Update on the Region III Drift Chambers Klaus Grimm Hadronic Physics Group College of William and Mary, Williamsburg, VA

What is the max. possible size of the VDC, so that the outer aluminum Frames will not be hit by electrons of the adjacent octant ? Shielding wall not shown Conclusion: Max overall VDC length allowed : 280cm (~110”) VDC outer length: 245cm (96.5”) + Ferris Wheel hookup/support (xxx cm) Dual VDC Massive aluminum support simulation

VDC design changes Inner active area : 80.5”x 21”, avoid field distortion close to frame Wire angle changed from 30º to 26.57º (arctan[1/2]), s= 4.97mm Precision Dowel Pins wire

G10/FR4, G11/FR5, Ertalyte, Stesalam, … or what ?! Pyralux cross section view ( 5.4 mil = 137μm) Pyralux Layout with signal routing Wire readout with 2x9 flexible Kapton board (Pyralux sheets) How to glue Kapton on the frame with an uniform overall thickness (O-Ring runs across on top) ?! How to keep out air/humidity entering the VDC due to bad gluing (bypassing the sealing) ?! General Solution: Use epoxy prepreg (adhesive sheet) Caveat : Laminates can only sustain heat without damages up to the glass transition temperature (Tg). Note : Regular (Pyralux) adhesive is cured between ºC for 1-2 hours ( 175ºC used in Mainz on 4411W frame) Qweak Solution: Use epoxy preform TF D-18-1F from TechFilm. Glue Pyralux sheet for MaterialTg [C] G10~ FR4~140 G11~150 FR5~ W~160

Material Max. Deflection (μm) 4411W 64.6 G Ertalyte Aluminum 27.4 Frame Deformation The SolidWorks CAD geometry can be exported exactly into Ansys for Finite Element Analysis. The wire load per side with a stringing weight of 70g is ~10kg. Frame width is 6” (~15cm). The frame deflection is proportional to L² Total frame deflection should be < 200µm, otherwise gain loss due to sagging. Intrinsic wire sagging due to gravitation is ~20µm. (G10 is slightly stronger than G11)

G10/FR4, G11/FR5, Ertalyte, Stesalam, … or what ?! In NIM papers from BNL, Fermilab, and CERN about the usage of G10 for drift chambers: … cryogenic grade G10 was chosen to avoid any problems with boron contaminants which are known to bind with free electrons and cause a loss of signal. Side Note:

VDC Design Overview Single VDC Outer Dimensions: 96.5” x 45” x 5.5” Front-Electronics embedded inside the aluminum housing Housing + alum. Gas windows: Faraday cage Allows to add a secondary gas sealing Single 4411W Frame: ~30kg Single Alu Frame: ~90kg Dual VDC Weight: 737 kg Massive support on the sides holding the two single VDCs Attachment plate for “Ferris Wheel”

VDC Design Overview: Front-End Electronics Split up in Top/Bottom Readout: 2x9 FE channels Multiplexed readout (delayline) to the VDC sides, but also allows for individual readout (debugging and/or additional TDCs)

VDC Design Overview: Cross Section

Ferris Wheel Status Engineer Paulo Medeiros from JLab is assigned for designing the Ferris Wheel. Up to now JLab favors a rotator covering two opposite octants. The rotator will consist of two sliding rings where a box type support frame will be attached. Not much is done for the Ferris Wheel … Paulo is also responsible for designing the Shielding wall, beam pipe shielding and beam pipe support

VDC Frame Machining Issues: Warping G10/G11 sheets (48”x96”) are not stress relieved and machining the surfaces will lead to warping, making it even more difficult to handle. G10 companies don’t care about internal stress in sheets, only Atlas Fiber offers stress reduced sheets by sandblasting both sides on request. Stesalit delivers stress relieved 4411W sheets in any thickness. Final frame thickness is 0.5”. The G11-CR price jumps from ~$1000 (0.5”) to ~$1800 (0.625”). One Stesalit frame costs ~€1600.

VDC Frame Machining Issues: Precision Vertical wire position is defined by a precision bridge (like a guitar). The dimensions of the bridge (80.5”x21”, ¼” wide) exceeds the milling range of most companies Best available/assured precision in milling (without steps due to realignment): ±100μm (Waviness), ±50μm Roughness (Stesalit) A vertical offset translates 1:1 into the extracted vertical drift distance. The tracking is affected if the position offsets don’t average out over 5-6 drift cells.

