a. alfier – rfx-mod programme workshop 2009 – 20/22 jan 2009 density issues & lithization in...

A. Alfier – RFX-mod PROGRAMME WORKSHOP 2009 – 20/22 Jan 2009

Density issues

& Lithization in RFX-mod

A. Alfier, A. Canton, R. Cavazzana,

S. Dal Bello, P. Innocente, P. Scarin


Summary

Density issues in RFX-mod

Proposed lithization techniques on RFX-mod

– Lithium pellet injector

– Capillary Porous System

Status, schedule, application, advantages, disadvantages

Expectations & open issues on Lithium in RFX-mod


Density issues on RFX-mod

RFX-mod first wall (graphite tiles) is an extended reservoir of particles

-> density at flat top (FT) it does not depend on the fuelled particles

-> it is entirely sustained by particles fluxes from the wall 0

5

10

15

20

0 2 4 6 8 10

Fuelled particles (1020 H atoms)

Ele

ctr

on

de

ns

ity

at

FT

(10

19m

-3)

Wall condition affects density: the capability of the wall to absorb particles influences the value of I/N more than the absolute number of particles stored in the wall0

2E-14

4E-14

6E-14

8E-14

1E-13

1.2E-13

1.4E-13

1.6E-13

1.8E-13

0 50 100 150 200

Des%

I/N (A

m)

Absorbing wall:wide range of density regimes

Not absorbing wall:I/N forced to the value 2x10-14 Am

Des% (desorption)=

outpumped-part. / filled-part (%)


0

2

4

6

8

10

12

14

0 50 100 150

Vt(0)*I (V*MA)

Cen

tral

ele

ctro

n d

ensi

ty (

101

9m

-3)

Plasma itself extracts particles from the wall (PWI): Density depends on Ohmic Power, that regulates particle influxes from the wall.

Particles stored in the wall are not enterely accessible by plasma (implantation depth, toroidal and poloidal asymmetries).

In RFX-mod we outgas a minimum part of the particles that we inject we should always fuel the discharge with the minimum gas to allow breakdown.

Wall pre-loading by means of H2 GDC is under test as a reproducible method to obtain a discharge with desired flat top density.

Density issues on RFX-mod


Why Lithium?

- More pronounced pumping effect than Boron (strong H and H+ retention, LiH)

- High impurity getter (O2, N2, CO, H2O, CO2…)

- Reduction of C chemical and physical sputtering (H. Sugai, JNM 1998)

- Ionization potential (1s2 2s1): 5.6 eV (I), 75 eV (II), 122 eV (III)

- Highest specific heat capacity of any solid element

Total wall inventory> 3 times, no sign of

saturation

Sanchez and the TJ-II Team, PSI 2008


1. Non-cryogenic pellet injector262.30°

equatorial port

2. Capillary Porous System262.30°

central bottom oblong port

Available lithization techniques on RFX-mod

Top view of RFX-mod


Injector characteristics

• Pellet speed: 50÷200 m/s

• Pellet size: Ø 0.5÷2 mm x 1÷4 mm

• 30 pellets in the charger

• Materials: Li, C, B

Aims

• Measurement of the pitch of the magnetic field lines

• Transport studies

• First wall conditioning

Pellet

On RFX-mod:Non-cryogenic pellet injector


•Pellet size: Ø 1.5 mm x 4 mm = 28 mm3

NLi≈ 1021 & SRFX=36.3 m2

≈ 2.6 monolayers if uniformely distributed

Schedule:

• Installation at middle/end of february ’09;

• Delivery of interface system with vessel (the injector is already here) at end of february ’09;

• Tests on RFX-mod available since middle/end of march (related to the RFX-mod 2009 experiments schedule).



Strategy:

1. first wall conditioning with He glow discharge;

2. injection in standard and then performing RFP discharges at the end of the current flat-top;

hint: the injection on tokamak discharge could be usefull to obtain a more uniform distribution of Lithium, but probably a tokamak discharge will not ablate entirely the pellet and sustain the incraese of density.

Advantages:

- control the amount of the injected Lithium;

- easy to use (well-established technique) and to compare with similar discharge w/o pellet;

- injected lithium of good pureness;

- lithium effective during the discharge;

- non uniform deposition (only where plasma touches the wall);

Disadvantages:

- thin Lithium layer deposited (few monolayers) short length beneficial effects (few shots);

- maybe non uniform deposition also where plasma touches the wall;

- Li-pellet injection perturbs plasma before its beneficial effects appear being at the end of the flat-top, it prepares the first wall for next discharge



On RFX-mod: Capillary Porous System (CPS)

500m

m

Hint: The gate valve should be installed below coils additionl 500÷800mm

CPS unit operating position

CPS unit storage position

Schematic layout of CPS on RFX-mod


On RFX-mod: Capillary Porous System

120mm clearness

Ø150mm valve

~120mm

General view of the CPS

RFX-mod oblong window port with CPS


Modification of the FTU support



Capillary Porous System on FTU


Strategy:

1. First wall conditioning in H2 GDC + Baking decrease impurity content;

hint: Li reacts with O, C, N (LiOH, Li3N, Li2CO3)

2. He discharge decrease H content (Li reacts with H);

3 Baking decrease He content.

hint: He can be captured in Li voids, and it could then released during several discharges

4. Define a “suitable” Tokamak dicharge (60-80 kA, n=1-21018 m-3, t=400ms, q=2-4);

5. Condition the first wall with CPS in tokamak discharges.

6. Extract the CPS.

6. RFP plasma @ Ip ~ 0.5-1.5MA, F=-0.03 ÷ -0.08.

7. …. We’ll keep you informed!


