I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 1 I. Monakhov, A. Walden, T. Blackman, D. Child, M. Graham, W. Hardiman, P.U. Lamalle 1, M. Nightingale, A. Whitehurst and JET EFDA contributors* Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK 1 LPP-EPM/KMS, Association Euratom-Belgian State, Brussels, B-1000, Belgium * Appendix of J.Pamela, et al., “Overview of JET Results”, Fusion Energy 2002, IAEA, Vienna (2002) Tests of external conjugate-T matching system for A2 ICRF antenna at JET system for A2 ICRF antenna at JET ICRH Conjugate-T antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 2 Outline Main topics : Matching procedures and typical examples Automatic control algorithm Cross-talk influence studies Matching peculiarities (strap balance, matching option etc) Outside the scope of this presentation: Test ELM-tolerance issues (!) Test power handling issues Full-scale proposal for JET - design, plans etc ITER-relevance Poster P3T-B-152 tomorrow morning Emphasis on experimental results of matching to quasi-stationary load

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 3 External conjugate-T matching of A2 antennas at JET Features:  Externally (outside the vacuum vessel) located coaxial T-junction  Coaxial line-stretches (trombones) for conjugate-T tuning  Variable trombone and stub tuner as impedance transformer Advantages:  Reliance only on tried-and-tested coaxial line components and technology  Manageable accuracy of control of the matching elements  Separation of launching and matching sub-systems  Capability to conjugate remote antenna straps  Straightforward strap loading RF diagnostic (directional couplers) prototype tests - quick, inexpensive and risk-free assessment of the principal features of the proposed scheme under the ‘worse-case’ conditions

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 4 External conjugate-T tests at JET: A2 antenna Straps involved in conjugate-T tests Different design  Loading asymmetry Same array, adjacent  Strong cross-talk Conventionally matched straps Normally not powered and deliberately mistuned during the tests* * Exception: cross-talk studies in L-mode plasma

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 5  One amplifier (‘C1’) feeds two adjacent straps of antenna array ‘C’  Switchable to usual configuration in ~10 min (between shots)  Extraneous elements - SLIMPs and ‘parasitic’ open-ended stub External conjugate-T tests at JET: scheme Straps C1 4m trombone 3m stubs C2 Amplifiers 1.5m trombones C1 C2 ‘Parked’ SLIMPs ‘Parasitic stub’ V ref V for Control signals: T- junction, R T =3-6  ~ 80 m transmission line

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 6 External conjugate-T tests at JET: matching procedures Network analyser vacuum matching High voltage operations in vacuum L-mode plasma operations ELMy H-mode plasma operations Five frequencies in MHz band Four R T values in 3-6 Ohm range Two matching options At all stages matching was originally achieved by ‘manual’ adjustments and later complemented and refined by automatic ‘real-time’ control system No really serious troubles and principal complications Predictable performance, adequate response to changes Time-consuming initially (network analyser in vacuum) Straightforward at later stages (first shot ‘direct hits’)

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 7 Conjugate-T matching: trombone setting accuracy  Simulation Dependence of amplifier output line VSWR on lengths of conjugate-T trombones  Network analyser measurement  Matching option 2 Matching option 1  Vacuum loading, F=42.1 MHz, R T =3 Ohm* * before impedance transformer settings optimisation C1 trombone length, mm C2 trombone length, mm C1 trombone length, mm Manageable setting accuracy: ~2-3 cm setting ‘target’ in vacuum (toughest case) ~3-5 mm trombone length control accuracy

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 8 Conjugate-T matching: high-voltage vacuum operations # 3969, f=50.3 MHz, R T =4   Generated power  Maximum voltages in transmission lines  Forward and reflected voltage wave amplitudes in amplifier output line  VSWR in amplifier output line Effortless matching on the basis of the settings found with network analyser ‘Perfect’ matching * Real-time tracking OFF

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 9  Maximum voltages in transmission lines Conjugate-T matching: L-mode plasma operations  Generated power  Forward and reflected voltage wave amplitudes in amplifier output line  VSWR in amplifier output line # 61646, f=42.1 MHz, R T =4  Straightforward matching on the basis of extrapolation of vacuum settings Trouble-free L-mode plasma operations VSWR< sec * Real-time tracking OFF

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 10 Conjugate-T matching: ELMy H-mode operations  Horizontal mid-plane chord D  signal  Generated power  Forward and reflected voltage wave amplitudes in amplifier output line  VSWR in amplifier output line # 60530, f=42.1 MHz, R T =3  Trip-free performance with VSWR  1.5-3* * depends on discharge scenario and circuit optimisation * Real-time tracking OFF

