G-plane biasing problem on APA-3 Serhan Tufanli
Turning on the detector after Christmas break ● Nominal wire bias voltages ● 100V/cm space charge test run ○ No tracks on APA3 APA3 APA2 APA1 collection plane ○ Barely visible tracks on U plane ● https://pdspelog.web.cern.ch/e lisa/display/9941
U plane signal Barely visible tracks on U plane
Tried to understand the reason.. ● We checked the Wiener power supply, all high voltage cables and connections on top of the cryostat. All of them were good. ● Changed the polarity of U plane → applied +370 V ● We measured the capacitance of the SHV center conductor to the ground for each wire plane on APA3. While U and X planes had 3nF capacitance, G plane had only 0.94nF. To cross-check, we performed the same measurements on APA5, and confirmed that all wire planes have ~3nF capacitance. This measurement confirms a connection problem between the high voltage cable and G plane wire biasing circuit on top of the APA. → SHV connector problem ?? Solder-joint problem?? G-plane electrically floating??
More tests… and G plane is charging up ● With different bias voltages run for half a day ○ Cathode = - 180 kV ○ G = off no voltage ○ U = - 370V (nominal) ○ V = 0V ○ X = 1640V (double that nominal to help pulling charge from G plane toward the sensing wires). We see tracks in induction and collection planes !!!! G-plane charging up and satisfies the transparency conditions!!! APA3 APA2 APA1
More tests… and G plane is charging up ● Repeat measurements with nominal voltages ○ Cathode = - 180 kV ○ G = off no voltage ○ U = - 370V (nominal) ○ V = 0V ○ X = 820V APA3 APA2 APA1 We see induction and collection tracks!!!
Conclusions, questions .. ● We have G plane biasing problem on APA3 due to SHV connection ● It is self-healing with G-plane charging up ● Was SHV cable already disconnected during the beam run? ○ No visual difference in Online monitoring tool ○ Any difference in data? ■ Need input from offline data analysis
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