Gas and Foil Stripping

NEC uses two different types of electron stripping and molecular dissociation techniques inside of a high voltage terminal: Gas Strippers and Foil Strippers.

Gas Stripper

In a gas stripper, argon or nitrogen gas is supplied to the terminal either through a bottle located in the terminal or a supply bottle with regulator outside the pressure vessel. An all-metal NEC metering valve is provided to meter gas to the stripper canal. Depending on the system, one, two, or even three turbo-molecular pumps are provided in the terminal to recirculate stripper gas so that only a very small amount of gas flows into the acceleration tubes. The turbo-pump output has a trap to prevent contamination of the stripper gas. This standard NEC design has been used with good success since 1985.

Specially designed pumping restrictions ensure that pressure in the acceleration tube near the terminal is at least 103 times lower than in the stripper canal. The stripper tube length is designed for stripping of the  ions beyond equilibrium. Such stripping is necessary to effectively reduce the hydrocarbon molecules in the ion beam.


Foil Stripper

Thin carbon foils are often used in tandem accelerators in place of, or in addition to, gas stripping. Like a gas stripper, the injected negative ion beam is charge-exchanged to multiply-charged positive ions in the terminal of the accelerator before the second stage of acceleration. This can often yield the +5 charge state (or higher), subject to the ion and the initial terminal voltage.

The NEC Foil Stripper can hold up to 360 targets. Various foil thicknesses can be placed inside for the foil stripper for a variety of experiments. From the control console, the operator can read the foil position and move new foils into position in the event that an old foil breaks. The entire assembly is fully bakeable and has an external pressure rating of 240 psig at 100°C.

Additional foil stripping can also be used beyond the accelerator to further increase charge states.

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