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 11 Conjugate-T matching: real-time control algorithm V ref V for  Existing trombone and stub matching at JET  Conjugate-T matching of ITER-like antennas reflection phase at couplers depend on frequency hence error signals require frequency correction  External conjugate-T matching at JET no need in frequency correction (for equidistant couplers) fully compatible with existing matching (no new electronics) V ref V for V ref V for Im(V ref /V for ) Re(V ref /V for ) Im(V ref /V for ) Re(V ref /V for ) Im(V ref /V for ) Re(V ref /V for ) new New control algorithm (compatible with the existing JET error signals)

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 12 Automatic matching control: theory and simulations Matching reactance 1 Matching reactance 2 Generalised symmetric conjugate-T error signal E=V ref /V for in the vicinity of matching point  VSWR in amplifier output line  Re(E)=0 and Im(E)=0 contours Solid lines - proposed algorithm Dotted lines - JET EP algorithm R C =1 , R T =5 , matching option 2 Y 0 - matching reactance, R C - coupling resistance, R T - T-junction reference resistance, Z 0 - line characteristic impedance Good algorithm convergence

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 13 Automatic matching control: performance  VSWR in amplifier output line Reliable and stable (after some teething troubles) Routinely used for matching refinement # 61863, f=42.1 MHz, R T =4   Generated power  Trombone length control error signal  Trombone length deviation from the matching value

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 14 Automatic matching control: troubleshooting Matching ‘run-away’ failure due to trombone tracking speed asymmetry (firmware fault)  VSWR in amplifier output line  Generated power  Trombone length control error signal  Trombone length deviation from the matching value # 3936, f=37.45 MHz, R T =4  Tracking speed symmetry between both matching elements is essential

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 15 Automatic matching control: troubleshooting Algorithm instability due to tracking inertia (trombones set to run at fast speed regardless of V err )  VSWR in amplifier output line  Generated power  Trombone length control error signal  Trombone length deviation from the matching value # 4012, f=42.1 MHz, R T =4  Inertia-free or variable-speed tracking is required for fast and stable matching

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 16 Automatic matching control: troubleshooting Control system auto-excitation due to tracking inertia (trombones set to run at fast speed regardless of V err )  VSWR in amplifier output line  Generated power  Trombone length control error signal  Trombone length deviation from the matching value # 4070, f=50.3 MHz, R T =4  Inertia-free or variable-speed tracking is required to avoid system auto-excitation

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 17 Automatic matching control: strap current reaction  Generated power  VSWR in amplifier output line  Strap C2 and C1 current amplitude ratio  Strap C2 and C1 current phase difference  Strap coupling resistance  Trombone length deviation from the vacuum matching value Strap currents sensitive to matching - potentially a source of troubles

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 18 Cross-talk influence: characteristics of A2 antenna A2 antenna strap cross-talk vs frequency solid lines - network analyser measurements in vacuum broken line - MWS simulation for vacuum loading P.Lamalle, et al, EPS-30, 2003, P dots - phase-ramp measurements under plasma loading P.Lamalle, et al, EPS-22, 1995, II-329 Cross-talk amplitude Typically increase with frequency Does not exceed |S ij |~0.1, i.e. relatively low Is overestimated by MWS simulations |S ij plasma | ~ |S ij vacuum | for near neighbours |S ij plasma| ~ 3-5 |S ij vacuum | for far neighbours

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 19 Cross-talk influence:experimental assessment Cross-talk influence: experimental assessment Simultaneous operations of two pairs of straps under plasma loading: C12 (conjugate-T matching) and C34 (conventional matching) High frequency (the highest cross-talk) ~180  relative phase sweep Modulated current amplitude ratio 3-8 cm antenna-plasma gap sweep Real-time tracking ON and OFF No dramatic influence on matching and strap current balance and phase No signs of matching algorithm instability Caveats: 1. JET A2 test layout doesn’t represent the case of ITER-like antenna toroidal cross-talk adequately 2. Initial settings were too close to ‘perfect’ matching to explore the ‘matching-from-scratch’ situation

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 20 Cross-talk influence studies:phase sweep Cross-talk influence studies: phase sweep # 63133, F=50.3 MHz, R T =4  * Real-time tracking OFF C12 (conjugate-T) + C34 (usual matching) with ~180  relative phase sweep  Generated power per each pair of straps  Conjugated straps current amplitude ratio  Conjugated straps current phase difference  VSWR in C1 amplifier output line Small matching perturbation due to cross-talk  Strap pairs current phase difference

