Density issues

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• Density issues
• Lithization in RFX-mod
• A. Alfier, A. Canton, R. Cavazzana,
• S. Dal Bello, P. Innocente, P. Scarin

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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

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Density issues on RFX-mod

• RFX-mod first wall (graphite tiles) is an
  extended reservoir of particles
• -gt density at flat top (FT) it does not depend on
  the fuelled particles
• -gt 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 ()
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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.
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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
• gt 3 times, no sign of
• saturation

Sanchez and the TJ-II Team, PSI 2008
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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
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On RFX-modNon-cryogenic pellet injector

• Injector characteristics
• Pellet speed 50200 m/s
• Pellet size Ø 0.52 mm x 14 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

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On RFX-modNon-cryogenic pellet injector

• Pellet size Ø 1.5 mm x 4 mm 28 mm3
• ? NLi 1021 SRFX36.3 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).

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On RFX-modNon-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

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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 500800mm
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On RFX-mod Capillary Porous System
120mm
RFX-mod oblong window port with CPS
120mm clearness Ø150mm valve
General view of the CPS
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On RFX-mod Capillary Porous System
Modification of the FTU support
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Capillary Porous System on FTU
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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, n1-2?1018 m-3, t400ms, q2-4)
• 5. Condition the first wall with CPS in tokamak
  discharges.
• 6. Extract the CPS.
• 6. RFP plasma _at_ Ip 0.5-1.5MA, F-0.03 -0.08.
• 7. . Well 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.

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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.

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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).

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• 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.

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• Thank you

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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)

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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
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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

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Lithium chemistry

• Low thermal expansion 46 µmm-1K-1
• Highest specific heat capacity of any solid
  element 24.860 Jmol-1K-1
• Thermal conductivity (300 K) 84.8 Wm-1K-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

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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 LiOHH2O), 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

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Effect on impurity on T-10
Carbon
High Z imp.
Before Li
with Li
Vershkov, IAEA 08
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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).
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Scanning quartz deposition monitor (QDM).
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Expose samples (of graphite, mirror and windows)
to plasma.
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Kaita et al. IAEA 2008
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Kaita et al. IAEA 2008