Plans for in-situ coating with a robotic mole at BNL Ady Hershcovitch 1, Michael Blaskiewicz 1, Wolfram Fischer 1, H. Joseph Poole 2, Mark Erickson 2, Art Custer 2, Nader Jamshidi 2, and Nikolay Sochugov 3 1-Brookhaven National Laboratory, Upton, New York, USA 2-PVI, Oxnard, California, USA 3-HCEI, Tomsk, Russia

What problems are needed to be solved in order to enhance RHIC luminosity? Lower vacuum chamber resistivity and control electron cloud formation! The RHIC vacuum chamber is made of 7.1 cm ID stainless steel tubing with 1.6  m surface roughness in cold bore (2.1  m in warm section). Stainless steel has high resistivity. Coat tube with copper! Electron clouds, which have been observed in many accelerators including RHIC can act to limit machine performance through dynamical instabilities and/or associated vacuum pressure increases. Formation of electron clouds is a result of electrons bouncing back and forth between surfaces, which cause emission of secondary electrons (electron multipacting effect). TiN or a-C coating!

Possible Solutions Coating the stainless steel walls with about 5 micrometers of oxygen free high conductivity copper (OFHC) can prevent problems arising from high resistivity. Covering the OFHC with a very thin layer of either TiN or amorphous carbon to reduce SEY (secondary electron yield) Edge magnetic fields ~ 50 Gauss to suppress SEY in warm section???

Coating Long Cold Stainless Steel Tube With OFHC & Other Materials A method involving a moving mole-like plasma deposition sputter device is at an initial stage of development at the Brookhaven Nation Laboratory (BNL) in USA, with the end goal for application in 500 meter long sections of the relativistic heavy ion accelerator (RHIC). Sputter devices based on magnetron, cathodic arc (a.k.a. vacuum arc), and diode configurations are being considered.

Possible Coating Configuration

Few Comments About OFHC Coating –Coating the inside of the RHIC vacuum tube with oxygen free high conductivity copper (OFHC) can prevent the beam walls from becoming insulators at cryogenic temperatures, which can lead to resistive wall instabilities, as well as prevent formation of electron clouds. Of all coating techniques, plasma deposition seems to be the only viable coating option due to need to coat in situ sections, which are about 500 meters long with a diameter slightly larger than 7 cm. –Coating 50 W/inch 2 = 5 Å/sec –10 4 Å = 1 μm –Can be 100 W/inch 2 –3 hours for > 5 μm move one cathode length every 3 hours –Cathode lengths can be 1 – 2 meters. Also rotated cathode or magnets. –Can also use diodes. –Water to spin cathode being sputtered: use water to spin (and cool) the magnet array; coat magnets with epoxy.

Status PVI just received SBIR phase I funding approval. Currently designing a 15 cm long 4 cm diameter magnetron with ring magnets. Near-term plans are to optimize its operation in a 30 cm long RHIC tube sample, copper coat the tube and measure RF resistivity.

Embryonic Concept: Are we doing anything stupid? Any Suggestions? Basically I came to mostly learn at this conference.