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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Subject: </th>
<td>[Accelerator_staff] Accelerator Seminar: Binping Xiao -
5/17/12</td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Date: </th>
<td>Mon, 14 May 2012 09:25:13 -0400</td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">From: </th>
<td>Audrey N. Barron <a class="moz-txt-link-rfc2396E" href="mailto:anichols@jlab.org"><anichols@jlab.org></a></td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Reply-To:
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<td><a class="moz-txt-link-abbreviated" href="mailto:anichols@jlab.org">anichols@jlab.org</a></td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Organization:
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<td>Jefferson Laboratory</td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">To: </th>
<td><a class="moz-txt-link-abbreviated" href="mailto:fel_team@jlab.org">fel_team@jlab.org</a>, <a class="moz-txt-link-abbreviated" href="mailto:acc_staff@jlab.org">acc_staff@jlab.org</a></td>
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<font face="Arial">ACCELERATOR SEMINAR<br>
<br>
<span style="font-family:
"Arial","sans-serif";">"Surface Impedance of
Superconducting Radio Frequency (SRF) Materials"<br>
<br>
Binping Xiao<br>
College of William Mary and Jefferson Lab<br>
<br>
</span><span
style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-no-proof:yes">Superconducting
radio frequency (SRF) technology is widely adopted in particle
accelerators. There remain many open questions, however, in
developing a systematic understanding of the fundamental
behavior of SRF materials, including niobium treated in
different ways and various other bulk/thin film materials that
are fabricated with different methods under assorted conditions.
A facility that can measure the SRF properties of small samples
in a range of 2~40 K temperature is needed in order to fully
answer these questions. The Jefferson Lab surface impedance
characterization (SIC) system has been designed to attempt to
meet this requirement. It consists of a sapphire-loaded
cylindrical Nb TE<sub>011</sub> cavity at 7.4 GHz with a 50 mm
diameter flat sample placed on a non-contacting end plate and
uses a calorimetric technique to measure the radio frequency
(RF) induced heat on the sample. Driving the resonance to a
known field on this surface enables one to derive the surface
resistance of a relatively small localized area. Tests with
polycrystalline and large grain bulk Nb samples have been done
at <15 mT magnetic field. Based on BCS surface impedance,
least-squares fittings have been done using SuperFit2.0, a code
developed by G. Ciovati and the author.<o:p></o:p></span></font>
<p class="MsoNormal"
style="text-align:justify;text-justify:inter-ideograph"><font
face="Arial"><span
style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-no-proof:yes">Microstructure
analyses
and SRF measurements of large scale epitaxial MgB2 films have
been reported. MgB2 films on 5 cm dia. sapphire disks were
fabricated by a Hybrid Physical Chemical Vapor Deposition
(HPCVD) technique. The electron-beam backscattering
diffraction (EBSD) results suggest that the film is a single
crystal complying with a MgB2(0001)//Al2O3(0001) epitaxial
relationship. The SRF properties of different film thicknesses
(200 nm and 350 nm) were evaluated using SIC system under
different temperatures and applied fields at 7.4 GHz. A
surface resistance of 9±2 μΩ has been observed at 2.2 K.<o:p></o:p></span></font></p>
<font face="Arial"><span
style="font-size:10.0pt;font-family:"Arial","sans-serif&
quot;;mso-fareast-font-family:
宋体;mso-ansi-language:EN-US;mso-fareast-language:ZH-CN;mso-bidi-
language:AR-SA; mso-no-proof:yes">Based on BCS theory with
moving Cooper pairs, the electron states distribution at 0K and
the probability of electron occupation with finite temperature
have been derived and applied to anomalous skin effect theory to
obtain the surface impedance of a superconductor with moving
Cooper pairs. We present the numerical results for Nb.</span></font>
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<font face="Arial"><br>
</font><span
style="font-family:"Arial","sans-serif""><font
face="Arial">Thursday, May 17, 2012<br>
11:00 a.m.<br>
CEBAF Center, Room F326/327 </font><br>
<br>
<o:p></o:p></span> <span style="font-size: 10pt; font-family:
"Arial","sans-serif";"></span>
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