Differentially-pumped ferrofluidic seal

Ferrofluid seal apparatus for use in an X-ray scanning device having a housing with an interior and a wall, a rotating anode enclosed by the housing and attached to a shaft passing through the wall, and a vacuum pump for evacuating the housing interior to a high vacuum, the apparatus comprising:

• a first ferrofluid seal comprising magnetic means with contiguous pole piece means for forming a hermetic seal between the shaft and the housing wall and comprising at least one stage, the first seal having a first side and a high vacuum side and being designed and constructed to have sufficient pressure capacity to maintain the high vacuum in the housing interior;
• a bearing located on the high vacuum side of the first seal and supporting the shaft in the housing;
• a second ferrofluid seal comprising magnetic means with contiguous pole piece means for forming a seal between the shaft and the housing wall, the second ferrofluid seal isolating the bearing from the high vacuum in the housing interior and being designed and constructed to minimize bursting of the second ferrofluid seal;
• and
• means for maintaining an interstage region bounded by the shaft, the housing wall and the first and the second seals at a vacuum near, but less than the high vacuum.

Ferrofluid seal apparatus for use in an X-ray scanning device having a housing with an interior and a wall, a rotating anode enclosed by the housing, and a vacuum pump for evacuating the housing interior to a high vacuum, the apparatus comprising:

• a magnetically permeable shaft attached to the anode, supported by a plurality of bearings and passing through the wall between a first environment at a first pressure greater than the high vacuum by a pressure difference and the housing interior;
• a first, multiple-stage ferrofluid rotary seal comprising magnetic means with contiguous pole piece means located between the housing and the shaft and having a first pressure side and a high vacuum side, the first ferrofluid seal being designed and constructed to have sufficient pressure capacity to withstand the pressure difference;
• a first bearing located on the first pressure side of the first ferrofluid seal for supporting the shaft in the housing;
• a second bearing located on the high vacuum side of the first ferrofluid seal for supporting the shaft in the housing and having a high vacuum side;
• a second, single-stage ferrofluid rotary seal comprising magnetic means with contiguous pole piece means on the shaft in series with the first seal and on the high vacuum side of the second bearing, the second ferrofluid seal isolating the bearing from the high vacuum in the interior of the housing and being designed and constructed to minimize bursting of the second ferrofluid seal;
• and
• means for maintaining an interstage region bounded by the shaft, the housing wall and the first and second seals at a vacuum near, but less than the high vacuum.

A high speed rotary device for supporting a high speed rotary anode, which anode is exposed to an electron beam and accumulates electric charge and heat from the electron beam, for X-ray generation in a CAT Scan apparatus or the like, and comprising:

• a magnetically-permeable electrically-conductive shaft passing between a first environment at a first pressure and a second environment at high vacuum and supporting the anode in the second environment, which shaft is rotatable and generates heat,
• a housing surrounding a portion of the shaft, first bearing means having a first pressure side and a high vacuum side disposed within the housing and supporting the shaft,
• a first multiple-stage ferrofluid rotary seal comprising magnetic means with contiguous pole piece means having a first pressure side and a high vacuum side on the shaft and on the high-vacuum side of the first bearing means, the first ferrofluid seal being designed and constructed to have sufficient pressure capacity to withstand the entire pressure drop between the first pressure and the high vacuum,
• second bearing means having a first pressure side and a high-vacuum side further supporting the shaft and on the high-vacuum side of the first rotary seal,
• a second ferrofluid rotary seal comprising magnetic means with contiguous pole piece means on the shaft in series with the first seal and on the high-vacuum side of the second bearing means, the second ferrofluid seal being a single-stage seal with a construction that has a low pressure resistance but that minimizes the possibility of bursting of the second ferrofluid seal,
• means for defining an enclosed interstage volume between the first and second seals, and a port for allowing the interstage volume to be evacuated to a pressure between the first pressure and the high vacuum,
• means for dissipating heat from the shaft and the rotary anode, and
• means for grounding the rotary anode in the environment at the first pressure.

A system for establishing electrical contact between a first rotatable electrical conductor in a first environment and grounded means, the system comprising:

• first intermediate electrically conductive means in continuous and static contact with the first rotatable conductor, and comprising at least one rotating portion extending outside of the first environment into a second environment;
• an intermediate electrically conductive belt means in continuous and static contact with the first intermediate means portion in the second environment;
• and
• a second rotatable electrical conductor in continuous and static contact with the intermediate conductive belt, and in continuous contact with the grounded means, such that said first rotatable conductor is effectively grounded.

A system for establishing electrical contact between a first electrical conductor rotatable means at a first speed and grounded means, the system comprising:

• first intermediate electrically conductive means in continuous and static contact with the first rotatable conductor;
• an intermediate electrically conductive belt in continuous and static contact with the first intermediate means;
• and
• a second electrical conductor rotatable at a second speed which is slower than the first speed and in continuous and static contact with the second intermediate conductive belt, and in continuous contact with the grounded means, such that said first rotatable conductor is effectively grounded.