Meeting-12092022

Also put in the NPS logbook https://logbooks.jlab.org/entry/4099123

Meeting Minutes for today's impromptu NPS meeting
Dec 9, 2022.  10 am
Attending:  Carlos Munos Camacho, Bogdan Wojtsekhowski, Mark Jones,
Bob Michaels (note taker), Vladimir Berdnikov, Brad Sawatzky.

Main topic: What to do for the French techs visiting Monday for 1 week ?
Should they proceed with assembly of 900 PMT blocks as planned or should
we wait for a modification to the PMT bases ?

Answer: YES, the techs can do their work as planned.

Vladimir will coordinate.  Alexandre may help with French translation
on day 1.  After day 1 the techs should be able to work independently.

The visitation by the techs in January for completion of the assembly ?
This is to be decided, pending what we do about the oscillation problem.

Other big topic: Update on the oscillation problem.
This discussion was mainly driven by Bogdan, who has been doing a lot
of work, together with Vladimir and Chris Stanislav.

There are 3 conceived approaches to solving the oscillation problem.

1. The most recent approach and most promising from a practical point of
view is to add a small capacitor (of order 1 nF) on the output
between the output signal and ground.  This suppresses the 210 MHz oscillation.
It was very successful and is a simple fix.  Next thing is to try 5 PMTs
and see if it still works, and then to try a larger bank (~100 PMTs).
The latter will require some work and will probably be ready in mid-January
(which is why the January visit of French techs is a indefinite).

2. Probably the most fundamentally correct approach is to adjust the
frequency bandwidth of the amplifier as discussed earlier in the logbook
and proposed by Jack Segal.  I believe this was tried and didn't work well
yet (it reduces but not sufficiently the amplitude of the oscillations).
However, it might be made to work.  At any rate, it does not seem practical
to implement this repair in the time between now and the March installation.
So, our present hope is that approach #1 works.  Gulp!

3. As previously reported in the NPS logbook, shielding the low voltage
cable seems to be helpful, but it's not completely reliable.  The lack
of reliability may be because the LV cable is only part of the "antenna".
Also the output is unshieled on the PCB, and so on.  Therefore, killing
the oscillation in the simple approach reported in #1 above might be the
way to go.  However, it needs to be demonstrated for multiple PMTs.



Other topics were discussed, notably.

(i). It would be useful to characterize the amplifier, says Bogdan.
This may be done with a setup that feeds the amplifier input with
a harmonic signal (single-frequency sinusoidal voltage with amplitude
of order 1 mV).  One may look at the output and vary the frequency.
Perhaps it could be done with help of Chris Stanislov and Yeranuhi
Ghandilyan.  Vladimir will do the initial coordination.

(ii). Ongoing concern about workforce.  Probably room 108 needs a nearly
full-time tech and 1 postdoc.  One approach to solving this was suggested
by Mark: the collaboration leadership can provide a list of tasks and
the persons assigned to them, then this could be reviewed informally.

(iii) Concerns about cable layout, strain-relief, making a clean setup, etc.