9 INCH VACUUM SYSTEM

The vacuum system is a straight forward diffusion pump system that is backed by a direct drive mechanical pump. The Precision mechanical pump has an absolute pressure of 1E-4 Torr, and a pumping speed of 195 liters/minute. The diffusion pump is a Veeco 4 inch water cooled pump that uses Dow Corning 704 oil, with water cooled baffles, and a liquid nitrogen trap. The ultimate pressure of this four inch pump is 1E-8 Torr and has a pumping speed of 425 liters/minute. Directly after the LN2 trap the plumbing steps down from a four inch flange to a two-inch KF40 Viton flange. A valve manifold and 18 inches of two-inch metal bellows connect the LN2 trap to the chamber. Only at the chamber does the vacuum line reduce to one-inch. After great care in assembling a clean and tight vacuum system the chamber can routinely be evacuated to 1E-5 Torr in approximately 30 minutes, and < 5E-6 Torr in less than 2 hours. The ion vacuum gauge on the chamber is the primary vacuum monitoring system, it also is a Veeco product, model RG-1002 Bayard-Alpart type gauge. Because it is mounted directly on a chamber accessory port, the gauge is in a significant magnetic field while the magnet is energized. Since the operation of the ion gauge utilizes low energy ion currents, even the slightest magnetic field will alter the ion current incident on the collector. This ion current change thereby guarantees erroneous pressure readings.

Chamber, shown removed from magnet, is being pumped down with the desrcibes vacuum system. Note Ion gauge at far end of the camber. Pumping line is in foreground.


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