|The SNICS II is the most versatile negative ion source presently available. This sputter cathode source, shown at left with the extractor/lens assembly, produces ion beams for all elements which form a stable negative ion. More than 80 SNICS II ion sources are in use on Pelletron® accelerators and other tandem accelerators throughout the world. Its unique design and metal/ceramic construction with no organic seals in the main housing of the source has produced a reliable system with superior performance for all negative ions across the periodic table.|
NEC maintains an ongoing research program to continuously improve the performance of the SNICS II source and to develop new ion beams. Cathodes for these ion beams are available from NEC. In addition, NEC maintains an active ion source test bench facility to develop new ion beams on request.
Principle of Operation
Cs vapor comes from the cesium oven into an enclosed area between the cooled cathode and the heated ionizing surface. Some of the cesium condenses on the front of the cathode and some of the cesium is ionized by the hot surface. The ionized cesium accelerates towards the cathode, sputtering particles from the cathode through the condensed cesium layer. Some materials will preferentially sputter negative ions. Other materials will preferentially sputter neutral or positive particles which pick up electrons as they pass through the condensed cesium layer, producing negative ions.
NEC developed the Multi-Cathode SNICS , or MC-SNICS, as a reliable sputter cathode ion source for all applications requiring rapid cathode change and precise, repeatable positioning without cathode exposure to air. There are two standard sizes available, the 40 sample and the 134 sample source.
In both cases, the cathode wheel is controlled via a pneumatic system both for cathode indexing and cathode disk retraction for replacement of the cathode disk.
As with the standard single cathode SNICS II source, the cathode disks are removed without disturbing the vacuum in the cesiated area. In this way, the rapid change of a large number of cathodes is accomplished quickly and easily.
|40 MC-SNICS: In this view, the beam exits to the left with the cathode disk retraction mechanism and cooling lines to the far right. For replacement of the cathode disk, the cathode is retracted through a gate valve which is closed to protect the vacuum in the cesiated area.|
An upgrade is now available for the 40 sample Multi Cathode MC-SNICS. This upgrade is the conclusion of the work done by several AMS groups involving Dr. John Southon and Dr. Guaciara Santos at the University of California, Irvine, Dr. Warren Beck at the University of Arizona and Dr. Baoxi Han and Dr. Mark Roberts at the Woods Hole Oceanographic Institute.
This upgrade consists of three major parts. The first is modification to the source housing to replace the cesium line feedthrough, move the ionizer feedthrough and blank off the cesium focus feedthrough which is no longer used. The second part is the replacement of internal components with a spherical ionizer, immersion lens, cesium flow diffuser, and spacers to revise the cathode/ionizer spacing. The third part involves the replacement of the cesium feedline with a vacuum insulated assembly. All of this results in a beam current improvement of 2 to 3 with much better emittance.
If you have the NEC 40 sample MC-SNICS, please contact NEC for an upgrade quote.
|134 MC-SNICS: This version of the multi-cathode SNICS source has 134 sample positions. The time for cathode change is less than five seconds. The time to change a complete cathode wheel is about 45 minutes. This source was designed primarily for high throughput AMS applications.|
Gas Cathodes: The standard SNICS II, 40 MC-SNICS and 134 MC-SNICS can all be equipped for running gas cathodes as well as the standard solid cathode. Contact NEC for further details.
There are now more than forty 40 MC-SNICS and 134 MC-SNICS in use. They have proven to be very reliable for many applications requiring rapid and precise cathode change. This has proven to be especially beneficial in the field of accelerator mass spectrometry (AMS) where the ability to return to the precise location on a particular cathode is critical.
The NEC RF-charge exchange ion source was developed primarily to produce He- beams for injection into tandem accelerators. Its use has been expanded to include H-, NH-, and O- beams. The source design is patterned after the RF-charge exchange ion source built by Professor H.T. Richards at the University of Wisconsin, Madison, Department of Physics. The design has been continuously improved since its introduction on the S-Series tandem Pelletrons in 1979. There are now almost ninety (90) NEC RF-charge exchange ion sources in use on tandem accelerators worldwide.
Besides being long lived, the NEC RF-charge exchange ion source is simple to operate and compact. On initial startup, the source can be expected to provide 2 microamps of He- and can be tuned to over 4 microamps.
The Air Cooled Direct Extraction Duoplasmatron (ACDED) is a relatively inexpensive source useful in producing modest currents of negative ions from many molecular gases. This source uses the sideways displacement of the intermediate (Zwischen) electrode to maximize the negative ion output. It is equipped with permanent ceramic magnets and uses a .025" tungsten filament. Lifetime of the filament is up to 50 hours depending on the gas species used and the beam current extracted.
A wide variety of Pelletron systems throughout the world have been supplied with the direct extraction ion source, which has proven to be very reliable with simple, routine operation.
The TORVIS source is our highest current source for negative ions of hydrogen and deuterium. It has produced 500 µAmps of continuous beam for H- and over 300 µAmps of continuous beam for 2H-. The emittance of the source is suitable for injection into the tandem Pelletrons at 5 pi mmmradians (MeV)1/2 or less. The source was first described by Prelec et.al., RSI Volume 61 (1), January, 1990.
National Electrostatics has designed and constructed the TORVIS source based on our expertise in metal/ceramic bonding for use in high voltage and vacuum. Pumping for the TORVIS source is critical. It requires two (2) 500 l/sec turbo pumps on each side of the extractor gap. A third pump station is recommended before injection into the accelerator.
|The TORVIS source is shown attached to the extractor/lens housing which is equipped with two (2) 500 l/sec turbo pumps. The red and black connectors are the high current leads to the ionizer.|
For high current He-: National Electrostatics Corp. now offers a high current He- injector for use on tandem accelerators. Three of these injector systems have been shipped.
During factory tests, a mass analyzed beam of He- with a beam current of 25 to 30 microamps was routinely obtained with an emittance sutiable for a tandem Pelletron.
Poster Presented at the IBA 2005 Conference
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