recent activities of the itpa microwave€working€group may - morning sessions/conway_irw10... ·...

G.D.Conway, 06-May-11 1

10th Intnl. Reflectometer Workshop - IRW10, Padova 2011

Recent activities of the ITPA Microwave Working Group

G.D.Conway*, M.E.Austin$, V.Udintsev# & G.Vayakis#

*Max-Planck-Institut für Plasmaphysik, Euratom Association, Garching, Germany$University of Texas, USA

#ITER Organization, Cadarache, France


ITPA – Topical Groups

● Diagnostics (R.Boivin - chair, G.Vayakis - co-chair)

● Active Spectroscopy Working Group● First Mirror Working Group● First Wall Working Group● Laser Aided Diagnostics Working Group● Microwave Diagnostics Working Group● Passive Spectroscopy Working Group● Neutron Working Group● Radiation Effects Working Group● International Diagnostic Database Working Group

● Pedestal

● SOL & Divertor

● MHD Stability

● Transport & Confinement

● Integrated Operational Scenarios

● Energetic Particles

Working Groups : sub-committees(originally ITER expert groups)were reorganized in late 2009

RWG MWG broader remit

Assist development and implementation of microwave diagnostics on BPX


Current members of the MWG

Praveen Kumar Atrey, IPR, India

Max Austin (co-chair), Univ. of Texas, USA

Prabal Kumar Chattopadhyay, IPR, India

Garrard Conway (Chair), IPP Garching, Germany

Calvin Domier, UCD, USA

Teresa Estrada, CIEMAT, Madrid, Spain

Greg Hanson, ORNL, USA

Soeren B Korsholm, Riso, DTU, Denmark

Akihiko Isayama, JAEA, Japan

S Kubo, NIFS, Japan

Ling Bili, IPP, Hefei, P.R.China

Maria Emila Manso, IST, Portugal

Atsushi Mase, Kyushu Univ., Japan

Hyeon Park, POSTECH, Pohang, S.Korea

Surya Kumar Pathak, IPR, India

Tony Peebles, UCLA, USA

Alexey Petroff, TRINITI, Russia

Vladimir Petrov, TRINITI, Russia

Roland Sabot, CEA, France

Seong-Heon Seo, NFRC, Daejeon, S.Korea

Dmitry Shelukhin, Kurchatov Institute, Russia

Gary Taylor, PPPL, USA

Tokihiko Tokuzawa, NIFS, Japan

Victor Udintsev (co-chair), ITER, Cadarace, France

George Vayakis, ITER, Cadarache, France

Vladimir Vershkov, Kurchatov Inst., Russia

Weiwen Xiao, SWIP, Chengdu, P.R.China

● Members nominated by party representatives

● Membership expanded to give broader spread of expertise: Refl. ECE, CTS etc.


Function of the MWG

● Assist in the evaluation of the physics requirements and basis for microwave based measurement techniques for BPXs

– New measurement techniques, diagnostic validation, physics issues etc.

● Consult on necessary physics and design studies and assist in the co-ordination of R&D studies under the voluntary arrangements

– Coordination of diagnostic simulation studies, expts.

● Advise on the feasibility and suitability of the system designs being developed

– Provide input to IO diagnostic reviews

– Respond to IO requests

● Encourage participation by other physicists in resolving microwave diagnostic issues for BPXs within the Parties

– Highlight outstanding tasks and research topics & opportunities

– Collate resources (information, codes web-site)

– Inform - Reflectometer workshop!

● Assist in the definition of space required for development, test and maintenance of equipment


Activities of the MWG

● MWG reports to the ITPA Diagnostics Topic Group twice a year

– Microwave WG Report to ITPA TGD-19 (Naka) 19-21 Oct. 2010– Microwave WG Report to ITPA TGD-18 (Oak Ridge) 11-14 May 2010– Microwave WG Report to ITPA TGD-17 (Pohang) 12-16 Oct. 2009 – Reflectometer WG Report to ITPA TGD-16 (St Petersburg) 20-24 Apr. 2009– Reflectometer WG Report to ITPA TGD-15 (Gandhinagar) 17-20 Nov. 2008– Reflectometer WG Report to ITPA TGD-14 (Lausanne) 14-18 Apr. 2008

– ...