Milling Oversize Groove Fill with Epoxy Mill again for O-Ring Groove Parker O-Ring Handbook: Max. 0.4μm surface roughness for gas sealing required. Stesalit tested surface roughness of medium size 4411W sheets after grinding (Epoxy resin + embedded glass fiber) : 5μm Surface Roughness can be reduced by refilling areas with Epoxy only (w/o glass fiber). Adding a secondary gas sealing (aluminum housing). (Primary Frame Sealing: ~48m O-Ring cord per Chamber) Possible Workaround VDC Frame Machining Issues: Gas Sealing

Wire Scanner: Wire Position Survey Purchased 48” standard ball screw translation stage ($5k) Includes position readout: 4μm resolution (attached glass rulers) Driven by a computer controlled stepper motor (1.8º/step -> 25μm translation) Wire Scanner Wire Frame Stringing Frame Custom 2 lense optics with CCD chip readout ( G Lense ~20, G total ~1000) Scanner will be controlled by LabView: first version of a working “Motor Commander” GUI To do: LabView CCD readout and wire centroid recognition Mechanical support for optics 2 nd optics looking at the same wire at 45º tilt angle for measuring a vertical wire offset Laser Table (10’ x 4’)

GARFIELD simulations What is the correlation between the vertical distance Yperp (above the wire) and the arrival time of the first drift electron hitting the wire ?! “xt-plot” Done : VDC characterization using Ar-C2H6 50:50 mixture (by volume), i.e. xt-plot, tx-plot, position resolution Currently : Simulation with different gas mixtures ratio - Ar-C2H6 for final operation (flammable) - Ar-C02 for initial operation (non-flammable) - include additives like Isopropyl, Ethanol, H20 Misc : Analysis of the raw Garfield output files is now entirely based on ROOT and superceds various Maple scripts

GARFIELD simulations Current Since ~summer 2005 Garfield is officially supported again by the Author Rob Veenhof at CERN ! With his support we managed to include the gas multiplication (avalanche) in Garfield. First test simulations were successful in extracting the induced wire signal, signal current, and signal charge. Upcoming: gain sensitivity (gas, HV, wire displacement/sagging).

The Front-End electronics will be controlled using an I2C bus for switching on/off individual channels, setting/reading thresholds, and chip temperature. Note: I2C is a low level serial communication bus system (~ dumb USB). Is e.g. used by INFN Italy to control straw chamber readout using MAD chips. Schematics Board Layout3D model JLab: - Schematics/Layout of FE and multiplexing (delayline) motherboard W&M: - Design of a PC->I2C adapter and some mockup boards which allows software development (Linux->I2C->FE) Front-End Electronics Honor student thesis

Software & Simulation to do list Global Tracking: How to combine the information of GEMs, HDCs, and VDCs for extracting the momentum, Q2, and background dilution ?! Tracking code must work for various magnet currents (QTOR and Mini-Torus) What is the impact of multiple scattering caused by the drift chamber foils (Mylar and Kapton foils) and possible Helium gas bags ?! What are the requirements on the drift chamber resolutions (position + angle) based on global tracking simulation?! Tim Smith: Global tracking was a non-trivial part of BLAST. It required iterative simulation for “swimming” electrons through the field for best Chi2. Event Generator: Geant4: Currently extracting the kinematics of scattered electrons from Geant3/PAW ntuple provided by Juliette and feed it into Geant4. Up to now only we have only a ROOT based elastic event generator (no internal Bremsstrahlung, no energy loss before/after vertex). Geant3/4: Simulate inelastic events + rates using the latest MAID version General Geant3/4: Include as much details of the experimental setup as possible, e.g. drift chambers, magnet support, target support/attachments, etc. Include Hall C background (Pavel code) Distribute and maintain up to date code and field maps via CVS. Start writing documentation … At some time … include CODA for mockup data simulation.

Problem: Current Geant4 visualization drivers don’t handle bodies created by boolean operations properly (union or subtraction). “What you see might not what you have defined” Example: chamfering the cerenkov detector (Michael Gericke) Coin3D Display Driver SolidWorks CAD Import + ( Industrial C++ Open Source 3D surface and solid modeling platform) Geant4 geometry -> OpenCascade geometry -> CAD import Workaround: Using OpenCascade for geometry validation Conclusion: Geant4 handles “boolean” geometry correctly but it is time consuming to validate it