Technology Challenges for Diagnostics for MFE Measurement and Control

1
Technology Challenges for Diagnostics for MFE
(Measurement and Control)

• K. M. Young (PPPL)
• FESAC Priorities Sub-Group
• May 21, 2004

2
ITER provides Unique Technical Challenges for
Diagnostics
Measurement requirements demand performance
capability for present-day machines
alpha-particle measurement, operation in
radiation environment, presence of blankets,
reliability, calibration maintenance, control
data for machine protection. Significant
engineering design issues.
Port-plug with penetrations for Thomson
scattering, interferometry, etc.

• 2m high x 1.8m wide x 3.5m long
• Weight 66 tonne
• Side and bottom 130mm thick
• Front port flange 200mm

Designs by C. Walker (JCT)
Equatorial port-plug concept
3
Technology Issues for Diagnostics

• Long-pulse (steady-state) device issues
• Maintenance of alignment, calibration,
  reliability,
• High temperature/neutral particle impact on
  windows (seals),
• Coating of optical components (metallic mirrors,
  windows).
• Cooling of active components (e.g. shutters,
  detectors),
• Design of supporting structures,
• Development of new detectors/sources (some
  examples)
• High temperature solid-state X-ray detectors,
• Compact solid-state magnetic sensors,
• Detectors for Alternate Concept Devices,
• Stable cw intermediate-power microwave sources,
• IR fiberoptics.
• Neutral Beams for Active Spectroscopy,
• Other neutral-particle sources??
• Criteria for the input to plasma control.

4
Additional Technology Issues for Diagnostics for
BPXs

• Neutron environment significantly raises the
  challenge
• Integration of components and shielding
  structures with remote handling (already an issue
  on JET),
• Radiation effects on components,
• Real-time changes in properties,
• Noise background,
• Survival,
• Neutronics calculations for viability, shielding,
• Operation of mechanical hardware (e.g. shutters,
  actuators, location sensors),
• Detectors for the environment
• Bolometers,
• High-temperature sensors for escaping a-particles.

5
Alignment, Calibration, Reliability

• With long port necks and plasma very close to
  limiting surfaces, diagnostics must maintain
  precise alignment independent of large structural
  movements near them.
• Techniques for checking on calibration during
  long pulses must be developed
• Present-day diagnostics have operated with
  extraordinary reliability after long shakedown
  but a new level is required
• e.g. Thomson scattering laser (and windows,
  mirrors) will have gt1x107 pulses (gt1x104 in one
  discharge).

6
Living with the Environment inside the Vacuum
Vessel

• Qualification of materials that can be used in
  vacuo at high temperature (and radiation?)
• Vacuum windows to withstand neutral-particle
  bombardment, high temperature excursions (plus
  hot walls) will probably have to be developed,
• Deposition of coatings and dust on windows,
  mirrors, sensitive detectors must be understood
  and be quantifiable. Can it be removed in vacuo?
• Cooling techniques (mounting or active cooling)
  have to be developed.
• Components must be designed for ease of
  replacement (possibly by remote handling).

7
Intense Neutral Beams are Critical for Diagnostics

• Measurements dependent on Neutral Beams
• Emission from plasma neutrals
• Ion temperature CXRS, X-ray Crystal, Neutrons
• Poloidal rotation CXRS, X-ray Crystal
• Toroidal rotation CXRS, X-ray Crystal
• Core impurities CXRS (low-Z), X-ray Crystal
  (high-Z)
• Core helium-ash CXRS
• Thermalizing Alphas CXRS
• Emission from beam neutrals
• Current density MSE, polarimetry, Zeeman
  (edge/Li-beam)
• Turbulence Beam Emission Spectroscopy,
  Reflectometry
• CXRS, MSE and BES provide local measurements.
  Requirements on spatial and temporal resolution
  for physics and control of advanced tokamaks may
  be met.

