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The 3 m long 4-rod RFQ accelerates the radioactive ions with a charge-to-mass ratio larger than 1/4.5 from 5 to 300 keV/u. This kind of RFQ is a well tested structure [1] which accelerates low energy ion beams efficiently. The rf quadrupole field provides transverse focusing for the low energy ions while a modulation of the four rods performs smooth bunching of the injected dc-beam and acceleration. RFQs similar to the REX-RFQ are used at the GSI HLI-LINAC [2] and at the Heidelberg high-current injector [3]. The design of the modulation of the rods has been optimized for the specific charge-to-mass ratio of 1/4.5. As the lay-out of the RFQ is conservative the maximum voltage which can be obtained provides acceleration of ions with charge-to-mass ratio of 1/6.5. The design electrode voltage for A/q = 4.5 is 42 kV. With a shunt impedance of 146 kΩm an rf-power of 35 kV is necessary. The calculated radial acceptance for a transmission of about 99 % is 200 π mm mrad at 5 keV/u. In longitudinal direction the phase spread and the energy spread are Δφ = ± 14 % and ΔW/W = ± 1.5 %. The RFQ was built by the LMU Munich group.
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| Figure 1. Photo of the REX RFQ with open tank |
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Energies Ein = 5 keV/u, Eout = 300 keV/u Frequency 101.28 MHz Tank length = 3 m, diameter = 35 cm Number of cells = 232 Electrode voltage Vrod = 42 kV (9.33*A/q) rf-power consumption for 42 kV is 30 kW Shunt impedance R = 146.5 kΩm Quality factor Qo = 4050 Phase and energy spreads Δφ = ±14%, ΔW/W = ±1.5% |