UST_1 is a low cost small educational stellarator built in a personal laboratory. Up to now it has shown good magnetic surfaces as designed and simulated. Presently plasmas as calculated are produced (Te>2eV , n~2e17) and the systems of ECRH, diagnostics, data acq. and vacuum are being improved to obtain better plasmas.
* Possibly it is the 3rd modular stellarator in the world, the most economical with acceptable quality, the first designed and built by only one person.
UST_1 is a 2 field periods compact modular st. with aspect ratio 6 and R=125mm, 12 resistive modular coils with precision ~0.3mm, partially optimised confinement using SimPIMF code, present p. supplies 21Kw and Bo 46mT (possible 87mT), 0.8kW 2.45GHz ECRH system, installation cost 2700€.
Key decisions Chronological milestones
|
Experimental Pulse parameters |
13-07-2007. Pulses from #261 to #265 :
Plasma density = 2 x 1017 m-3 +-1 x 1017m-3
Plasma temperature Te = 3eV +- 1eV
These values surpass slightly the calculated plasma parameters. *
___________________
06-07-2007. Pulse #248 .
Evolution of the parameters during the pulse. More Expand
Presently only very basic information is received by the Data Acquisition system. The Langmuir probes are not installed yet. However they are very necessary to know T and n at this low temperature.
_____________________
* The signal from the Langmuir probe located at 1/2a, and for several pulses, have been analysed. The uncertainty is large due to limitations, errors, and interferences in the A/D cards and because the data come from several pulses (presently only pulse #264 & #265). Some unknown errors and inaccuracies might appear in the future. It will be further validated or refuted the results.
Several months might be necessary to achieve a stable plasma at the nominal temperature, Te=~2eV, and pressure, so these low quality plasmas are only first promising experiences.
24 -
January
2007 : First plasma
Video
24-01-2007. Pulse #222 . First plasma, but still a low quality plasma. The period of higher quality plasma lasts 0.7 seconds and later it almost disappears, perhaps due to excessive outgassing. However the plasma is very unstable at any time. TF coils are ON (Bo=~43mT , 2nd harmonic at 2.45GHz) while the plasma is or seems toroidal although it is difficult to assure because of the perspective of the camera. A Type N connector is used to feed the RF. Pressure raised from ~0.06Pa to 1Pa in 0.5 seconds (P from inverted magnetron, 1Pa~1x1020 m-3). The outgassing is excessive.
23 - August
2006 : Magnetic Surfaces recorded
Video
More
Expand
In cyan (505nm from the fluorescent P24 phosphor) the poloidal projections of the e-beam for pulse #202. Several images are overlapped and not digitally modified. The successive theoretical intersections of the orbit with a poloidal plane at 0º toroidal angle are numbered and coloured. Intersection 1 is near the red circle but it is faint due to saturation of the image and the same for intersections 4, 7 and 8. Intersections 2, 3, 5, 6 and 9 are clearly defined. SimPIMF code simulates the orbit and projections. Poor vacuum still limits the number of turns. Circles are 3mm in diameter so the e-beam diameter is ~1.5mm, a good value but too large for this small stellarator. Date : 23 - August
1 - August : Points on the magnetic surfaces
More >
 |
 |
 |
||
| Pulse #128 | Pulse #127 | Pulse #126 |
Poloidal projections of the e-beam for some pulses. Several images are overlapped. Original images, not digitally filtered. In red, orange and yellow circles projection of the theoretical e-beam from SimPIMF code using the experimental electron energy (53eV) and thrown from the experimental position. Simulation including drifts. Vacuum is still too poor. Points are relatively large. The framing of the theoretical points is the same for the three pulses. Observe that point nº1 in red moves according to the e-gun location.
29-July : Definitive coils finished More >
Top view of UST_1 stellarator. 12 definitive modular coils (11 in red and coil number 0 in black) . Leadings with pressure brass rod for minimum resistance. Two terminals are available. July 2006 .
11-June : First Field Mapping More >
Image 1: Original image from camera Image 2 : Treated image*
* A turquoise (~505nm , P24 phosphor) point appears on the fluorescent rod in a particular frame, see Image 1. Image 2 is the result of digital cyan filter.
