multi-physics modeling of transients in superconducting ......extraction at 25ms, fem decays in qp...

Lucas Brouwer, Emmanuele Ravaioli, Diego Arbelaez, Shlomo Caspi, Maxim Marchevsky, Heng Pan, and Soren Prestemon

US Magnet Development Program

Lawrence Berkeley National Laboratory

Multi-physics modeling of transients in

superconducting magnets in ANSYS and

LEDET

MT25: August 31st 2017

Outline

2

• Eddy Current ANSYS Models

o Example: mandrel lamination size and thermal margin for CCT

proton gantry magnet

• Circuit-Coupled Eddy Current Models

o Example: large role of eddy currents in structure for protection of

CCT3

• Current Focus: Adding Conductor Losses to Circuit-Coupled

Models (CLIQ for CCT)

o Approach 1: coupling of ANSYS and LEDET

o Approach 2: use of custom elements in ANSYS

Eddy Current Models for a Proton

Therapy Gantry Magnet

3

The curved CCT mandrels are built up from aluminum laminations with machined conductor channels

Choice of lamination size affects

(1) Eddy current losses during magnet ramping (smaller is better)

(2) Manufacturability and assembly (larger is better)

(3) Thermal behavior for conduction cooling (larger is better)

Motivation for

development of

ANSYS model

Combined Function Magnetic Field

Profile and Transient ANSYS model

44

Dipole only: ~2.5 T Quadrupole only: ~2.8 T

layers 3,4 layers 1,2 - alternating along length

Combined: ~5.2 T

alternation of the field cancellationex. dipole layer +

laminated mandrelAll layers + structure

Solid97: A (air), A+volt (eddy)Desired fields for ~20 %

momentum acceptance

Eddy Current Losses vs. Lamination

Width at Peak Ramp Rate (0.02 T/s)

5

As expected

• Larger width = longer time constant

• Larger width = larger loss

φ Lam. (deg) Net Loss (W)

2.5 0.15

5 0.53

7 1.02

12.5 2.75

Thermal Modeling of Worst Case Treatment

Scenario Predicts Thermal Margin

6

.02 T/s

Magnet ramping

during treatment

Distribution at peak temp time

Peak conductor temperature

Mandrel + conductor heating transferred to thermal model Current sharing temperature of superconductor

Thermal margin

7




• Circuit-Coupled Eddy Current ANSYS Models


CCT3





CCT magnets have a large amount of bronze and aluminum around the windings

8

Impact of Structural Eddy Currents in CCT3

Al-bronze

mandrelsCCT with Al shell

What role do the large metallic parts play in magnet protection?

• how much energy is deposited in eddy currents?

• what are the relative roles of the mandrels and shells?

Motivation for

development of

ANSYS models

9

conductor layers

SCR (switch)

Rdump

FE

M

Cap bank trigger

Power Supply

FEM: Layers, shell,

bounding box for

magnetic B.C.

ANSYS solves the coupled electric-magnetic problem to predict

the current decay of the magnet in the test facility circuit• no assumptions about the magnet inductance or decay curve (part

of simulation)

• no quench resistance growth or conductor losses (only structure

eddy currents for now)

• Soild97 (A,curr,emf), Circu124 (V,curr,emf), Solid237 (Az,V,emf)

simplified test facility circuit

conductor and Al-bronze mandrels

Circuit-Coupled Eddy Current Models in

ANSYS

10

3D Model vs. CCT3 Test Data suggests eddy currents

in shell dominate large deviation from L/R

loss in Al shell

loss in Al-bronze mandrels

• MIITS is halved due to eddy losses

• 52% of the stored energy is

dissipated by eddy currents, the

majority of which is in the shell

extraction at 25ms, FEM decays in QP circuit (40mOhm dump)

MIITS Edump (kJ,%) Eshell (kJ,%) Eman (kJ,%)

ANSYS (no eddy) 3.76 150 (100%) 0 0

ANSYS (eddy) 1.80 72 (47%) 70 (46%) 7 (5%)

Test Data 1.76 71 (47%) unknown unknown

11

Location and Time Constant Effects:

Power Density

11

Initial Heating: 0-15 ms• short time constants: small loops + bronze resisitivity

dominated by the thin

midplane ribs between turns

Central cross section

Heating: 15+ ms• long time constants w/big eddy currents: large loops + aluminum resistivity

Layer 1

Deposited right next to the conductor!

Dominated by the aluminum shell

Coupling the Extraction Modeling with

Temperature

What is the rise in temperature during the extraction just due to eddy currents?

