Ionization vacuum measuring cell

An ionization vacuum measuring cell comprising:

• a) an evacuatable housing (10) having a measuring connection (8) relating to the vacuum to be measured,
• b) a first and second electrodes (3, 4), which are arranged to each other essentially in a coaxial and spaced apart relationship, and comprising a common axis (7), therefore a measuring chamber (20) is formed between both electrodes, said measuring chamber communicating with the measuring connection (8), wherein the first electrode (3) forms the outer electrode comprising a substantially cylindrical surface,
• c) the electrodes (3, 4) being adapted to be connected to a voltage source (16),
• d) the electrodes (3, 4) being adapted to have connected between them, a current measuring means (17) to monitor a discharge current which constitutes a function relating to the vacuum pressure to be measured,
• e) at least one permanent magnet ring (1) surrounding the coaxial electrode (3, 4) arrangement, having a magnetization direction (13) substantially radially to the axis, and comprising a soft-magnetic yoke (2) surrounding the permanent magnet ring (1), characterized in that said yoke (2) extends axially away from the permanent magnet ring (1) on both sides, and extends in a radial direction towards the axis (7) and the first electrode (3) on both sides upon a predetermined distance (d) from the permanent magnet ring (1), wherein said first electrode (3) forms the outer electrode of the coaxial arrangement of the electrodes (3, 4), such that the yoke (2) forms two annular poles (9a, b) on both sides of the permanent magnet ring (1) and spaced apart therefrom, from which at least a part of the field lines of the permanent magnet ring (1) forms a closed loop within the measuring chamber (20), penetrating the first electrode (3), wherein, in particular, inside the measuring chamber (20) an annular tunnel-like magnetic field (14) on top of the first electrode (3) is generated.