Vladimir Yu. Sergeev1), Boris V. Kuteev2), Aleksey S. Bykov1), Sergey V. Krylov2), Viacheslav G. Skokov1), Vladimir M. Timokhin1)

1)State Polytechnic University, Polytekhnicheskaya 29, Saint Petersburg, 195251, Russia2)NRC “Kurchatov Institute”, Kurchatov Square 1, Moscow, 123182, Russia

Lithium technologies for edge plasma control

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Outline

Background Experimental setup Results and discussion Summary Lithium in reactor

ISLA 2011

Outline

Background Experimental setup Results and discussion Summary

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Lithium technologies are extensively considered and used for discharge control in magnetic confinement devices (T&S)

The major goal of lithium supply to plasma is control of plasma-wall interaction

Approaches to deliver lithium into the plasma: Li pellet injection [1], liquid [2] and/or capillary-pore limiters [3] and divertor plates [4], prior evaporation [5], dust injection [6]

Li pellets had been injected at T-10 tokamak earlier [7]

Background

1. J.A. Snipes et al., J. Nucl. Mat. 196-198 (1992) 6862. R. Majeski et al., Nucl. Fusion 45 (2005) 519–5233. Mirnov S.V. et al., Plasma Phys. Control. Fusion 48 (2006) 8214. M.L. Apicella et al., J. of Nucl. Mater.363-365 (2007) 13465. M.G. Bell et al. Plasma Phys. Control. Fusion 51 (2009) 1240546. D. Mansfield et al., NIFS-CRC Symposium Toki, Japan, 20107. Timokhin V.M. et al., 33nd EPS Conf. on Plasma Phys. Roma, 19 - 23 June 2006, P-4.092 (2006)

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Background (continued) Models which couple core and SOL regions of multi-species plasma (like

with Li dust injection) are necessary for the technology development. An improved version of simple semi-analytical model [1] for simulation

of steady state tokamak regimes with a broad range of plasma actuators was developed and applied to study the influence of Li dust injection in ITER&DEMO conditions [2].

Recently improved version of the model explore the “2 point onion skin” approach of [3]. This model has been applied for simulations of divertor operation in the compact fusion neutron source based on spherical tokamak [4].

New injector for Li dust had been designed and tested at T-10 tokamak. First results are presented here.

1. V. Sergeev, B. Kuteev, Contrib. Plasma Phys. 2010, 50, No. 3-5, 285 – 291.2. B.V. Kuteev et al., Nucl. Fusion, 2010, 50 075001.3. P.C. Stangeby 2004, The Plasma Boundary of MF Devices, Inst. of Phys. Publ., Bristol, Philadelphia.4. B.V. Kuteev et al. in Fusion Energy 2010 (Proc. 23rd Int. Conf. Daejon, 2010) (Vienna: IAEA) CD-

ROM file FTP/P6-10.

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Edge plasma control for reactor SSO is a challenge

Steady state and long term operation of tokamak reactor requires a sufficient reduction and distribution over the first wall the heat loads coming from the core plasma due to heat and particle transport

Impurity injection into the radiative scrape-off layer (SOL) seems like a reasonable way to solve the problem

Recently, the interest to lithium injection has started to grow up. This material has the lowest Z and highest acceptable concentration in the plasma core. However, its radiation is rather low, so it was not clear whether the reactor regimes in tokamak be controlled by lithium injection

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Layout of heat, particle and radiation flows in a tokamak

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Contrib. Plasma Phys.3 (2010) 285Nucl. Fusion 50 (2010) 075001

The droplets are ablated in SOL and the lithium ionized migrates to divertor plates that etermines its density level in SOL

Lithium is injected in small droplet form with the characteristic size of 20-30 microns and the velocity 30-500 m/s

Collectors in divertor region provide closed cycle Lithium collectors

Outline

Background Experimental setup Results and discussion Summary

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Major problems for Lithium technology, experiment and modeling

Closed cycle - T

Acceptable injection rate + E

Radiation level recycling controlled! E

Core transport +/- E/M

Divertor loads + E/M

AH compatibility + E

Experimental setup: dust feeder schematic

Hopper volume 60 cm3 (30 g of lithium)

Scattering angle <7º

Transient time of switch on/off ~20 ms

Injection duration 50 ms-continuous

Rotation axis angle -8o- 8o to horizon

Hoper rotation velocity 0-50 rps

Dust flow rate 10-100 mm3/s (5-50 mg/s of Li)

Dust flow constancy ±5%

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B.V. Kuteev et al.

JNM, 2011

DOI information

10.1016/j.nucmat. 2011.02.23

The industrially produced SLMPTM powder [1] is used as the injection material.

SLMPTM - metal Li particles of ~40 m diameter covered by the micron layer of lithium carbonate (passivated surface).

Photos: dust feeder and dust particles

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1. FMC Lithium – Headquarters, Seven LakePointe Plaza 2801, Yorkmont Road, Suite 300 Charlotte, NC 28208, USA, http://www.fmclithium.com

Experimental setup: installation at T-10

Mechanical decoupling

Dust jet mechanical cutting off

Dust flow rate diagnostics

Independent pumping

Dust jet redirection to T-10 port axis

(Forced) dust jet cross-section profile forming and dust jet velocity decrease due to a system containing three funnels

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Pumping

Rail limiter

Pumping

Li

Fast valve

Light barrier

Experimental setup: connector

Funnel system

The motion axis of dust jet particles falling due to gravitation was tilted to the axis of tokamak port at 6 degree angle.

