<html><body><div style="color: rgb(0, 0, 0); font-family: arial,helvetica,sans-serif; font-size: 12pt;"><div> </div><hr id="zwchr" data-marker="__DIVIDER__"><div data-marker="__HEADERS__"><b>From: </b>"anichols" <anichols@jlab.org><br><b>Sent: </b>Thursday, January 29, 2015 9:04:49 AM<br><b>Subject: </b>[Accelerator_staff] Accelerator Seminar: M.A. Mamun - 1/29/15 - ROOM CHANGE<br></div><div><br></div><div data-marker="__QUOTED_TEXT__"><div style="color: rgb(0, 0, 0); font-family: tahoma,new york,times,serif; font-size: 12pt;" data-mce-style="font-family: tahoma,new york,times,serif; font-size: 12pt; color: #000000;"><div>This seminar location has changed. The seminar will now be in CC F113 at 11:00 a.m.<br></div><br><hr id="zwchr"><div><b>From: </b>"Audrey Nichols" <anichols@jlab.org><br><b>To: </b>"acc staff" <acc_staff@jlab.org><br><b>Sent: </b>Thursday, January 29, 2015 8:15:00 AM<br><b>Subject: </b>Re: [Accelerator_staff] Accelerator Seminar: M.A. Mamun - 1/29/15<br></div><br><div><div style="color: rgb(0, 0, 0); font-family: tahoma,new york,times,serif; font-size: 12pt;" data-mce-style="font-family: tahoma,new york,times,serif; font-size: 12pt; color: #000000;"><div>Reminder!!</div><br><hr id="zwchr"><div><b>From: </b>"Audrey Nichols" <anichols@jlab.org><br><b>To: </b>"acc staff" <acc_staff@jlab.org><br><b>Sent: </b>Friday, January 23, 2015 4:28:20 PM<br><b>Subject: </b>[Accelerator_staff] Accelerator Seminar: M.A. Mamun - 1/29/15<br></div><br><div><div style="color: rgb(0, 0, 0); font-family: tahoma,new york,times,serif; font-size: 12pt;" data-mce-style="font-family: tahoma,new york,times,serif; font-size: 12pt; color: #000000;"><div>ACCELERATOR SEMINAR<br></div><br><div>"Alkali Antimonide Photocathodes Using Co-Deposition and Effusion Source"<br></div><br><div>M. A. Mamun<br></div><div>Old Dominion University and Jefferson Lab <br></div><br><div><p style="margin: 0px; text-align: justify; vertical-align: baseline; unicode-bidi: embed; direction: ltr;" data-mce-style="margin: 0px; text-align: justify; direction: ltr; unicode-bidi: embed; vertical-align: baseline;"><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">Some proposed experiments and some next-generation accelerator designs require very high electron beam currents, ranging from 10 to 100 mA, and even higher. For example, consider the Dark Light experiment – which we hope to conduct at the Jefferson Lab energy recovery </span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">linac</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;"> (aka JLAB FEL) – aimed at searching for dark photons and operating at 10 mA. Jefferson Lab’s othe</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">r proposal on Electron Ion Collider, MEIC, requires an electron gun feeding 100 mA to an energy recovery </span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">linac</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;"> that will be used to cool a proton beam. It seems unlikely that </span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">GaAs</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;"> photocathodes can satisfy these ambitious projects because residual gas within the </span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">photogun</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;"> vacuum chamber becomes ionized by the extracted electron beam, leading to ion-bombardment of the delicate photocathode, and severely limiting the operating lifetime of the gun. But recent experiments, including one conducted at Jefferson Lab have shown that alkali-</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">antimonide</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;"> photocathodes are far less sensitive to ion bombardment than GaAs photocathodes. In this talk, we report successful manufacture of CsK2Sb photocathodes having maximum QE ~10% at 532 nm, using an “effusion source”, which was a common device used on </span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">GaAs-photoguns</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;"> during the 1970’s and 1980’s, and offering some advantages over other commonly used alkali sources. The high-capacity effusion source enabled us to successfully manufacture alkali-</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">antimonide</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;"> photocathodes via the co-deposition method, and using relatively thick layers of antimony (>100 nm thick). We believe co-deposition supports the formation of alkali-</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">antimonide</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;"> photocathodes having a more optimized stoichiometry compared to manufacture using sequential deposition. We also speculate that the antimony layer serves as a reservoir, or sponge, for the alkali. Thick Sb layers require more alkali, and photocathodes grown with thick Sb layers exhibit the best low-voltage lifetime. A scanning electron microscope was used to evaluate Sb-layer morphology, as a function of Sb-layer thickness. Thin Sb layers provide a relatively smooth amorphous surface, whereas thick Sb layers appear </span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;">pourous</span><span style="color: black; font-family: Arial; font-size: 12pt; language: en-US;" data-mce-style="font-size: 12.0pt; font-family: Arial; color: black; language: en-US;"> and comparatively rough.</span></p></div><br><div>Thursday, Jan. 29, 2015<br></div><div>11:00 a.m.<br></div><div>TED, Room 2561<br></div><br><div>------<br><b><span style="font-size: small;" data-mce-style="font-size: small;">Audrey N. Barron</span></b><br><span style="font-size: small;" data-mce-style="font-size: small;">Administrative Assistant</span><br><span style="font-size: small;" data-mce-style="font-size: small;">Center for Advanced Studies of Accelerators</span><br><span style="font-size: small;" data-mce-style="font-size: small;">Jefferson Lab</span><br><span style="font-size: small;" data-mce-style="font-size: small;">757-269-7327</span><br><span style="font-size: small;" data-mce-style="font-size: small;"><a href='http://<a href="mailto:anichols@jlab.org">anichols@jlab.org</a>Email Me</a> ' target="_blank" data-mce-href='http://<a href="mailto:anichols@jlab.org">anichols@jlab.org</a>Email Me</a> '>anichols@jlab.org</a></span> / <span style="font-size: small;" data-mce-style="font-size: small;"><a href="http://www.jlab.org" target="_blank" data-mce-href="http://www.jlab.org">www.jlab.org</a></span> <br><br><img style="border: 0px currentColor;" src="cid:2def466482cdff9c02a43ffb6e2c1dd42fa99f6b@zimbra" data-mce-style="border: 0px none;" data-mce-src="cid:2def466482cdff9c02a43ffb6e2c1dd42fa99f6b@zimbra"><br></div></div><br>_______________________________________________<br>Accelerator_staff mailing list<br>Accelerator_staff@jlab.org<br>https://mailman.jlab.org/mailman/listinfo/accelerator_staff<br></div></div><br>_______________________________________________<br>Accelerator_staff mailing list<br>Accelerator_staff@jlab.org<br>https://mailman.jlab.org/mailman/listinfo/accelerator_staff<br></div></div><br>_______________________________________________<br>Accelerator_staff mailing list<br>Accelerator_staff@jlab.org<br>https://mailman.jlab.org/mailman/listinfo/accelerator_staff<br></div></div></body></html>