1. ProtoDUNE TPC Electrical Design Bo Yu 7-March-2016

2. Outline ProtoDUNE TPC Overview Resistive cathode HV bus HV feedthrough cup HV filtering Modular field cage  Ground plane  Roll-formed field cage configuration  Beam plug  Laser window Overall schematic Summary 2

3. The Current TPC Model End wall field cage modules Top field cage modules with ground plane Calibration laser (4 total) HV feedthrough APAs CPAs Bottom field cage modules with ground plane Cable conduits TPC suspension pipe 3

4. Cathode Plane: Flat with Internal Frame Despite of moving the cathode planes away from the cryostat walls (LBNE configuration), there is still nearly 100 J of energy on each interior cathode when energized to 180kV due to the sheer size of the cathode planes. In the event of a discharge from a cathode edge to the facing cryostat wall, there is a risk of physical damage to either the cathode or the membrane. The voltage on an all metal cathode will collapse very quickly, injecting high current into the cold electronics through the APA wires, risking damage to the front end ASICs. This issue has been studied in detail. See Sergio’s talk. To minimize these risks, we have developed several cathode designs that use nearly all highly resistive surfaces (1-100M  /  ). This will greatly reduce the peak power transfer to the cryostat and peak current injection into the front-end ASICs in a HV discharge. Several types of resistive surfaces have been investigated (See talk by Francesco). The preferred solution is to use Dupont 100XC10E7 Kapton film (surface resistivity about 2M  /  ) laminated on G10 substrates. 4

5. Cathode Plane: Flat with Internal Frame The cathode plane is constructed from 6 columns, each is half the width of the 2.3m wide APA. 3 modules per column to form the 6m total height Resistive panels tile over internal G10 frame Total CPA thickness: ~ 2.5cm Nearly completely flat outer surface 5

6. Cathode Plane: Rounded Outer Edges Metallic brackets connect panels both mechanically and electrically Main hanger internal stainless steel reinforcement G10 hanger Resistive tube Metal elbow & tee 6

7. Cathode Plane: Thin with External Frame Similar module sizes and assembly Majority of the cathode surface area is only about 3mm thick The thicker frame has outer resistive surface electrodes bias at a different voltage to improve the external drift field. Fiberglass channel (63x63x6mm) Resistive panel (3mm thick) Resistive strips with a different bias 1.15 m Vc+1587V Vc 7

8. HV Distribution Bus Concept HV cable without shield Or stainless rod wrapped in Mylar or Kapton insulation Bulk resistive material to limit peak current Conductive ring Screws to connect to the CPA Pin Center cable clamp Socket Omega Shielding Products 099-543-00-20 Coiled wire for cable contraction Since the entire cathode is highly resistive, we must find a different way to distribute the cathode bias voltage to all the CPAs without significant voltage drop. The rounded outer edges of the cathode plane is a good place to implement such a bus 8

9. HV Bus Integrated into a CPA Module This concept needs to be modified to allow for a few mm of vertical relative movement between CPA modules to accommodate roof deflection: Change the circular pin and socket into rectangular ones Or use screw and wire lug to connect the bus together. Stainless steel reinforcement 9

10. HV Feedthrough Receptacle Dan checks the alignment of the 35ton HV feedthrough receptacle. The donut is completely vented Rotate along this tube Dan checks the alignment of the 35ton HV feedthrough receptacle. The arm length can be a adjusted We need to design a spring loaded tip to allow height tolerance 10

11. Surface Field Near the HV Feedthrough Wall to FC distance 1m, FT center to FC: 44cm, FT shield rim lined up with ground plane. 11

12. Surface Field Near the HV Feedthrough Wall to FC distance 1m, FT center to FC: 29 cm, FT shield rim lined up with ground plane. Moving the donut closer to the cathode reduces the field on the donut Prefer to have the shield of the FT lower in the liquid to reduce the chance of LAr boiling at the bottom of the shield to avoid HV discharge. As the FT is lowered, the field on the bottom of the FT shield increases, because it gets closer to the field cage. 12

