Presentation in TOFE USA 2014 (TOFE Congress, 3D-Printed UST_2 Stellarator)

3D-Printed UST_2 Stellarator Status and First E-Beam Mapping Experiments Vicente Queral, CIEMAT L 1

3D-Printed UST_2 Stellarator Status

and First E-Beam Mapping

Experiments

Vicente QueralNational Fusion Laboratory, CIEMAT

ANS Topical Meeting: Technology of Fusion Energy (TOFE)

Anaheim, CA, USA

10-13 November 2014



Outline

▪ Background

▪ UST_2 conceptual design

▪ Engineering concepts and design

▪ Pictures of UST_2 construction status

▪ E-beam field line mapping experiments

▪ Results

▪ Potential future lines of R&D


Background. Objectives

► The work is carried out with very low funds. Therefore, the

importance of the work resides in the developed manufacturing

methods, not in the size of the device or the plasma performance.

♦ The geometrical complexity of stellarators is one of their main

drawbacks. To try lo lessen such drawback,

the objectives of UST_2 work are:

▪ Contribute to the development of new better (faster, cheaper,

simpler) construction methods for experimental stellarators, and

other fusion devices.

▪ Try to accelerate the R&D cycle of: design → construction →

experiments → results → improved design → construction …


Background. UST_2 essential data

▪ UST_2 is a small three period

stellarator of major radius 0.26 m and

plasma volume 10 litres.

UST_2

design

▪ UST_2 has been designed to

be fabricated by 3D printing

(additive manufacturing).

Construction

status


UST_2 conceptual design


▪ UST_2 is based on a 3 period Quasi-isodynamic stellarator with

poloidal closed contours (QIPCC3) supplied by German researchers,

[Mik 04]. It exhibits high confinement at any β<4%, middle compactness, high iota ~0.7

QIPCC3 LCFS, [Mik 04]

Modification

▪ Complex optimization process using several

codes (CASTELL, NESCOIL and DESCUR codes for

stellarator calculations).

UST_2 based on a 3 period Quasi-isodynamic stellarator

UST_2 Last Closed Flux

Surface (LCFS) showing the

achieved straight section


1) Wide port

1) Wide ports for fast in-

vessel access, maintenance

and remote handling.

2) Potential maintenance of

full (half)periods, i.e. similar

to concepts in [Wan 05].

3) Allocate space for

possible innovative power

extraction systems, i.e.

concepts [Kul 06], [Ima 11]

[Hir 09], [Wer 89], [Hir 97].

Potential advantages of the design (if it were a larger experimental

device or reactor)

2) Independent

module with

splitable

vacuum vessel

3) Space for power

extraction systems

Modification of QIPCC3 for enhanced engineering

~350 mm


Engineering concepts and

design


+

Approach for the coil frame manufacturing method

Resin casting

Concept of 3D-printed light truss structure

covered by a thin shell (internal surface removed

in the figure) formed by two joined halves.

The shell=‘mould’ (700€) remain

attached to the matrix after casting.

The two halves are split after casting.

Combination of 3D printing + casting (→ accurate & low cost)


Coil frame split in two halves

Assembling concept

Introduction of the vacuum

vessel in one half coil frame

Two halves

of the coil

frame after

casting and

splitting

Closure with the second

half coil frame

Concept of fully modular vacuum

vessel and coil frame !!


Approach for the vacuum vessel manufacturing

Central Vacuum Vessel (VV) Section

Cu strip

shaping

on form ↓

Finished VV liner

Concept of modular VV

Metal liner epoxy resin reinforced (→ low cost for large VV)

Finished Curved VV

sector. Copper liner

epoxy reinforced


Slide → contact of 3D-printed

positioning elements on

circular central ring

Assembling and positioning concept

Advantages:

