Author: Antonsen, T.M.
Paper Title Page
MOPC065 Ion Motion in the Vicinity of Microprotrusions in Accelerating Structures 232
 
  • D.G. Kashyn, T.M. Antonsen, I. Haber, G.S. Nusinovich
    UMD, College Park, Maryland, USA
 
  Funding: This work is supported by Office of High Energy Physics of the U.S. Department of Energy.
It is known that newly fabricated accelerating structures have almost ideally smooth surface. However, ‘post mortem’ examination of these structures reveals that their surface can be significantly modified after high-gradient operation. This surface modification can be caused by the appearance of microscopic protrusions*. One of the factors leading to heating, melting and evaporation of these protrusions (factors resulting in the RF breakdown) is ion bombardment**. In our study we analyze ion motion in the vicinity of microprotrusions both analytically and numerically. First, we study the ion motion in the RF electric field magnified by the protrusion in the absence of electron field emitted current and show that most of the ions do not reach the structure surface. Then we add into consideration the interaction of ions with Fowler-Nordheim current emitted from the tip of protrusion (dark current). First, we develop a model describing this interaction and then we supplement it with numerical results using PIC code WARP***. We show that the ions move towards the area occupied by the dark current, but this does not increase the bombardment of micro-protrusions.
* R.B. Palmer,et al, Phys. Rev ST Accel. Beams 12, 031002 (2009).
** P. Wilson, AIP Conf. Proc., 877, Melville, New York, 2006, p. 27.
***J.-L. Vay, et al, Physics of Plasmas, 11, 2928 (2004).
 
 
TUPC041 Self-consistent Time-dependent Quasi-3D Model of Multipactor in Dielectric-loaded Accelerating Structures 1090
 
  • O.V. Sinitsyn, T.M. Antonsen, G.S. Nusinovich
    UMD, College Park, Maryland, USA
 
  Funding: This work is supported by the Office of High Energy Physics of the US Department of Energy.
Multipactor (MP) manifests itself as a rapid growth of the number of secondary electrons emitted from a solid surface in the presence of the RF field under vacuum conditions. The secondary electrons appear as the result of surface impacts of energetic primary electrons accelerated by the RF field. MP occurs in various microwave and RF systems and usually severely degrades their performance. Therefore, theoretical and experimental studies of MP are of great interest to researchers working in related areas of physics and engineering. In this paper we study MP in dielectric-loaded accelerating (DLA) structures. We started our work with the development of a self-consistent time-dependent 2D model of MP in such structures*. To benchmark that model, we compared its results with available experimental data**. The comparison showed good agreement between theory and experiment for DLA structures of larger diameter, however for structures of smaller diameter a significant discrepancy was observed. Therefore, we decided to develop a new quasi-3D model of MP that would allow us to take into account the effects ignored in our 2D studies. Results of our 3D analysis are presented in this paper.
* O. V. Sinitsyn, G. S. Nusinovich and T. M. Antonsen, Jr., Phys. Plasmas, 16, 073102 (2009).
** O. V. Sinitsyn, G. S. Nusinovich and T. M. Antonsen, Jr., AIP Conf. Proc., 1299, 302 (2010).