Transcript – A WAY TO STEADY STATE PROJECT EPSILON HIGH FUSION REACTOR

Russian Research Center “Kurchatov Institute”
Nuclear Fusion Institute
PROJECT EPSILON – A WAY TO STEADY STATE
HIGH  FUSION REACTOR
V.M. Kulygin, V.V. Arsenin, V.A. Zhil’tsov, A.V. Zvonkov,
A.A. Skovoroda A.V. Timofeev
IAEA XXI Fusion Energy Conference, 16 -21 October 2006, Chengdu, China
Abstract
•
Pseudosymmetry (PS) principle being used for hot plasma
confinement magnetic systems construction could provide
realization of all the magnetic confinement potential. Namely: to
realize hot plasma confinement at steady state operational mode
with a “tokamak” confinement time level. The high  regime lets a
possibility to think about advanced fuels (D- 3He, D-D).
•
It is proposed to check the main idea and preliminary theoretical
examination experimentally in frame of EPSILON project – closed
crimped magnetic trap without rotational transform and with poloidal
PS. The EPSILON consists of two (or more) crimped mirror traps
(OME), closed with curvilinear elements (CREL). MHD stability and
plasma cleaning are provided with axially symmetrical divertors
disposed along the mirror traps with zero magnetic field at
separatrix.
Introduction
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The fusion parameters of magnetically confined hot plasma will be
got in ITER – the first experimental thermonuclear reactor that is
now prepared for construction.
As the nearest principal goal of magnetic fusion development is
coming near, next stage problems become actual. They are the
problems of magnetic confinement system optimization from reactor
technology point of view.
Power reactor should have high power, technology and economic
efficiency, be serviceable and meet safety and ecology demands.
Because of the reason, world fusion development efforts along with
the largest tokamak experiment realization should take aim at
search for possible improvements of magnetic confinement
systems. The improvements can consist in inherent steady state
high  operation, technology simplification, efficiency increasing and
possibility to use ecologically attractive fuels (D-3He).
EPSILON is Closed Mirrors
• Closed Mirrors = Linked Mirrors, closed magnetic
systems without rotational transform
• All previous attempts to use Linked Mirror configuration
were unsuccessful
• Now the reason of that is clear: all of the previously
tested systems contravened the principle of the same
type pseudosymmetry for each element
Kadomtsev’s Rippled Trap (1958)
KADOMTSEV B.B., Magnetic traps with rippled magnetic field, Plasma Physics and the Problem of Controlled
Thermonuclear Reactions, Ed. by M.A.Leontovich (Pergamon Press, New York, 1960). Vol.3.
Summary:
At H0/Hm <<1, particle losses in curvilinear
elements can be comparable with classical losses in
rippled solenoids
EPSILON magnetic configuration
OME sell
The main Improvement: Toroidal drift with correspondent particle losses is
eliminated. The ripped magnetic configuration in the solenoids is arranged
With coils of opposite current (toroidal divertors)
EPSILON fundamentals
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Pseudo symmetrical geometry of a
magnetic configuration
Nested drift surfaces
Practical absence of rotational transform
MHD stability is provided by a magnetic
“hump” instead of a magnetic “well”,
divertor stabilization
High β
Pseudosymmetry Principle
•
The PS General Condition
Φ is toroidal magnetic flux,
F is a bounded function
B    B  F
B  B
F=F(ρ,θ,B) – weak isometry or quasiisodynamic (QID)
F=F(ρ,θ) – isometry
F=F(ρ) - quasisymmetry
F=0 - isodynamic or orthogonality condition
The PS physical meaning: all |B| =const contours on the equilibrium
magnetic surface encircle either the magnetic axis (Poloidal PS) or the
major axis of the torus (Toroidal PS)
No superbananas in that case
SKOVORODA, A.A., 3D Geometry of Currentless Magnetic Configurations with Improved Plasma Confinement,
Plasma Phys.Control.Fusion 47 (2005) 1911
Kinds of symmetry
Red circles –
isomagnetic lines
Red circles –
isomagnetic
lines
Toroidal symmetry
Poloidal symmetry
Poloidal pseudosymmetry
PS
system
Magnetic
axis
Isomagnetic
lines
Breaking of
the PS
Divertors influence on particles confinement.
The collisionless transversal particle losses take
place only from rather thin plasma layer (its thickness
is of Larmor radius, ρ, order of value) close to edge
magnetic surface (of confinement region). For fusion
products ρ is relatively large, but they are born rather
far from the separatrix.
For some little fraction of passing particles the losses
because of non adiabaticity can be important. That
can occur if such a particle endures displacement
from one magnetic surface to another during passing
through a CREL. It takes place in a layer with a
thickness of ρ order of value as well.
Plasma equilibrium in mirror trap with a
divertor
Plasma equilibrium in mirror trap with a divertor was calculated for
anisotropic plasma( p   p|| ) on base of generalized Grad – Shafranov
Equation and taking into consideration longitudinal equilibrium equation
(which binds p  and p|| )
The result is: presence of a divertor don’t prohibit from equilibrium
achievement at  ~ 1 , where the  value should be calculated
using plasma pressure and vacuum magnetic field in a divertor centre.
It should be noted that because of unlimited rising of U
U   B dl
1
near the separatrix, the equilibrium isn’t destroyed by CRELs influence.
