Ion Pumps

Pumps use two titanium cathodes in each pumping element. They are the pump of choice for most applications for their long life, reliability and high speed per unit . These pumps are not recommended when significant amounts of hydrogen or noble gases are to be pumped or where frequent high-starting loads are encountered.

Noble diodes were developed to pump noble gases. In every instance but one they are identical to a standard diode. The difference is the use of one tantalum cathode in place of one of the two titanium cathodes in the standard pump. The tantalum, because of its larger atomic number, produces a greater number of energetic neutrals which can bury themselves in locations which are less subject to resputtering.

Pumps are also similar to standard diodes. There are two differences in construction. The first is a thicker cathode. Because hydrogen diffuses into titanium like water into a sponge, the more titanium, the more capacity for hydrogen the pump has. This absorption of hydrogen can lead to a structural problem, however. Titanium swells and distorts as it absorbs large amounts of hydrogen. Therefore, hydrogen pumps have special structural modifications to prevent distortion from causing electrical shorts.

Pumps use reverse electrical polarity and a radically different cathode design to achieve two important advantages over the diode pumps: (1) an electrically isolated cathode allows the starting glow discharge to be confined at significantly higher pressures, resulting in shorter starting times; (2) the sputter cathode design allows noble and non-noble gases sputtering. Triodes have the highest speeds for noble gases and freedom from argon instability in the event of an air leak. Disadvantage: because of the sputter cathode design, the triode pumps require more frequent service.

Thermionics manufactures a full line of sputter ion pumps

  • Standard Diode Pumps (IP Series)
  • Noble Diode Pumps (NP Series)
  • Hydrogen Diode (HP Series)
  • Triode Pumps (TP Series)
 

Each pump features:

  • Specific application design
  • Able to provide continuous and contaminant free pumping
  • Reliable from one micron to 2 x 10-11 Torr (measured)
  • Free from backstreaming
  • Bakeable to 300°C assembled
  • Bakeable to 450°C magnets removed
  • Able to act as its own vacuum gauge

All pumps are manufactured to exacting UHV standards. Pump bodies, flanges and element anodes are made of 304 stainless steel, bakeable to 450°C. Double reentrant electrical insulators are made of high-quality aluminum oxide, bakeable to 450°C, and are equipped with sputter shields. Pump magnets are high-strength ferrites bakeable to 300°C.


Pump Characteristics Normalized to the Standard Diode

Pump
Type
Air
Speed
Argon Speed
(% of air)
Hydrogen
Speed
Starting
Performance
Life Time at 
1 x 10-6 Torr
Standard
Diode
100%1%200–270%
Light duty only
Average
10µ
5 x 104
hours
Noble
Diode
95%6 to 20%Not
Recommended
Below average
5 x 104
hours
Hydrogen
Diode
100%1%200–270%
Light duty only
Average
10µ
7.5 x 104
hours
Triode85%21%200–270%
Light duty only
Average
10µ
5 x 104
hours

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