Polarized Cathode Change


On Tuesday, 6 May 2003, the Sources Group (Jym Clendenin, Jim Turner, Axel Brachmann, Dah-An Luh and Tom Galetto) and Takashi Maruyama along with visiting scientist from St. Petersburg State Technical University, Alexander Rochansky, began the installation and activation of a new cathode for the SLAC Polarized Electron Source PES) in preparation for the next E-158 run scheduled to start in mid-June. The work was done with breaks for filling PEP (with the thermionic gun) whenever possible.

During the first day, the SF6 vessel was removed and the transporter set up. Then the cathode tray was installed and pumped down, baked, and finally the vacuum in the tray left to recover overnight. This was also a planned Repair Opportunity Day (ROD) when work in PEP and BaBar continued until late in the evening.

Second day, May 7th, PEP collisions were just getting established at 11:00, so decided to wait until next day to continue PES work.

7 May 2003 Alexander Rochansky in the SLAC Injector Control Area
click on photos to see enlarged version

The third day, May 8th, the cathode was moved into the preparation chamber, activated (1-hour at 600 C, cool down, then apply Cs and NF3), then positioned in the gun. After a PEP fill, the transporter was removed, the SF6 vessel replaced, and purging with SF6 started while PEP resumed normal operations.

8 My 2003 Takashi Maruyama and Tom Galetto prepare to activate a new cathode       8 May 2003 Tom Galetto, Jim Turner and Dah-An Luh monitor cathode activation        8 May 2003 Jim Turner and Takashi Maruyama

8 May 2003 Lasermeister Axel Brachmann at work         8 May 2003 Alexander Rochansky and Tom Galetto prepare to activate cathode at CID          8 May 2003 Alexander Rochansky preparing to adjust cathode position


The fourth and final day, May 9th, the thermionic gun was vacuum isolated, then the beamline valves for the laser gun opened, the cathode bias (-120 kV) was turned on and various tests of the cathode made using a variety of lasers. Finally the transmission of the beam was checked in the first few meters using the installed PMTs, the timing checked, and accelerator operations resumed but now with the polarized beam. Unfortunately the cathode showed a severe surface charge limit (SCL).

Postscript: On the morning of Friday, May 16th, PEP started a 3-shift downtime to repair a vacuum leak in the LER. The Sources Group (same people as above) was given permission to change the cathode at CID. This time a backup cathode that was put in the cathode tray last week was sucessfully activated and the gun closed up by about 6 pm. The SF6 can was purged, and early in the moring of the 17th the HV brought up. This time the SCL was much less severe, so that it appears this cathode will be ok for the E-158 run!!

Last updated 17 May 2003