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 21 Cross-talk influence studies:amplitude modulation Cross-talk influence studies: amplitude modulation # 63135, F=50.3 MHz, R T =4   Generated power per each pair of straps  VSWR in C1 amplifier output line  Conjugated straps current phase difference  Conjugated straps current amplitude ratio C12 (conjugate-T) + C34 (usual matching) with modulated current amplitude ratio (  =-90  ) * Real-time tracking OFF  Strap pairs current amplitude ratio Small matching perturbation due to cross-talk

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 22 Cross-talk influence studies:loading variation Cross-talk influence studies: loading variation * Real-time tracking ON # 63130, F=42.1 MHz, R T =4  C12 (conjugate-T) + C34 (usual matching) during antenna-plasma gap variation (  =-90  )  Generated power per each pair of straps  Conjugated straps current amplitude ratio  Conjugated straps current phase difference  VSWR in C1 amplifier output line Algorithm stability in presence of cross-talk  Mid-plane antenna-plasma distance

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 23 Conjugate-T matching: strap current balance and phase Strap current amplitude balance: Anticipated asymmetry due to different strap design Observed imbalance in matched straps: I C2 /I C1 ~ Observed imbalance during ELMs: I C2 /I C1 ~ Strap current phase difference: Sign defined by the matching option Difference reduces under loading, typically - vacuum:~  L-mode plasma: ~  ELM:~  Both amplitude balance and phase difference are sensitive to the matching option used

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 24 Conjugate-T: matching option choice Loading asymmetry and complex* loading perturbation cause noticeable difference in circuit response between the two matching options Both simulations and ELM observations during the tests show that the matching option choice has a strong influence on magnitude and sign of strap current amplitude ratio variation magnitude and sign of strap current phase difference variation VSWR variation in matched line (load-tolerance) Judicious choice of the matching option is important * Plasma loading (including ELMs) = strap resistance increase AND inductance decrease

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 25 ELM Strap C2 and C1 current amplitude ratio: option 1 - ratio decrease, small variation option 2 - ratio increase, large variation Simulations of strap current ratio I C2 /I C1 amplitude during asymmetric loading ( F=42 MHz, R T =4  ) strap 2 impedance variation is 75% of strap1  Matching option 1 (capacitive matching reactance in C1)  Matching option 2 (inductive matching reactance in C1) Conjugate-T: current balance and matching option ELM

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 26 ELM Strap C2 and C1 current phase difference: opposite signs for the matching options variation is smaller for matching option 2 Simulations of strap current ratio I C2 /I C1 phase during asymmetric loading ( F=42 MHz, R T =4  ) strap 2 impedance variation is 75% of strap1  Matching option 1 (capacitive matching reactance in C1)  Matching option 2 (inductive matching reactance in C1) Conjugate-T: strap phasing and matching option ELM

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 27 trip ELM Conjugate-T: load-tolerance and matching option  Matching option 1 (capacitive matching reactance in C1)  Matching option 2 (inductive matching reactance in C1) Simulations of VSWR in the matched line during asymmetric strap loading ( F=42 MHz, R T =4  ) strap 2 impedance variation is 75% of strap1 Load-tolerance depends on the matching option Smaller VSWR values expected for option 2

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 28 Strap C2 and C1 current amplitude ratio Matching option 1 # 62103, f=42.1MHz, R T =4  Matching option 2 # 62099, f=42.1MHz, R T =4  ELM System response to ELMs depends on the matching option ( as predicted by simulations) Strap C2 and C1 current phase difference VSWR in amplifier output line Conjugate-T: response to ELMs and matching option  Horizontal mid-plane chord D  signal   small decrease large increase   positive sign, large reduction negative sign, small increase   large perturbation small perturbation 

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 29 Advantageous factors of JET A2 conjugate-T configuration: Relatively high resistive loading (~2-3 Ohm compared with expected ~0.5-1 Ohm JET ITER-like strap) Relatively low cross-talk between the conjugated straps (~-20dB compared with ~-7dB Alc-C Mod) Manageable matching element control accuracy (~0.5 cm compared with ~0.1 mm) Familiar, well documented and well diagnosed strap load (privilege of external matching) External conjugate-T tests at JET:summary External conjugate-T tests at JET: summary Successful plasma loading matching on the basis of vacuum settings Adequate and predictable circuit response to changing conditions Reliable new automatic control algorithm for matching refinement No dramatic influence of strap cross-talk on circuit matching Importance of matching option choice in presence of loading asymmetry

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 30 The next slides are not a part The next slides are not a part of the presentation and included to facilitate discussions only

