Vacuum Pumping Control
Pumping control regulates the removal of exhaust gas during a pulse, setting particle throughput while protecting each pump's operating window.
Pumping during operation
While the plasma runs, fueling adds particles and pumping removes them; their balance sets the density and the exhaust of helium ash and impurities. Pumping speed at the divertor determines how effectively spent fuel and ash leave the chamber, so pumping is a control actuator in the particle balance, not just a background utility.
Cryopumps and throughput
Large cryopumps provide high pumping speed by freezing gas onto cold panels. Their speed depends on the panel temperature and the gas species, and they saturate as they fill, so control tracks the accumulated inventory and schedules regeneration before saturation. During regeneration, released gas, including tritiated species, is routed to the fuel cycle rather than vented.
Controlling conductance
Because a cryopump's raw speed is not easily varied, throughput can be trimmed with adjustable baffles or valves that change the conductance between the chamber and the pump. Control uses these, together with fueling, to hold the target density and to manage helium removal so ash does not dilute the fuel. Divertor neutral pressure, sensed by gauges, is a key feedback signal.
- Pumping and fueling together set the density
- Cryopumps saturate and need scheduled regeneration
- Regenerated gas returns to the fuel cycle
- Adjustable conductance trims effective pumping
Helium ash
A D-T plasma produces helium ash that must be pumped out or it dilutes the fuel and quenches the reaction. Efficient helium exhaust is a design and control target. In the Kronos burner, which runs D-3He, helium chemistry differs, but ash and impurity removal remain a pumping-control task. The machines are simulation and design cases, and this page describes pumping control in general terms.
Pumping control is the removal half of the particle balance the plasma depends on.