1. Status of the CEDAR project DY with kaons / antiprotons I. Gnesi, A
Status of the CEDAR project DY with kaons / antiprotons I. Gnesi, A. Maggiora, F. Tosello – INFN-Torino June 3, 2014

2. Contents Required CEDAR resolution
Issues from the analysis of DCS data
T gradient in CEDARs
T_CEDAR vs T_hall
P/T behaviour
PMT Majorities
PMT test bench
CEDAR DAQ
Conclusions

3. CEDAR design specs (from CERN 82-13)
@ 190 GeV/c : (βπ - βK ) / βπ = •10-6

4. DCS data of the 2009 run – T gradient in CEDARs
Time [s]
Temp.Diff. [°C]
Temperature [°C]
CEDAR-1
THEAD
TMID
TTAIL
CEDAR-2
THEAD-TMID
TTAIL-TMID
THEAD-TMID [°C]
TTAIL-TMID [°C]

5. DCS data of the 2009 run – T gradient in CEDARs
In CEDAR 1 : THEAD > TMID > TTAIL and THEAD – TTAIL can be >1 K during colder days
Effect of the magnets of the beam line , as already suspected ?
In CEDAR 2 : THEAD > TMID but TTAIL > TMID ; THEAD > TMID can be >1 K
Effect of the gate of the hall which is faced to the middle of CEDAR 2 ?
Temperature gradient in the vessel should be avoided like stated in CERN 74-4 p.7
To improve long-term stability in the two vessels , some additional thermal shield seems necessary :
a tent (like attempted in the past) : simpler a less expensive
an active shield (with controllable heaters)

6. DCS data of the 2009 run – THALL / TCEDAR (1)
Each CEDAR is also equipped with a PT100 screwed on one of its “feets” (ambient THALL)
Looking at the temperature excursions in an interval of t(hours) for every sensor of each CEDAR and evaluating the three ratios, THALL / THEAD , THALL /TMID , THALL > TTAIL , as a function of t(hours) we obtained that :
the ratios (insulation factors) have their maximum at t ≈ 12 hours
the value of the ratio depends on the considered “internal” sensor
the highest value in the two CEDARs is 5
Therefore the effectiveness of the internal shield (rigid polyurethane foam) seems to have reduced from the factor 20 (determined at the production time, ~1980) to a factor < 5
This can represent an further demand for some additional thermal shield
Some additional test should be peformed to confirm this observation.
Chritophe Menezes Pires said that an additional PT100 for ambient temperature measurements is already available (in the DCS chain) , if a cross-check is needed.

7. DCS data of the 2009 run – THALL / TCEDAR (1)
Cedar 1-2 (row 1-2) Insulation Factors
The three mentioned ratios vs t(hours) from HEAD / MIDDLE / TAIL temperature probes (from left to right).
The insulation factor seem to be factor 3-5 while the design specs reported a factor 20-80

8. DCS data of the 2009 run – P/T behavior (1)
Cedar 1-2 (row 1-2) P/T values given in mol/m^3
for the HEAD(red)/MIDDLE(green)/TAIL(blue) temperature probes.
The first column shows the correlation between the temperature of the precision pressure probe (°C, x-axis) and the gas pressure (bar, y-axis)

9. DCS data of the 2009 run P/T behavior (2)
P/T of CEDARs 1-2
Zooms: gas density variation are shown
They show both increasing and decreasing trends and are not always related to pressure scans
The relative variation of the density is ~2.5•10-3 while CEDAR reuirements by desing are ~10-4

10. CEDAR PMT Majorities Ratios
Ratios 8-fold/6-fold (red), 8-fold/7-fold (green) and 7-fold/6-fold (blue) for CEDARS 1 (top) and (bottom)
Obtained by asking time differences between majorities 8,7 and 6 less than 1 second, so that they should be related to the same spill.
Nevertheless they are often > 1 → a better understanding of these DCS data is needed

11. CEDAR PMT test bench (1)
CEDARs will be used to tag kaon, which are about 2.5% of a beam having an intensity of about 108 particle/s .
Due to beam divergence, the PMTs receive photons from pions too, therefore they work at a rate > 2.5•106 Hz but < 107 Hz.
Output of P.K.Jasinski's MC assuming a beam divergence of divX = mrad (FWHM) divY = mrad (FWHM)
(2008 run)
Radius of Cerenkov ring [mm]
Counts
Light Diaphragm = 0.5mm

12. CEDAR PMT test bench (2)
This high rate suggests to test the PMTs and the associated voltage dividers (and the electronic chain) in the same conditions.
A test bench will be produced to this purpose.
The Laser driver has been designed and Pspice-simulated for the three tunable parameters : pulse height, width and rate (up to 10 MHz)
The PCB is in production
The temperature-compensated readout of SiPM is prototyped.
The mechanics is being designed
PMT being tested
Light tight box
Uniform
ND filters
460 nm
Laser
diode
variable
ND filter
SiPM (to tune the filters)
Reference PMT (for high
rate tests)
semi-reflective mirror

13. CEDAR DAQ
Since the working rate of the PMT will likely be > 2.5•106 the DAQ front-end has to be fast.
Considering the characteristics of the GANDALF board ( , it seems the correct choice .
GANDALF has been already used for the CEDAR readout (although at lower PMT rates).
Horst Fischer agreed to provide the needed module(s) as soon as we decide which specific configuration we want to implement (transient recorder or TDC).

14. Conclusions
Some questions have been raised by the analysis of the DCS data (P/T stability, ratios of the PMT majorities)
We need a discussion with the DCS group to understand possible mistakes in our analysis and/or evaluate the feasibility of a monitoring of those parameters based on the DCS data
The analysis of few raw data is being started in order to study the CEDAR performance in an off-line analysis
Temperature gradients seem to exist in the CEDAR vessels. Insulation performance of the existing PUR-foam shield is not well understood. PMTs should be tested at the expected rates.
In order to settle these issues we requested an early installation of the CEDARs . Johannes Bernhard and Lau Gatignon approved this request (but the date has not yet been fixed).
New tests / monitoring of pressure and temperature should allow to make a decision on the type of the additional temperature shield (passive vs active).
A PMT test bench is being built.
DAQ choice has to be finalized.
We likely need a discussion with the Freiburg group to understand if the GANDALF configuration used in the past for the CEDAR readout can cope with the expected new rate.