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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

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slide1
Density issues

& Lithization in RFX-mod

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

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

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

summary
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

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

density issues on rfx mod
Absorbing wall:

wide range of density regimes

Not absorbing wall:

I/N forced to the value 2x10-14 Am

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
  • 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 wall

Des% (desorption)=

outpumped-part. / filled-part (%)

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

density issues on rfx mod1
Density issues on RFX-mod
  • 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.

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

why lithium
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

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

available lithization techniques on rfx mod
Available lithization techniques on RFX-mod
  • Non-cryogenic pellet injector
  • 262.30°
  • equatorial port

2. Capillary Porous System

262.30°

central bottom oblong port

Top view of RFX-mod

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

slide7
On RFX-mod:Non-cryogenic pellet injector
  • 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

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

slide8
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).

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

on rfx mod non cryogenic pellet injector
On RFX-mod:Non-cryogenic pellet injector
  • 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

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

on rfx mod capillary porous system cps
On RFX-mod:Capillary Porous System (CPS)

CPS unit operating position

500mm

CPS unit storage position

Schematic layout of CPS on

RFX-mod

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

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

on rfx mod capillary porous system
On RFX-mod:Capillary Porous System

~120mm

RFX-mod oblong window port with CPS

120mm clearness

Ø150mm valve

General view of the CPS

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

on rfx mod capillary porous system1
On RFX-mod:Capillary Porous System

Modification of the FTU support

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

capillary porous system on ftu
Capillary Porous System on FTU

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

on rfx mod capillary porous system2
On RFX-mod:Capillary Porous System
  • 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=1-21018 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.

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

on rfx mod capillary porous system3
On RFX-mod:Capillary Porous System
  • 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.

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

expectations open issues on lithium in rfx mod
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
    • tE 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).

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

slide17
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.

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

slide18
Thank you

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

available lithization techniques
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)

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

available lithization techniques1
Available lithization techniques

3. LIThium EvaporatoR - LITER (NSTX)

  • R. Kaita & H. Kugel, APS 2008
  • Li heated inside an “oven”
  • tE improved, Te profile broadened

Lowered recycling

4. Lithium aerosol with powder (NSTX)

  • Mansfield, APS 2008
  • 98.5% Li +1.5% Li2CO3 particles (Ø =50mm)
  • Similar effect of LITER, with even more

reduced impurity accumulation

100 mm

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

available lithization techniques2
Available lithization techniques

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
  • tE improved, lower Zeff, lowered recycling

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

lithium chemistry
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

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

slide23
Lithium chemistry
  • 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

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

slide24
Effect on impurity on T-10

High Z imp.

Carbon

Before Li

with Li

Vershkov, IAEA ‘08

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

slide25
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).

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

scanning quartz deposition monitor qdm
Scanning quartz deposition monitor (QDM).

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

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

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

slide28
Kaita et al. IAEA 2008

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

slide29
Kaita et al. IAEA 2008

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

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