Abstract
Molecular desorption coefficients from electron bombardment of the warm Relativistic Heavy Ion Collider beam pipe are derived from measurements for both baked and unbaked stainless steel. For this, we analyze electron detector and pressure gauge signals in the presence of an electron cloud. Finally, we present a comparison between the measured and simulated energy spectrum of the cloud electrons.
Highlights
The knowledge of molecular desorption coefficients is a key ingredient in understanding the electron cloud induced pressure rises, which are limiting machine operation in Relativistic Heavy Ion Collider (RHIC) since 2001 [1
RHIC was not equipped with electron detectors when the first pressure rises occurred
Assuming the beam pipe is a periodic structure with vacuum pumps of pumping speed 2S spaced by the distance 2L, the pressure distribution along the longitudinal position z between two vacuum pumps is [5]: P z
Summary
The knowledge of molecular desorption coefficients is a key ingredient in understanding the electron cloud induced pressure rises, which are limiting machine operation in Relativistic Heavy Ion Collider (RHIC) since 2001 [1–. Using Eq (3), the pressure due to an electron cloud at a given position of the beam pipe z is 1010 protons e- flux, dI/dl [mA/m]. Equation (4) shows that, at a given location z the pressure is directly proportional to the electron desorption coefficient, e. This coefficient depends on the energy of the striking electron, the surface material, and the accumulated dose on the surface. From the analysis of the experimental data, the desorption coefficient and its evolution over weeks of operation is obtained This analysis is done for two different locations, with two different surfaces, and during two different runs. The common beam pipe at ‘‘IR12’’ during 2004 was baked stainless steel
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