Mandrel eddy currents heat up conductor

then come to same temp (0-150 ms)

Shell is still transferring

heat to layer 2

13




• Circuit-Coupled Eddy Current ANSYS Models


CCT4





14

ANSYS standard distribution struggles with conductor losses which is critical for CLIQ, two options:

1) bring conductor losses from outside -> coupling to LEDET

2) find a way to implement conductor losses in ANSS -> custom ANSYS element

Both are a work in progress, with initial model generation and benchmarking being completed

ANSYS and LEDET

LEDETIncludes

- conductor losses (IFCC,ISCC)

- thermal

- influence on differential inductance

Challenges

- structural eddy currents

- 3D

- iron yoke contribution with current

ANSYSIncludes

- thermal

- iron yoke contribution

- coupling to external circuit

- 3D (could be important for CCT)

Challenges

- conductor losses

Circuit-Coupled ANSYS model for MQXF

15

coil blocks

bronze wedges

Ti poles

Dump resistor

CLIQ circuitEx. coil section

coupling to circuit

plane53 elements

Az (air)

Az+volt (eddy)

Az+curr+emf (cond)

Comparison of ANSYS and LEDET

16

Benchmarking: first comparison is with no conductor losses in FEM or LEDET

Circuit + CLIQ parametersmagnet length = 1.192 m

Rdump = 30 mOhm

I0 = 16471 A

Ccliq = 80 mF

Vcap = 200 V

Rcliq = 20 mOhm

ANSYS and LEDET agree within 0.1 % for current and voltage decay with CLIQ + dump

-> validates circuit-coupled model approach in ANSYS before adding conductor losses

Available

- node location

- loads

- node temperature

- material prop.

- ANSYS functions

ANSYS custom elements

17

Geometry Generation

Meshing

Boundary conditions

Loads

SolutionPost processing

Load transfer between models

custom ANSYS.exe is compiled => easy to share with community

• all use of ANSYS is the same, just need to select custom element

• conductor losses can be implemented with modified VP formulation following the example of

TU-Darmstadt, CERN, etc.* (part of LBNL collaborative effort with PSI)

• status: 2D plane53 and plane42 have been reproduced, ready to add in equiv. magnetization

Replace code which builds element matrices: uel.f, uec.f

Element customized by defining

- element shape functions

- material properties: if complex function desired

(T,B,Jc,etc.)

- formulation

Element matrix generation is now

determined by user program

- stiffness, damping, etc.

*L. Bortot, et al. “Simulation of Electro-Thermal Transients in Superconducting Accelerator Magnets with COMSOL Multiphysics”

18

Structural eddy current models were developed in ANSYS for

o eddy current heating in the proton gantry structure

o circuit-coupled behavior of CCT3 and CCT4 with eddy currents

We are in the beginning of the effort to add conductor losses

to simulate CLIQ for CCT



Summary

Extra Slides

19

Straight-Section Models for the CCT are

3D Periodic

20

2D axial symmetry

“cross section”

3D periodic axial symmetry

“lamination”

Cos θ CCT3D fields and forces2D fields and forces

The CCT’s minimum axial symmetry is 3D

=> development of new techniques

Periodic Magnetic Modeling in

Opera3D/ANSYS (Static)

21

ANSYS• Solid237 edge element

• continuous mesh

• directional coupling of edge DOF

between faces

Opera3D

• mesh only periodic region

• periodicity can be specified

using internal commands

ANSYS Comparison to Opera3D (CCT4): current of 18.1 kA, energies are in MJ/m, fields are in T

Without Iron With Iron

Energy Bbore Bcond Energy Co-Energy Bbore Bcond

Opera3D 0.675 8.35 9.22 0.795 0.834 9.85 10.67

ANSYS 0.687 8.41 9.10 0.794 0.849 9.87 10.52

diff (%) 1.7 0.6 1.2 0.1 1.8 0.2 1.4

CCT4 field at conductor

22

3D Periodic Model vs. CCT3 Test Data

22

extraction at 25ms, FEM decays in QP circuit (40mOhm dump)

MIITS Edump (kJ,%) Eshell (kJ,%) Eman (kJ,%)

Full ANSYS (no eddy) 3.76 150 (100%) 0 0

Full ANSYS (eddy) 1.80 72 (47%) 70 (46%) 7 (5%)

Per. ANSYS (no eddy) 4.58 173 (100%) 0 0

Per. ANSYS (eddy) 2.38 96 (55%) 72 (41%) 4(3%)

Test Data 1.76 71 (47%) unknown unknown

The periodic model is not as accurate for a short magnet like CCT3 (no end effects => larger energy)

• looks promising for long magnet parametric studies (i.e. 16 T)

FEA connected to circuit

with symmetry factor

(2*64 turns)

23

Both electrical resistivities are fairly constant up to ~80K

Al-Bronze

15.8e-8 ohm-mAl 6061-T6

1.4e-8 ohm-m

Material Properties

From: Handbook on Materials for Superconducting Machinery. ARPA, NIST. 1974

multi-physics modeling of transients in superconducting ......extraction at 25ms, fem decays in qp...

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