# Presentation: 033285

_***J.H. Schultz***_***, P. Titus, J.V. Minervini***
_**M.I.T. Plasma Science and Fusion Center**_
**Burning Plasma Science Workshop II**
****
****
- May 1-3, 2001

- Advanced Magnets and Implications for BPX-I

## Issues in BPX Advanced Magnet Systems

- 1. Magnet System Goodness Factors
- 2. Progress in BPX Magnets
- 3. Progress in BPX Magnet Materials

## Tokamak Magnet Systems are Scaleable

- B=Const
-  = Const
- J = R-1
- t = R2

- Any advanced magnet system can be scaled-up to FIRE or ITER
- There are no advanced magnet systems, not even close

- Dimensionally same as Bt, but:

- IpA/R as Tokamak Magnet
-  System Goodness Factor

- IpA/R Historical Survey

** **

- FIRE IpA/Ro 2x as high as world record
- IGNITOR IpA/Ro 70% higher than other designs
- FIRE IpA/Ro 2x as high as ITER

## The Superconducting Shortfall(and the Absence of Scale Models)

- Existing  and Tokamaks Under Construction

**Tore Supra: World's Best Superconducting Tokamak, IpA/R only 1/3 that of Alcator C-Mod**
**KSTAR: 56 % improvement,**
**C-Mod IpA/R still 89 % better than KSTAR**** **

- Tokamaks Under Design

**ITER/ITER-FEAT: 88 % improvement on KSTAR, **
**= CMod**
**IpA/R half as good as FIRE, **
**27 % of Ignitor**

## 1) Plate construction, adiabatically nitrogen-cooled 	(e.g. Alcator)

**1) Plate construction, adiabatically nitrogen-cooled ****	****(e.g. Alcator)**
**2) Bucking/Wedging**
**3) Compression Rings**
**4) Zero-turn loss scarf joints**

## 1) No divertor, plasma optimized for low OOP

**1) No divertor, plasma optimized for low OOP**
**2) Active clamping**
**3) Recool to 30 K**

## Buck/Wedged Design with Copper Inner Leg (FIRE)

**Bladder preinserted before assembly**
**- epoxy shims injected after assembly**
**(high reliability with reasonable tolerances)**

**Cu replaces 68 % IACS BeCu**
**Main benefit to power supply**

**Stress in inner leg reduced x 2**
**Expect IpA/R improve by 20 % (2 ****1/4****)**
**IpA/R improvement only 10 % in FIRE**
**- desensitized by Copper Alloy selection**

## The FIRE Compression Rings

** **

**External rings prevent excessive shear between TF plates, **
**due to OOP moments**
**Add compression to bond between insulating sheets and cases**
**Without compression rings, insulation shear allowables are exceeded at ~ 1/10 IB product**
**i.e. 4 T x 2 MA (TPX) vs. 12 T x 7.7 MA**

**50 turns, welded 1 cm 304 SS plate**
**Turns, insulated, bonded**
**Mechanical connection from inside-outside**

## Active Compression Rings

** **

** **

**Ignitor Magnetic Press**
**Reduces/eliminates primary membrane stress in nose**
**Active - can track thermal and Lorentz stresses: e.g. FIRE: peak stress after assembly, not operation**
**Can match "shear advantage" for special case of PF field lines nearly parallel I****TF**
**Advantage of 13 % over FIRE compression ring**

## Zero Turn Loss Scarf/Transition Joint

- Inner Joint for Pancake Wound Coils
- No Stress or Stiffness anomaly - Working Stress is the Same as for the Winding.
- No Thermal Anomaly in Normal Conductor Coils - No Differential Thermal Strains
- No Turn Loss
- No Projection into the Bore
- Electrodeposited joint as strong as base metal

- Peak local stress reduced x 2
- Ip improvement ~ 10 %

- Tinit,Ignitor = 30 K; Tinit,FIRE=77 K
- Entropy generations ~ equal, lower temperature vs. smaller size
- 5 hr cooldown, Ignitor; 3 hr, FIRE
- Neither has activated lN2
- FIRE flushes with He gas, after lN2 cooldown
- 40 % improvement in J2t
- 20 % in Jcu, 10 % in IpA/R

- Subcooling in Ignitor

*Z*(*T**f*)  functions: 1. Silver (99.99%); 2. Copper (RRR 200); 3. Copper (RRR 100); 4. Copper (RRR 50); 5. Aluminum (99.99%)

## Advanced Structural Concepts for Global Machine Behavior

- Bucked and Partially Wedged - ATBX - FDR ITER concept with partial wedging to control CS torsion.

- OOP displacements of the toroidal field coil are  imposed on CS. Torsional shear stress in the CS is  reduced by partially wedging the TF case. Set gap obtained with inflatable and removable shims.

- IpA/R ATBX was 12 % higher than ITER

## Advanced Structural Concepts for Global Machine Behavior

- Sliding Joint Picture frame TF Coils.
- 	(NSO C-Mod Scale-up Studies)
- 	(Ron Parker Proposed Steady Burn Experiment, SBX)
- 	The in-plane behavior of the Inner Leg of C-Mod is structurally decoupled from the rest of the machine.

- Upgrade to 2.5 MA planned
- Original 3.0 MA design IpA/R=FIRE

## TF Finger Spring Upgrade

- Felt Metal was degraded
- Failure Analysis Yielded no Clear Cause
- Increased Spring Plate Pressure and Extension Improved FM Contact
- “4 Pack” Replaced “2 Pack”
- C-Mod has Worked OK Since

- 1) IpA/R > 15 MA/m tokamaks appear available for BPX's
- 	- not yet demonstrated x factor of 2, C-Mod can come close
- 	- superconducting tokamaks need to catch up
- 2) Key to high IpA/R to tokamaks is topology, not materials
- 	Buck-wedge, Compression Rings, Magnetic Press, Scarf Joints,   	Sliding-Joints, Subcooling
- 3) Beyond Ignitor and C-Mod?
- - Ignitor topology highly optimized - but possible extension to 30-370 K
- - Further optimization of C-Mod topology possible

- Conclusions-I