<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: arial,helvetica,sans-serif; font-size: 12pt; color: #000000'><DIV style="FONT-STYLE: normal; FONT-FAMILY: Helvetica,Arial,sans-serif; COLOR: #000; FONT-SIZE: 12pt; FONT-WEIGHT: normal; TEXT-DECORATION: none">Reminder!<BR><BR>
<HR id=zwchr>
<DIV style="FONT-STYLE: normal; FONT-FAMILY: Helvetica,Arial,sans-serif; COLOR: #000; FONT-SIZE: 12pt; FONT-WEIGHT: normal; TEXT-DECORATION: none"><B>From: </B>"Audrey Nichols" <anichols@jlab.org><BR><B>To: </B>"acc staff" <acc_staff@jlab.org><BR><B>Cc: </B>gurevich@odu.edu<BR><B>Sent: </B>Monday, October 27, 2014 4:17:04 PM<BR><B>Subject: </B>[Accelerator_staff] Accelerator Seminar: 10/30/14 - Alex Gurevich<BR><BR>
<STYLE>p { margin: 0; }</STYLE>
<DIV style="FONT-FAMILY: tahoma,new york,times,serif; COLOR: #000000; FONT-SIZE: 12pt">ACCELERATOR SEMINAR <BR><BR>Nonlinear Surface Resistance and the Extended Q(H) Rise in Alloyed Nb Cavities <BR><BR>Alex Gurevich<BR>Old Dominion University<BR><BR>
<P style="TEXT-JUSTIFY: inter-ideograph; TEXT-ALIGN: justify; MARGIN: 0in 0in 0pt"><SPAN style="FONT-SIZE: 12pt">A theory of dissipative nonlinear surface resistance R<SUB>s</SUB>(H) of superconductors under strong electromagnetic fields at low temperatures is proposed. Closed-form expressions for the surface resistance R<SUB>s</SUB>(f,H) have been obtained by solving equations of nonequilibrium BCS theory in the dirty limit for which R<SUB>s</SUB>(H) has a significant minimum as a function of a low-frequency (hf << kT) rf magnetic field H<SUB>a</SUB>. The calculated microwave suppression of R<SUB>s</SUB>(H<SUB>a</SUB>) is in good agreement with recent experiments on Ti-alloyed Nb cavities from JLab. The Q(H) rise can extend up to the fields </SPAN><SPAN style="FONT-SIZE: 12pt">≈</SPAN><SPAN style="FONT-SIZE: 12pt">(0.5-0.7)H<SUB>c</SUB> and can be strongly sample-dependent due to the subgap states in the density of states caused by materials defects and impurities. The latter suggests new opportunities for tuning the SRF performance by optimizing the density of states and producing appropriate dirty layers at the cavity surface.<SPAN style="mso-spacerun: yes"> </SPAN>It is shown that superimposed dc and ac fields, H(t)=H<SUB>0 </SUB>+ H<SUB>a</SUB>sin(</SPAN><SPAN style="FONT-SIZE: 12pt">ω</SPAN><SPAN style="FONT-SIZE: 12pt">t) can be used to reduce rf dissipation by tuning R<SUB>s</SUB>(f,H<SUB>0</SUB>) with the parallel dc field H<SUB>0</SUB>. </SPAN></P><BR>Thursday, October 30, 2014<BR>11:00 a.m.<BR>CEBAF Center, Room F113<BR><BR><BR>
<DIV><SPAN style="BACKGROUND-COLOR: rgb(255,254,196); FONT-FAMILY: Helvetica, Arial, sans-serif; FONT-SIZE: 12pt" id=DWT1557 class=ZmSearchResult><SPAN id=DWT2053 class=ZmSearchResult><SPAN id=DWT1799 class=ZmSearchResult><SPAN id=DWT952 class=ZmSearchResult>Seminar</SPAN></SPAN></SPAN></SPAN><SPAN style="BACKGROUND-COLOR: rgb(255,255,255); FONT-FAMILY: Helvetica, Arial, sans-serif; FONT-SIZE: 12pt"> </SPAN><SPAN style="BACKGROUND-COLOR: rgb(255,255,255); FONT-FAMILY: Helvetica, Arial, sans-serif; FONT-SIZE: 12pt">archives are found here:</SPAN><SPAN style="BACKGROUND-COLOR: rgb(255,255,255); FONT-FAMILY: Helvetica, Arial, sans-serif; FONT-SIZE: 12pt"> </SPAN><SPAN style="BACKGROUND-COLOR: rgb(255,255,255); FONT-FAMILY: Helvetica, Arial, sans-serif; COLOR: rgb(0,0,139); FONT-SIZE: 12pt; CURSOR: pointer" id=OBJ_PREFIX_DWT1558_com_zimbra_url class=Object><SPAN style="CURSOR: pointer" id=OBJ_PREFIX_DWT3142_com_zimbra_url class=Object><SPAN style="CURSOR: pointer" id=OBJ_PREFIX_DWT2054_com_zimbra_url class=Object><SPAN id=OBJ_PREFIX_DWT1800_com_zimbra_url class=Object><SPAN id=OBJ_PREFIX_DWT953_com_zimbra_url class=Object><SPAN id=OBJ_PREFIX_DWT804_com_zimbra_url class=Object><A style="COLOR: rgb(0,0,139); CURSOR: pointer; TEXT-DECORATION: none" href="http://wwwold.jlab.org/accel/seminars.html" target=_blank>http://wwwold.jlab.org/accel/seminars.html</A></SPAN></SPAN></SPAN></SPAN></SPAN></SPAN></DIV><BR><BR>
<DIV><SPAN></SPAN>------<BR><B><FONT size=2>Audrey N. Barron</FONT></B><BR><FONT size=2>Administrative Assistant</FONT><BR><FONT size=2>Center for Advanced Studies of Accelerators</FONT><BR><FONT size=2>Jefferson Lab</FONT><BR><FONT size=2>757-269-7327</FONT><BR><FONT size=2><A>anichols@jlab.org</A></FONT> / <FONT size=2><A href="http://www.jlab.org/" target=_blank>www.jlab.org</A></FONT> <BR><BR><IMG style="BORDER-BOTTOM: 0px; BORDER-LEFT: 0px; BORDER-TOP: 0px; BORDER-RIGHT: 0px" src="cid:88ab42b883f0b15349b776fcd5876f6cefb923db@zimbra"><BR><SPAN></SPAN><BR></DIV></DIV><BR>_______________________________________________<BR>Accelerator_staff mailing list<BR>Accelerator_staff@jlab.org<BR>https://mailman.jlab.org/mailman/listinfo/accelerator_staff</DIV><BR><BR>_______________________________________________<BR>Accelerator_staff mailing list<BR>Accelerator_staff@jlab.org<BR>https://mailman.jlab.org/mailman/listinfo/accelerator_staff</DIV><BR></div></body></html>