Recent RHIC in-situ coating technology developments

TL;DR

This paper reports on the development of an in-situ robotic plasma deposition technique for coating RHIC cold bore tubes with copper and amorphous carbon to reduce electron cloud effects and improve superconducting magnet performance.

Contribution

It introduces a novel robotic plasma deposition method for in-situ coating of RHIC cold bore tubes with copper and amorphous carbon, addressing electron cloud and heating issues.

Findings

Copper coatings of 2-10 μm thickness reduce wall resistivity.

Amorphous carbon coatings exhibit low secondary electron yield at cryogenic temperatures.

Coating techniques successfully applied to RHIC cold bore tube samples.

Abstract

To rectify the problems of electron clouds observed in RHIC and unacceptable ohmic heating for superconducting magnets that can limit future machine upgrades, we started developing a robotic plasma deposition technique for $in-situ$ coating of the RHIC 316LN stainless steel cold bore tubes based on staged magnetrons mounted on a mobile mole for deposition of Cu followed by amorphous carbon (a-C) coating. The Cu coating reduces wall resistivity, while a-C has low SEY that suppresses electron cloud formation. Recent RF resistivity computations indicate that 10 {\mu}m of Cu coating thickness is needed. But, Cu coatings thicker than 2 {\mu}m can have grain structures that might have lower SEY like gold black. A 15-cm Cu cathode magnetron was designed and fabricated, after which, 30 cm long samples of RHIC cold bore tubes were coated with various OFHC copper thicknesses; room temperature RF resistivity measured. Rectangular stainless steel and SS discs were Cu coated. SEY of rectangular samples were measured at room; and, SEY of a disc sample was measured at cryogenic temperatures.