig. 5. Temperature lower limit control curve

Fig. 6. Temperature upper limit control curve

Fig. 7. Pressure control curve

Fig. 8. Pressure control data (60 Torr)

Fig. 9. CO₂ isotope abundance measurement data