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 31 Involves ½ of the existing RF plant – modules C and D  currently matched by stub and trombone circuit  SLIMPS are installed, but currently not used  35kV voltage limit  ~1MW per strap in L-mode plasma Conjugate similar straps of different antenna arrays  symmetric conjugate-T loading  better load tolerance  arbitrary phasing between straps within antenna array  same frequency and phasing for both arrays Switchable to the existing configuration between JET pulses  keep advantages of the existing system (different array frequency&phase)  fallback in case of installation delays or operational problems  four spare 2MW amplifiers during conjugate-T operations SLIMPs are modified into Z 0 =30  trombones  used to match the T-junction to Z T =3-6   increase flexibility of the existing matching scheme  reduce project costs Stub-trombone wideband variable impedance transformer  based on stub and trombone used for conventional matching  additional 2m trombone for full frequency coverage Straightforward low-power RF diagnostic and tuning  change-over switches for easy access to measurement ports  four-port network analyser for array vacuum matching Same error signals for real-time matching of both configurations  Re(V ref /V for ) and Im(V ref /V for )  Conventional configuration: adjust lengths of 1.5m trombone and stub  Conjugate-T configuration: adjusts lengths of 1.7m trombones D2 Antenna straps 1.5m trombone stub amplifier SLIMP: 24 & 105  External conjugate-T at JET: the next step 1.7m trombone T-junction Network analyser D1 D2 D3 D4 C1 C2 C3 C4 D1 C1 2m trombone V ref V for

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 32 Resistive loading change in both branches of tuned parallel resonant circuit (conjugate ‑ T) causes smaller variation of the resulting impedance than the equivalent loading change in a single branch of the circuit (conventional schemes)  comparatively high load-tolerance Conjugate-T: why is it load-tolerant ? Conjugate-T - a parallel connection of two loads with their impedances modified to present the T-junction with complex conjugate values and to ensure purely real resulting impedance (i.e. equivalent to a tuned parallel resonant circuit with losses in both branches).

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 33 Conjugate-T tests at JET: frequency coverage Discrete windows due to limited trombone length variation (1.5m) Adequate representation of typical JET ICRH frequencies Comparable with the existing stub/trombone matching at JET The diagram is based on network analyser measurements in vacuum, R T =3  Test frequencies Amplifier dead band Amplifier band edges Allowed frequencies (conjugate-T matching possible)

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 34 ‘Proof-of-principle’ test: installation T-junction Change-over switch ‘Big trombone’ (4m) 1.5 m trombone3m stub Done during the experimental campaign without disruption to RF operations

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 35

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 36 Simulations: load tolerance under symmetric loading F=42 MHz, R T =4 , symmetric strap loading  Contours of amplifier output line VSWR versus strap impedance Strap resistance Strap reactance change Measured ELM ‘footprint’ Load tolerance of symmetric pair: looks promising in general reactance perturbation narrows the tolerance margins matching option doesn’t matter

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 37 Simulations: load tolerance optimisation F=42 MHz, symmetric strap loading  R T =5  : good for big perturbations, but very narrow margin at low coupling  R T =3  : good at low coupling, but limited tolerance for big perturbations T-junction reference impedance choice: optimum setting depends on coupling scenario no ‘magic’ setting covering all situations hence variable transformer is needed

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 38 ‘Proof-of-principle’ test: summary of results ‘Proof-of-principle’ test: summary of results Vacuum matching over MHz band (at typical JET ICRH frequencies) High voltage (up to V ATL ~35 KV) vacuum operations over the frequency band Real-time matching control on the basis of the existing error signals ‘Perfect’ matching and high power* (<1MW) long pulse (  15sec) operations at different frequencies during L-mode plasma discharges Trip-free performance during strong sawtooth activity, L-H transitions and ELMy (including Type-I) H-mode at generated power levels up to 0.8 MW * Demonstration of ELM-tolerance optimisation and insensitivity to cross-talk * 1. Power is from one amplifier (1/4 of a module or 1/16 of the plant) 2. Limit due to arcing in a makeshift rectangular section of ‘big trombone’

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 39 Conjugate-Tload tolerance: sawteeth Conjugate-T load tolerance: sawteeth  RF module ‘A’ - conventional matching (superimposed traces from four amplifiers)  Amplifier ‘C1’ - conjugate-T matching Forward and reflected (x5) voltage wave amplitudes in output lines of RF amplifiers  RF module ‘B’ - conventional matching (superimposed traces from four amplifiers)  RF module ‘D’ - conventional matching (superimposed traces from four amplifiers)  Soft X-ray emission intensity signal # f=42.1 MHz, R T =3  Comparatively small reflection perturbation

