See answers to questions from Aseet on 17/7/201 “TOC.doc”
Backup documents are: 3879, 2310, 2535, 5777, 5331, 1808, 5256, 5246, 2633, 1343.
1.
Looking at
the layout the straws do not overlap around the straw center. Can you provide
plots from MC of the straw resolution versus distance including
electronics? (even if it is not exactly within the scope to review the
performance requirements).
I believe these plots exist, I hope Dave B. can provide
links to them.
a.
How do you
verify these with the prototypes?
An 8-straw prototype being tested at LBNL includes a
pixel detector. Although not it’s
primary function, this will also measure resolution.
b.
Does the
MC include the discriminator threshold level achieved with the prototype
electronics?
Yes, but using thresholds achieved with shielding
around the straws. This is fair only if the interior of the DS can be kept
quiet.
c.
What is
the gas gain and how has it been measured?
We expect to run ≲5·104. Gain is
measured using total current with Fe55 and using the known primary
ions from Fe55.
d.
Has the
noise level been measured?
Yes and it agrees well with Spice simulation
e.
Can you
meet the required resolution and efficiency specs with present S/N?
Yes, with gas gain of 5·104
2.
Can you describe in more detail the cooling system?
Have you done any simulations or tests with realistic geometry of heat loads
(boards) and cooling interfaces? What is the temperature of the coolant and
electronics (overall temperature gradient)?
Documents 2068 and 2013 provide considerable detail.
Both simulation and bench tests have been done. See documents 4087 and 4085.
Revisions since that time in panel design improve heat transfer (more aluminum)
and lower power. These have been analyzed but presented in a less
self-contained manner; see for example document 5208. The coolant will run ~25C
and gradient is ~3C.
3.
Can you provide details (drawings) of the vacuum
sealing of the panels and how the assembly and leak testing is carried out?
Hopefully we can go over this interactively with 3D
models.
4.
What are the characteristics of the fuses and have
they been tested?
The fuse consists of a small torsion spring soldered
under tension to conduct HV. One side uses a low-temperature solder which is
melted using a heating resistor. It was tested extensively this summer and the
document for it will be uploaded soon.
5. How have you
reached the conclusion that the inside and outside of the straw do not have to
be connected?
No. Given the ambiguity of the conclusion, and the
difficulty of assuring there is no connection, we have (tentatively) decided to
make the connection.
6. Can you explain
in some more detail with a drawing or diagram the connections of the services
(HV, LV and gas) i.e., patch panels, position of connections and modularity?
We do not yet details of the layout. Planned modularity
is:
- One pair of LV lines per panel, 48V, with stepdown at the panel
- One pair gas lines per plane, with “fanout” outside the DS.
- We have left space for 960 HV lines inside the DS, fanned out from 192 HV
channels outside the DS. We have not yet settled whether we need so many or how
to distribute them if we do.
7.
Can you describe the plan in case of failure/problem
with HV, LV, leaking straw and readout problem?
The general short-term solution to any problem is to
disable the smallest possible segment of the detector and continue running.
Longer term the plane is removed and the panel replaced. The defective panel
can then be repaired while data taking continues. “Smallest possible segment”
is a panel for LV or readout; a single straw for (most) HV problems; a plane
for gas problems.
8.
It would
be good to produce a detailed circuit diagram with characteristics and values
of the components.
These exist, but perhaps should be coalesced into a
single document.
9.
In the aging test you have seen no change in gain up
to 1C/cm. Have you seen any effects on the straws?
Straws were cut open to examine for discoloration or
other visible damage. End to end resistance measurements were also done. There
was no indication of radiation-induced damage.
10. Can you outline the development plan towards the final electronics?
a.
What additional prototypes are planned?
The push right now is for 2-channel preamps. Work on
analog and digital motherboards is in progress. Prototypes for mother boards
will be produced by early CY16.
b.
What questions remain unanswered and when do they
think they will know enough to go into production?
Two vs single channel preamps, and details of the
preamp to straw connections, are major concerns. I expect them to be settled by
the end of this year. A lower probability, but higher impact, issue is
radiation damage. Tests will be performed at LBNL this fall (October).
c.
What risks do they see in the near
future?
The biggest risk is radiation sensitivity. In the
unlikely event it is a problem, it could require major changes.
d.
How much schedule and cash contingency
do they have in the baseline plan?
We cannot begin with production electronics till CY17,
which is adequate time. We have ~40% contingency. Sadly not cash, we have to
beg and plead to get it released.
Comments:
1.
It is
important to do the radiation test of the electronics.
2.
It is
recommended to repeat the discharge tests with the smaller blocking cap.