1/10 Irradiation test of CW bases Yu. Gilitsky / IHEP (Protvino)

2/10 The irradiation test was done to compare performance of different CW configurations at high doses. The test was conducted Nov 2008 at the HiLum facility (IHEP, Protvino) constructed for the irradiation tests of the ATLAS LAr. The 50 GeV proton beam (extracted using bent crystal technique) has intensity up to p/spill (9 sec interval, 1.7 sec duration) Four samples with different configurations were places behind Absorber I (1λ I steel). U CTRL was fixed to ~2V by a resistor divider arranged on each board. The output HV was monitored during the whole irradiation period. ECAL CW samples

3/10 Absorber I (1 λ 0 of steel) D1 CW1 D3D4D2 CW2CW3CW4 Proton beam 50 GeV Actual beam positionExpected beam position D1-D4 – film dosimeters CW #configdetailskrad CW1HCALmc2 Cf=100pF, Rf=62kΩ, CJ=47pF, C1=C2=0, RJ=0 800 CW2ECAL orig C1=C2=47nF (C1  MV), Rf=0, Cf=0, CJ=0, RJ=0 900 CW3HCALmc1 Cf=100pF, Rf=62kΩ, CJ=47pF, C1=C2=0, RJ=5.6kΩ 700 CW4ECALmc C1=C2=47nF, Rf=62kΩ, Cf=100pF, CJ=0, RJ=0 500

4/10 Protons rate from beam monitors start of irradiation start of degradation CW1 and CW3

5/10 November 2008 HV, V base HVout in HCAL mode, V expectedright after irradiation in 2 days in 5 days in 50 days CW CW CW CW4835 Significant HV drop was observed in both HCALmc bases after ~500 krad; the ECALxx bases were not affected. In order to proof that the drop was determined by the configuration, in 5 days after the irradiation the CW2 base (900 krad) was modified to: ▪“ECAL+HCAL” (ECALorig + Rf=62kΩ+Cf=100pF): OK ▪ECALmc (C1=C2=47nF): OK ▪HCALmc (C1=C2=0): HV≈670V, unstable ▪ECALmc: OK High rate test (with PM) in the ECALmc mode: ▪ HV=1500V stability checked up to 30 μA OK ▪ HV=850V – checked up to 50 μA OK One can conclude that configurations where C1 is present (connected either to MV or to ground) (“ECAL” type) are more “rad hard” than those where C1 is absent (“HCAL” type) Summary on HVout in “HCAL” modes

6/10 HV OUT as a function of U CTRL Conditions: MV=80V, LV=+6V -6V Same conversion factor, but different max HV, in “HCAL” and “ECAL” modes. For more detailed studies 4 sets of oscillograms were taken: # conf U CTRL, V HV, V 1 HCAL HCAL ≈ *saturated* 3 ECAL ECAL Each set consisted of ~20 oscillograms taken in different points, such that it was possible to calculate currents in places of interest. On 08/01/09 (~50 days after the irradiation) the CW1 base (800 krad) was studied in details in both “HCAL” and “ECAL” configurations. Switching was done by soldering / unsoldering capacitors: “HCAL”: C J =47pF present, C1 and C2 absent “ECAL”: C J absent, C1=47 nF and C2=3.3nF present always present were: RJ=10kΩ, Rf=62kΩ and Cf=100pF

7/10 set #2 As a result of irradiation: ▪The oscillator produces 25 kHz sine-like wave, 4 V p-p. ▪op amp gain is ~2-5 at 25 kHz (U OUT (t) and ΔU IN (t) of the oscillator op amp shown; note gain = U OUT /ΔU IN ≈ 5 and ~90 o phase shift of U OUT wrt U IN ) ▪ DC gain is at least several hundred: < 20 mV change in ΔU IN flips the output (measured later 14/01/09) ▪op amp gets significant output impedance (output current limitation?); differential output impedance of saturated regulator op amp shown, set #2 ▪npn transistor β’s become 5-7 (Q1 & Q2 shown) set #2 set #4

8/10 Looking at “HCAL” set #2, to find out the reason for limiting HV Q1 is always saturated, Q2 active  insufficient current into Q2 base I PUMP (current in R J =10k): Q3 part (up) OK, problem with Q2 part (down) Q1 I C NB I C negative (reverse) for part of period Maximum Q2 base current possible in HCAL conf.

9/10 Compare to “ECAL” set #4, HV=1140 V Factor of >2 wrt “HCAL” in charge injected into the Q2 base I PUMP : both Q3 and Q2 half-periods OK

10/10 Possible explanation of the difference between “HCAL” and “ECAL” type bases Because of low gain of irradiated transistors, the irradiated oscillator op amp (with lowered load capabilities) has to draw non-negligible current into Q2 and Q3 bases. The presence of capacitor C2b means that the amount of charge delivered into [Q2 b-e junction || R2e] during the half period when Q2 is open should be returned back during next half period, when it is closed (Q3 open) In the “ECAL” configuration, C2b is recharged from C1 through R2e and R2b. In the “HCAL” configuration, the return path is more difficult: as C1 is not present, charge comes from the regulator op amp, passing through R1b, b-c junction of Q1 and then R2e and R2b (this is the reason why in the “HCAL” configuration the Q1 collector current is reversed during ~ half a period). And max possible returned charge is insufficient for operation at higher HV. As a proof of correct understanding the problem: to boost the C2b recharge in the “HCAL” configuration, a diode was added || R2e. The max HV increased till the same 1320 V as in the “ECAL” configuration.