● Report on recent diagnostic developments of general interest to the Topic Group

● Bring forward new or critical issues impacting on BPXs

● No longer report on hardware progress of ITER specific diagnostics DA responsibility

● Respond to action items & IO requests

● Return to role of expert advisory group


Activities of the MWG

● Recent Working Group Actions

– (Apr. 08) 14a291: Reflectometry WG to prepare a "position paper" on LFS measurement requirements to help guide the LFS system design.

– (Apr. 08) 14a292: Reflectometry WG to investigate and assess options for Refl./ECE protection from stray ECRH radiation and to summarize known experience by survey of present machines.

– (Apr. 09) 16a312: Microwave WG to assess generic test/validation requirements of microwave transmission system and reflectometer/ECE diagnostic calibration needs.

– (May 10) 18a335: Microwave WG to collate the history and actual performance of in-situ calibration for ECE and reflectometry across machines.

– (Oct. 10) 19a340: Microwave WG to assess the options for the ITER low-field-side reflectometer antenna configuration.

● Usually 6 months or a year to complete

● Each action has resulted in a formal written report – available in ITER IDM, MWG web-site & from lead author


Stray radiation protection

Stray radiation protection of ITER microwave based diagnosticsG.D.Conway, M.Hirsch, E.Doyle, T.Estrada, R.Sabot, A.Silva, V.Vershakov, G.Vayakis

ITER_D_33PKHG (RWG-55F-0901)

● There are several sources of potential danger to all microwave and FIR diagnostics on ITER. Active effort must be made to either “harden” the diagnostics or to protect them from partial or total destruction

● Issues

– Which diagnostic and what problems– How bad is the problem?– Simulation codes & “stray-light” modelling– Protection options for ITER microwave diagnostics refined– Recommendations and high priority R&D topics



Range of problems

● Signal/data corruption – Power loading of microwave mixers signal distortion– Enhanced background noise reduced S/N ratio below detection threshold

● Destruction of sensitive detectors & ex-vessel microwave components

● Damage to in-vessel components (windows, etc.) due to thermal effects + outgassing etc.

Diagnostics at risk

● Direct interaction– Microwave and FIR :– Reflectometry, ECE, Interferometry / Polarimetry

(fast detectors, mixers, pin-switches, windows, ferrite isolators, circulators, filters, ...)

● Thermal effects– Bolometry (absorbing films), SXR cameras (detectors, foils) & IR detectors– Spectroscopy, VUV & Optical diagnostics (windows, lenses, fibre-optics {heating changes

optical properties}, CCD, Channeltrons, ...)

● Cavity resonances in small gaps arcing– Microwave :– Polarizer & Combiner/splitter grids etc. as well as in-vessel components– Probes :– Langmuir & magnetic (dielectric insulation breakdown, cables, etc.)



Sources of danger

● Narrow freq. band, high power – ECRH

– No absorption

● Fault condition – No plasma / sudden termination, gyrotron/operator fault

● Non-resonant CTS probe beam

● Over-dense plasma ECRH cutoff Total reflection of ECRH beam

– Poor absorption

● ECRH assisted breakdown

● O2, X3 or O-X-B heating schemes

● Broad band radiation

– Disruptions & fast electrons

Fre

quen

cy (

GH

z)

4 5 6 7 8R (m)

0

50

100

150

200

250

O-mode

1st harmECE

Xu-mode

Xl-mode

2nd harm.ECE

Scenario 3a Te(0) = 32keV

PP

(O

)E

CE

Rad

. (O

)E

CE

Mic

. (O

/X)

Rad

. (X

)

Ref

l. (O

)Ref

l. (X

u)

Ref

l. (O

)R

efl.

(Xl)

60 GHz CTS (2MW)

5 GHz LH(20 MW)

170 GHz ECRH (24 MW)


Protection options for ITER microwave diagnostics

● Fast acting waveguide shutters interlocked to calibrated sensors– Mechanical / pneumatic shutters (slow, <40dB isol.)– Plasma shutters / breakdown chambers (fast)– Power sensors (one per cluster of waveguides)

● Waveguide filters (notch & band-pass)– QO dichroic / FSS plates or FP resonance filters (ECE & Refl.)– Fundamental iris or cavity filters (Low Refl.)– Plus isolators are obligatory (All systems)– Combination of 2 or more filters (QO + fundamental) in series

● Absorbing gases (e.g. H2S) in oversized waveguides (ECRH freq. selective)

● Arc detectors (visible & audible) in sensitive w/g sections / comp.

