Seminar given in UCSD, USA, 2014 (Univ. California San Diego, California)

3D printed UST_2 stellarator, a small innovative fusion device Vicente Queral, CIEMAT L 1
3D printed UST_2 stellarator,
a small innovative fusion device
Vicente Queral
National Fusion Laboratory, CIEMAT, Spain
TM
Seminar given in
UC San Diego, CA, USA
17 November 2014

This is not a sculpture or fine art presentation !
It deals with fusion…
Perhaps, you might apply the developed
techniques for your work or projects,
think on it during the presentation!

Outline
▪ Two stellarator issues. Previous conceptual solutions.
▪ Hints about the previous UST_1 stellarator.
▪ UST_2
∙ Devising, test and selection of concepts.
∙ Engineering concepts and design.
∙ Pictures of UST_2 construction status.
∙ E-beam field line mapping experiments.
∙ Results.
▪ Potential future lines of R&D.

Two stellarator issues.
Previous conceptual
solutions

There are many different fusion approaches. Source
of figure [Woo 04]
We are going to
talk about these
devices, named
stellarators.
Fusion approaches
▪ Each type of
device has its
own advantages
and drawbacks
(no time to discuss
about it).

Comparative plasma size and shape of real stellarators. Again, each one has
advantages and drawbacks. Source of figure [Tri 11], modified.
Some real stellarators in the world
Working in brief Construction
halted. No
plasmas
UST_1
Somewhat
similar to
several
linked
mirrors
UST_2
~10 m

♦ 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]

Main objectives of the work
♦ The geometrical complexity of stellarators is one of their main
drawbacks. To try lo lessen such drawback,
the main objectives of UST_2 work:
▪ Contribute to the development of new better (faster, cheaper,
simpler) construction methods for experimental stellarators,
and other fusion devices.
▪ Accelerate the R&D cycle of: design → construction →
experiments → results → improved design → construction …
Other objective: Build a small stellarator to prove the results of
the R&D, and able to be used by a university (formation, basic
experiments, etc.).

Background

► Currently I work in CIEMAT in Remote Maintenance for DEMO.
Previously in RM for IFMIF (International Fusion Materials Irradiation
Facility) and ITER.
I developed UST_2 work majorly on my own, with low personal and
crowdfunding funds, in my personal laboratory (~garage), during a
leave of absence period, with some help and contribution from
CIEMAT (codes, help from fusion expert colleagues,…).
► The work is R&D and innovation in engineering, focused in
new construction methods for stellarators (small stellarators now,
larger ones in a future!). It is not focused on physics and plasma
experiments.
Background

Background. UST_2 essential data
▪ UST_2 is a small three period
stellarator of major radius 0.26 m and
plasma volume 10 liters
UST_2
design
▪ UST_2 has been designed to
be fabricated by 3D printing
(additive manufacturing)
Construction
status

• UST_1 stellarator was designed,
built and operated from 2005 to
2007 in my personal laboratory.
• Cost of the whole facility ~ 3000 €
(many 2nd hand pieces).
• The coils were built by a new
toroidal milling machine.
• Motivation: Develop innovative
construction methods for stellarators,
edification and generation of
demonstration effect. UST_1
stellarator
UST_1
facility
UST_1 modular stellarator
Background. There is a previous UST_1

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. Patented.
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
2) 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.
E-beam field mapping experiments
Recorded magnetic surfaces. Comparison calculation-experiment

• The toroidal milling machine is unsuited for very convoluted winding
surfaces and expensive to build only one device. Additive rapid
manufacturing methods might be better.
► The combination of a single monolithic frame with grooves and
compression of wire in the groove resulted effective and fast.
Essential experiences learned and results
► Inspiration has been generated in
other researches and countries, i.e.
the SCR-1 stellarator being built
in Costa Rica is based on the
UST_1 design.
Status of
SCR-1
Status of SCR-1

Devising, test and selection
of concepts

Hull concept and Truss concept developed
Hints about the development of engineering concepts
Assembling of the test
coil frame sector
Truss concept: 3D printed truss structure. Nylon.
Results: Long casting process, too inaccurate (250 €)
Hull concept: 3D printed
piece conceived as a
double hull structure.
Nylon. Results: Accurate,
slightly expensive (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

UST_2 is based on QIPCC3, [Mik 04].
High confinement at any β<4%,
middle compactness, high iota ~0.7
QIPCC3
Modification
Complex CASTELL code optimization process
using integrated NESCOIL and DESCUR codes
(codes for stellarator calculations).
UST_2 Last Closed Flux
Surface showing the achieved
straight section
Why not to modify QIPCC3 for enhanced engineering?

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 [Wan 05].
3) Allocate space for
potential 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

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=‘mold’ (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 !!

