# Presentation: 302173

## TQC  Progress R. Bossert

***bnl - fnal- lbnl - slac***

_**US LHC Accelerator Research Program**_

- LARP Collaboration Meeting
- April 26-28, 2006

## Introduction

**The TQC structure is an extrapolation of successful work done on previous magnets.  Many cos theta magnets with the collar/yoke/skin structure have been made at Fermilab and elsewhere.**

**Tevatron dipole and quadrupole, SSC dipole, Tevatron LBQ, MQXB (LHCIR Quadrupole) all have been produced at Fermilab using a similar structure.  **

**TQC01 is the first of the TQC short model series to be built.  Coil manufacturing is complete. Mechanical model work has been taking place over the last 6 months and is being completed this week.   Assembly is beginning this week. **

## TQC01 Objectives 

** ****Design, fabricate and test a 1m long, 2 layer, 90mm Nb3Sn quadrupole model using mechanical support structure based on 25mm thick SS collars.  Compare magnet performance with the design parameters.**
** ****Provide input for a consistent comparison between the properties of a collar-based structure and an aluminum shell-based structure (TQS model).**
** ****Use the same coil design for both TQS and TQC models. **

## TQ coils

**TQC coils are identical to the coils used for TQS models assembled at LBNL. **

**Coil:**
**2-layer shell-type**
**Inner-layer wedges**
**Inner-layer pole glued into the coil**
**Cable:**
**Strand – MJR, 0.7 mm**
**Number of strands – 27**
**Keystone angle – 1 deg**
**Width – 10.077 mm**
**Thickness – 1.26 mm**
**Insulation: 0.125 mm S2-glass sleeve**

## TQC parameters

| 
Parameter | Unit | TQC01 |
| --- | --- | --- |
| Number of layers |  | 2 |
| Number of turns |  | 136 |
| Coil area (Cu + non Cu) | cm2 | 29.33 |
| Assumed non-Cu Jc at 12T, 4.2K | kA/mm2 | 2.0 |
| Quench Gradient 4.2K/1.9K | T/m | 215.6/233.1 |
| Quench Current  4.2K/1.9K | kA | 12.94/14.07 |
| Peak field in the coil at quench 4.2K/1.9K | T | 11.2/12.1 |

_**TQC01 Specifications**_

## TQC  Structure - Design Approach

- _MQXB cross-section._

**This basic structural system was used at Fermilab on the Tevatron magnets.  Variations have been used successfully on the Tevatron LBQ, the SSC dipole, and most recently the MQXB (LHC IR quad).  **

**The TQC design is based on the MQXB mechanical structure (collar, yoke, skin, end plate,etc.). **

**The collar/yoke/skin structure has proven to be reliable and reproducible for short as well as full-length magnets. **

## TQC mechanical structure

**Based on structural analysis, specific features of the LHCIR quadrupole have been modified, and features have been added to allow this system to meet the requirements of the higher field Nb3Sn magnets.**
**Shims are added between collar and yoke at each midplane to allow preload to be shared between skin and collars and control collar-yoke interference.**
**Outer layer poles have been retained for coil alignment.  Inner poles are impregnated into coil.**

_**TQC cross-section.**_

## TQC Mechanical Structure

**A radial cut is made in each yoke quadrant to provide symmetrical loading to the collars. **
**Control spacers are introduced for collared coil alignment and yoke motion control.**
**12 mm thick stainless steel skin, increased from 8mm used for MQXB. **
**Mechanical structure and coil pre-stress is studied and optimized using a series of mechanical models.**

## TQC mechanical structure – End Loading

**End load in TQC01 will test the “minimal” axial end loading system.  Load is applied by a combination of radial force through the collars by the skin, and end force applied by four preload screws, or “bullets” through 50mm thick stainless steel end plates.  A total force of 14000N (3000 lbs.) is applied to each end.**

**This system is identical to that which has been proven effective on Nb****3****Sn dipoles at Fermilab.  It is designed to ensure that the magnet ends are in contact with the bullets during all phases of cool-down and operation.  HFDA06, a recent dipole model, was tested with this system and remained preloaded during all phases of operation.  The TQ structure is similar to that of Nb3Sn dipoles.  **

**3D FEA of structures has taken place at both LBNL and FNAL.  Analysis indicates that, depending on input parameters and end loading, separation between end parts and first turn of coils of between 20um and 200 um can take place when the magnet is powered. **

