From: owner-project-blm-lhc@listbox.cern.ch on behalf of Gianluca Guaglio [Gianluca.Guaglio@cern.ch]
Sent: Monday, July 28, 2003 2:38 PM
To: project-blm-lhc (beam loss detection for the LHC)
Subject: Lauvain data

Categories: CERN SpamKiller Note: -49
At least, here the Lauvain data analysis.
In bold my suggestion for future experiments
 
GENERAL SETUP
We pointed the beam on a collimation copper plate of width 5 mm with an hole of 11 mm of diameter.
The plate have been fixed with adhesive tape to the board. Improve the collimator fixing.
The electronic board consist in 4 channel of integrator+threshold comparator+monostable. Into the Channels, a constant current of 10 pA has been injected.
We used a ionization chamber (IC) kept in vertical position, such as the beam enter diametrically into it.
The IC was connected to the channel 4 , the input of this channel has been disconnected and deviated to the ground.
The beam faces, in the order, the collimator, the component on the board, the ionization chamber.
We used the Labview Virtual Instrument  CFC_v11timegraph_lauvin.vi contained in the library CFC_v11timegraph.llb
 
Fix current mode (FIX)
This measurement has been token injecting a constant current of 1 nA in the CFC.
Initially, we measure the output signal (almost 5 Hz) without the beam on the 4 channels. Obviously, the channel 4 didn't see the injected current and so it gave a frequency of around 0.05 Hz. After few points, we switch the beam on and we register the variation in the answer during the irradiation. After some points,  we switch the beam off and recorded again few points without beam, to see if there is an integral effect.
 
Scan mode
This measurement has been token injecting a current from 1 mA to 30 pA in 7 steps. Precisely 1 mA; 0.5 mA; 0.1 mA, 1 microA; 10 nA; 100 pA; 30 pA.
The scans are recorded with constant beam.
 
Procedure
For each component to be irradiate, we make a scan without the beam, then, in the order,  a Fix and a scan at  5E6 p/cm2/s, 1E7 p/cm2/s and 5E8 p/cm2/s. Finally we make a scan without the beam and we changed the irradiated component.
We irradiate the following components: JFETs, Amplifier of the integrator (AMPL), the threshold comparator (COMP) and the monostable (MONO). 
 
Measurements
All the measurements have been collected in the folder \\srv2_home\DIV_SL\BI\PM\labview\CFC\data\lauvainLN.
The files are saved in the form: YYYYMMDD_hhmm_cc_note.cfc where
YYYY =year, in our case 2003
MM =month, here 06,
DD =day, here 02 or 03
hhmm = hour and minutes
cc= number of channel
note= generally contain the mode of measurement (fix or scan), the component irradiated and a progressive number.
 
The data are summarized and analyzed in the excel files present in that directory.
All the file recorded the 02 June are testing files. I take the files 20030602_1846_??_zero as reference and I reported it in every fix*.xls files.
 
ANALYSIS
General
From the files 20030602_1846_??_zero we can see that there is a temporal drift of the channel 2. We tried, in the files *_2257_??_scan0.cfc To verified if it a proportional drift or it is a parasitic current in the channel. It looks like the second possibility, with an extra current of 30 pA. In the files *_2323_??_fix0.cfc we have tried to change the amplifier (1st point) and also the JFETS (2nd point) but without success.
In the followings *_fixch2.cfc we change the resistor for the bias current and we see, obviously, a signal changing. We reused the previous resistance. Finally we change the monostable, but always with the same result. So we decide to stay with this current and we report everything in the original configuration.
Our machine time stared with the 20030602_* files, following the above operation mode. There have been only few exceptions:
 
At the end of the irradiation, we put the chamber in horizontal (the beam pass it longitudinally) ad we recorded the *_mono5.cfc file. Then we remove the collimator and the board, recording the last files with different beam intensity.
For each irradiation we recorded also the fluence given us by the local operator.
We irradiate each components until almost 500 Gy.
We have also tried to correlate the IC frequency with the flux intensity.
 