13. WA105 HV Feedthrough Design HVFT for 300kV with Rogowsky profile electrodes 13

14. HV System Filtering Requirements The Heinzinger PNChp power supply has a ripple spec of 10 -5. In order not to inject significant charge to the ASIC ( 2000 at the ripple frequencies. ENC of ASIC600e max noise injection100e 1.6E-17c capacitance of an APA to CPA5.09E-11F capacitance of a G wire to CPA8.48E-14F capacitance of a U wire to CPA1.70E-14F maximum ripple voltage9.43E-04V Cathode Voltage180000V Power supply output ripple @ 1E-51.8V attenuation factor needed in the filter1908 14

15. PD Calibration Fiber Diffusers 6.9 m 6.0 m UV diffuser locations, to illuminate the left APA (similar arrangement would be realized on the opposite side of the CPA, to Illuminate the right APA). Quartz Fiber SMA Connector Fiber End Quartz Diffuse Glass UV Reflector CPA See Zelimir’s slides 15

16. The Field Cage Components Top and bottom field cage modules have integrated ground plane panels to shield the high voltage from leaking into the top and bottom service regions:  Top: gas ullage and rails  Bottom: cryogenic pipes End wall field cage modules have no accompanying ground planes. Beam plugs and calibration laser windows are integrated into certain end wall modules Each field cage module has its own resistive divider network to maintain a linear voltage distribution along its length. The field cage profiles are electrically isolated between modules to minimize peak energy dump in case of sparks 16

17. The Ground Plane The purpose of the ground plane above the field cage is to shield the fringe field from the CPA/FC from entering the gas ullage to cause breakdown. The top and bottom FC modules are designed to be symmetrical: there is a ground plane by default on the bottom. It is not clear if the bottom ground plane is needed if the cryogenic services are not too close. The ground plane is stamped from 1mm thick stainless steel sheet. With corner radii of 5mm. The grounding of the ground plane should made away from the APA/CE feedthroughs: grounding the modules to the mechanical feedthroughs? 17

18. Field Cage with Roll-Formed Profiles 18 A more robust field cage than the PCB construction in the 35ton can be constructed with roll-formed metallic profiles. The example below shows the electric field on the highest biased field cage electrodes can be controlled to under 12kV/cm using this profile even with only a 20cm ground clearance. If we can find a safe way of dealing with the ends of the profiles, this construction could allow a reduction in the top and bottom TPC clearance and make more efficient use of the LAr.

19. E Field at the Corner with PE Caps 20cm ground clearance, -180kV, UHMW PE cap thickness: 5mm The exposed field in the LAr is ~ 25kV/cm The field in the LAr is ~ 50% higher than the PE cap surface due to dielectric constant difference Plot of the E field on the symmetry plane bisecting the metal profiles 19

20. Outer FC Surfaces Aligned with CPA 180kV on CPA, 3kV between profiles, 50mm CPA tube, 20cm ground plane clearance at top and 30cm on left. Ground: 20cm Ground: 30cm 20

21. Drift Field Uniformity Near FC Edge Gray contours: 2% of nominal drift field Profiles at 6cm pitch, ground plane 20cm above Active volume is 5cm away from the inside surfaces of the metal profiles 21

22. Roll-Formed Field Cage Test Setup To validate the field cage concept in pure LAr Designed to fit in the ICARUS 50 liter cryostat Roll-formed metal profiles with UHMW PE caps –Choice of metal (Al, SS) and surface finish Pultruded fiberglass I-beams form 4 mini panels All profiles are at same potential to simplify HV connection Ground planes only 66mm away Requires 1/3 of FD bias voltage to reach same E field Ground planes can be connected to external amplifiers to monitor micro-discharges Video camera to monitor bubbles and sparks Holding 100kV (see Francesco’s talk) 22

