LAPPD research mailing list

[Mikhail Osipenko <osipenko AT ge.infn.it>]

Dear Jerry,

since you sent this to entire list I may add my 5 cents: HRPPD is very large 12x12 cm^2, each of the two internal MCPs is about 1 mm thick. Thus, the intrinsic capacitance of the MCPs:

C_MCP=4.7*8.85 pF/m*12x12 cm^2/1 mm=0.6 nF,  (Q_buffer~C*V=0.6 nF*800 V=0.5 uC=3*10^12 e, tau=0.6 nF*5 MOhm=3 ms, R_max=3*10^12 e/10^3/3 ms~10^12 Hz)

adding 10 nF parallel capacitors didn't help us in terms of HV-stability. Although, I don't know about high rates.

Best Regards,

                         Mikhail.

On 5/11/24 22:35, Vavra, Jerry via Lappd-l wrote:

Dear Alexander,

   That is good that you will be able to bias each MCP independently. I would, however, personally worry about inductance in ground returns. I also do not know how you handle decoupling capacitance, which are necessary to provide charge instantaneously. That is why Burle installed the resistor chain and capacitors within MCP housing. I managed to find a NIM paper from 2022 describing ATLAS forward TOF detector, which was originally started by Mike Albrow, Anatoly Ronzhin and Andrew Brandt, but later taken over by other Europeans. This is the only paper, where there is some sort of detail how Photonis is handling internal circuit. It is signed by Jeff DeFazio, a key Photonis guy who built the MCP. He used to work for Burle during our time. It is also worthwhile to look at Melykian’s paper from 2020 describing FIT experiment’s MCPs. The advantage you have is that you have 100% control over external components. If Photonis does not want to provide a circuit diagram for the latest design, one can always open one, say after aging test is finished. Maybe Albert is thinking about that too.

Best regards, Jerry

 

From: Kiselev, Alexander <ayk AT bnl.gov>
Date: Saturday, May 11, 2024 at 9:36 AM
To: Vavra, Jerry <jjv AT slac.stanford.edu>, lappd-l AT lists.bnl.gov <lappd-l AT lists.bnl.gov>
Subject: Re: [Lappd-l] LAPPD / HRPPD #4 Workshop, final remarks

  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.

 

 

 

 

 

---

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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Mikhail Osipenko
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