Limiting Effects of Conductance on Pumping Speeds:For molecular flow through a circular cross-section, the pumping speed is controlled by the conductance of the pipe. The following

equation given by A. Roth shows the relationship between the pipe diameter, length, and conductance. (D,L (cm), Cair (Torr) )

When the effective pumping speed is calculated, it is severely limited by the conductance, as seen in the formula below:

Further work is in progress to optimize the vacuum system to be pump-dependent, rather than conductance-controlled. Here are

some preliminary results:

Mag-Lev Hydrogen HybridsA magnetically levitated TMP is coupled with the output stage of a drag pump, all in the same housing. These pumps increase pumping speeds, operational pressure ranges, and compression ratios for lighter gases.Blades are designed to maximize hydrogen pumping speeds.Pumps are completely oil free when backed by a dry roughing pump.

Magnetically Levitating TMPsBearings are suspended by a 5-axis magnetic field eliminating the need for conventional bearings and their corresponding oil/grease.Can be mounted in an arbitrary orientation.Reactor’s magnetic fields may interfere with the mag-lev bearings, causing overheating in the blades and diminishing performance. Can use Mu metal (high nickel content) to

shield pumps.

Conceptual Design for a Mechanical Vacuum Conceptual Design for a Mechanical Vacuum Pumping System for aPumping System for a 2 GW Inertial Fusion 2 GW Inertial Fusion Energy Direct-Drive Power ReactorEnergy Direct-Drive Power Reactor

K. Tresemer K. Tresemer 11, A. Burstein, A. Burstein22, , C. GentileC. Gentile33, C. Priniski, C. Priniski33, T. , T.

DodsonDodson33

11 George Fox University, Newberg, OR George Fox University, Newberg, OR22 Wesleyan University, Middletown, CT Wesleyan University, Middletown, CT

33 Princeton Plasma Physics Laboratory, Princeton, NJ Princeton Plasma Physics Laboratory, Princeton, NJ

Abstract Presented is a conceptual design for a mechanical pumping system to support the needs of a 2 GW IFE direct drive fusion power reactor. The reactor operates at 5 Hz, consuming approximately 450,000 deuterium-tritium targets/day, injected at >100 m/s into the target chamber and uniformly illuminated by laser light, leading to detonation. To minimize target-particle interference, the chamber must be kept at <0.5 mTorr. A solution may lie n the use of magnetically levitated turbomolecular pumps (TMPs) and corresponding backing pumps. Initially, the reactor design called for dry-bearing TMPs, however an investigation is underway comparing bearing-based TMPs to magnetically-levitated TMPs and ceramic-based TMPs. Pumps are evaluated on a wide range of specifications, the most crucial being the maximum hydrogen pumping speed, largest values for mean time between failure (MTBF), and the least amount of oil (if any) present in the vacuum system. Information collected from journal articles, industry, and operational TMP experience in other fusion related venues indicates that the employment of magnetically-levitated TMPs appears to be a superior vacuum pumping solution in the IFE environment. Thus, as a direct result of this research, magnetically levitated TMPs will be advanced to the next phase of design and review for the IFE reactor.

Five Axis Magnetically Levitated Bearing

Pumping Speed vs. Outlet Pressure for Hybrid TMPs

Ceramic TMPsPump design was created specifically for plasma confinement conditions involving tritium. The turbine blades, pump shaft, and thrust disk are all fabricated from silicon nitride ceramic, resulting in a completely oil-free TMP.Ceramic does not interact with the magnetic fields. As a result, there is no heating of the turbine and consequently, the pump runs more efficiently. Still an evolving technology.

Ceramic TMP and Schematic

17th HAPL Meeting, October 29 – 31, Washington D.C.

Pumping System Responsibilities: Maintaining a vacuum of 0.5 mTorr for a volume of

~1300 m3 with a gas load of 141 torr-liters/sec. Removing the products of target detonation, including

unused gaseous tritium, for processing and recycling.

Vacuum Pump Is Required To: Operate w/high RPM to maximize volumetric pumping. Utilize little or no oil which poses a contamination hazard. Successfully function in magnetic fields of ~ 50 gauss. Be durable, require little maintenance, and have a large mean time between failure (MTBF).

Possible Pump Solutions: