LAPPD research mailing list

["Kiselev, Alexander" <ayk AT bnl.gov>]

  Dear Jerry,

  Thank you for the reference. Indeed, both LAPPDs and HRPPDs allow one to bias the MCPs independently. In the attached picture you can see three single wire HV cables at the top and three at the bottom (GND, PC, 2x2 MCPs). Real life implementation should have shielded cables and local ground connections of course. 

  We are going to try asymmetric biasing of the two MCPs in HRPPD #15 at BNL once Mark confirms a safe HV limit one can apply to the bottom one.

  Best regards,

    Alexander.

 

 

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From: Vavra, Jerry <jjv AT slac.stanford.edu>
Sent: Friday, May 10, 2024 7:14 PM
To: Kiselev, Alexander <ayk AT bnl.gov>; lappd-l AT lists.bnl.gov <lappd-l AT lists.bnl.gov>
Subject: Re: [Lappd-l] LAPPD / HRPPD #4 Workshop, final remarks

 

Dear Alexander,

   I was searching for some reference about our discussion and found old Donati’s paper about PMTs. If you look at Fig.9, it has two MCPs inside vacuum envelope. He recommends reducing the gain in MCP facing photocathode to reduce the ion feedback. In case of Burle Planacon, built-in voltage divider was as shown on the next included picture. There was no way to adjust the first MCP gain independently. I do not know how you have it now in new tubes.

Regards, Jerry

 

    Donati says:” Instability then sets in for example, if the PMT gain is 10^8 and barely 10^-8 ions/electron go back and ionize at the input. This phenomenon is aggravated, in a glass microchannel PMT, by the tendency of MCP to release, in the useful life, gas molecules adsorbed on its surface when bombarded by ions. With a suitable stagger, opposite in the adjacent stages (chevron-type, Fig. 9), ions produced in the second stage cannot reach the input of the first. So, if the gain per stage is kept low (for example, o10^4), the ion feedback effect becomes negligible. MCP PMTs have typical multiplication gains of 10^4 (1-stage), 10^6 (2-stages), and 10^8 (3-stages).”

 

 

 

From: Lappd-l <lappd-l-bounces AT lists.bnl.gov> on behalf of Kiselev, Alexander <ayk AT bnl.gov>
Date: Friday, May 10, 2024 at 9:01 AM
To: lappd-l AT lists.bnl.gov <lappd-l AT lists.bnl.gov>
Subject: [Lappd-l] LAPPD / HRPPD #4 Workshop, final remarks

  Dear All,

 

  Thank you everybody who attended the workshop, participated in the discussions and presented their work. Pretty much all talks are by now uploaded, as well as a recording, which can be accessed from the indico Web page:

 

https://indico.cfnssbu.physics.sunysb.edu/event/265/

 

  Be aware that the recording is split in two parts.

 

  Slide 16 of my presentation was updated with a 0% PiLas laser tune and 200V on the photocathode plot (see v01 version), following a discussion during the Workshop: https://indico.cfnssbu.physics.sunysb.edu/event/265/contributions/923/attachments/257/431/ayk-2023-05-08-lappd-hrppd-workshop.v01.pdf .

 

  Best regards,

     Alexander, for the Organizers.

 

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