23. Field Cage Transient Response in a Discharge The resistors along the divider provide a linear DC voltage gradient. However, at shorter time scale (<<1s), the electrical behavior of the divider is determined by the varies capacitances on and between each electrodes. This divider is no longer linear at this time scale. A perfect capacitive divider requires the capacitance of each node to ground to be 0. In reality, there is always a finite capacitance from each node to ground. These capacitances “resist” change in the voltages on the nodes. In the event of a HV breakdown between the cathode to ground (cryostat), the cathode voltage quickly collapses to ground, but the first field cage strip to ground capacitance keeps its voltage from changing instantaneously to follow the cathode voltage, results in a momentary larger voltage differential between the cathode and the first field cage strip. This voltage differential can be a significant fraction of the cathode operating bias, large enough to cause HV breakdown between the two electrodes, or worse yet, destroy the resistors between the two electrodes. The natural solution to this problem is to add additional capacitance between the nodes of this divider. See MicroBooNE docdb 3307 for summary of the analyses 23

24. Surge Suppressor Studies An alternative to adding capacitance between divider nodes is to use surge protection Extensive tests have been done by MicroBooNE (docdb 3242, arXiv:1406.5216v2) on the use of varistors and GDTs (gas discharge tubes) as a mean of limiting the over voltage condition in the event of a HV discharge in the TPC. Both types will work for the purpose of restricting the voltage differential between field cage rings in LAr temperature. A GDT quickly shorts the terminals when the voltage differential exceeds a threshold A varistor changes its resistance to keep the voltage differential near the threshold voltage. The smooth transition and well defined clamping voltage of the varistors are preferred to the abrupt switching of the GDTs. The varistors would also function as redundant “resistors” in a divider chain. Left: varistor Right: GDT 24

25. Resistive Divider Network We need to use 3 such varistors in series between profiles if we want to have the ability to reach more than 500V/cm drift field in ProtoDUNE. Two resistors in parallel to provide redundancy. 25

26. Divider Resistivity Range 26 LAr TPC signal current due to surface cosmic rays length of CR tracks14904m/s total energy loss3159648MeV/s2.12MeV/cm total charge deposition2.14213E-08C/s23.6eV for Argon survived charge1.42809E-08C/s equivalent current1.42809E-08A14nA let the divider current be 100 times1.42809E-06A total resistance over 3.6m is1.3E+11ohm130Gohm field cage strip pitch6cm number of divider60 resistance per divider2.1E+09ohmthis is the upper limit Power supply side limitation HV power supply current limit1mA number of field cage panels64 worst case, middle CPA, double field cage max allowed current on each panel15.63uA set to 1/3 power supply limit5.21uA total resistance2.2E+10ohm resistance per divider3.7E+08ohmthis is the Lower limit

27. The Current Design of the Beam Plug 27

28. Potential Contours at Beam Window Center Plane The field cage has a cutout, and the 20cm beam window (insulating plug) is placed through this opening, 5cm into the field cage. This plug is assumed to be air (thin wall ignored) in this model. Due to the ground plane (cryostat wall, ~30cm away in this model) and the hole in the field cage, there is a strong E field pushing electrons toward the face of the plug. If the plug penetrates much deeper, the distortion near the beam window face diminishes. However, there could be surface charging on the side wall of the insulating plug, causing other kind of field distortion. Cathode side Anode side 28

29. Potential Contours at Beam Window Center Plane with Field Shaping Strips over the Beam Plug 29

30. Schematic for Resistive Dividers with Beam Plugs Need to make electrical connection to the cryostat wall 30

31. Laser Windows on the Field Cage Calibration laser beams have angular coverages of ±45° in both vertical and horizontal directions. Beam windows size ~ 2x the laser port center to FC distance Need two crossing beams to uniquely identify a 3D point inside the TPC Top view (1 drift) Side view Laser heads and beam windows in SBND (an earlier design) If the windows are not located at the boundary between two FC modules, we need to have two R divider chains (one above and one below the opening). 31