- Accurate, fast and

simple halfperiod

positioning. Slide →

contact → slight final

rotation. Approach similar

to Remote Handling

philosophy.Sliding on horizontal

smooth base

Non-3D-printed

CIRCULAR

central ring

Contact, accurate

positioning


Pictures of UST_2

construction status


UST_2 status on January 2014


One finished halfperiod and

one ongoing

Status on June 2014

Decision of device to build

Conceptual design

Detailed design

Validation by e-beam mapping

Construction 25%


Set-up for the e-beam

mapping experiments

Status on July 2014

Oscillating e-gun


E-beam field line mapping

experiments


E-beam experimental set-up

Free oscillating e-gun

Video frame of the fluorescent ZnO

lines on screen, and mirror image

of the oscillating e-gun

Sketch of the

experimental set-up

E-gun arc (black) and

e-orbits (red) of 60 eV

electrons, calculated

by CASTELL code


Overlapping of the consecutive frames shown above

Detail of the series of frames containing

fluorescent points for pulse #15 Overlapping of

perspective-

transformed

experimental

fluorescent

points (in cyan)

and calculated

intersection of

oscillating e-

beam with the

screen (blue line)

Comparison calculations-experiments


Video recording of pulse #15

Video recording

N202_F70-135.mpg

4st-Flu-points_Frame-1m-04s_e__VID_20140621_195659_Cut.mpg

4st-Flu-points_Frame-1m-04s_e__VID_20140621_195659_Cut.mpg


Results


♦ Manufacturing the twisted UST_2 vacuum vessel was time consuming

and needs further R&D, i.e. using electrodeposition, electroforming, etc.

♦ ±0.3% dimensional accuracy has been achieved, still excessive.

Thermal warping seems the reason.

► The positioning strategy for the coil frames resulted satisfactory.

► A construction method for stellarators based on 3D printing + casting

has been developed.

► A method to fabricate a liner epoxy-reinforced twisted vacuum vessel

has been advanced.

► The low cost of this small device (2400 € in materials up to now)

suggests reasonable cost for larger devices.

Experiences learned and results


Potential future lines of R&D


1) Either Combination of metal 3D printing + metal casting

+


Metal (Zn, Al

…) casting in

the Titanium

shell ?

Titanium

shell ?

2) Or Use of large direct

metal laser 3D printers

Titanium piece 3D-printed by

AVIC Laser, China. Presented

in a Beijing fair [AVI 13].

Source of picture [3de 14]

http://imageshack.us/photo/my-images/809/3dprintedpartsfighter2.png/

http://imageshack.us/photo/my-images/809/3dprintedpartsfighter2.png/


A) A hybrid stellarator/tokamak

(with two coil-sets, ∞ intermediate configurations?)

For example the

compact A=3

Quasi-

axisymmetric

stellarator being

developed in

China/PPPL,

[Zhe 14]


3D printing of low or high aspect ratio stellarators by 1) or 2)

method (previous slide)B) A high <β>lim large

aspect ratio stellarator,

thick copper coils

<β>lim ~10% A=10 [LKu 10]

<β>lim ~ 9% A=12 [Sub 06]

Quasi-isodynamic stellarator, 6

periods, [Sub 06]

QA-LAx stellarator, Source of figure [Zhe 14]

Perhaps

<β>lim

~15% ??


Acknowledgement

I would like to give thanks to all the people and researchers helping

in the development, in particular:

Jefrey Harris, Donald Spong and team (ORNL, QPS LCFS and coils)

Juergen Nueremberg and team (IPP Max-Planck, QIPCCs LCFS)

H. E. Mynick (PPPL, NCSX-TU LCFS)

Jesús Romero (NESCOIL teaching, other)

Antonio Lopez-Fraguas (DESCUR code update and teaching)

Gerardo Veredas (CAD teaching)

Juan A. Jiménez (VMEC teaching)

Víctor Tribaldos (stellarators)

Jose A. Ferreira (vacuum)

Cristobal Bellés (I. T. help)

Other


[3de 14] Web site, http://www.3ders.org/articles/20130529-china-shows-off-world-largest-3d-

printed-titanium-fighter-component.html, 2014.

[AVI 13] AVIC Laser (AVIC Heavy Machinery subsidiary), ‘16th China International High-tech

Expo’, Beijing, 21-26 May 2013, web site www.france-metallurgie.com, August 2014.

[Hir 97] ‘Steady state impurity control, heat removal and tritium recovery by moving-belt plasma-

facing components’, Hirooka et al., Proc. 17th IEEE-SOFE, San Diego, Oct. 6th-10th, 906, 1997.

[Hir 09] ‘Active particle control in the CPD compact spherical tokamak by a lithium-gettered

rotating drum limiter’, Y. Hirooka, et al., Journal of Nuclear Materials 390–391, 502–506, 2009.

