Accelerators – SPC1 Flattop System


A 600 proton beam can be extracted with a 94% efficiency from SPC1 using the newly installed flat-top system [1]. The system reduces the energy spread in the beam and allows beam extraction from the ion source over a larger fraction of the RF cycle. A second buncher,  that operates at a harmonic frequency of the existing one, is under construction and will be installed in the transfer beam line between the cyclotrons to accommodate the longer beam pulses that are extracted with the flat-topping system in SPC1. The longer beam pulses fall outside the linear range of the present buncher. A fixed-frequency flat-topping system has been installed in the SSC to prevent the longer beam pulses from acquiring excessive energy spread during acceleration [2]. It is expected that a beam current of 400 μA will be available from the SSC with these new additions. The present targets for radionuclide production cannot handle such high beam currents. A vertical beam line and a second target station have therefore been built and installed for production of radionuclides at the higher beam intensities. A beam splitter and another production beam line are now under construction to deliver beam to two target stations simultaneously. The design of the flat-topping systems, the additional buncher and the new beam lines are discussed below.

2. The Flat-topping System for the light-ion Injector Cyclotron 



One of the two flat-topping systems [1] of SPC1 is shown in Fig.1. A fifth harmonic, 81.8 MHz, of the main RF frequency is superimposed on the main voltage. The flat-topping resonators, that can be tuned by moveable short-circuit plates, are capacitively coupled to the main resonators and are driven by remote power amplifiers through 50 Ω cables. The main and flat-top dee voltages are 49 kV and 1.96 kV, respectively. The power consumption for a flat-topping dee voltage of 1.96 kV, is 900 W. Although both the main and harmonic power amplifiers deliver power to the same dees care has been taken that power is not fed from one amplifier into the other.

SPC1 with the two flattop resonators




  1. [1] J.L. Conradie et al., “Cyclotrons at iThemba LABS”, this Conference.
  2. [2] D.T. Fourie et al., “New Beam Lines for the Production of Radioisotopes at iThemba LABS”, this Conference.

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