# Presentation: 864559

## Quench Protection for High Field Magnets (>12T)(Accelerator Type)

- A.D. McInturff
- Superconducting Magnet Program
- Lawrence Berkeley National Laboratory
- May 24 - 26, 2000

## Conditions assumed in talk

- •	Protection to be accomplished by a close proximity heater
- •	Highly efficient coil winding package Jcu > 1000 A/mm2
- •	Examples given will be limited to Nb3Sn coils.  “Should be applicable to other A-15’s”
- •	Heater constructed composites of Kapton/SS(cu)/ Kapton plus glue

## Definitions

- Conductor Miits		 	106 Amp2 -sec to reach 450 K
- 						a)  measured
- 						b)  adiabatic calculation
- Critical ramp rate		 	Rate of current change at which 					conductor exceeds its critical 					temperature of the average winding 				field in a 0.1 operating current loss
- Minimum ProtectionWinding  	That length of conductor which will
- volume transitioning 		result in a L/R time constant that will
- 					stay below the conductor Miits budget

## Design input needed

- _Conductor_
- 	dimensions
- 	composition
- 	geometry
- 	critical current, field, and temperature profile
- _Windings_
- 	operating current, (load line)
- 	geometry
- 	electrical parameters
- 	magnetic parameters
- Note:	Any of these can be obtained by measurement (all the better) or 		calculated.  Operational characteristics LHe II or I, open or closed 		winding.
- Comment:	(will not consider cryostable operating point coils due to time constraints)

## Typical Design of a heater for a Nb3Sn Race Track Coil

**Conductor Parameters:**
**	****26 strand cable**
**	****0.8 mm strand diameter**
**	****J****c****(non-cu) = 2000****+**** amps/mm****2**
**Typical design input:**
**	****Quench output page**
**Typical Miits Curve:**
**	****Quench’s Miit’s Curve RD3**
**First order heater considerations RD3:**
**	****Induct. = 18mh**
**	****L/R = ?****	****	****at 10kA/turn  yields 100 Miit’s/sec**
**	****	****	****	****Miit’s limit “Quench” =12.4**
**	****	****	****	**_**=**_**> 125 milliseconds****	**
**	****	****	****	****    ****-**_**   40**_**	****“****	****detection & diffusion **
**	****	****	****	****        ****85****	****“**
**	****	****=>0.17 seconds = ******(effective)**
**	****	****	****R = 0.018/0.17 ~ 0.1 ohms**
**	****	****Outer coil’s room temperature resistance = 0.75 ohms**
**	****	****	****	****	****20K R(expected) = 0.02 ohms**
**	****	****	****	****	****20K R(measured)= 0.058  “**
**	****	****	****	****=> 1⁄4 of the coil driven normal will work**

## “Quench” code input/output for Miit’s 

## RD- 3 outer winding cable Miit’s Curve

## Protection of D20

**A very conservative approach was taken:**
**	****	****	****70% of the magnet was under heaters**
**	****	****	****The power levels were for SF operation**
**	****	****	****	****Layer 1 = 53 watts/cm****2**
**	****	****	****	****Layer 2 = 23  “**
**	****	****	****	****Layer 3 = 29   “**
**	****	****	****	****Layer 4 = 27    “**
**The data for Quench was:**
**The Miit’s Curve:**

## Miit’s Curves for C0/D0 Quads, Tev, & D20

## Integrated Stainless Steel Specific Heat versus Peak Temperature

**Table**
**	****	****Temperature****	****	****	****Energy/unit volume**
**	****	****Adiabatic(K)****	**** ****	****	****joules/cubic ****	****	****	****	****	****	****	****centimeter**
**	****	****100****	****	****	****	****80**
** ****	****	****200****	****	****	****	****316**
**	****	****300****	****	****	****	**** 642**
**	****	****400****	****	****	****	****1034**
**	****	****500****	****	****	****	****1494**
**Kapton Failure****	****770****	****	****	****2700**
**Typical Resistivity (Stainless Steel) ****	****	****50 micro-ohm-cm****	****	****       ****	****	****RRR****	****	****	****1.5**
**Typical Time constants (1/e) **
** ****Heater pulse****	****	****	****	****30 – 10 milliseconds**
**Typical detection plus thermal**
**Diffusion time at 70% short Sample****	****	****40 milliseconds**
**(typical peak Miit value)**
**Typical heater Power supply****	****	****	****450v**
**Parameters (x2 if stacked)****	****	****	****2 to 20 millifarad**

## Summary of typical process

- Obtain Miits curve for magnet		Calculate from “Quench” code or Measure
- 					the 450K point
- Calculate minimum coil volume		I (operate), L (millihenries)
- Design heater area greater than		Heater area calculated
- that to switch min. coil vol.
- Heater design resistances calculated	ohms to few 10’s of ohms
- Temperature (heater) targets		150K to 200K
- Wattage (heater) at the surface		20w/cm2 for LHe & 40 for SFHe
- Time (heater) constants		30 millisec. to 100 millisec.
**An efficient heater should:**
- Include an active length (non-cu plated)	1 cable transposition length
- Minimum heater thickness (ss)		13 micron preferred, but 25 micron is normal
- Min. thickness Kapton under layer and/or	15 microns (3 kV checked)
- Alumna filled Kapton (x2 thermal conduct.)	           “		3kV?
- Can include diagnostic wiring traces