[Ima 11] ‘Status and plan of gamma 10 tandem mirror program’, T. Imai, et al., Transactions of

Fusion Science and Technology vol. 59 Jan. 2011.

[Kul 06] ‘Project EPSILON – a way to steady state high b fusion reactor’, V.M. Kulygin, V.V.

Arsenin, V.A. Zhil’tsov, et al., IAEA XXI Fusion Energy Conference, 16 -21 October 2006,

Chengdu, China.

[LKu 10] ‘New Classes of Quasi-helically Symmetric Stellarators’, Report PPPL 4540, L.P. Ku

and A.H. Boozer, August, 2010.

[Mik 04] ‘Comparison of the properties of Quasi-isodynamic configurations for Different

Number of Periods’, M. J. Mikhailov et al., 31st EPS Conference on Plasma Phys. London,

28 June - 2 July 2004 ECA Vol.28G, P-4.166 (2004).

References


[Que 10] ‘High-field pulsed Allure Ignition Stellarator’, Stellarator News, n. 125, 2010.

[Sub 06] ‘Integrated physics optimization of a quasi-isodynamic stellarator with poloidally closed

contours of the magnetic field strength’, A.A. Subbotin, M.I. Mikhailov, V.D. Shafranov, M.Yu. Isaev,

C. Nührenberg, J. Nührenberg, et al., Nuclear Fusion 46 921–927, 2006.

[Wer 89] ‘A high-speed beam of lithium droplets for collecting diverted energy and particles in

ITER’, K. A. Werley, Los Alamos N. L. report LA-UR--89-3268, 1989.

[Wan 05] ‘MAINTENANCE APPROACHES FOR ARIES-CS COMPACT STELLARATOR POWER

CORE’, X.R. Wang, et al. and the ARIES Team, Fusion Science and Technology 47(4) 1074-1078,

2005.

[Zhe 14] ‘Systematic study of modular coil characteristics for 2-field periods quasi-axisymmetric

stellarator QAS-LA’, Jinxing Zheng, Yuntao Song, Joshua Breslau, G. H. Neilson, Fusion

Engineering and Design 89 (4), 487–501, 2014.

References





Extra slides intended

for the questions


Hints about the previous

UST_1 stellarator


Toroidal milling machine

Method to build the modular coils

Concept of toroidal milling

machine

The milling head of this special milling

machine moves in toroidal and poloidal

coordinates → simplicity and reduced field

errors.

Concept of a toroidal

milling machine for

stellarators


Compressing

conductors in the groove

Winding process and result

12 coils finished

1 ) Concept and implementation

of single monolithic frame

Two main concepts developed

Concept of conductor

compressed in groove


Pulse #202. Overlapping of

calculated (numbered circles) and

experimental points (cyan). Notable

agreement is observed.

Pulse #202. Video recording of

experimental fluorescent points

on a oscillating rod. 94 eV

beam.

Field mapping experiments

Recorded magnetic surfaces. Comparison calculation-experiment


Overview of the facility

CODAC systems

Power supplies. 20 kW

ECRH

1kW

More information in www.fusionvic.org and [Que 13]


• The toroidal milling machine is unsuited for very convoluted winding

surfaces and expensive if building only one device. Additive rapid

manufacturing methods might be better.

• Winding one turn per layer may be simpler and faster than two turns.

► The combination of a single monolithic frame with grooves and

compression of wire in the groove resulted effective and fast.

Experiences learned and results

► A construction method for stellarator

coils based on a new toroidal milling

machine was developed.

► Inspiration has been generated in

other researches and countries.

Formation. i.e., the SCR-1 stellarator

being built in Costa Rica is based on

the UST_1 design.Status of

SCR-1


UST_2 stellarator


♦ The geometrical complexity of

stellarators is one of their main drawbacks

Coils and supports are shaped and

have to be very accurate (relative

errors ~<10-3). Source of W7-X figure,

http://lecad.fs.uni-

lj.si/research/fusion/W7X/index

One issue of stellarators. Previous proposed solutions

Beam truss

structure to support

the coils, [Jak 11]

Continuous structure and coils

wound in grooves, [Naj 05] [Naj 06]

Concept of 3D-

printed structure and

internally wound

coils, [Wag 08]


♦ In-vessel remote maintenance

(for reactors) is very complex and

downtime-expensive

Small maintenance ports in the

named Helias reactor. Source of figure,

[Bei 00] → slow (expensive

downtime). And, what if a

superconducting coil fails?