JFET
Integral effect (no beam): from the FIX, we don't see any relevant variation of the channels before and after the irradiation. There is only a shift (+3%) on the channel 1 during before the last measurement.From the SCAN files we can observe a residual parasitic current of almost 30 pA.
Cross section effect (with beam): from the FIX file we can see an increase of 70% (+ 700 pA) during the highest irradiations, only of 2% during the lowest irradiation (5E6). To mark the fact that, during irradiation, there is a decreasing trend: could it be a recovering effect?  From the SCAN files we see an increasing during irradiation at low current. Equivalent parasitic current: almost 200 pA. Minor increasing in channel 2.
 
AMPL
Integral effect (no beam): from the FIX, we don't see any relevant variation of the channels before and after the irradiation. From the SCAN files too.
Cross section effect (with beam): from the FIX file we can see a decrease of 25% (- 250pA) during the 1E7 irradiation, of >-100% during the highest irradiation (5E8). From the SCAN files we see a decreasing during irradiation: -10 pA at 5E6, -200pA at 1E7, -800pA at 5E8 .  It is also relevant the fact that the channel 2 increase his equivalent current up to +150 pA during the 5E8 irradiation (both in FIX and SCAN)
 
COMP
Integral effect (no beam): from both the FIX and SCAN, we don't see any relevant variation of the channels before and after the irradiation. (Excluded the probable error in the final scan on channel 3).
Cross section effect (with beam): from the FIX file we can see an increase up to+10% (+ 100pA) during the 5E8 irradiation. Minor increasing in channel 2 and 3. From the SCAN files we see an increasing of +75 pA at 5E8. 
 
MONO
Integral effect (no beam): from both the FIX and SCAN, we don't see any relevant variation of the channels before and after the irradiation. (Excluded an error in the FIX on channel 1). Note the decrease in the last FIX measurement in one point before the switching on. (Alimentation problem?)
Cross section effect (with beam): from the FIX file we can see really small increase. From the scan we can see a probable error in the 5E6 scan on channel 3. 
 
Chamber
We have collected all the channel 4 average data in the fix_chamber.xls file, "summary" sheet. From this file we can see that there is not a good linear correlation with the recorder intensity and the flux values, particularly for the 1E7 values.
What's more, we can see a general increasing of the values with the time. Activation of some chamber material? Temperature drift? It is on going the analysis of a long time measurement to verify this assumption.
Finally we have to note that, for the horizontal position, the thicker wall reduce the number of counts of about a factor 300 with 5E8 p/cm2/s.
The values between the collimated and the not collimated are almost the same, with the exception of the lowest intensity beam: ratio free/collimation ~300?
 
CONCLUSIONS
The most sensible components are the JFET and, secondly, the amplifier.
There are some crosstalk between the channels, probably through the power alimentation.
The chamber is not linear in low proton energy fluxes.
 
Proposed actions
Improve collimator fixing.
Insert the alimentation measurements in the SW.
Analysis of a long time measurement.
Better uncoupling of the channels to avoid crosstalks.
Resolve spikes problem from the source-switch.
 
Lessons learnt
Reproduce entire measurement set up in house (we lost a lot of time in Lauvain trying to fix the collimator better)
Radiation could also force the component to extract current signal (see AMPL)
It is better to calibrate the amplifier gain after a warm up (see channel 2 drift)
 
 
For the moment I think this is enough.
See you for further discussions
 

Gianluca Guaglio

 

Nuclear Engineer

CERN

AB Division BDI Group BL Section

Site de Meyrin CH-1211 Genève 23 (Switzerland) or

Site de Prevessin F-01631 CERN Cedex (France)

Building 865/R-A19, mailbox Z15700

Phone 0041 22 76 78079

Fax 0041 22 76 79560

e-mail gianluca.guaglio@cern.ch