The ISAC 35 MHz split-ring RFQ is designed to accelerate ions of A=q ऊ 30 from 2 keV/u to 150 keV/u in cw mode at a constant synchronous phase of ,25 ae . Beam tests with 7 of the 19 split rings installed (E aen = 0 :55 keV/u) have recently been completed. The tests demonstrated that a constant synchronous phase RFQ with external buncher works splendidly for low beta, low intensity applications. One peculiar aspect of the RFQ is that the longitudinal acceptance is larger for beams injected off-center. The test set-up and results of both the measurements and the simulations are presented and discussed.
Abstract.A LabVIEW program running on a Sun SPARCstation 5 controls a Tektronix TDS820 6 GHz sampling oscilloscope via an Ethernet to GPIB adapter. A PC based X Window terminal continuously displays the trace, refreshed at 7 Hz. Functions such as gain, time base and application specific controls are selected by menus, buttons and dialog boxes. We have used the system to observe signals from fast (>1 GHz) Faraday cups (FFC) in the radio frequency quadrupole (RFQ) section of our Radioactive Beam Facility (ISAC). The setup utilizes the accelerator control display terminals while allowing the oscilloscope to be closer to the FFC's. ISAC uses the RFQ to accelerate singly charged ions to 0.15 MeV/u where they are stripped prior to acceleration in a drift tube linac (DTL). The time structure of the beam at the RFQ entrance was measured on a FFC placed 4 m downstream of the RFQ pre-buncher. Additional 50 Ω coaxial cone FFC's were installed downstream of the RFQ near the RFQ exit, just ahead of the stripping foil and at a double focus following the charge selection slit. The last FFC shows the increase in the mean drift time and broadening associated with the increase in energy loss and straggling caused by foil thickening under ion bombardment. Although the phase broadening cannot be corrected, the increase in the mean drift time can be corrected by changing the bias voltage on the stripper foil and thus keeping the ions in phase with the rebuncher rf.
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