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Chamber and pumps
Pressure follows V dP/dt = Q - S P in each stage, solved exactly over each step. The roughing pump removes the bulk gas, the turbo pump takes over at low pressure, and the gate valve may only open once the rotor is fast enough and the chamber is below 8 Pa. The speed slider compresses time.
Valve and pump controls
Model checks
The science
What is modelled
A chamber volume pumped by a roughing pump (displacement type, with an ultimate pressure) and, after it is isolated, by a turbomolecular pump in series with the port conductance. The foreline of the backing pump is a second small volume. Gas loads are a decaying outgassing term, a constant residual outgassing and a background leak.
Equations
- Chamber:
V dP/dt = Q - S (P - Pult), integrated with the exact exponential step. - Series conductance:
1/Seff = 1/Sturbo + 1/C, with the turbo speed falling at high pressure and scaling with rotor speed squared. - Outgassing:
Q = Qres + Q0 exp(-t/tau). - Closed chamber:
P = P0 + (integral of Q dt) / V.
Checks run in the page
- Roughing time to 1000 Pa against an independent RK4 integration.
- Turbo series conductance.
- Closed-chamber pressure rise.
- The interlocks refuse the gate valve and turbo start at atmosphere.
- Ultimate pressure after the automatic sequence.
Honest simplifications
Lumped volumes, a smooth empirical pump-speed law, no molecular-flow conductance of tubes, no gas species, no temperature effects and no cryopumping. Educational, not a vacuum-system design tool.
What to try
- Switch on the automatic sequence at 20x speed and read the pressure fall through the regimes.
- Try the gate valve straight away: the interlock refuses and says why.
- Press Dirty chamber and see the outgassing set the ultimate pressure instead of the pump.