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Meeting notes with Hamamatsu 4/21/09




Here are a few notes I took at our meeting with Hamamatsu on Tuesday.

Meeting notes with Hamamatsu 4/21/09
------------------------------------
Attending: JLab: Eugene Chudakov, John Domingo, Elton Smith, Carl Zorn;
Hamamatsu: Thomas Bailey (phone), Earl Hergert, Yuji Iwai
Notes by Elton.

Thomas lead the meeting. summarized issues
- testing and evaluation of MPPC
- Discuss with JLab custom packaging and specifications

Carl reviewed slides which showed Hamamatsu devices have a very narrow
operating range.
- likely due to afterpulsing
- must be operated at fixed bias and this bias mantained
- arrays are not very compact with a 44% coverage
- Will likely need to maintain an environment with a restricted
temperature range and also use a thermister to compensate via changes
in bias for temperature changes.

Eugene: does the sensor itself generate much heat? No, if operated at
nominal rates.

- Need to limit differential heating. One source is the heating through
the pins which can heat the sensor non-uniformly.
- Present back of sensor is a PC board with poor heat conduction. Other
options are possible, but likely more expensive.

John: How uniform is the temperature/voltage dependence of the sensors.
[Note: typical dependence is well documented in Hamamatsu literature]. It
was not clear how the temperature and voltage slopes vary from sensor to
sensor.
* Hamamatsu will measure the temperature slope across wafers/lots

Thomas returned to the question of custom packaging
- possibility of non-recuring engineering (NRE) costs
- custom packages run in the tens of k$.

Earl mentioned that already the 18x18 package (44% coverage) has been
shrunk down to 16.1x16.1 mm2 (55% coverage)

Eugene asked about the radiation hardness of the sensors.
* Hamamatsu would send us papers on the subject.

Thomas reviewed the schedule for ordering sensors
- The plan remains to put out an order in 2010.
- JLab would like to purchase 10-20 prototypes in summer for testing in
early Fall

Elton inquired about options for supplying electronics
- To date, Hamamatsu has focused on providing the sensor only.
- However, temperature compensation circuits have been implemented by
adjusting the bias voltage. This electronics could be supplied.
* Hamamatsu to give feedback on the temperature range over which this
scheme will work.

Carl has measured the amplitude variation between cells at fixed bias and
they vary by about 5%.
- Amplification (transimpedence) boards at JLab were developed by James
Proffitt
* JLab will supply the circuit to Hamamatsu for review and reference.


Discussion regarding rise time and the possible need to isolate
capacitance of individual cells using individual amplifiers (this is done
on James' board). There is evidence from studies of SensL units that this
may be necessary to keep the rise time below 15 ns.
* Hamamatsu can check rise time for summed output.

Thomas on Hamamatsu production capability
- With a lead time of 3-4 months (includes wafer production and
packaging), they can supply about 500 sensors/month.

Feedback on the possible options:
1. sensor alone
2. sensor + temperature compensation (feedback) circuit using bias
3. sensor + temperature compensation + transimpedence amplifier.
Include pricing for each of these options.

Discussion on Backup options

APDs.

Earl: Ballpack cost of APD coverage/SiPM coverage is 1/2.
- Hamamatsu has provided monolithic APD up to 16x16 mm2; however, large
arrays suffer from reduced yield. [Note: operation, especially at high
gain, is limited by small regions of imperfections that reduce yield]
- 12x12 mm2 structures can operate at gains of 250
- 6x6 mm2 structures routinely used at gains of 250, can be built into
arrays such as a 2x2 matrix for our application. These operate at 200-300
V.
- Rise time of 5x5 mm2 is about 9 ns.
- Rise time of 10x10 mm2 is about 32 ns, so rise time may select smaller
APDs which must be placed into arrays to cover larger area.
- Noise also increases with capacitance (and therefore larger area
devices). Again buffering might be needed to keep effective capacitance
low.

Review of action items
- jlab: Carl to send evaluation report
- hamamatsu: send papers on radiation hardness
- hamamatsu: provide temperature characteristics for wafers/lots
- hamamatsu: measure rise time of summed output
- jlab; provide preamp circuit design
- hamamatsu: provide pricing and time scale for various options

Other systems
JLab: no major changes in other areas; time scales unchanged
- tagging hodoscope (Franz Klein, CUA)
- start counter (Werner Boeglin, FIU)
- outer barrel calorimeter
- time-of-flight (Paul Eugenio, FSU)
- Fcal (Matt Shepherd, IU)
 - possible replacement tube for FEU-84-3 pmts
 * JLab to send specs of this tube to Hamamatsu

Action items
- jlab: FEU-84-3 specification sheets
- hamamatsu: recommendation on best option for using APDs with Bcal,
including monolithic vs arrays; stages of summing and amplification.


Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
(757) 269-6331 fax