Schedule:

• Procurements of materials on loan from FTU: end of summer 2009.

• Installation and test : autumn 2009.

• Tests on RFX-mod available beginning of winter 2009.


Advantages:

- on loan from FTU for first attempt on RFX-mod.

- easy to handle;

- injected lithium of good pureness;

- high heat load threshold (10 MW/m2) compatible with reactorial previsions

Disadvantages:

- not usefull during RFP discharges (Li would be deposited in +-20 tor. deg. from CPS)

- the amount of Li deposited on the first wall not straighforward to control.

- requires first wall conditioning with tokmak discharges.

- never used before on other RFP experiments.



Expectations & open issues on Lithium in RFX-mod

Expected effects (from experience on other machines):

- lower & controlled recycling with absorbing wall

- lower Zeff and radiation losses

- Te increase E improved

Open issues:

Lithium deposition on optics if Li+ born in field lines, it does not result in window coating

Effects on internal probes : Li does not react with Mb, Fe, Ti, Stainless steel Li reacts with Cu, but no effect reported in literature & no relevant effect

on NSTX and TFTR if not with evaporator (priv. com.)

Effect of Li penetration (“intercalation”) in graphite tiles experience from other experiments

Too low recycling fuelling issues

3-8 hours He GDC used to recover wall condition w/o lithium (Vershkov, IAEA ’08 & in Sugai, J. Nucl. Material ’95).


Further tasks:•Real time or inter-shot measurement of the deposited Lithium (e.g.: quartz crystal oscillator).

•Expose samples (of graphite, mirror and windows) to plasma. three experimental proposal for 2009.


Thank you


Available lithization techniques

1. Lithium pellet injection (TFTR)

J.A. Snipes et al. J. of Nucl. Mater. (1992) 686 - 2 mm Ø x 2 mm

1-2 Monolayers coated on TFTR graphite limiter

Pellet injected in conditioning He discharges and standard discharges

2. Lithium aerosol - DOLLOP (TFTR)

D.K. Mansfield et al. Nucl. Fusion 41 (2001) 1823

Li contained in a small (17.5 cm3) boron nitride cauldron positioned 15 cm below the shadow of the TFTR RF limiter edge

The highest total energy confinement time was obtained in TFTR with this technique (about 80% improvement, Zeff = 1.2-1.3)



3. LIThium EvaporatoR - LITER (NSTX)

R. Kaita & H. Kugel, APS 2008

Li heated inside an “oven”

E improved, Te profile broadened

Lowered recycling

4. Lithium aerosol with powder (NSTX)

Mansfield, APS 2008

98.5% Li +1.5% Li2CO3 particles (Ø =50m)

Similar effect of LITER, with even more

reduced impurity accumulation

100 m


5. Li Capillary Pore System (CPS)

Tested in T-11M and FTU Tokamaks (S.V. Mirnov et al. Fusion Eng. Des. 65 (2003) 455, M.L. Apicella at al. J. of Nucl. Mater. (2007) 1346.

See previous talk.


6. CDX-U low aspect ratio tokamak (PPPL)

Lithium tray limiter filled with a total of 300 g (0.6 l) of lithium + evaporator

E improved, lower Zeff, lowered recycling


Lithium chemistry

• Low thermal expansion: 46 µm·m−1·K−1 • Highest specific heat capacity of any solid element: 24.860 J·mol−1·K−1 • Thermal conductivity: (300 K) 84.8 W·m−1·K−1 heat transfer applications

• Melting point: 180.54 °C• Boiling point: 1342 °C

• High electrochemical potential, light weight, and high current density lithium-ion batteries• 6Li + n → 4He + 3H (blanket of ITER)• high surface tension effect on physical sputtering


• Ion Li+, which have a smaller diameter, can easily displace K+ and Na+ and even Ca2+, in spite of its greater charge, occupying their sites in several critical neuronal enzymes and neurotransmitter receptors.

• Although Li+ cannot displace Mg2+ and Zn2+, because of these ions' small size and greater charge (higher charge density, hence stronger bonding), when Mg2+ or Zn2+ are present in low concentrations, and Li+ is present in high concentrations, the latter can occupy sites normally occupied by Mg2+ or Zn2+ in various enzymes.

• Lithium hydroxide (LiOH) is an important compound of lithium obtained from lithium carbonate (Li2CO3). It is a strong base, and when heated with a fat, it

produces a lithium soap. Lithium soap has the ability to thicken oils and so is used commercially to manufacture lubricating greases

• lithium peroxide (Li2O2) • 2 Li2O2 + 2 CO2 → 2 Li2CO3 + O2. • lithium hydroxide (LiOH and LiOH·H2O), lithium nitride (Li3N) and lithium

carbonate (Li2CO3, the result of a secondary reaction between LiOH and CO2).• Lithium carbide, Li2C2: molten lithium + graphite are reacted at high

temperature

Lithium chemistry


Before Li

with Li

CarbonHigh Z imp.

Vershkov, IAEA ‘08

Effect on impurity on T-10


Wall control on T-10

Vershkov, IAEA ‘08

He GDC used to recover wall condition w/o lithium (also in Sugai, J. Nucl. Material ’95).


Scanning quartz deposition monitor (QDM).


Expose samples (of graphite, mirror and windows) to plasma.


Kaita et al. IAEA 2008

a. alfier – rfx-mod programme workshop 2009 – 20/22 jan 2009 density issues & lithization in...

Documents

rfxmod available

rfxmoddensity issues

wall conditioning

wall pwi

cryogenic pellet injector262

density issues lithization

particles fluxes

fuelled particles