CLAS12 Drift Chamber Review

Mechanical Engineering

Presented by

David Kashy – Hall B Lead Engineer

Presentation Overview

• System review

• Design strategy

• Status of the design for each Region

• List of mechanical calculations

• Concepts for handling and installation

• Cabling

• Survey, alignments, maintenance

• Safety implementation in the design

• Summary

CLAS 12

An upgrade to Experimental Hall B

Much of the infrastructure including some detectors, magnets and power supplies and structures will be kept.

CLAS 12 Detectors

Region 3Downstream of the Torus

Region 2Between the Coils

Region 1 Upstream of the

Torus

Design Strategy

• R1 and R3 wire loads taken by the structure of each sector independent of other sectors or external supports

– R1 will have a frame that supports the end plates

– R3 will be similar to R3 of CLAS with regular struts on the upstream face and a stiff shell at the exit

• R2 wire loads will be transferred to the CLAS12 Torus

– This is similar to how R2 was implemented in CLAS

– It minimizes the material in the particle path for accurate tracking

• All regions mounted to CLAS12 Torus

Forward Tracking Assembly

Three regions of 6 sectors each are connected to the CLAS12 Torus.

Mounts must support the chambers, and provide positive position knowledge and electrical isolation.

Mounting all chambers to the torus will allow repeatable positioning and accurate surveying will give knowledge of the locations.

Region 1 - A self supporting detector

•This frame is designed to:

• Support the end plates

•Take all forces including gravitational, window and wire loads

•Support onboard electronics boards

•Support patch panels (not shown)

•Provide points for lifting, mounting and alignment

Region 1 Assembly

•Assembly shows:

•Frame

•End plates

•Some of the almost 5000 wires

•Space for electronics boards

•On board cables not shown

•Central mounting hub

R1 Design Status

• Collaborative effort with Old Dominion University

• Stress and deflection analysis completed for the R1 Prototype

• The prototype includes significant details of final detector

• End plates for prototype out for fabrication

• Box frame design complete and drawings out for bid

• Survey and alignment plan being developed

• Support and lifting hardware to be done

R1 Prototype End Plate Drawing

Two end plates released to local vendor for fabrication

Datum hole

4925 x 3.96 mm diameter feed through holes with true position tolerance of 0.20mm

Alignment hole

1890mm

FEA deflection of R1 Prototype

Peak deflection 1.83mm

Peak stress 43 MPa (~6.3ksi)

R2 Design Status

• Similar to R2 design of CLAS

• CLAS12 R2

– Will also use tension transfer

– Non conducting end plate (no eddy currents)

– Chamber walls (end plates, back plate and nose plate) will be assembled and temporary struts will be installed.

– During installation wire loads to be transferred to the Torus Vacuum case

– Spring mounts will be used very similar to CLAS. A displacement of the vacuum case of 2 mm will result in 30% change in force on the end plates and less than 30% load change in the wires.

• Preliminary stress and deflection analysis completed

• Interdependent with the TORUS Design (we have provided guidance to the ITEP/Efremov group)

R2 3D Model

• Non conducting end plate selected to avoid eddy currents in case of a Torus magnet quench

• Deflection analysis complete

• During stringing there will be struts to hold the end plate locations (not shown see next slide)

• Notice the holes for attachment to the Torus

Mounting holes for

spring mounts

Mounting holes for

hard mounts

CLAS R2 on stringing fixture

Photo Summer 1995

R2 support system from CLAS

Hard mount side Spring mount side

End Plate

Region 3 Design Status

• Collaborative effort with Idaho State University Similar to design for CLAS

• Design basis is again a self supporting chamber– with 4 permanent compression rods (thin wall

carbon tubes) on the upstream face – full carbon sandwich skin on the downstream

face• A preliminary deflection analysis completed

List of Calculations

• End plate stress and deflection due to wire and window loads

• Wire deflection due to gravity• Temperature change effects• Support system stress and deflection• Strongback stress and deflection• Lifting tooling stress and deflection

R1 Wire Analysis

Material Units  W Al SST

Number of wires - 1344 3136 448

Diameter micron 30 140 140

Length of longest wires m 1.60 1.60 1.60

Density g/cc 18.5 2.7 7.8

Tension load g 20.7 63 185

Yield strength ksi 225 37 260

Operating stress ksi 41615 5816 17078

Longest Wire sag mm 0.20 0.21 0.21

Wire stretch (longest) mm 1.42 0.85 0.98

% of yield strength % 18% 16% 7%

Wire Sag and End Plate Results

   UnitsRegion

1Region

2Region

3

Max wire length m 1.60 2.61 3.50

Longest wire deflection due to gravity mm 0.20 0.54 0.97

Number of intermediate supports - 0 3 4

Total bow of end plate in both directions mm 1.83 0.36 0.32

Window effects

• The gas pressure will cause additional loads on the end plates tending to bring the plates together

• Greater bow will reduce this effect.