8-June : The e-beam rotates More >
Original image from camera Treated image
23-May : First pulses in UST_1 More >
09-May : UST_1 Stellarator is finished*
* But the definitive coils are needed, field mapping, maybe corrections and to heat the plasma, not easy tasks!!.
Interior view of the grooves before intalling the windings.
Some key decisions to obtain a low cost stellarator
Note : Take the correct decisions was far more difficult than might look from the short descriptions below. At that time all were doubts, partial knowledge and risky decisions. A posteriori all seems much easier
Options
Many different ideas and combinations of systems were possible:
* Circular poloidally and toroidally winding surfaces or 3D general winding surfaces.
* Superconducting coils or resistive coils.
* Modular, classical, torsatron, or perhaps a new style of stellarator.
* Coils in the vacuum vessel like in QPS and CNT or external like in most of the devices.
3D general winding surfaces?
Little attention was given to this idea because the coils, frames and vaccun vessel would have been too expensive. Moreover no means to optimise and even design the coils were available in those days.
Superconducting versus resistive coils
Superconductor techniques and materials were studied. Improved bulk low cost YBCO was analysed but it seemed unsatisfactory. Bi-2223 tape for UST_1 was estimated from EAS to cost 6300€ -too much. Resistive coils were chosen.
Modular, Classical stellarator or Torsatron
Options were ordered from more to less convenient : 1) Modular coils: The best. Only one layer of coils with complexity of the grooves similar to helical grooves. But I had no means to optimise the system.
2) Classical coils: The same torus could support both layers of coils, but the two interlocked layers of coils will be difficult to made accurately and assembly/disassembly.
3) Torsatron : Two different and precise structures are needed for poloidal and helical coils. It was estimated more expensive and/or inaccurate.
Optimization of confinement
Initially a classical stellarator was chosen because I had no means for the optimization of modular coils. Luckily, after the optimization of a classical stellarator using SimPIMF (a code I developed) it seemed that the code could be upgraded to optimise modular coils. A basic optimization of modular coils was obtained after programming for one day and some days of simulation-optimization. Later the code was improved to partially optimise 6 variables.
Coils outside the vacuum vessel
The question was how to made notably accurate modular coils at very low cost. Different alternatives were discovered and analysed for long time. The rough price for a method similar to the one in CTH was asked (very expensive). Finally some experiences were done to test the feasibility of an original device, a milling machine exclusively dedicated to mechanise modular coils for stellarators. An innovative milling machine working in toroidal coordinates with some additional particularities was invented, designed, patented, built, tested and finally the grooves were accurately cut on the surface. Plaster was chosen because of easy conformability, low cost, and moderate strength. Other materials and composities are adecuate.
Finally UST_1 resulted to be an optimised modular stellarator with external resistive coils on a circular toroid, plaster frame for grooves and copper vacuum vessel.
Now, when the stellarator is pleasingly finished*, I believe that most of the decisions were correct. But, were they the best?.
* Some issues remain
Several modular stellarators are presently being built or designed, W7-X (Europe-Germany), NCSX (USA), QPS (USA, designed) or have been recently finished, HSX (USA).
Some of the rejected alternatives could be revived in a new and more expensive UST_2 stellarator or in an upgrade of UST_1.
About the cost
The cost of the device has been paid with personal savings. Additionally an important income from remunerated work was not earned. However only ~0.5m2 of flat can be bought in a big city with the total cost of this development (Including laboratory materials, vacuum system, UST_1, but not work).
Currently,
I offer myself:
* to collaborate in reactor studies in my free time.
NOTE : Presently I am working in the development of the Remote Handling system for IFMIF (International Fusion Materials Irradiation Facility) in LNF, 'National fusion Laboratory', in CIEMAT, Spain. IFMIF is a facility to test and characterise the materials for the future fusion reactors, especially DEMO.
