Beam-profile measurements

A beam position monitor (BPM) at the focusing system of the Super-FRS will allow the non-intercepting determination of the transverse position of the bunched ion beam. Wire profiles providing precision 2D beam profiles will be used for targeting and transporting of the slow- and fast extracted beams. More than 25 SEM profile monitors will be distributed along the separator. Accurate position and time-resolved data registered for each spill will be used for tune determination.

A standard GSI monitor DG1010 designed with wire spacing of 1.5 mm and diameter of 0.1 mm was installed in vacuum at the FRS and irradiated with uranium beams in 2014. To simulate similar experimental condition like in the case of the Super-FRS the wire signals were transported over a long cable (length >50 m). The current-to-frequency converter QFW POLAND  was used to measure the horizontal and vertical profiles of the beam. The intensities of the different uranium charge states produced at the target were simulated and compared with the measured ones. For 3x108238U73+/s at 300 MeV/nucleon the measured charge was 0.7 times lower than the estimated one (using Sternglass approximation). In presence of pulsed 238U88+ beam at 125 MeV/nucleon the ratio between measured, see figure below, and simulated charges decreased up to 0.36 for the maximum intensity of 1010 ions/spill.

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Horizontal profile of 238U(Q=88) pulsed beam at 125 MeV/nucleon (October 2014).
Horizontal profile of 238U(Q=88) pulsed beam at 125 MeV/nucleon (October 2014).

Although a larger geometric coverage is required at the Super-FRS present results ensure that a standard operation along the separator is possible. Because of the higher power absorption at the Super-FRS target the use of different SEM material is under investigation.

 
Partners: Helsinki IP, Jyvaskyla Uni and GSI