In-Vessel Electronics Infrastructure Craig Thorn LAr40 Cold Electronics Far Site Review, December 6-9, 2011

In-Vessel Electronics Infrastructure Implications of LAr purity requirements For Feedthroughs Cables in warm Ar gas (ullage) outgassing For Power Distribution DC-DC converters in Ar liquid causing boiling

Purity Requirements for LAr Electron Attachment Reaction is e + S S - Rate is dn e /dt = k n S n e  = (k A n S ) -1 With n S = 3.49x10 -8 x ppb at 500 V cm -1 v D = 1600 m s -1 k A (O 2 ) = 8.1x10 10 M -1 s -1 k A (H 2 O) = 8.6x10 11 M -1 s -1 y mean (O 2 ) = 0.57/ppb (110 ppt for 5 m) y mean (H 2 O) = 0.053/ppb (11 ppt for 5 m) Electron Attachment Rates q(y) = q(0) Exp[-y/(v D  )] Need extremely high purity LAr to avoid charge attenuation along drift See Andrews, et al., NIM A608 (2009) 251

Getting, and Keeping, High Purity LAr Impurity injection, transport, and removal At equilibrium, Henry’s law determines impurity concentrations: x(liq) = k H,xx x(gas) with k H = for an ideal solute in Ar Independent of where the solute is introduced (gas or liquid) Not relevant for dynamic system. For LAr cryostats, dominant process is k DESORP (T G ) Rate constant for each process implies a differential equation Solution of all eight coupled differential equations determines dynamic and steady- state impurity concentration in LAr (Henry’s Law}

Avoiding Contamination of Pure LAr Water Desorption by FR4 K. Weide-Zaage et al., Microelectronics Reliability 45 (2005) 1662 Desorption rate depends strongly on temperature 1.Keep sources of impurities in liquid or cold gas 2.Maintain large flow in gas to dominate diffusion k D (T) = Exp[-E A /k(T-T 0 )] E A = 0.32±0.06 eV LAr gives flow rate of 0.12 m/hr above liquid 42 nozzles for feedthroughs 4% of flow (1.6kW) thru nozzles produces 1.2 m/hr in nozzles 26 W heat loss per nozzle to flowing gas Lesson: In the liquid, don’t care; in the gas, beware!

Ambient Vacuum LAr Vacuum Feedthroughs Conceptual Design 1.Sense Wire Bias3 coax1kV 2.FE Power235 A 3.Digital Power2 5A 4.Control8 5.Output8 List of Connections ATLAS Barrel Cryostat Feedthrough Double flange design One flange: ambient - vacuum One flange: vacuum - LAr Cables in vacuum, LAr, and ambient only

FE Power Supply Lines DC-DC Converters vs. Direct Connections DC-DC Converters in LAr 1.2A = 57.6W FE Power + Lower heat input from leads + Regulation at load - Boiling of LAr - Local noise source Direct Connection thru LAr 32A = 57.6W FE Power - Higher heat input from leads - Regulation is remote + No boiling of LAr + No noise source

FE Power Supply Lines Computing heat load of power leads Solve steady-state 1D conduction equation to compute the temperature in power leads. Include: Joule heating in gas and liquid:  J 2 Convection in gas: -h(T(y)-T A (y)) Boundary condition in gas: 90K (liquid) & 298 (ambient) Solution gives: Heat into gas Heat into liquid Joule heat input Ambient heat input Temperature of leads in liquid is T(y) = 90K Since there in no thermal conduction through these leads, larger conductors can be used. FE power is 15 mW x 3840 channels Per APA = V and 32 A

Power Supply Line Temperatures Bare copperInsulated Copper32 amps Isothermal gas Minimum power is 3.94 W for 7 AWG Total power into cryostat is 1570 W for 7 AWG in gas and 4 AWG in liq.  V = 60mV (top) and 99mV (bottom) Minimum power is 6.07 W for 7 AWG Total power into cryostat is 2287 W for 9 AWG in gas and 4 AWG in liq.  V = 81mV (top) and 120mV (bottom)

Power Supply Line Temperatures Bare copperInsulated Copper32 amps Stratified gas Minimum power is 2.51 W for 4 AWG Total power into cryostat is 1088 W for 4 AWG in gas and 4 AWG in liq.  V = 41mV (top) and 80mV (bottom) Minimum power is 3.68 W for 6 AWG Total power into cryostat is 1480 W for 6 AWG in gas and 4 AWG in liq.  V = 63mV (top) and 102mV (bottom)

In-Vessel Electronics Infrastructure Summary Vacuum (or Ar gas) enclosure for cables Prevents contaminants in cables from entering LAr May interfere with installation Increases costs (budget assumes single flange) Direct powering of FE electronics FE power per APA is 58W Cable power loss per APA is 8-14W Total efficiency is 81% to 90% For power into LAr efficiency is ~93% Comparable to or better than DC-DC converter efficiencies Removes risk of LAr contamination from boiling Reduces costs (budget assumes DC-DC converters) Removes noise source But large voltage drops in lines And thick conductors difficult to route in APAs