English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

BNL is responsible for the design and construction of the US Spallation Neutron Source (SNS) accumulator ring. Titanium Nitride (TiN) coating on the stainless steel vacuum chamber of the SNS accumulator ring is needed to reduce the secondary electron yield (SEY) and the undesirable resonant multiplication of electrons. The total SEY of TiN coated stainless steel material has been measured after coating samples were exposed to air and after electron and ion bombardment. We report here about TiN coating system setup at BNL and SEY measurements results at CERN, SLAC and KEK. We also present some simulation results of SNS accumulator ring electron-cloud effects using different SEY values. INTRODUCTION US Spallation Neutron Source (SNS) is an acceleratorbased neutron source being built in Oak Ridge, TN. The SNS is a partnership among six DOE national laboratories (Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge). At a total cost of $1.4 billion, construction began in 1999 and is scheduled for completion in 2006. Brookhaven is undertaking the design and construction of the SNS accumulator ring and beam transport lines. The operating pressure of the ring vacuum system [1] will be 10 Torr and is needed to minimize the beam-residual gas ionization. At the designed vacuum level, the rate of ionization and electron production is approximately 10 electrons per proton over the one-millisecond accumulation cycle. The electron cloud effect (ECE), due to multipacting, can limit the achievable proton intensity when excessive electrons are generated and trapped. The electron cloud density depends on characteristics of the proton beam (bunch length, charge and spacing) and the secondary electron yield and secondary emission spectrum of the vacuum chamber wall surface. The number of multipacting electrons can be effectively reduced by surface treatment of the vacuum pipe. The material of SNS ring vacuum chamber is stainless steel with a secondary emission yield (SEY) peak value typically in the range 2.5~3.0. A SEYlowering coating (TiN) has been applied to the SNS stainless steel vacuum chamber wall. The thickness of the TiN coating, typically about 100nm, is chosen because such coated section in PSR was shown to effectively suppress the electron flux by a factor of more than 100[2]. For critical elements, e.g., the injection kicker ceramic chambers and the ferrite of the extraction kicker inside the vacuum pipe, different pattern and thickness of the coating are selected to reduce the coupling impedance and to avoid eddy-current heating. Magnetron DC sputtering was developed for SNS ring vacuum chamber TiN coating. The total secondary electron emission yield of TiN-coated stainless steel has been measured after samples of beam chamber material were exposed to air and again after electron and ion beam bombardment, as a function of the incident electron beam energy. The measurement values were used to simulate the electron build-up in the SNS straight section. TiN COATING PROCESSING Figure 1 shows the sputtering coating system for SNS chambers. The system has a water-cooled coaxial magnetron sputter source of 38mm in diameter. The maximum transverse component of the magnetic field at the face of the titanium target is about 1000Gauss. A DC power supply of 10kW maximum is used as the power source. High purity argon and nitrogen are used as the sputtering and reactive gases, respectively. All coatings have been done with the chamber at a temperature of 250oC. The chamber pressure is usually reduced to 5x10 Torr before deposition. At the beginning, the Ti cathode was pre-sputtered in a pure argon atmosphere for about 10mins, and then the nitrogen is introduced into the chamber through a 6mm diameter Ti Proceedings of EPAC 2004, Lucerne, Switzerland

Secondary Electron Emission Measurements for Tin coating on the Stainless Steel of SNS Accumulator Ring Vacuum Chamber