Therefore I lack of time for the design of UST_2 or any other major design.
and I am searching for :
* funds to built UST_2 and/or
* collaboration in UST_2 development
I will thank any comment : vmqueral@vodafone.es
State of installation in August 2006 . Main elements.
Key words and sentences for search engines :
Stellarators are an attractive alternative to tokamaks. A home-made personal torus like UST_1 is more difficult to be built as a tokamak. Fusion energy, named also thermonuclear energy, is expensive for a homemade personal device in the magnetic confinement paradigm. It is an educative fusion device that could be useful for students in universities, secondary schools, high schools, laboratories, research centres, school. Prove of principle can be experimented at low cost. Fusion reactions are no so clean as renewable energy but renewable fuels and renewable energies seem weak to feed the present and future energy needs. UST_1 is not an amateur torus, it is intended to be a serious device in spite of the lack of funds.
Palabras clave y frases para buscadores:
Stellarators son una atractiva alternativa a los tokamaks. Un reducido toro personal de construcción casera como el pequeño UST_1 es más difícil de construir como tokamak. La energía de fusión, llamada también energía termonuclear, es cara bajo el paradigma de confinamiento magnético. UST_1 es un aparato educativo de fusión que podría ser útil para estudiantes de universidad, de bachillerato, en la escuela, laboratorios, centros de investigación. A bajo costo pueden probarse primeros principios. Las reacciones de fusión no son tan limpias, ecológicas, como las otras fuentes de energía renovable pero quizás los combustibles renovables y las energías renovables son escasas para las necesidades presentes y futuras. UST_1 no es un toroide amateur sino que intenta ser un aparato serio a pesar de la carencia de fondos. El bajo coste es necesario en tal caso. Un stellarator universitario no necesita unos requerimientos como el de un gran centro de investigación.
Phrases et mots clés pour moteurs de recherche:
Stellarators sont une alternative attrayante aux tokamaks. Un tore personnel fait a la maison comme UST_1 est plus difficile à être construit comme un tokamak. L'énergie de fusion, appelée également énergie thermonucléaire, est chère pour un dispositif personnel dans le paradigme de confinement magnétique. C'est un dispositif éducatif de fusion qui pourrait être utile pour des étudiants aux universités, écoles secondaires, lycées, laboratoires, centres de recherche, école. Premiers principes peut être expérimenté à bas coût. Les réactions de fusion sont moins propre, écologique, que les énergies renouvelables, mais les carburants renouvelables semblent faibles pour alimenter les besoins énergétiques présents et futurs. UST_1 n'est pas un appareil toroïdal d'amateur, amateur, il est prévu pour être un dispositif sérieux malgré le manque de fonds. Prix réduit est nécessaire dans ce cas-ci. Un stellarator d'université, université, n'a pas besoin de bons caractéristique tels qu'un grand centre de recherches.
State of the installation in August 2006 . Main elements.
Magnetic Surfaces recorded More
Final design of the system of modular coils. 12 coils on a circular toroidal surface. Confinement optimised for wide plasma size, Iota in the gap below 0.333 , enough shear, maximum magnetic well, low Bmin and magnetic ripple, and smooth magnetic surfaces.
Obviously UST_1 cannot be compared with Wendelstein 7-X, one of the most advanced stellarators now being built in German [Figure comes from "Status of WENDELSTEIN 7-X Construction" M. Wanner and the W7-X Team]
Final design of the system of modular coils. 12 coils on a circular toroidal surface. Confinement optimised for wide plasma size, Iota in the gap below 0.333 , enough shear, maximum magnetic well, low Bmin and magnetic ripple, and smooth magnetic surfaces.
Wendelstein 7-X
has all the important features (superconductor coils, full 3D shaped coils,
advanced optimization and large size) that UST_1 does not enjoy. [Figure
comes from
"Status of WENDELSTEIN 7-X Construction" M.
Wanner and the W7-X Team]
CTH is a
medium-size compact
stellarator/tokamak hybrid device focussed in the research
of current-driven instabilities (disruptions
...)
in Auburn
University. [Figure comes from "Specification for the CTH vacuum
vessel" Greg
Hartwell and Steve Knowlton]
