Ion Pump Applications

Ion pumps create high vacuum and ultra-high vacuum (UHV) environments in a variety of applications, ranging from portable mass spectrometers to large scale particle accelerators. Ion pumps can create the lowest possible vacuum at an economical cost.

Ion pump technical advantages over other technologies include:

• Vibration-Free Operation
• Low Operational Cost
• Bakeability
• Low Maintenance
• Pressure Indication
• Permanent Gas Capture
• Radiation Tolerance
• Long Operational Life
• Non-Contaminating Technology

Ion Pump Operation

What are Ion Pumps?

Ion pumps are electro-physical vacuum pumps that remove gases from their environment by turning them into solid materials.

See all our videos at: https://www.youtube.com/user/GammaVacuum

How do Ion Pumps work?

Ion pumps use a four-step process to remove gases from the vacuum chamber.

Step 1: Create a high magnetic field
The ion pumps have magnets located outside the vacuum. Those magnets generate a 1200 gauss magnetic field, which contains and guides electrons within circular anode rings.

Step 2: Generate a plasma
After an initial rough pumping to remove much of the gas, high voltage is applied to the element assembly. Electrons are pulled into the anode tube assembly where they spin in a cloud; this cloud is commonly referred to as plasma. The plasma is trapped by the high magnetic field.

Step 3: Ionize gas molecules
As gases move into the anode assembly, electrons strike the gas molecules. This collision removes electrons from the gas molecule's valence shell, and changes the gas molecule into a positive ion (it has a positive charge). The positive ion is forced out of the anode tube by the high voltage field at a high velocity toward the cathode plate.

Step 4: Capture gas ions
When the positive ion strikes the cathode plate, that impact is called sputtering. Cathode materials are ejected toward the anode tube and the ion chemically and physically reacts with the cathode material.

You must install Adobe Flash to view this content.

Ion Pump Element Styles

CV Element (solid titanium cathodes)

Ions impact a titanium cathode directly or at a slight angle. Reactive gases chemically react with the titanium and can either lodge in the cathode or reflect onto the anode as high-energy neutrals, where they then remain.

Advantages: high reactive gas pumping, optimal pressure indication, superior electrical stability, superior vacuum stability

Disadvantages: low noble gas capacity, lower starting pressures, potential Ar instability

DI Element (solid titanium/tantalum cathodes)

In addition to reactive gas pumping using titanium, noble gas ions that hit the tantalum cathode are reflected back toward the anode structure. There they are permanently deposited in the non-sputtered areas and covered by fresh sputtered material.

Advantages: noble gas pumping, optimal pressure indication, electrical/vacuum stability, 80% of CV reactive gas pumping

Disadvantages: lower starting pressures, high material cost

TR Element (slotted titanium cathodes)

Ions glance off the cathode, physically and chemically reacting with the titanium cathode materials. The glancing action directs most sputtered materials toward the vacuum chamber wall of the ion pump.

Advantages: higher starting pressures, noble gas pumping, tantalum not required, 75% of CV reactive gas pumping

Disadvantages: Lower UHV pumping speeds, high manufacturing costs, electrically unstable (arcing), vacuum instability (arcing)

You must install Adobe Flash to view this content.

Pump Speed Information

The pumping speed of capture technology vacuum pumps is measured according to ISO/DIS 3556-1-1992.

Key points to note in this specification include:

• The ion pump is required to be fully saturated after pressure stabilization.
• There is no method provided for testing ion pumps in an unsaturated state.
• This method does not allow for testing of ion pumps below 10 l/s.
• This test method specifically calls for the use of nitrogen and is subject to interpretation for other gases.

ISO/DIS 3556-1.2 (pdf)

For additional information on speed testing of ion pumps, please contact us directly.

Pressure Measurement

Current to Pressure Conversions

Gamma Vacuum ion pump controllers determine pressure in the ion pump from the current in the ion pump. That current is subject to several variables, including different types of leakage. Provided all leakage currents are minimized and the controller is properly calibrated, the equation used in the controller provides an accurate representation of the pressure in the system. When calculating pressure using the current of the controller from the front panel, analog outputs, or RS232 port, the following equation can be used:

Amps = Current reading in Amps
volts = Voltage reading in volts (MPC is constant 7000 or 5600, SPC is variable)
Units = Conversion factor (Torr = 1, mbar = 1.33 & Pascal = 133)
Cal Factor = MPC/LPC programmed calibration factor (typically set to 1)
Pump Size = The size of the ion pump is liters per second (l/s)

Individual Curves

Individual pump current vs. pressure curves are provided in the download information for any ion pump. These curves are based on the equation above.

See below for Perkin Elmer controllers.

Leakage Current

High leakage current does not appreciably affect the operation of the pump, but it does render the pump incapable of giving accurate pressure readings. Pressure can still be read, however, by determining the total leakage current after removing the magnets and then subtracting this value from the total current drawn by the pump. To reduce electrical leakage:

1. Connect the Gamma Vacuum control unit to the ion pump.
2. With the pump pressure in the low micron range (10-2torr), turn on the control unit.
3. Several applications of this technique may by necessary. Be sure to allow the control unit to discharge completely between each application.
4. If this procedure does not eliminate the leakage current, disconnect the high voltage feedthrough from the connector straps inside the pump body. Check the feedthrough for leakage as described.
   CAUTION: THESE CONTROL UNITS ARE CAPABLE OF DELIVERING 7000 VDC UNDER OPEN CIRCUIT CONDITIONS.
5. OBSERVE SAFETY PRECAUTIONS IN THE USER'S MANUAL. If leakage is not eliminated, replace the feedthrough.
6. If the feedthrough is not the cause of the leakage current, the pumping element ceramic insulators are the conduction path and should be replaced.

Historical Ultek, Perkin Elmer and PHI controller equation

Gamma Vacuum maintains historical information on older controllers such as the DIGITEL 100, 500, and 1000. Contact us directly for available information including manuals and line drawings. For determining the pressure given by the front panel or serial outputs of controllers built before 1995, the following equation can be used:

Amps = Current reading in Amps
Number of Elements = 25L: N = 1, 60: N = 2, 120: N = 4, 220: N = 8

Individual Curves

Individual pump current vs. pressure curves are still available for Ultek, Perkin Elmer, and PHI ion pumps. Please contact Gamma Vacuum for availability.

Magnetic Field

Stray Magnetic Field

Directing particles can require extensive use of sensitive magnetic instruments. Coincidentally, ion pump operation utilizes a magnetic field of up to 1500 gauss. This intensive magnetic field is used to increase the mean-free path of electrons and is only needed in the element of the ion pump. The primary objective on the external sides of the ion pump is to eliminate any stray field that can affect system applications. Low Profile Ion Pumps are constructed with a closed magnetic loop that reduces stray magnetic field to near ambient levels. This is up to 10 times lower than other widely available standard designs. Eliminating stray magnetic fields reduces design effort in focusing, bending, and insertion devices that rely on the Lorentz force.

Pumping Speed and Temperature

The magnetic field directly affects the pumping speed of an ion pump. Above 85°C, the pumping speed declines with temperature. Ion pumps have difficulty maintaining operation above 250°C because of magnetic field loss. The ceramic magnets used exhibit reversible field loss of 0.2% per degree Celsius and an irreversible field loss of 7% at 350°C. This loss is non-cumulative (subsequent bakeouts to 350°C do not cause an additional irreversible loss). Above 350°C, permanent magnetic and/or physical damage can occur.

TiTan Low Profile 400 (blue = 0.2 gauss)

TiTan Tall Profile 150 (red = 3 gauss)