Model 600-B Velocity Filter
Model 300 Velocity Filter
The Colutron type velocity filter is an E x B type “Wien filter”, and consists of an electromagnet and a pair of electrostatic deflection plates. Using an electromagnet instead of the more traditional permanent magnet design enhances versatility and adjustability of the filter. The inherent focal property of the standard Wien filter has also been overcome by the velocity filter by properly biased guard ring electrodes. These electrodes guard the electric field from the magnet pole pieces, and also allow the electric field to be shaped for focussing and non-focussing configurations. The electric field plates are mounted between the magnet poles to produce an electric field E perpendicular to the magnetic field B (crossed E and B fields). The Model 300 (shown in diagram below) is 4.4″ long and 3.5″ wide. The Model 600 and 600-B are similar except that the overall length is 9.10″and width is 4.40″. In most cases, the velocity v = (2qV/m)1/2 of charged beams are obtained by accelerating the particles of mass m, and charge q across a constant electric potential V. Different masses in the beam will be dispersed by the filter since they have different velocities. The filter’s ability to disperse masses makes it a superior tool in mass spectroscopy, and some of its main features are:
- Straight line system
- Electromagnet design
- Adjustable dispersion and focus ability
- Small size; up to 50 times smaller in weight and size compared to a sector magnet analyzer.
- The filter will also select the same velocity for both negative and positive particles simultaneously.
The velocity filter is normally operated as a non-focusing device. However, by a slight adjustment of one or two guard ring potentiometers (balance or middle shim of the Model GR-3-6 control unit) the filter becomes a cylindrical lens. This feature is often used when a line image at the target is required. The capability of the filter is determined by the following formulas:
D ~ [laE (D M)]/[4VM], where D = the dispersion between the masses M and (M - D M), and undeflected and M=2qV[B/E]2 where M = the mass (mass number) which is passing through the filter collected on the target. a = the length of the filter l = the drift distance from the center of the filter to target (drift distance). E = the electric field strength in V/m. V = acceleration voltage or ion energy. B = magnetic field strength. q = the ionic charge. M/D M = maximum mass resolution; D M= the full width at half maximum intensity.
The model 300 and 600 velocity filters are non-bakeable and can be used in vacuum systems with pressures as low as 1 x 10-7 Torr. The model 600-B is bakeable to 200 C and can be used in UHV applications.
|Velocity Filter Specifications|
|Model 300||Model 600||Model 600-B|
|Max Electric Field (E)||12,500 V/m at 225V||16,800 V/m at 300V||16,800 V/m at 300V|
|Acceleration Voltage (V)||10eV to 10keV||10eV to 10keV||10eV to 10keV|
|Max. Magnetic Field (B)||1,100 Gauss||1,100 Gauss||3,000 Gauss|
|Resolution (M/D M)||~200||~400||~400|
|Beam Aperture||1.91cm x 1.91cm||1.78cm x 1.78cm||1.78cm x 1.68cm|
|Max. Magnet Power||30 Watts||30 Watts||400 Watts|
|Max. Bakeout Temp. (C)||-||-||200°|
|Model 300||Model 600||Model 600-B|
(Horizontal deflection plates)
|350V, 120mA||350V, 120mA||350V, 120mA|
|Magnet||9.5V, 3A||9.5V, 3A||28V, 14A|
Model 600-B has magnet coils encapsulated in a stainless steel jacket for liquid cooling. Please use only an ozone safe refrigerant such as Dupont R-134a or Kerosene for cooling. BIS recommends the model CU-1 cooling unit which uses the R-134a refrigerant. DO NOT USE WATER. Cooling rate is 0.5 liters/min.
Simple Mass Spectrum
H-Series Velocity Filters
BIS also offers velocity filters mounted in vacuum housings (300-H, 600-H and 600-B-H). The model 600-H is shown above. The model 600-B-H, which has the same dimensions as the 600-H, also has cooling connections for the magnet coils that are not shown in the diagram. The overall length of the model 300-H is 6.750″ instead of 10.25″ as shown in the drawing. Also, the feedthrough ports are centered between the two rotatable 8″ conflat flanges with 6″ ID. Custom chambers are also available. Please send your drawing for a quote.
- All the BIS velocity filters are available mounted in vacuum housings (H-Series Filters, see above)
- Model GR-3-6 Guard Ring Control Unit (Supplied with 300-H, 600-H, 600-B-H and Gun Systems).
- Model CU-1, HFC-134a cooling system (Cooling required for Model 600-B velocity filter).
- BEAM OBSERVATION SYSTEMS. Velocity filter resolution can be vastly improved by optimizing beam profile using the BOS systems (see S.G. Hall et al., Rev. Sci. Instrum., 68, 3335 (1997)).
This picture was made with the BIS model G-2 ion gun with model 600-B velocity filter, BOS-18 beam observation system with optional CCD camera (BOS-18-OPT02) and image processing system (IPS-1). The picture above shows the spatial profile of 4 keV, H3+ (at top), H2+ (middle) and H+ ion beams. The velocity filter dispersion was set low to get all three ion beams onto the viewing area of the BOS-18. Below, is a SIMION 3D ion beam trajectory simulation of the above example. (SIMIOM GEOMETERY FILES AVAILABLE UPON REQUEST).