● Replaceable / sacrificial element (fuse)

● Absorbing materials (TiO2 or graphite loaded ceramics) to reduce stray-light in QO sections

Positionsensors

Pneumaticpiston

A range of protection techniques may be required for different diagnostics and different situations

All options require varying degrees of R&D – eg. Power handling & destructive testing!


1. Gyrotron operation will curtail measurement ranges:

● 170 GHz restricts LFS Xu-mode profile refl. (Each band will require one or two filters)

● 60 GHz CTS restricts PP refl. upper probing freq. (detectable density) + creates wide measurement hole in middle of profile refl. range

● Gyrotron freq. chirping/drift during start-up means very wide filters. Dump gyrotron power until frequency stabilizes? (High cost of many loads and fast, high-power waveguide switches)

2. No firm predictions available of how much stray power diagnostics will really experience. High priority is development of prediction codes for calculating individual diagnostic exposure levels

3. Employ stray radiation test facilities to identify critical components. Incorporate diag. testing & hardening procedures in diagnostic procurements

4. Lower frequency band – maybe standard w/g filters are sufficient? Filter performance at high power is critical issue – need measurements, up to and including destructive testing

5. Higher frequency band protection is still open issue. R&D needed for ECE systems

6. Full risk assessment needed – how often & bad a fault is expected; how much effort to expend on protection. Balance cost of protection system against component replacement

7. Diagnostics most at risk during ECRH start-up assist. If diagnostic not required during breakdown phase (ECE may not even be possible) then isolate!

Recommendations


LFS reflectometer assessment

Physics basis for reflectometer measurements in ITER and an assessment of the low-field-side reflectometer requirements

G.D.Conway, G.Vayakis, T.Estrada, G.R.Hanson, V.Petrov, V.Udintsev, V.Vershkov, .....

ITER_D_3DD6K5 (RWG-55F-0903)

● “Position-paper” on measurement requirements to help guide the LFS system design – should complement / feed-into the UCLA/ORNL assessment activity

– Update the Diagnostic Physics Basis. Original doc. 1997 DDD (ITER_D_22EKM), current status = obsolete document!

– Recommendations for further R&D work– Assessment of options & minimum requirements

● Independent assessment of measurement prioritization. Criteria:– ITER defined PR measurement requirements (ITER_D_2LSDBA)– Reflectometer physics basis

● Feasibility of measurement● Status of measurement technique – well or poorly developed?

– Value, i.e. contribution of measurement to the diagnostic suite


LFS reflectometer measurement aims

● PR measurement requirements (ITER_D_2LSDBA) defines IO consideration of measurement role, the expected diagnostic contribution & required measurement error/reliability

● Assessment exercise reached similar conclusions as IO and US assessments

Measurement Oper.Role

Diag.Contrib.

Additional

06. Line-averaged electron density 1a.2 BC 3.S

08. Locked modes 1a.1 MP 3.S

09. MHD modes 1a.1 MP 3.S

10. Plasma rotation 1b. AC 2.B

14. ELMs & L-H transition 2. PHY 1.P

24. Density profile (edge / core) 1b. AC 1.P / 2.B

25. Current & q-profile 1b. AC 3.S

27. High freq. instabilities 2. PHY 1.P

Operational Role (PR): MP = machine protection, BC=basic control, AC = advanced control, PHY=physics

Diagnostic Contribution (PR): P = primary, B = backup, S = supplementary

Items in orig. 1997 DDD also re-assessed


Physics basis for reflectometer measurements

24. Density profile (edge/core): Primary for edge Backup for core– Well developed/proven techniques. Some technical issues, but no show-stoppers– Issue of sensitivity to vertical plasma movements– Requires many dedicated O & X-mode antenna pairs

06. Line averaged electron density: Supplemental– Refractometry = group delay of pulse robust, fringe-free <n.l> measurement. Piggy-back?

10. Plasma rotation: Backup– Multiple techniques: Correlation or Doppler refl. Gives vExB NOT impurity fluid velocity– Requires dedicated optimized antennas: either tilted or clustered

27. High frequency instabilities (turbulence): Primary– Phase & returned power fluctuations good sensitivity. Important meas. for physics – Need high gain antennas? Use X-mode profile ant. or dedicate more antennas?

14. ELMs and L-H transition: Primary– Measurement techniques well developed, high spatial & temporal ELM resolution– Obtain information parasitically to profile and fluctuation measurements

09. Low order MHD modes: Supplemental– Detected phase fluct. / distortion in ne profile Piggy-back on profile/fluct. Antenna cluster?

