The RFQ ion beam buncher


The RFQ ion buncher connected to the ISOLDE beam line. 
(Visible are  the inner and outer HV cage, one of the  60kV isolators, one of the 1000l/s turbo pumps ...) 

Electrodes structure of the RFQ ion buncher. 
(Visible are the elliptically shaped injection electrode followed by the segmented 4 rod structure)

The first step of the ISOLTRAP experiment is the stopping and preparation of the 60keV ISOLDE ion beam for the injection into the Cooler Trap. The ISOLDE ions are therefore electrostatically decelerated and then injected into a buffer-gas-filled 4-rod structure. Similiar to a quadrupole mass filter there is a radio frequency applied to the 4 rods so that an oszillating quadrupole field is formed that confines the ions radially. The rods are segmented and by applying an appropriately shaped DC potential the ions are dragged into the trapping reagion close to the end of the 4-rod structure. Due to the interaction with the buffer gas the ions lose kinetic energy and are finally accumulated as a small ion cloud in the trapping reagion. This cold ion cloud can be ejected as a well defined bunch out off the trapping reagion with only e few keV kinetic energy. After a potential adaption in a pulsed drift tube the ion bunch is transported to and injected into the Cooler Trap.

BB_eggcup_med.jpg (53662 bytes) BB_inject1_med.jpg (55878 bytes) Injection side with the specially shaped injection electrode (eggcup).
RFQ_4rod_med.jpg (34855 bytes) BB_trapsection_med.jpg (46473 bytes) Left: The four rod structure and the support of the rods.
Rigth: The linear Paul trap section. The electrodes having the same RF-phase are connected with kapton-isolated copper wires (sealing cylinder with extraction optics removed).
BB_extract_med.jpg (44694 bytes) BB_extract_bad_med.jpg (44230 bytes) Extraction side with an x-y steerer and an einzel lens.