A system composed of three sequential funnels inside the connector was used.

The system shrunk the dust jet cross-section profile and changed essentially the temporal behavior of the flow rate of dust particles leaving the rotary feeder.

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Experimental setup: injection modesTwo modes of the injection operation (I&II) were realized:

(I) 3 rps, rotation axis angle 0, rotation duration time 500 ms

(II) 3 rps, rotation axis angle -1, rotation duration time 200 ms

At the exit of the funnel system the time evolution of dust flow rate depends on the rotation axis angle and differs for modes I&II

The injection duration time grows and the measured transient time of the dust flow rate are significantly longer than those of the rotary feeder

This time behavior is reproducible in more than 10 sequential T-10 shots for each mode of operation

Following slides illustrate the mode operation in T-10 experiments

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Outline

Background Experimental setup Results and discussion Summary

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Results and discussion: mode I (SS)Density

LiII

Bolometer

D

0 500 1000time, ms

U

CIII

Li flow0

02

1021

at/s

1013

cm-3

0

0

0

0

2

1

2

2

0

4

3

a.u.

a.u.

a.u.

V

a.u.

Mode I of Li dust injection, OH Black - #59471 without Li, blue - #59481 with Li

A steady state behavior of LiII radiation in plasma was observed.

Plasma density is slightly increased for a small (up to 81020 at/s) lithium flow rate. Most diagnostics signals are practically undisturbed at these conditions.

A slight decrease of the radiation level from plasma (bolometer) at higher plasma density can be considered as footprints of discharge conditioning.

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Results and discussion: mode IIDensity

LiII

Bolometer

D

0 500 1000time, ms

U

CIII

Li flow0

02

1021

at/s

1013

cm-3

0

0

0

0

2

1

2

0

4

3

a.u.

a.u.

a.u.

V

a.u.

2 Mode II of Li dust injection, OH. Black - #59609 without Li, red - #59707 with Li.

A moderate flow rate injection (up to 1.5 1021 at/s)

The disturbance of plasma parameters is more significant.

A decrease of the D signal when the electron density increases may be explained by a decrease of the recycling coefficient of plasma main component.

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Results and discussion: mode II with disruptionDensity

LiII

Bolometer

D

0 500 1000time, ms

U

CIII

Li flow0

02

1021

at/s

1013

cm-3

0

0

0

0

2

1

2

0

4

3

a.u.

a.u.

a.u.

V

a.u.

2 Mode II of Li dust injection with disruption, OH. Black - #59609 without Li, magenta - #59702 with Li.

Enhanced flow rate (up to 51021 at/s).

A decrease of the D along with the density growth during first 50 ms after the injection reveals the significant drop of the deuterium recycling coefficient.

After a series of minor plasma disruptions the major disruption occurs at 900 ms.

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Density

LiII

Bolometer

D

0 500 1000time, ms

U

CIII

Li flow

0

02

1021 at/s

1013 cm-3

0

0

0

0

2

1

2

0

4

10

a.u.

a.u.

a.u.

V

a.u.

2Results and discussion: mode II with ECRH

ECRH

Mode II of Li dust injection, OH+ECRH (140 GHz, 1.5 MW) Black - #59660 without Li, red - #59711 with Li

Moderate flow rate injection (up to 1.01021 at/s)

A rise of density and a decay of both bolometer and D signals due to Li injection during the ECRH pulse can be seen in comparison with the reference shot

The discharge conditioning effects are evident

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Outline

Background Experimental setup Results and discussion Summary

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SummaryTwo operation modes with a novel rotary feeder of lithium dust

have been realized on the T-10 tokamak

A quasi steady-state and pulse regimes with the Li flow rate up to 21021 atoms/s

are compatible with both OH and OH+ECRH plasmas

A higher flow rate of ~51021 atoms/s initiated a series of minor disruptions, which were completed by the discharge termination (major disruption)

Effects of wall conditioning during lithium dust injection have been detected. The injection reduced hydrogen recycling which was observed as the decrease of D signal accompanied by growing electron density. (Might be unfavorable for divertor loads)

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Lithium in ReactorInherent safety mission for major disruption mitigation

A liter of lithium placed on the first wall surface might be evaporated without any external control by the radiation emitted during thermal quench

The energy needed for ablation 10kJ/cm-3*1000cm-3 = 10 MJ

Plasma energy in DEMO 500MW*2 s = 1 GJ

This amount is sufficient to overcome the Rosenbluth density and might provide a safe current quench

The technology will be tested on T-10. The disruption will be initiate after massive Li-dust injection and such disruption characteristics will be compared with disruption without lithium

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Lithium in ReactorCorrosion problem is extremely sensitive to impurities.

Purification system is critical issue

Divertor plates nearby strike points will be definitely at higher temperatures than those acceptable for lithium (200-400 C). Functions of divertor targets and lithium collectors should be separated

ELM loads at a level of 3% of plasma energy (about 50 MJ) are capable to evaporate 5 liters of lithium from capillary targets. This is inacceptable without lithium recycling

Recycling with characteristic time of microseconds may reduce the ablated amount like the ratio ELM/Rec ~5

Reduction seems too small. Recycling is critical issue. Transverse flows are needed.

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Lithium in Reactor

What do we need for Lithium in Reactor?

We need new machines like NHTX and FNS-ST

-steady state

-high power density ( 10 MW/m3)

-flexible first wall thermo-hydraulic and shaping

-special design of divertor

What should we do?

“We must work harder!”

J. Hogan. EPS-discussions, 1980, Moscow

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