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 40 # 60531, f=42.1 MHz, R T =3   Horizontal mid-plane chord D  signal  Forward and reflected voltage wave amplitudes in amplifier output line  VSWR in amplifier output line  Antenna strap coupling resistance Zoomed to show fast data for three ELMs Trip-free performance with R C  ~9  * Real-time tracking OFF Conjugate-T load tolerance: big ELMs

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 41 Conjugate-T load tolerance: L-H mode transition  Horizontal mid-plane chord D  signal  Antenna strap coupling resistance; note fast R c reduction during L-H transition - theoretically troublesome for Conjugate-T  Forward and reflected voltage wave amplitudes in amplifier C1 output line  VSWR in amplifier output lines A1,B1 D1 (conventional matching) C1 (conjugate-T matching) L-H mode transition # 61865, f=50.1 MHz, R T =4  No problems due to fast R C reduction

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 42 Conjugate-T load tolerance: comparative performance Instantaneous and moving average power generated by RF modules  module ‘B’ - conventional matching (total power from four amplifiers; 75 trips)  module ‘D’ - conventional matching (total power from four amplifiers; 33 trips)  amplifier ‘C1’ - conjugate-T matching (power from one amplifier; no trips) # 62111, f=42.1 MHz, R T =3   module ‘A’ - conventional matching (total power from four amplifiers; 167 trips) Higher average power, better waveform control, lesser strain on end-stage tubes DD

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 43 Conjugate-T load tolerance: limitations  Strong and variable coupling resistance asymmetry between two straps R C1 > R C2 - between ELMs  R C1 <  R C2 - during ELMs  Strong and asymmetric strap electrical length perturbation during ELMs  L C1 ~30 cm (!) ;  L C1 >  L C2  VSWR in amplifier output lines Asymmetric strap loading and strap reactance perturbation # 62107, f=42.1 MHz, R T =5  * Also note high T-junction impedance setting, see next slide Noticeable matching perturbation* during some types of ELMs DD

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 44 Conjugate-T optimisation: T-junction impedance choice R T =4  # f=42.1 MHz R T =5  # f=42.1 MHz Different R T settings  Different VSWR response during similar ELMs R T =3  # f=42.1 MHz DD VSWR R C1 R C2  better still  better

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 45 optimisation: matching option choice Conjugate-T optimisation: matching option choice Two matching options have different ELM-tolerance characteristics (in presence of loading asymmetry and reactance perturbation - see slide 7) Horizontal mid-plane chord D  signal VSWR in amplifier output line Matching option 2, # 62099, R T =4Ohm, f=42.1 MHz Matching option 1, # 62103, R T =4Ohm, f=42.1 MHz Better load-tolerance

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 46 Conjugate-T optimisation: fixed offset matching Matching between ELMs can be intentionally fixed at (reasonable) VSWR > 1 VSWR decrease during ELMs  a ‘safeguard’ against trips&arcs Real-time matching, # f=42.1 MHz Fixed offset matching, # f=42.1 MHz Strap C1 and C2 coupling resistance Horizontal mid-plane chord D  signal VSWR in amplifier output line VSWR decrease during ELMs 

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 47 Conjugate-T at JET: new research opportunities Conjugate-T at JET: new research opportunities (outside the scope of this presentation) (outside the scope of this presentation) Antenna coupling during big ELMs  no trips regardless of ‘severity’ of ELMs and applied power levels  disabled generator frequency fast feedback loop Antenna electrical strength deterioration during and after ELMs  no mismatch trips during ELMs regardless of strap voltage ICRH heating efficiency and power deposition during ELMs  RF power delivered to plasma not only between, but also during ELMs Allows to investigate a number of important problems previously inaccessible for experimental studies

I. Monakhov, ICRH CT antennas matching, SOFT-23 satellite meeting, Venice, Italy, September 21, 2004, Slide 48 External conjugate-T: ITER-relevant advantages Allows robust and simple launcher design  high reliability and longevity in hostile environment, easy maintenance  bigger non-RF design margins: stresses, cooling, pumping, diagnostics etc Possibility to conjugate remote straps  better phasing  higher coupling and better load tolerance  lower cross-talk  higher load tolerance and matching stability Independent launching and matching sub-systems  easy reparability or ‘inexpensive’ replacement  straightforward upgrades or new versions of either of the systems Well-established coaxial line matching technology  manageable tuning accuracy with simple drive systems Straightforward RF diagnostic of individual straps  better antenna and generator protection  transparent coupling interpretation and simplified matching