• First round calculations for each chamber have been performed.

• Design based on getting an increase of less than 10% of the wire load during normal operating conditions. Important because increase of load after stringing will reduce wire preload and change sags.

Window Calculation

Window Load and stress Calculation  

R1 PeakR1 Normal Operating

R2 PeakR2 Normal Operating

R3 PeakR3 Normal Operating

Maximum bow in the window in 1.5 0.9 5 2.7 1.5 1

Pressure in the detector in H20 0.2 0.04 0.2 0.04 0.2 0.04

Window film thickness in 0.001 0.001 0.001 0.001 0.001 0.001

Equivalent OD of window in 57.6 57.6 94.1 94.1 59.0 59.0

Stress in window film psi 1000 340 800 300 1000 350

Window Diameter in 57.6 57.6 94.1 94.1 59.0 59.0

Window Radius in 28.8 28.8 47.1 47.1 29.5 29.5

Window Thickness in 0.001 0.001 0.001 0.001 0.001 0.001

Window Curvature in 276.8 470.56 221.44 415.2 276.8 484.4

Window depth in 1.50 0.88 5.06 2.68 1.58 0.90

linear elongation - 1.0014 1.0005 1.0058 1.0016 1.0014 1.0005

modulus of elasticity psi 720000 720000 720000 720000 720000 720000

stress stress 980.2 338.1 4147.6 1162.8 1027.1 334.3

end plate load due to films lb 144.1 49.0 188.2 70.6 157.3 55.1

end plate load due to pressure lb -5.4 -1.1 -13.4 -2.7 -22.4 -4.5

total load on end plate lb 138.7 47.9 174.9 67.9 134.9 50.6

Percent increase on end plate   20.4% 7.1% 25.8% 10.0% 19.9% 7.4%

Cabling

The overall cabling concept has on chamber cables tied into a patch panel. Cables to the main electronics will tie to that patch panel. Thus cables can removed when necessary for major maintenance. The layout shown above will be detailed and proven out in the R1 prototype effort.

Cable Keep Out Zones

Blow up pic

•Keep out zone for running cables to the Space Frame will allow service by the crane for other detectors

(View from overhead crane)

DC Handling and Installation

• Goal to pick up each sector of the chambers by the back plate using a “strong-back” lifting fixture. This will allow minimal down time for repairs.

• DC wire tension should not change more than 20% while doing maintenance. This will minimize the chances of wire breakage during maintenance or original installation

CLAS R3 at original installation

Survey and Alignment

• JLab S&A group tooling

– Laser tracker

– 3D manual probe

• Planned surveys include

– End plate hole to hole accuracy

– End plate hole to frame transfer

– End plate deflection during and after stringing

– Surveys of mounting hardware on the Torus

– As found surveys on all sectors relative to the Torus

SafetyHazards:• Electrical (Chris will address these)• Mechanical

– Window bursting – Protected by control system and over/under pressure bubblers

– Rigging – Lead by persons with “Master Rigger” qualification and using reviewed and tested hardware, while following approved procedures

– Temperature – Hall is temperature stabilized, and backed up with automated On-Call system to call in experts

• Gas– We are using non flammable gases

– Cryogenic liquid Ar and CO2 - Standard Cryogenic Safety procedures are part of the JLab EH&S program

Summary• Detailed analysis of R1 prototype stress and deflection complete

and mostly applicable for final R1 chamber.

• First round analysis of R2 and R3 endplates and wire done

• Hardware for R1 prototype is being fabricated

• R1 prototype will help confirm that our analyses are correct and complete. It will help in reducing the startup time for fabrication of the other chambers

• Tooling for stringing and handling the chambers will be similar to CLAS but have yet to be detailed.

• Most of the original Hall B staff that built similar but more complex and larger drift chambers are on this project. This experience will help us to be successful with all aspects of the CLAS12 Drift Chamber System