ARSENIN, V.V., KUYANOV, A.YU., Plasma Equilibrium in Axisymmetric Open Divertor Configurations, Plasma Phys. Rep.,
26 (2000)741.
Plasma stability questions
Kadomtsev – Bernstein MHD flute mode stability condition
| U |
 p  U  p
0
U
2
wMHD
Marginally stable profile
U 
p  p0  
 U0 


  5/ 3
KADOMTSEV, B.B., On convective instability of plasma, Plasma Physics and the Problem of Controlled Thermonuclear
Reactions, Ed. by M.A. Leontovich (Pergamon Press, New York, 1960). Vol.4.
Plasma stability questions
II
Displacement in balloon
disturbance
1 – long wave disturbance
which defines in MHD
model;
2 – disturbance with zeros in
each divertor, which defines
with account of trapped
particles;
3 – antisymmetric mode
localized in divertor;
1
a
 cr ~ 
|  | L2
2
2
a
 cr ~ 
2
| | l
2
ARSENIN, V.V., KUYANOV, A.YU., Nonparaxial plasma equilibria in axisymmetric
mirror, Trans. Fusion Sci. Tech., 39 1T (2001) 175.
About Rotational Transform
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Project EPSILON does abandon in fact the rotational transform. MHD
stabilization is provided by plasma compressibility effects
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Magnetic surface topological stability against magnetic field disturbances is
provided in reality because any such disturbance generates unipolar
longitudinal plasma current, which results in small rotational transform that
provides topological stabilization of magnetic surfaces.
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The plasma compressibility stabilizing effect will be kept at presence of such
rotational transform up to values
~
i R
a
2
where i - ion Larmor radius, a – minor radius, R – major radius,
Some problems of high β
High β could raise some problems. For instance we should meet the QID conditions for
passing particles. At low average β the QID conditions are realized with magnetic
hump conditions. At high β those can be provided with magnetic well. But there is
some intermediate range of the parameter where the J contours are fully destroyed
that leads to high losses. So, high mode of operation should be achieved with some
force crossing of that barrier.
Radial and azimuthal dependence of the longitudinal invariant J for trapped
particles with different pitch angles in closed mirror trap
at <β> = 0.1%.
at <β> = 8%.
EPSILON magnetic configuration
а)
b)
(a) EPSILON magnetic
configuration with plain magnetic
axis and divertors in solenoidal
parts. Color of “near separatrix”
magnetic surface depends on
magnetic field module
value (minimal magnetic field at
solenoid axis 0.1T).
(b) Magnetic surface (U=const, above) and drift surface for strongly passing
partcles (full length of magnetic force lines L=const). Two cross sections for
CREL (different curvature positions) and for central section of solenoid.
External circles – turns with a current.
EPSILON Reactor Features
• Steady state operational mode. Current drive is not
necessary i.e. energy injection systems are necessary
only for ignition stage.
• High β mode of operation provides more flexibility for
in D-T reactor reactor realization and exploitation.
Advanced fuel cycles (D-3He and D-D catalyzed) can
be considered for EPSILON type reactor in connection
with high β operational mode.
• Magnetic system structure additivity. Each OME
length can be prolonged without principal limitations that
let increase reactor installed nuclear capacity.
EPSILON Reactor Features II
specific power, MW/m
3
10
1
0,1
0,01
0,00
0,05
0,10
0,15
beta
0,20
0,25
0,30
Specific power, MW/m3,
in D-T reactor at T=15
keV, B=5T,as a function
of β. It's increasing
(limited by wall thermal
load) lets to get more
compact reactor.
EPSILON geometry
causes more uniform
power flow to the first
wall
EPSILON Reactor Features III
1E25
1000
2
2
1E24
nTtE, [m keV s]
100
-3
tE, s
3
1
10
3
1E23
1
1E22
0,1
1E21
1
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
beta
Critical confinement time tE, [s],
as function of β at B=5T.
1) D-T,2) D-D cat.,3) D-3He
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
beta
Critical triple product, ntET, [m-3s
keV] as function of β at B=5T.
1) D-T,2) D-D cat.,3) D-3He
Proof-of-Principle Experiment EPSILON-M
(Proposal)
1
Plasma volume, m3
1.2
2
Average plasma diameter in solenoids, m
0.3
3
Main axis dimensions, m
1.6 x 5.2
4
Maximal plasma density, m-3
1019
5
Plasma temperature, keV
0.5
6
Confinement time, s
0.005
7
Average  in solenoids
0.1
8
Magnetic field in solenoids, T
0.1
9
Magnetic field in CRELs, T
1
10 Heating power, MW
0,5
Mode of operation – steady state. Working gases – hydrogen, deuterium. Plasma
heating methods: ICR, ECR, LH. Magnetic system – water cooled copper coils
Conclusion
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Theoretical investigations show that the proposed magnetic
confinement system should provide mirror confinement of majority
of plasma ions in practically axisymmetric mirror traps (solenoids
with set of divertors) and confinement of significant part of passing
particles. Plasma stability should be also provided by the divertor
system.
Previous mirror experimental activity can be used for EPSILON
development. In particular it is possible to use the ambipolar
methods of particle and energy confinement which are well
developed and checked.
The CRELs have a service function of energy loss diminishing. They
should liquidate thermal plasma loss to a wall along magnetic lines
and solve the problem of electron temperature.
Due to high β operational mode and specific structure, the system
seems to be rather attractive from its possible reactor perspective
point of view.