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Description
A RF H$^{-}$ source with external antenna is under construction for China Spallation Neutron Source (CSNS) project Phase-II, which requires a H$^{-}$ beam of 40 mA peak current, 25 Hz repetition rate, and 1 ms pulse length. The plasma chamber is made of Si$_3$N$_4$ ceramic to endure high thermal shock. The water-cooled antenna is brazed on the outer wall of the plasma chamber to enhance heat dissipation of the chamber. The antenna is powered with a solid-state amplifier of maximum 80 kW via an isolation transformer and an impedance transformer. To produce a flat-top H$^{-}$ current, we aim to program the amplitude of RF input signal, so that the fluctuation of the beam current is compensated with the change of the RF power within a pulse. An online plasma cleaning technique is also under development to clean the electrodes with Helium plasma. The work principle of the cleaning technique is simulated with SRIM program (http://www.srim.org), which is to calculate the sputter rate of ions on different surfaces. Up to now the mechanical construction of the source is finished, and the RF match network is still under test. The source is expected to produce H$^{-}$ current at the end of 2017.