32. Field Near a Laser Window An opening on the field cage causes distortion in the drift field near the opening: the electron drift lines bend out toward the opening. The larger the window, the greater the extend and severity of the distortion. Extending the FC electrodes out toward the cryostat wall can reduce the distortion, but increase the E field on the exterior field cage surface. 32

33. HV System Schematic Diagram 33

34. APA Bias Schematic Diagram 34

35. Summary Resistive cathode design is progressing well  2 configurations, need a decision this week Field cage electrode configuration has been verified in a small setup with full E field  1 configuration (fully assembled modules) almost complete, ready for mechanical mockup  Transition toward assemble sub modules in cryostat A beam plug design available,  Working on FC integration (mechanical / electrical) Laser windows not yet designed  Decide on the laser feedthrough ports locations this week Need to update HV system electrical schematic and submit to the Grounding/Shielding committee for feedback. 35

36. Backup slides 36

37. Proposed design of DUNE HV FT (UCLA) Total length: 3 meters (30 inch airside, 88 inch argon side) UHMW-PE Insulation: OD= 4in, ID = 0.75 inch OD Stainless steel tube precision bored by gun barrel drilling company UHMW-PE ID drilled by same same company Inner conductor using solid core to avoid gas pockets: Cable plug scaled from existing plug design (not shown) 8 inch long grooved tip Integrated guide ring 10 inch long cryo-fit seal 37

38. New SBND Calibration Laser Configuration Place the laser beams at the 4 top corners of the TPC. Pros: –Full coverage –Shorter column – more stable Cons: –Somewhat more complex –Need prototyping/testing 38

39. SBND Laser Port: A View from Below 39

40. Field Cage with Profile # 1097 Ground plane 20cm above -180kV -177.5kV -175kV Max. E field <15kV/cm 5cm 40

41. Field Cage with Profile # 1746 Ground plane 20cm above -180kV -177.5kV -175kV Pitch: 5cm (2.5kV) Max. E field <13kV/cm 5cm 41

42. Field Cage with Profile # 1746 Ground plane 20cm above -180kV -177kV -174kV Pitch 6cm (3kV) Max. E field ~15kV/cm 6cm 42

43. Field Cage with 38mm tube (1.5”) Ground plane 20cm above Pitch 6cm (3kV) Max. E field ~15kV/cm 6cm 43

44. Field Cage with Profile 1763 Ground plane 20cm above Pitch 6cm (3kV) Max. E field <13kV/cm 6cm -180kV -177kV -174kV 44

45. Field Cage with Profile 1071 Ground plane 20cm above Pitch 6cm (3kV) Max. E field ~12kV/cm 6cm -180kV -177kV -174kV 45

46. E Field at a GTT Knuckle When faced with a 180kV conductive plane 20cm above the knuckle tip: The maximum E field at the tip of the knuckle is 40kV/cm. The field at the ridges of the corrugation is about 20kV/cm. The facing HV plane has a maximum E field of 7.5kV/cm, average about 7.4kV/cm. At 50cm clearance: The tip field <15kV/cm At the HV plane: E~3.3kV/cm Based on these field values, the equivalent “flat” membrane distance is about 3cm above the real membrane flat: 180kV/7.4kV/cm ~24 cm, 180kV/3.3kV/cm~54cm. 40kV/cm in the liquid near the top of cryostat is high. But on the bottom of the cryostat where the pressure is 2atm higher and boiling point is 11K higher than the liquid temperature, the field may be acceptable. 46

47. Fiducial Cut on the Thin CPA Design If we apply a fiducial cut of 100mm around the frame, the area of 174mm x 133mm would be the cut at the cathode every 0.58m (half of the new half width CPA). This averages to ~40mm over 0.58m instead of ~110mm in the case of the double walled configuration. 47