June 30th 2008Jacques Lefrancois1 CW base studies Last week June 24th at calo meeting : news that preliminary test done by Yuri Gilitski indicated that the suggested addition of 5.6K to the CW chain had a very positive effect on the CW noise.Last week June 24th at calo meeting : news that preliminary test done by Yuri Gilitski indicated that the suggested addition of 5.6K to the CW chain had a very positive effect on the CW noise. Decision to launch very rapidly studies using FEB electronics to quantify the effect.Decision to launch very rapidly studies using FEB electronics to quantify the effect. Decide test to be done on test bench by Anatoli and JL ThursdayDecide test to be done on test bench by Anatoli and JL Thursday If test positive => modification and measurement on 4 PMT at the pit by Irina and TengizIf test positive => modification and measurement on 4 PMT at the pit by Irina and Tengiz

June 30th 2008Jacques Lefrancois2 Schematics of pumping voltage generation 5.6K ajouté ici

June 30th 2008Jacques Lefrancois3 Test done in test bench (office 1-R-002) by Anatoli and J.L. Single PM CW + Anatoli's contol box and power supplies+ test crate and FEB of FEB test benchSingle PM CW + Anatoli's contol box and power supplies+ test crate and FEB of FEB test bench Purpose was to identify effect of 5.6K, check that no violent instabilities are created, measure quantitative effect on noise, verify effect of extra load current on the CW chain.Purpose was to identify effect of 5.6K, check that no violent instabilities are created, measure quantitative effect on noise, verify effect of extra load current on the CW chain. Verify effect of varying the 5.6K value.Verify effect of varying the 5.6K value.

June 30th 2008Jacques Lefrancois4 Without 5.6Kohms & no extra ground Without 5.6Kohms & no extra ground Each slide has two scope pictures showing the rising and falling edge of the pumping square wave. Square wave rise & fall time is about 100 ns. Yellow at 2mv/cm is the anode signal (red is average), green is oscillator drive used for trigger, black is the 35 volts pumping square wave (thru probe). The conditions are V medium voltage = 50 volts V control (replacing DAC) = 2 volts Note that the parasite is very different according to edge (-2,+3 mv or a long -1.2 mv). The rms noise measured on 10K events is 4.2 ADC count.

June 30th 2008Jacques Lefrancois5 With 5.6Kohms & no extra ground With 5.6Kohms & no extra ground Square wave rise & fall time is now about 700 ns (the RC is about 400 ns). Note that the parasite is still very different according to edge. It is now mv or a longer -0.8 mv. Note also that for the rising edge it happens before the pumping voltage rise which could indicate pick up from another source. The rms noise measured on 10K events is 1.42 ADC count

June 30th 2008Jacques Lefrancois6 With 5.6Kohms and extra ground wire added With 5.6Kohms and extra ground wire added Square wave rise & fall time is the same about 700 ns. The control voltage is 2 volts the medium voltage was increased to 70 volts => explanation after. Note also that for the rising edge noise was happening before the pumping voltage rise which indicated pick up from another source, this effect has now disappeared. The pick up is now very small and more important for the fast electronic it is now slow. The rms of noise measured on 10K events is 1.28 ADC count vs 1.18 for amplifier alone and with base but without +-6v and without 70 volts. The extra CW noise is, by a quadratic subtraction, only 0.38 ADC and hard to estimate!!!

June 30th 2008Jacques Lefrancois7 Study of effect of added load current Study of effect of added load current To simulate an extra current a 2 megohm resistor was connected between the 4th stage of the CW and ground The DC voltage from the CW chain at this point fell to 135 volts instead of 163 "normally". This indicates that the medium voltage was too critical at 50 volts at 60 volts we are back to => =>166 The control voltage is 2 volts. So in case of high dynode current (80 microamp here which is very large) the medium voltage should be high enough. There is no obvious difference in pick up noise. But the pumping voltage rise time is slightly faster. The rms of noise measured on 10K events is ADC count, not statistically different from the without 2 Megohm.

