RFQ Beam Coolers

RFQ stands for Radio-Frequency Quadrupole (also known as a Quadrupole mass analyzer when used as a mass filter), an instrument that is used in mass spectrometry. The RFQ was invented by Prof. Wolfgang Paul in the late 50's / early 60's at the University of Bonn (Germany). Paul shared the 1989 Nobel prize in Physics for his work.

By aligning four rods and applying an RF voltage between opposite pairs, a quadrupole field is created that alternates focuses in each transverse direction. Samples for mass analysis are ionized, for example by laser (MALDI) or discharge (electrospray or Inductively Coupled Plasma, ICR) and the resulting beam is sent through the RFQ and "filtered" by scanning the operating parameters (chiefly the RF amplitude). This gives a mass spectrum, or fingerprint, of the sample. Residual gas analyzers use this principle as well.

A "cooler" is a device that lowers the temperature of an ion beam by reducing its energy dispersion, beam spot size, and divergence - effectively increasing the beam brightness (or brilliance). Several ion beam cooling methods exist. In the case of an RFQ, the most prevalent one is buffer-gas cooling, whereby an ion beam loses energy from collisions with a light, neutral and inert gas (typically helium). Cooling must take place within a confining field in order to counteract the thermal diffusion that results from the ion-atom collisions.

Applications of ion cooling to Nuclear Physics (notably, mass...
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