**Effect of this separation on training behavior is not clear.  There is evidence from racetracks at LBNL that a correlation exists between gaps and training.   Many magnets built and tested at Fermilab, both Nb3Sn and NbTi, with minimal and no end loading, have not exhibited excessive training quenches in the ends. **

## TQC 2D Mechanical Analysis

## TQC Assembly – Insulation and Collaring

**Impregnated coils are assembled and surrounded by layers of Kapton ground wrap.**
**Assembly is hung vertically over collaring press, and collar packs are placed over coils.**

## TQC Assembly –Collaring

**Initial pressure is applied by main cylinders, then key cylinders are energized.  Multiple passes are applied, with key depth controlled and incrementally increased with each pass.**

**Collars are incrementally keyed, in 8 cm. longitudinal sections, applying azimuthal preload to the coils of 70MPa after keying is complete.**

**Mechanical model studies indicate that differential pressure between keyed sections can be controlled to within 15 MPa.  **

## TQC Assembly – Yoke and Skin

**Control spacers, preload shims, yoke packs and skin are assembled in the yoke press.**
**Hydraulic pressure is applied and skin is welded in several passes, applying the fully assembled preload of 140MPa to the coil through the preload shims.**
**Preload to coils from yoke/skin is limited by the control spacers at room temperature.**
**During cooldown, parts shrink, allowing preload on coils, still limited by the control spacers, to increase to 150MPa.**

## TQC Assembly – Ends and Splices

**End plates are welded, and torque is applied to end preload bolts.**

**NbTi midplane leads are formed into appropriate shapes, and leads are spliced.**

## TQC01 Status - Coils 

**4 coils were wound and cured at Fermilab, reacted and impregnated at LBNL.  Now ready to assemble at Fermilab.**

**Spot heater**

## TQC01 Status – Mechanical Models 

**Several mechanical models have been produced.  Purpose of the Mechanical models:**

** ****Understand coil size, midplane shims and collar yoke shims.**
** ****Compare coil preloads with anaylsis.**
** ****Understand how collaring process works with Nb3Sn coils.**
** ****Understand and verify yoke welding process.**

**Mechanical Model #1 - A preliminary model using an aluminum tube with collar structure was used to confirm analysis of collared coil assembly.  Strain in the aluminum tube was measured while the collaring keys were inserted, incrementally, in small steps until they were fully inserted.  Azimuthal stress in the aluminum tube increased by approximately 15 MPa per mm of key depth.  Since key depth can be controlled during the keying operation to about 1mm, the incremental stress between keyed sections can be controlled to within 15 MPa.  **

## TQC01 Status – Mechanical Models 

**Mechanical Model #2 – Used practice coils 1 and 3 – End areas were collared with “full round” collars.  Purpose was to understand collaring process over ends using full round collars as well as understand yoke welding process with TQ coils.   Some straight section was also collared with full round collars.  **

**Results:**
**  ****Collaring with 125 micron (5 mil) midplane shims yielded preloads within the acceptable range.**
**  ****Yoke welding alignment gap and weld pass numbers were established which provide necessary movement for yoke to close onto control spacers, therefore providing the 140 MPa to coils necessary for completed magnet .**

_**Mechanical Model #2**_

## TQC01 Status – Mechanical Models 

**Mechanical Model #3 – Used practice coils 1 and 3 – intended to understand collaring process over straight section with “tabbed” collars and differences between inner and outer preload.  Capacitor gauges placed at all inner and outer midplanes.    Collar deflections and gauge readings after keying showed large differences in size and preload between quadrants, indicating  side-to-side variations between coils. **

_**TQC01 Mechanical Model Configuration**_

_**Normal TQ configuration**_

**Q4**

**Q3**

**Q2**

**Q1**

**S**

**S**

**S**

**S**

**L**

**L**

**L**

**L**

**As a result, a “full round” configuration was chosen for TQC01, until precision and placement of components within the coil cross section is completely understood.**

## TQC01 Status – Coil Measurements 

**Due to the results shown in mechanical model #3, measurements of the coil cross section were taken on an optical comparator.  Two sections of practice coil #4 have so far been measured.  Preliminary results indicate that coils have no significant side-to-side variations.  More sections still need to be measured to understand coil consistency.  **

