Rotating disc gauge for absolute total pressure measurement in high vacuum

Abstract

An absolute vacuum gauge exploiting molecular drag between coaxial discs, a configuration suggested by Langmuir, is being further investigated. The device operates in a range similar to that of the spinning rotor gauge. It consists of a silicon disc 92 mm in diameter suspended on a calibrated torsion fiber a few mm above a metal disc of the same size which rotates at speeds up to 50 000 rpm. Molecules leaving this rotor communicate a torque to the suspended disc by molecular drag. The angular deflection thus produced is sensed optically and is about 2° at 10−6 mbar. The critical factors relevant to absolute measurement, such as tangential momentum accommodation, geometry, and edge effects have been investigated and experimental comparisons with a spinning rotor gauge demonstrate that absolute pressure measurements with uncertainty better than ±5% are possible at pressures ∼ 10−6 mbar. Measurements of similar uncertainty will be possible at 10−7 mbar.

Measurement of Continuum Breakdown During Disk Spindown in Low-Pressure Air

“…Millikan performed a coaxial cylinder experiment to quantify the interaction between gas molecules and a material by measuring TMAC in the continuum slip flow regime [28]. Chambers et al measured the torque on a stationary disk by placing it near a rotating disk [29]. Gabis et al magnetically levitated a spinning metal sphere and measured the deceleration torque with the sphere spindown [30].…”

Control of Gas Flow in Narrow Channels Using an Electric Field To Modify the Flow Boundary Condition

“…In general, the tangential momentum is difficult to calculate and can in principle be affected by the roughness of the surface, the elasticity of collisions, and the relative masses, bonding, and arrangement of the atoms. Accommodation coefficients have been measured by a variety of researchers (e.g., refs − ), and theoretical aspects are described in two reviews. , …”