Recent Changes to the FD TPC Design Bo Yu Oct. 20, 2015

Intro At the DUNE CD1-R review, and in the CDR, both the CPAs and the field cage were presented with their alternative designs. – CPA: All resistive material to reduce/slow the stored energy dump in case of a HV breakdown – Field cage: use metal roll-formed profiles to increase robustness and lower production cost An engineering meeting was organized Sept 7-11 to progress the design such that an integrated detector+cryostat ProtoDUNE CAD model could completed by year end. A few design decisions were made at the meeting, a list of questions (for FD optimization WG) collected and a list of engineering action items formulated. 2

Key Changes Field Cage – Progress toward the roll-formed field cage Lower cost, lower E field at given ground clearance, lower risk of damage – Reduce the field cage to cryostat / liquid surface clearance – Adding a ground plane 20cm beyond the field cage to prevent large E field in the gas ullage Mainly for the top. Although design will be identical for the bottom if needed CPAs – Construct the CPAs with resistive material – Baseline design is a ¾” thick construction with all flat external resistive surfaces 3

TPC Integration and Interfaces TPC suspension scheme – TPC Contraction: longitudinal ~ 10cm, transverse: ~ 2cm APA/Field Cage/CPA interconnect (mechanical and electrical) TPC interface with cryostat, cryogenics – Feedthrough sizes and locations – Cryogenic piping sizes and locations Installation (FD and ProtoDUNE) 4

Conceptual Layout of the TPC Top 5

Alternate Field Cage Design A more robust field cage 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. 6

Additional Views of the Design 7 Resistive divider and surge suppressor chain Corner treatment (UHMW PE caps, and optional PE angles) to minimize the exposed electric field

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 Perforated ground planes 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 PMT detects any light from discharges 8

Field Cage + Ground Plane Perforated ground plane 20cm above the field cage/CPA edge 9

Ground Plane Tile 1mm thick stainless steel, perforated with 10mm holes at 15mm center. Edges rolled up with 5mm radius of curvature, 2.3m x 0.5m each tile 10

Corner of the Ground Plane 45kV over 5cm, 5mm radius of curvature, 1cm gap between tiles, gas pocket 1cm above ground plane bottom surface. Max E at corner: 18kV/cm 11

Perforated Metal Sheet, Larger Holes 10mm holes at 15mm center, square pattern, 1mm thick 4 rounding radii: 0.8mm, 0.4mm, 0.2mm, 0.1mm Max. E field at R=0.1mm hole is about 30kV/cm A 2D (cylindrical) FEA shows 27kV/cm on the edge of a 10mm hole with 0.1mm edge radius 12

Side Panel Stainless Steel Elbow Internal stainless steel tube for added rigidity at the support Elbow Connections Vertical Pipe Previous Resistive CPA Construction 13 Small metal parts are allowed Missing features: “HV bus” Field cage interface May be difficult to make the frame member resistive (apply coating on non-flat surfaces) Raised frame structure distorts local drift field.

New Resistive CPA Design Resistive flat panels (1/4” thick) cover both sides of a thin frame (1/4” thick) structure. Total thickness: ¾” flat over the entire active surface Surface resistivity: M  /square Q: will a uniform 19mm thick dead space preferable than the previous design (50mmx50mm frame, 2mm face)? 14

HV Distribution Bus Concept HV cable without shield Or stainless rod wrapped in Mylar or Kapton insulation Bulk resistive material Conductive ring Screws to connect to the CPA Pin Center cable clamp Socket Omega Shielding Products Coiled wire for cable contraction With an high resistive cathode, we need a low resistance connection to each of the field cage dividers so that there is no accumulative voltage drop along the 60m long cathode. A HV distribution bus is inserted into the outer edge tube of the CPA

APA mounting (Workplan Int 1) 30 Sept 2015 Dan Wenman 16 Simple but custom trolley with swivel for compactness.

Rail mounting (Workplan Int 3) 30 Sept 2015 Dan Wenman 17 Chain for connection to adjustable mount point above roof. Yoke and clevis connection through slots in beam flange collar spring Seal plate

A New Electronics Installation Concept 18 A more modular electronics enclosure concept to allow access to the cold electronics board from only one side of the APA. This may also simplify the argon boil-off containment design for the lower APAs.