08. Locked modes (disruption precursors, sawteeth): Supplemental– Detection same as for MHD. not clear if technique is reliable enough for control purposes

25. Current and q-profile: Supplemental– Techniques poorly developed with limited operational range Supplemental info. on q


LFSR – Recomendations for further R&D

1. Assess toroidal B-field ripple effects using beam-tracing and simulations w/o ferritic inserts. Maybe necessary to tilt antennas toroidally

2. Assess refraction effects on SOL meas. + impact of density peaking on edge toroidal refraction

3. Assess impact of half Bt operation on microwave access

4. Assess optimal grouping of antennas for turbulence correlation length meas. / MHD – note can only measure toroidal projection of L – impacts on decision whether to cluster antennas

5. Small bore plasma cross-section growing from LFS during start-up high curvature & ill-defined magnetic axis height. Maybe difficult to measure in this phase Need dynamic equilibria studies

6. Also, need better equilibria to quantify refraction effects during vertical plasma movements

7. Optimize profile antenna gains (beam divergence) for minimal sensitivity to vertical movement, plus identify minimum number of antennas required to cover mag. axis height variation

8. O-mode Doppler refl. for rotation / Er profiles looks feasible – Need more beam-tracing studies to optimize location and line-of-sight (poloidal & toroidal tilt angles). Optimize beam divergence

9. Assess beam spreading effects due to high turb. levels in SOL/edge region (Need full-wave simulations) – effective high gain antennas may be difficult to achieve

10. Assess measurement possibility during ECRH plasma breakdown assist

11. Assess refraction / density peaking effects on LFS refractometry. Assess inner wall reflection


Microwave diagnostic calibration & test requirements

Requirements for calibration & testing of ITER microwave based diagnostic front-end components

G.D.Conway, G.Vayakis, G.R.Hanson, S.B.Korsholm, V.S.Udintsev, V.Petrov, M.E.Austin, W.A.Peebles & T.Estrada

ITER_D_33ZRFR (RWG-55F-0902)

Assess generic test/validation requirements of microwave transmission system and reflectometer / ECE diagnostic calibration needs.

● Established test & calibration procedures (before, during & after installation) are essential to ensure optimal operation of all diagnostics

● Microwave diags. (ECE, Reflectometry, Refractometry, CTS, ...) have many common features

● Front-end components are generic common test requirements, but diagnostic back-ends are specific individual test requirements

● Overall system performance depends on careful front-end installation & alignment most critical testing


Test measurements – 1: Categories

4 test measurement categories

Pre-installation checks performed on lab-bench or on vessel mock-up

Sub-system assembly checks during and after in-vessel installation

Post-installation system/assembly tests & documentation

Periodic operational performance checks & system calibrations

Test measurement Category

1. Microwave component performance pre

2. Antenna radiation pattern pre

3. Antenna cross-coupling pre/post

4. Antenna alignment post

5. Electrical isolation / DC breaks during

6. Waveguide continuity during

7. Waveguide microwave performance post

8. System protection pre & op.

9. Calibration hardware pre & op.

● Series of test measurements identified & compiled

● System calibration requirements also considered

● (Component) manufacturing compliance (tolerance) checks are implicit


Test measurements – 2: Examples

● Many components & lots to go wrong

● Insertion loss, reflection coefficient, mode conversion, ...

● Must document individual component performances

● Check for faults + documentation allows subsequent identification of system degradation

● Front-end components = antennas, oversized w/g, mitre-bends, swivel joints, vacuum windows, expansion joints, air-gaps, mode-filters, tapers, splitters, combiners, polarizers, QO couplers ...

● Oversized w/g prone to high order modes power loss & freq. holes

● Measure system w/g performance: losses, power trans. curve (holes & resonances) + polarization rotation..

● Check operation of passive w/g comp. splitters, tapers, QO-couplers, ..

● Antenna rad. pattern is fundamental. Must characterize all antennas

● Measure pattern in far-field @ 3 freq. in O & X-mode polarization

● 3 dB half-width vs distance from ant.

Test measurement Category

1. Microwave component performance pre

2. Antenna radiation pattern pre

3. Antenna cross-coupling pre/post

4. Antenna alignment post

5. Electrical isolation / DC breaks during

6. Waveguide continuity during

7. Waveguide microwave performance post

8. System protection pre & op.

9. Calibration hardware pre & op.


Assessment of LFS reflectometer antenna options

Antenna configuration options for the ITER low-field-side reflectometerG.D.Conway, W.A.Peebles, G.R.Hanson, A.Stegmeir,..

