RF system test for CSNS external antenna negative hydrogen ion source
- Dr. Weidong CHEN
- Dr. Weidong CHEN (Institute of High Energy Physics, Chinese academy of sciences)
An RF H-minus source with external antenna is under development for the upgrade of China Spallation Neutron Source (CSNS), which requires a H$^-$ beam of 40 mA peak current at 25 Hz repetition rate and 1 ms pulse length. The 2 MHz RF power is generated by a solid-state amplifier. Then a 50 kV insulation transformer is used to protect the amplifier from electric flash. The matching circuit consists of a 13:2 impedance transformer, a tunable capacitor, and a water-cooled dummy load. In the off-line test, the amplifier produces a maximum peak power of 80 kW at a duty factor of 2.75$%$. And the total transmission efficiency from the amplifier to the load is higher than 90$%$. The on-line plasma coupling test is in preparation and expected to start in June. Since the impedance of the RF plasma changes with RF power, RF frequency, and gas flow, an RF network without impedance transformer is under development to match the impedance of plasma within a wider range.