Design of a 500 MHz TM020-mode cavity with elliptical choke for the high-current Super Tau-Charm Facility

Abstract A compact TM $$_{020}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>020</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> -mode RF cavity was proposed and studied by KEK and RIKEN for the storage ring of the NanoTerasu facility. However, performance limitations due to accelerating mode leakage into the coaxial slots have been identified. This paper presents an improved TM $$_{020}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>020</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> -mode cavity design to solve this issue. By employing an elliptical choke, the leakage power can be significantly reduced. Harmful parasitic modes other than the TM $$_{020}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>020</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> -mode are effectively suppressed using the elliptical choke placed at the magnetic node of the TM $$_{020}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>020</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> -mode. Through optimization, this improved TM $$_{020}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mn>020</mml:mn> <mml:mrow/> </mml:mmultiscripts> </mml:math> -mode RF cavity meets the requirements of the Super Tau-Charm Facility (STCF) collider rings with a beam current of up to 2 A. Detailed mechanical design and thermal analysis confirm the feasibility and stability of the improved cavity.