Primary Investigating of Radiation Research on HL2A

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Primary Investigating of Radiation Research on
HL-2A
Pan Yudong 2004.3.15
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Impurity transport
Recent research state in the worldThe mainly
impurity transported in the core plasma is radial
and anomalous, but sometimes it arrives to
new-classical level. The impurity transport in
the peripheral plasma has no experimental
research until now. The impurity study in the
divertor is in the middle level. Plasma radiation
is important part of impurity transport. Impurity
particles can be transported far from where they
are born. Accumulation of impurities and the
accompanying radiation losses in the core plasma
are serious problems in efforts to achieve a
reactor grade plasma. On the other hand,
radiation localized in the peripheral plasma is
sometimes favorable. Use of poloidal divertor is
one of the most effective methods of impurities
control. The main question of the impurity
transport Could we arrive a balance with enough
low impurities accumulation in the core plasma
area and enough high impurity density localized
in the edge plasma?
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Principal Method
Bolometry is used to measure the integral
radiation losses from the plasma in widely
spectral ranges. The radiative power includes all
types of plasma emission, not only from photons
but also from the neutral particles. For example,
the Bremsstrahlung,the line radiation of
impurities, electron cycle radiation and
recombination radiation.The plasma in Tokamak
device certainly mixes with impurities particles.
According to our present understanding, the
radiative power density from the plasma varies
with electron density, impurity content and its
emissitivity
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System Constitution
AXUV detectorPreamplifierAuxiliary Units ADC
Data Processing System Auxiliary unitsPower
Supply unit,high voltage optoelectronic galvanic
isolation unit,Pinhole,Shutter protection unit
,simple throughout testing/calibration unit, etc.
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Two kinds of detectors comparison AXUV detector
and Metal detector
Type metal-resister bolometers
(ReferenceNuclear Fusion, Vol.22,
No.12.(1982). Spectral regioncore plasma10
A2000A (with gold coating) divertor10A
(With Blackened surfaces) Response
time110ms. Type AXUV Photodiodes Spectral
region1eV10keV(12,400A1.24A)
Rise/fall time(1090)0.5
Flat response spectral range0.26 A/W
5(306000eV) Disadvantage No window, No
response to neutral particles.
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AXUV (Absolute Extreme Ultra Violet) silicon
photodiodes

• Major features
• Fast response
• Low piezosensitivity
• High detector radiation hardness
• Input window protecting shutter

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AXUV Operating Principles
When these diodes are exposed to photons of
energy greater than 1.12 eV electron-hole pairs
(carriers) are created. These photogenerated
carriers are separated by the p-n junction
electric field and a current proportional to the
number of electron-hole pairs created flows
through an external circuit. For the majority of
XUV photons, about 3.7 eV energy is required to
generate one electron-hole pair. Thus more than
one electron-hole pair is generally created by
these photons. This results in device quantum
efficiencies (electrons seen by an external
circuit per incident photon) much greater than
unity, which increase linearly with photon
energy.
High quantum efficiencies for XUV photons. 1)the
absence of a surface dead region. 2)extremely
thin (3 to 7 nm), radiation-hard silicon dioxide
junction passivating, protective entrance window.
Typical quantum efficiency of the AXUV
photodiodes.
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HL-2A bolometer cross-section and channel
information
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Radiation profiles in the limiter configuration
Chord intensity profiles and total power
evolution. (a) a38cm,Ip100kA,Nelt0.5x1013cm-3,sho
t992(b)a40cm,Ip100kA,Ne0.7x1013cm-3,shot1190?

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Radiation profiles in the divertor configuration
Chord profiles and the main plasma parameter in
HL-2A divertor configuration. (shot1654,flat
top,Ip139kA,ne0.91019m3).
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Statistic Conclusion Radiation power ver Plasma
Current
Limiter discharges in ASDEX(Prad/Poh4585), JET
(Prad/Poh7090),TFTR (Prad/Poh80).
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Statistic Conclusion Radiation power ver Plasma
density
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Conclusion
   New designed single array (AXUV detector
diagnostic system, 16 channels) is installed in
the HL-2A. After Argon absolute calibration, it
can provide accurate measurement of the core
plasma radiation of the HL-2A in the limiter and
divertor configurations. The statistic result
shows the main chamber radiation (Prad/Pohmic
4580) in the limiter configuration is larger
than that in the divertor (Prad/Pohmiclt50). In
Contrast with the symmetric radiation profile in
the limiter configuration, the radiation profiles
are poloidal asymmetric in the divertor
configuration. It is found that an enhanced
plasma radiative region existed near the X-point
area. In the range of Iplt150kA,nelt1.5e1019m-3,
Prad/Pohmic is independent of the plasma current
and density both in the limiter and divertor
discharges. In the divertor discharges, the heat
load onto the divertor plate and divertor chamber
is more than 50 input heating power. It is very
necessary to consider the protection of divertor
plate to avoid the sputtering of the impurities.
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Question and proposal

• The main question of the impurity transport
  Could we arrive a balance with enough low
  impurities accumulation in the core plasma area
  and enough high impurity density localized in the
  edge plasma?
• For more detail, in order to keep the
  impurities in the main divertor area,what can we
  do? Could the target plates and divertor chamber
  of HL-2A stand the most part of heating power?
• (1)The experience of HL-1,HL-1M,HL-2A shows
  robust plasma body always has strong radiation in
  the edge plasma area. There is no impurity
  accumlation in the core plasma even with no
  coating processing wall.
• (2)The combine work from VUV, Bolometry,
  thermocouple, IR Camera is very important to
  study the energy balance.
• (3)single chord-single array(multi chords)-multi
  array is developing way to obtain more local
  radiation information.