ITER_D_33AHBB (MWG-55F-1104)

● Ongoing discussion of best antenna configuration for ITER low-field-side reflectometer LFSR. Several options have been proposed in last few years – all monostatic array vs bistatic pairs etc.

● Assess pros and cons of various antenna configurations – report distributed for review

Poloidal array(monostatic)

Rpol

tor

Poloidal pair(bistatic)

Toroidal pair(bistatic)

Hybrid cluster(bi + mono)

qq

d

d

Poloidal(tristatic)

f f


Basic reflectometer behaviour

● Document basic antenna/beam behaviour– Beam propagation & dispersion– Beam displacement– Beam alignment

● Concentrate on edge/pedestal region – primary objective of LFSR

1.2

0.4

0.8

z (m

)

1.0

0.6

7.8 8.0R (m)

8.4 8.68.2 -0.2 0.0 0.2y (m)

Tx Rx

Footprint in receiver plane

84GHz O-mode

0.9Antenna height z (m)

0.80.60.50.4 0.7

-12

20

Pol

oida

l dis

plac

emen

t (cm

)

-4

0

16

12

8

4

-8

84GHz

60GHz

18GHz

Rant = 8.498m(solid)

Rant = 8.798m(open symbols)

O-modezma

A.Stegmeir etal FED submitted (2011)

● Critical issue is beam sensitivity to plasma vertical movement investigate dependence using beam tracing + power coupling

● Assess optimal antenna diameter (gain), placement, orientation, recessing etc.


Assessment of system issues

● Design constraints – physical port space, financial etc.

● Antenna issues– Monostatic vs bistatic antennas– Low gain vs high gain antennas– Normal vs aligned antennas– Toroidal vs poloidal bistatic antennas– Profile vs fluctuation measurements– Doppler vs fluctuation requirements– Impact of antenna recessing– Antenna pairs vs arrays

● Transmission line (TL) issues– TL reflections– TL & system degradation

● Calibration & testing issues

● Multiplexing and electronics issues

63.5mm : 5o : 78.5mm

18 GHz

60 GHz

84 GHz

-40

-35

-30

-25

-20

-15

-10

-5

0

Cou

plin

g (d

B)

0.0 0.5 1.0 1.5 2.0Distance x (m)

a w s

Bistatic parallel

Bistatic aligned

Monostatic

xc

Antenna power coupling (vacuum) vs reflection distance for monostatic ( ), parallel bistatic ( ) & aligned bistatic ( ) antenna pair; O-mode config. Bistatic loses coupling at close distance


Antenna options

● All-monostatic (single and arrays)

– Good depth-of-field – especially for close-in coupling, ie. SOL measurements– Must combine / separate transmit & receive signals onto single ant. power loss– Subject to parasitic TL reflections

● Aligned bistatic pairs

– Need to optimize for a measurement region – poor close-in coupling– Good experimental basis & minimal risks Current ITER baseline proposal

● Hybrid configurations

– Combine benefits of bistatic & monostatic Risk mitigation

● Open issue of antenna gain optimization to minimize height sensitivity

● Open issue of (high gain) antenna arrays for core probing (and TL switching issue etc.)

● Port constraints severely limit number and placement of antennas non-ideal compromises

● No consensus on best antenna configuration Unable to make specific recommendations

● However, antenna configuration must satisfy measurement requirements on a priority basis


ECE & Reflectometer calibration survey

Survey and assessment of ECE and Reflectometer calibration techniquesMany contributors ,..

ITER_D_3622CE (MWG-55F-1105)

● Aim is to collate the history and actual performance of in-situ calibration for ECE and reflectometry from all the experts from various machines - before they retire and the information is lost!

● Systematically document:– Calibration techniques (what methods actually used and tried)– Long & short term calibration performance – drifts etc.– How robust is the calibration – ie. reliability of calibration & how to check the calibration of the

calibration method/source– Associated problems, tricks and successes– Other issues such as known discrepancies, eg. between ECE and Lidar and impact of non-

Maxwellian distributions

● Contributions solicited – extensive range of responses received and collation is on-going

● Further contributions welcome (and awaited)

● Should lead to a “best procedure” for ITER diagnostics

recent activities of the itpa microwave€working€group may - morning sessions/conway_irw10... ·...

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