Other issue of stellarators. Previous proposed solutions

Vertical maintenance approach. Even

more difficult coil design [Wan 07]

Tokamak Stellarator

Full period disassembly concept,

[Wan 05]. Source of figure [Naj 05]


Hull concept and Truss concept developed

Hints about the development of engineering concepts

Assembling of the test

coil frame sector

Truss concept: 3D printed frame structure.

Nylon. 250 €. From company ‘Shapeways’.

Hull concept: 3D printed

piece conceived as a

double hull structure.

Nylon. Was test filled with

dental plaster. 80 €.


Hints about the assessed magnetic configurations

QPS, QIPCC2,

QIPCC3, NCSX-TU,

other, assessed

QPS (Quasi-

poloidal

stellarator)Last Closed Flux Surfaces supplied by J. Harris & D. Spong, Nühremberg and team [Mik 04] and H. Mynick [Myn 10]

QIPCC2 (Quasi-isodynamic

stellarator with poloidal

closed contours) 2 periods

QIPCC3, three periods.

Selected

LCFS for NCSX, NCSX-

Turbulence Improved

and Mixed

▪ Calcula-

tions by

CASTELL

code (Java

code

developed

by me

during

several

years)


UST_2 essential properties

Element Specification

Number of periods 3

Plasma volume (litres) 10

R, plasma major radius (mm) 260

a, ave. plasma minor radius (mm) ~ 37

Aspect ratio ~ 7

Type of coilsModular

coils

Number of pancakes = coils 90

Number of non-planar coils 84 (14 x 6)

N. of large planar non-circular

coils6 (1 x 6)

Vacuum magnetic surfaces at φ = 0


Concept and test of coil winding and crossover

Testing the crossover

performance

Compression in groove

and special crossover

• Results :

- Reasonable pressure of

conductor on groove walls.

- One coil was wound in

about 30 minutes, OK.

- The conceived crossover

was feasible and

satisfactory.

Finished crossover

Test

coil

Concept. One

turn/layer compressed

in groove to allow fast

winding and many

coils (low curvature

radius)


Approach for the vacuum vessel manufacturing

Curious picture of the 3D-printed

mold for epoxy resin casting

Soldering external

claws (brass ball chain)Finished Curved VV sector.

Copper liner epoxy reinforced

Electrodeposition, electroforming, metal 3D

printing and other methods will be also tested


Modification of QIPCC3

Why not to modify QIPCC3 to enhance some

engineering features of UST_2?

Insight came from,

►Initially:

9/13? = 0.692

Planned divertor for the

GAMMA 10 Tandem mirror.

Source of figure [Ima 11]

Linked mirrors. Source [Kul 06]

New QI configurations.

Source [Spo 10]

► Later, after searching, from:


Process of modification of QIPCC3

The straight section is stretched by CASTELL code,

plus re-optimization

• Automatic CASTELL code processes: The

QIPCC3 straight section is stretched (addition of

poloidal cuts and compression of QIPCC3 sections),

CASTELL DESCUR-like code application, two

NESCOIL runs, confinement, iota and magnetic well

profiles calculated by Monte Carlo method.

• Only about 500 configurations have been

compared. Long lasting computations.

• Increasing elongation of the straight section gave

decreasing confinement for the best configuration.

• The re-optimization is poor (about 3 times less

confinement than the original QIPCC3). However,

the main objective is engineering.

Stretched and

compressed

poloidal cuts


A mix of the Hull Concept and Truss Concept is chosen

Perspective and top view of the first 3 coils being 3D printed. A test

3D printed

thin cover

surfaces

and

internal

truss

structure

UST_2 engineering design


Internals of the coil frame


Sequential low-cost rapid manufacturing of larger devices

Cost and performance is only a coarse value

for rough comparison among devices

Concept : High-field

pulsed Allure Ignition

Stellarator (AIS) (2010).

[Que 10] High-field,

few ignition pulses.

Somewhat similar to

the IGNITOR, FIRE and

FAST concepts, but for

a stellarator.

Possible long term activities

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