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Modular: Argon purification and handling

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Modular: Argon purification and handling Claudio Montanari INFN - Sezione di Pavia Outline Basic considerations Standard procedures from ICARUS experience Large ... – PowerPoint PPT presentation

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Title: Modular: Argon purification and handling


1
Modular Argon purification and handling
  • Claudio Montanari
  • INFN - Sezione di Pavia

2
Outline
  • Basic considerations
  • Standard procedures from ICARUS experience
  • Large volumes challenges
  • Dimensioning and design of purification systems
    for ModuLAr
  • Conclusions

3
Basic Considerations
  • Considerable experience of the Icarus
    Collaboration has shown that free electron
    lifetimes of several milliseconds are currently
    realised with commercial purification systems
    based on OxysorbTM and molecular sieves.
  • In order to ensure a free electron lifetime for
    the longest 3 ms fly path a vigorous
    purification of the LAr must be kept at all
    times
  • In analogy with what is currently performed with
    T600 and all previously constructed detectors,
    the purification must be performed both in the
    liquid and in the gaseous phase.
  • The reference schemes developed so far within the
    Icarus Collaboration can be rescaled
    straightforwardly up to volumes of some thousands
    cubic meters.

4
Attainable Free Electrons Lifetime
Free electron lifetimes in excess of several
milliseconds are routinely achieved with the
standard procedures developed within the Icarus
Programme. Present best result is in the range
of 10 ms actually limited by our capability to
measure longer lifetimes due to the limited size
of the detector.
Free Electron Lifetime evolution during
recirculation of 50 liters chamber
5
Basic Requirements
Required Lifetime for 4m drift 10 ms ?? 0.03
ppb (O2 equiv) Required Lifetime for 2m drift 5
ms ?? 0.06 ppb (O2 equiv)
6
Basic Requirements
Use of larger drift fields brings several
advantages, including a reduction in the
requirements for the free electrons lifetime. 1
kV/cm could be attained rather easily for 2 m
maximum drift corresponding to 0.5 kV/cm for 4 m
maximum drift.
7
The Standard Icarus Procedure
  • The standard Icarus procedure for purification
    and handling LAr consists of 5 steps
  • Use ultra high vacuum standards for detector
    components design, construction, cleaning and
    assembly
  • Removal of air and outgassing of surfaces by
    evacuating the argon container volume to the
    molecular vacuum level (lt 103 mbar)
  • Fast cooling (to reduce pollution from
    outgassing) and filling with argon ultra-purified
    by means of chemical filters and molecular
    sieves
  • Recirculation of the gas phase to block the
    diffusion of the impurities coming from the hot
    parts of the detector and from micro-leaks on the
    openings (typically located on the top of the
    device) in the bulk liquid
  • Recirculation of the bulk liquid volume to
    further reduce the impurities concentration up to
    the required level.

8
Large volume challenges
  • Extrapolation of the standard Icarus procedure to
    volumes potentially very large (up to 10000 m3 or
    more) is almost straightforward except for step 2
    (evacuation to molecular vacuum of the detector
    volume).
  • A detector of several thousand m3 is very hard to
    evacuate and a new method has to be applied. The
    idea is to perform successive flushing in the
    gaseous phase in order to attenuate the presence
    of gases other than Argon with an approximate
    exponential chain.
  • An improvement in the liquid purification system
    is also needed to enlarge in a significant way
    the TPC volume. New purification devices have to
    be implemented, possibly operating near or
    directly inside the detector. They should be
    simple, robust and without moving parts, to
    guarantee total reliability.

9
Large volume challenges (II)
  • Uniformity in the free electrons lifetime is a
    major issue for very large volume detectors.
    Convective motions provide a natural mechanism
    for mixing the liquid volume. For such a
    mechanism to be effective in providing uniformity
    of the liquid purity, liquid motions and the
    effect of the presence of the detector structures
    have to be carefully studied at the design level.
    Trapped volumes have to be avoided the
    distribution network of the purification and
    recirculation system have to be designed
    accordingly.
  • In running conditions, monitoring of the
    uniformity of the liquid properties can be easily
    performed by means of cosmic muon tracks.
  • A number of dedicated devices (purity monitors)
    have to be installed in the non active zones
    (behind the wires and the race tracks) to
    complete the information and to check the purity
    during the initial filling and the startup phases
    of the detector.

