IPAC2011 - List of Authors (Kashyn, D.G.)

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).

Paper

Title

Page

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).