June 30th 2008Jacques Lefrancois8 No 2 Megohm. Varying the 5.6Kohm (I) No 2 Megohm. Varying the 5.6Kohm (I) The 5.6Kohm was replaced by a 10 Kohm: this is to check that the even with a larger resistance there is no problem with operational amplifier stability. Which is seen to be the case. There is nevertheless interest in verifying also noise in those condition. The medium voltage is 70 volts the control voltage 2 volts. The rms of noise measured on 10K events is ADC count, significantly different from 1.28 with 5.6K but a very small difference. Nevertheless using the quadratic difference of rms the CW noise contribution would be reduced again by a factor of two compared to the 5.6K case to 0.18 ADC count. This reduction is confirmed by the scope picture however the square wave rise and fall time are now about 1.4 microsec to be compared with the about 7 microsec half period of the CW

June 30th 2008Jacques Lefrancois9 No 2 Megohm. Varying the 5.6Kohm (II) No 2 Megohm. Varying the 5.6Kohm (II) The 5.6Kohm was replaced by a 1 Kohm (no 2Kohm available at that time): this is to check that a smaller resistance makes a real difference. The rms noise becomes on the front end electronic; and the noise as seen on the scope pictures above increases very significantly compared to the 5.6 Kohm case. This is consistent with the rise and fall time of the square wave decreasing to about 200 ns. From quadratic evaluation the rms cw contribution would be 0.95 ADC count compared to 0.38 with 5.6K and 0.18 with 10K.

June 30th 2008Jacques Lefrancois10 Test done at the pit (Irina +Tengiz) Four PMT + CW bases were removed by Tengiz at the lower edge of ECAL Outer, and modified.Four PMT + CW bases were removed by Tengiz at the lower edge of ECAL Outer, and modified. Channel 7 and 15 show bases modified by adding a 5.6KChannel 7 and 15 show bases modified by adding a 5.6K Channel 23 modified by a 5.6K and a short wire improving the grounding of the delay line ground.Channel 23 modified by a 5.6K and a short wire improving the grounding of the delay line ground. Channel 31 modified by 5.6K + improved grounding + 22 pfd load after the 5.6K (in effect in parallel with the 100 pfd stray capacitance of the 42 CW diodes)Channel 31 modified by 5.6K + improved grounding + 22 pfd load after the 5.6K (in effect in parallel with the 100 pfd stray capacitance of the 42 CW diodes) Pulses were acquired and analysed by Irina on FEB using CATPulses were acquired and analysed by Irina on FEB using CAT The first 4 have 100Kevents the next 4 have 10KeventsThe first 4 have 100Kevents the next 4 have 10Kevents

June 30th 2008Jacques Lefrancois11 Plots before and after modifications :#7 With 5.6K alone the rms is reduced from to 1.426

June 30th 2008Jacques Lefrancois12 #15 Same as 7

June 30th 2008Jacques Lefrancois13 #23 With 5.6K and improved ground the rms is reduced from 3.24 to ADC counts

June 30th 2008Jacques Lefrancois14 #31 With an addition of a 20pfd capacity the rms goes from to 1.304: no further improvement compared to #23

June 30th 2008Jacques Lefrancois15 Plots with CW on (red) and CW off(blue) #7

June 30th 2008Jacques Lefrancois16 CW on (red) and CW off(blue) #15

June 30th 2008Jacques Lefrancois17 CW on (red) and CW off (blue) #23 As seen before, the rms with 5.6K and improved ground is Less than 10% increase from without CW. Even the tail is almost identical

June 30th 2008Jacques Lefrancois18 #31

June 30th 2008Jacques Lefrancois19 Conclusion With two simple modifications the CW noise problem can be solved almost completely. (less than 10% increase of electronic noise). The test bench measurements and pit measurements give identical resultsWith two simple modifications the CW noise problem can be solved almost completely. (less than 10% increase of electronic noise). The test bench measurements and pit measurements give identical results Further test can be done for example:Further test can be done for example: Verification of stability vs rate with LED Study of consumption Study remaining 80KHz ripple on HV => gain variation => effect on LED width However in view of rate test done on test bench and circuit analysis I am 99.99% sure that there are no problems.However in view of rate test done on test bench and circuit analysis I am 99.99% sure that there are no problems. The resistance have to withhold < 70 volts pulsed so it should not be too small. The power dissipated in R is f X CV**2<0.04 Watts OK.The resistance have to withhold < 70 volts pulsed so it should not be too small. The power dissipated in R is f X CV**2<0.04 Watts OK. The main problem is to plan the intervention to be fast enough to leave time to test and repair inevitable breakage (connectors)The main problem is to plan the intervention to be fast enough to leave time to test and repair inevitable breakage (connectors)