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
Central Vacuum Vessel (VV) Section
Cu strip
forming
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 ~ CIRCULAR
central ring and 3D-printed
positioning elements
Assembling and positioning concept
Advantages :
- Accurate, fast and
simple halfperiod
positioning (slide +
contact + slight rotation
~ Remote Handling
philosophy).
Sliding on horizontal
smooth base
Non-3D-printed
CIRCULAR
central ring
Contact,
accurate
positioning

Pictures of UST_2
construction status

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%

Finished
halfperiod
assembled
in position
Status on June 2014

Set-up for
the e-beam
mapping
experiments
Status on July 2014 and future work
Oscillating e-gun
Future work (undefined term ~ funding)
▪ Fabricate the remaining 5 VV
sectors and 4 coil frames.
▪ Assembling.

E-beam field line mapping
experiments

E-beam experimental set-up
Free oscillatiing e-gun
Picture 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

Results

♦ ±0.3% dimensional accuracy has been achieved, still excessive.
► A suitable 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 enhanced.
► The positioning strategy for the coil frames resulted satisfactory.
► 1/3 of a fusion device has been produced with low budget. It was
possible since integrated innovations have been devised and
developed.
► The low cost of this small device (2400 € in materials up to now)
suggests reasonable cost for larger devices.
► Other types of fusion devices might be built by similar techniques.
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 photo [3de 14]

A) A hybrid stellarator/tokamak
For example the
compact A=3
Quasi-
axisymmetric
stellarator being
developed in
China/PPPL.
Source of figure
[Zhe 14]
3D printing of low or high aspect ratio stellarators by 1) or 2)
(previous slide) with liquid Li walls
QA-LAx stellarator,
Source of figure [Zhe 14]
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]
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

The list does not include the references in extra slides.
[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.
[Bei 00] ‘The Helias Reactor’, C.D. Beidler, G. Grieger, E. Harmeyer, et al., Presentation, ~ 2000.
[Hei 06] ‘Design of Narrow Support Elements for Non Planar Coils of Wendelstein 7-X’ B. Heinemann, 1-4244-0150-X
IEEE, 2006.
[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.
[Jak 11] ‘Alternative conceptual design of a magnet support structure for plasma fusion devices of stellarator type’, Nikola
Jaksic, Boris Mendelevitch, Jörg Tretter, Fus. Eng. and Des. 86 689–693, 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, Chengdu, China,16 -21 October 2006.
[LKu 10] “New Classes of Quasi-helically Symmetric Stellarators”, Report PPPL 4540, L.P. Ku and A.H. Boozer, August,
2010.
[Men 11] ‘Prospects for pilot plants based on the tokamak, spherical tokamak and Stellarator’, J.E. Menard, et al.,
Nuclear Fusion 51 103014, 2011.
[Mik 04] “Comparison of the properties of Quasi-isodynamic configurations for Different Number of Periods”, M. J.
Mikhailov et al., 31st EPS Conf. on Plasma Phys, 28 June - 2 July 2004 ECA Vol.28G, P-4.166 (2004).
[Myn 10] ‘Reducing turbulent transport in toroidal configurations via shaping’, H. E. Mynick, N. Pomphrey and P.
Xanthopoulos, Physics of Plasmas 18 056101, 2011.
References

[Naj 06] ‘Recent progress in the ARIES compact stellarator study’, Farrokh Najmabadi, A. Rene Raffray, and the ARIES
Team, Fusion Engineering and Design 81 2679–2693, 2006.
[Naj 05] ‘Recent Progress in ARIES Compact Stellarator Study’ ,Farrokh Najmabadi and the ARIES Team, Presentation
in 15th International Toki Conference 6-9 December 2005, Toki, Japan, 2005.
[Que 10] ‘High-field pulsed Allure Ignition Stellarator’, Stellarator News, n. 125, 2010.
[Que 13] V. Queral, Coil fabrication of the UST 1 modular stellarator and potential enhancements, Fusion Engineering
and Design 88 683-686, 2013.
[Spo 10] ‘New QP/QI Symmetric Stellarator Configurations’, Donald A. Spong and Jeffrey H. Harris, Plasma and Fusion
Research: Regular Articles, Volume 5, S2039, 2010.
[Sub 06] A.A. Subbotin, et al., Integrated physics optimization of a quasi-isodynamic stellarator with poloidally closed
contours of the magnetic field strength, Nuclear Fusion 46 921–927, 2006.
[Tri 11] ‘Stellarators & Stellarator Reactors’, V. Tribaldos, University Carlos III lecture pres., Spain, 2011.
[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.
[Woo 04] S. Woodruff, An Overview of Tokamak Alternatives in the US Fusion Program with the Aim of Fostering
Concept Innovation, Journal of Fusion Energy 23 n. 1, March 2004.
[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.
[Wag 08] ‘ARIES-CS COIL STRUCTURE ADVANCED FABRICATION APPROACH’, Lester M. Waganer, Kevin T.
Slattery, John C. Waldrop iii, and ARIES Team, Fusion Science and Technology Vol. 54, 2008.
[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.
[Wan 07] ‘CONFIGURATION DESIGN AND MAINTENANCE APPROACH FOR THE ARIES-CS STELLARATOR
POWER PLANT’ X.R. Wang, et al., Fusion Science and Technology Vol. 52, 2007.
References

Seminar given in UCSD, USA, 2014 (Univ. California San Diego, California)

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