## TQC01 Status – Coil Measurements 

**Conclusion:  differences in size of inner and outer layers on optical comparator measurements are due to the coil being relaxed slightly when sectioned in the free state.  **

**Also, practice coils 2 and 4 were pressed in a fixture at azimuthal preloads up to 60 MPa with Fuji film placed at the midplanes.  Results show very uniform preload across both layers, indicating there are no significant differences between size of inner and outer layers.  **

## TQC01 Status – Mechanical Models 

**Mechanical Model #4 – Practice coils 1 and 3 were re-collared using full round collars and capacitor gauges on both inner and outer coils.  Results showed that large variations in collar deflections were eliminated, as expected, but capacitor gauges indicate large preload variations between outer coil quadrants.  Conclusion:  Either practice coil 1 or 3 has an anomalous size at some cross section or the coils have been damaged from extensive handling and use.   **

**As a result, MM4 is not being used to determine mid-plane shims, but can still be used to verify weld processes and collar-yoke shim size.  This model is ready to be welded.  Welding will be completed on May 1****st****.  **

**Mechanical Model #5 – Practice coils 2 and 4 have been collared with full round collars, using a range of shims from 0 to 125 microns, and Fuji film at the midplanes.  Purpose is to determine preload shims.  This model has been completed.  Based on this data, preload shims of 50 um will be placed at each midplane when coils are assembled.  **

## TQC01 Instrumentation 

** ****Voltage taps applied to coils through traces, as in TQS  design.  Outer coil positions identical to TQS.  Inner coil positions identical to the TQS positions, with 2 taps added.**
** ****1 strain gauge on inner surface of each pole, on lead end key/island, measuring longitudinal stress, identical to gauge position on TQS01.**
** ****Strip heaters embedded into outer coil  traces (identical to TQS01).**

## TQC01 Instrumentation 

** ****Spot heaters on outer layer of two coils. **

** ****Strain gauges on control spacers.**

** ****4 strain gauges bonded to inner surface of each inner coil to measure inner coil preload.**

## TQC01 Instrumentation 

** ****Strain gauges on skin.**

** ****2 temperature sensors, one near each end in yoke.**

** ****Strain gauges on end preload screws (bullets).**

## TQC01 Schedule 

_**FY05**_:
- Design of cable, coil, and tooling: 	FNAL+LBNL;	01/15/2005  Complete
- Fabricate and insulate practice cable: 	LBNL; 	  	04/15/2005  Complete
- Procure coil fabrication tooling/parts: 	FNAL; 	  	05/01/2005  Complete
- Procure mech model parts:	 	FNAL; 	  	07/15/2005  Complete
- Wind & Cure 2 practice coils: 		FNAL+LBNL;  	08/01/2005  Complete
- React & impregnate 2 practice coils:	FNAL;		09/15/2005  Complete
_**FY06:**_
- Wind/cure coils: 			FNAL;		12/20/2005  Complete
- React/impregnate coils:		FNAL; 		04/15/2006  Complete
- Assemble and test mechanical model: 	FNAL; 	  	05/1/2006
- Assemble magnet:			FNAL;		06/16/2006
- Test magnet: 			FNAL;		07/07/2006

**Construction of TQC01 is beginning this week.**

## TQC02  

**Objectives are: **
** ****To fabricate and test a 2nd 1-m long, 2-layer, 90-mm Nb3Sn quadrupole model using the collar/yoke mechanical structure. Compare magnet performance with the design parameters and the performance of TQC01 and increase the statistical “database” for TQ short models.**
** ****Provide input for a consistent comparison between the properties of a collar-based structure and an Aluminum shell-based structure (TQS models).**
** ****Refine design features based on construction experience and/or testing of TQC01.**
** ****Incorporate RRP strand in TQ coils and structure.**

**6 unit lengths of TQC02 cable has been fabricated, but there are some questions concerning stability.  Coil fabrication will begin as soon as new cable will be manufactured.**

## Summary

** ****Coils for TQC01 are complete.  They are at Fermilab ready to be assembled.**

** ****Mechanical model work on collared coils for TQC01 is complete.  Yoke and skin welding of the final mechanical model will be completed Monday May 1****st****.**

** ****Construction of TQC01 has begun.  Coils are being instrumented this week.  Assembly will begin May 1****st**

** ****Coil winding of TQC02 has not started, but will begin as soon as new cable is available.**