10
Alternatives to vacuum (I)
  • Standard procedures, adopted to pre-condition
    industrial storage cryostats before first
    filling, reduce air concentration at the level of
    ppm in the gas phase, corresponding to ppm level
    in the liquid phase, after filling. These
    procedures are based on high rate flushing of the
    connecting pipes and of the container inner
    volume from the bottom to the top.
  • Tests have been made by the ICARUS Collaboration
    to avoid high vacuum before filling
  • With the 10 m3 prototype, empty, no structures
    inside high rate flushing of the connecting
    pipes plus compression / expansion cycles in the
    main volume
  • about 100 cycles from 1.0 to 1.1 bar,
    corresponding to 10 volumes exchange ?? 5 ppm
    residual air concentration for perfect gas
    diffusion results from computation
  • Free electron lifetime after filling 30 µs.
  • For these procedures to be effective, the
    geometry of the internal detector structures have
    to be carefully studied in order to eliminate
    trapped volumes (tubular elements, preferential
    flow paths, etc.). This matches with the
    requirement for the uniformity of the liquid
    purity.

11
Simulations
  • A detailed simulation of the basic ModuLAr design
    has been performed using the FemLabTM code (a
    professional tool to solve gas transport
    problems).
  • Several options have been considered
  • Gas injected on one side of the volume and
    extracted from the opposite side
  • Gas injected on the bottom of the volume and
    extracted from the top
  • Different flow rates.
  • Results of the simulation indicate that the best
    solution consists in injecting the argon on the
    bottom of the container and extracting it from
    the top (due to the larger weight, argon
    concentrates on the bottom, pushing the air to
    the top)
  • few volumes ( 6) of gas flow are required to
    reach a residual air concentration lt 1 ppm (lt 1
    ppb in the argon liquid phase).

12
Filling procedures
T600 Purification Unit
  • Filling rate should match the maximum supply rate
    of liquid Argon. Reasonable estimate for supply
    speed from a single dealer is 100 m3 / day (5
    trucks). This leads to a filling rate 4 m3 /
    hour (6 at the design level) about 40 days will
    be necessary to fill a 4000 m3 detector.
  • Single HydrosorbTM / OxysorbTM cartridge (type
    R20, maximum size commercially available) like
    the ones used for the T600 (see right)
  • Purification rate 0.5 m3 / hour
  • Adsorption capacity 40 normal liters of O2
  • The number of purification cartridges required
    for the initial purification of the liquid volume
    is correlated with the purity of the argon
    provided by the supplier. Very low Oxygen (and
    other contaminants) concentrations (small
    fractions of ppm or less) can be obtained at the
    production level and can be part of the
    requirements of the supply contract.

13
T600 purification Units
Liquid recirculation pump
Purification unit
14
A self cleaning cryostat
  • With a good control of the input heat and then of
    the convective motions, it could be possible to
    realize a self cleaning liquid circuit,
    collecting the LAr inside a number of cleaning
    boxes placed on the walls.
  • The mass of LAr moved is potentially very large.
  • It is an improvement that will allow to avoid an
    external circulation.
  • For a 4000 m3 liquid argon volume, a rate 240
    m3/day (6/day or purification cycle of 16.6
    days) would allow to reach in 60 days the target
    purity (0.03 ppb) if the initial e-negative
    concentration is at the level of 1 ppb (O2
    equiv.).

cleaning
15
Gas Recirculation System
Gas recirculation scheme
Recirculation of the gas phase is used to prevent
diffusion of impurities coming from to hot parts
of the detector and from openings (almost all
located on the top) in the liquid volume. In this
case the T600 scheme can be used with no
modifications.
Required gas recirculation rate scales like the
top surface of the liquid volume. Extrapolating
from the T600 case we have that, for an exposed
surface of 9 x 51 m2 (4000 m3 ModuLAr) there is a
factor 6 surface increase with respect to the
T600. A gas recirculation rate of about 600 Nm3 /
hour will be required .
16
LAr Purity Monitor working principle
Lifetime ??Determination
17
T600 purity monitor
ReadOut Electronics
RD is in progress for new photocatodes to
improve the sensitivity.
18
Conclusions
  • Free electron lifetimes of several milliseconds
    are required for the operation of 4.5 kton or 9
    kton ModuLAr detectors. Such purities are
    routinely achieved using standard procedures
    developed within the ICARUS programme.
  • Extrapolation of the standard ICARUS procedures
    for the basic ModuLAr designs is almost
    straightforward with one relevant exception
    removal of air from the main argon volume and
    pre-conditioning of the internal surfaces before
    filling with LAr has to be done by high rate
    flushing of pure Argon gas.
  • For such a procedure to be effective, geometry of
    the internal detector structures must not contain
    trapped volumes.
  • Standard procedures used to pre-condition
    cryogenic storage dewars are able to remove air
    to the level required for the filling of the
    experiment.
  • Our simulations also demonstrate that a residual
    concentration of air in the argon volume of less
    than 1 ppm can be reached in less than one month
    with a rather modest gas flow rate.
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