8
The Development Issue for a DNB
Approximate numbers
Compression of beam size by factor 90 for ITER
DNB (using HB source) is extreme (not including
divergence). Current density extrapolation is
huge.
9
Operational Issues for the Neutral Beams

• For ITER Heating Beam
• Primary function to heat and drive
  current/rotation,
• Wide range of energies planned (400 - 1000 keV),
• Variable angle capability (?),
• Control diagnostic (MSE) should not be dependent
  on a system being controlled.
• For ITER Diagnostic Beam
• Same beam hardware is planned as for heating
  beam, even though ve beam may be better at 100
  keV.
• For ve beam no optimization considered to
  maximize signal strength versus beam energy,
  including beam neutralization.
• For IDNB
• Major development effort required
• Frequency and reproducibility of source,
• Divergence and neutralization are key issues not
  yet addressed.
• Note for NCSX a lower energy, lower power beam
  is required (STTR?)

10
Integration of Systems to provide Plasma Control

• AT tokamak performance will be controlled using
  (noisy) plasma profile information.
• BPXs must operate close to the b-limit based on
  plasma parameter profiles.
• Amelioration must be triggered early,
• Too far short of limit gives low-Q,
• Over limit causes hardware damage.
• Active MHD control will be required.
• Raw diagnostic data must be integrated with
• software and responding systems to allow for best
  
• plasma performance for extended periods.

11
Integration of Diagnostics with Shielding and the
Impact of Radiation Streaming in Penetrations

• Radiation streaming is a critical concern for
  FIRE. Impacts
• Coil insulation and local diagnostic components
  in real time,
• activation levels in the hall.
• Pre-conceptual designs done of penetrations of
  two ports for first streaming calculations.
• First calculations of average fluxes at the
  back-plate (150 MW pulse, 1.1 m plug)
• No penetrations 1.0x107 n/cm2/s,
• With 100 mm dia. 1.3x1011 n/cm2/s,
• straight penetration,
• With 100 mm dia. 2.0x109 n/cm2/s,
• 4-bend penetration.
• Activation levels acceptable with 3.4m port neck
  filled by shielding and additional component
  shielding.

1.1 m shield

• No full engineering design of the port
  configurations or remote handling interface has
  been done for FIRE.

12
Electrical Impact and Concerns of Radiation
Radiation-induced Conductivity (RIC) in Ceramics

• Insulators for Diagnostics
• RIC Concern for FIRE Radiation dose at first
  wall 8 x 103 Gy/sec, significantly higher than
  for ITER magnetic diagnostics.
• Radiation-induced emf (RIEMF) and
  radiation-mediated thermoelectric potential
  (RMTP) in MI cable may be most severe issue (work
  in progess in EU JA).
• Rapid time behavior in studies of RIEMF?
• Nuclear heating (200C in 20 s. in FIRE).
• Damage to electronic components.
• FIRE (and ITER) still require
• intensive RD on radiation effects.

Conductivity too high
______________
X
13
Optical Impacts of Radiation
Recent Russian measurements on ITER- preferred
fibers.
Lost-a diagnostic on TFTR suffered from
luminescence in fiberoptic outside vacuum vessel.
TFTR shot at 5MW (5x10-2 MW/m2 at first wall).
Dose at front end of shielded fiber estimated
30 Gy/s.
700 Gy/s, gtgt ITER/FIRE flux outside port.
Prompt luminescence (and absorption) in fibers
and windows are critical issues in quantitative
diagnostic measurement.
14
Other Considerations for the Radiation Environment

• Development of an International Data Base of
  diagnostic materials and components
• ITPA Activity.
• Neutronics modeling facility to rapidly validate
  shielding designs and diagnostic integration.
• Capability to carry out validation tests on
  materials and components
• Selection of parts to be used,
• Pre-operational testing for BPX.
• Facility for prototyping and testing of major
  components,
• Development program of moveable mechanisms,
  actuators, motion-sensors for use in the
  environment (incorporate cooling?)
• Capability for assessing tritium-contamination
  impact.

15
Concluding Comments

• The engineering of diagnostics is amongst the
  most challenging tasks for future fusion devices
• Provide data throughout all the plasma
  performance,
• Large physical scale,
• Control and machine protection,
• Reliable operation.
• Many of the technology issues are common to many
  diagnostics.
• Extremely costly to duplicate efforts,
• Extensive testing capabilities.
• An urgent, aggressive RD program in diagnostics
  should be started (revived?).
• A central capability (real or virtual in
  location) could provide a necessary and desirable
  resource.
• My emphasis has been on tokamaks - others could
  better define work for other devices.