Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Automatic Matching of ITER-like structures Automatic Matching of ITER-like structures G. Bosia, and the CEA ICRF Group

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – ITER ICRF system requires hands-off operation Manual preset of array frequency, phase and power time profiles With an efficiency > 90% Automatic acquisition of perfect match Uphold of match against load variations Protection of array and transmission lines agaist breakdown Fast detection of arcs, extinction, power re-application. This scenario, is a necessary condition for ICH to be included in ITER auxiliary heating systems

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Effects of coupling in a single ITER-like structure The effects of coupling are negligible if the coupling is less than 20 dB. This condition is verified on the TS ITER prototype. Inductive coupling between half sections is one of the several possible sources of electrical asymmetry of the circuit Asymmetry makes the half sections currents not complex conjugate (and load resilience is reduced) if the coupling coefficient is high (k p > 1 %) and if one tries to match to a resistive input impedance (R 0 ). For any level of coupling, the half sections currents remain complex conjugate and load resilience essentially unaffected if the ILS is matched to Z in = R 0 + i k p X. k p 2 = X m 2 / X 1 X 2 Z in = R 0 Z in = R 0 + i k p

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Effects of coupling on “load resilience” k p =0.00 k p =0.02k p =0.04

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Array of ITER-like structures ITER Reference Design 2 x 4 ILS CEA upgrade proposal 3 x 4 ILS TS ITER Proto 1 x 2 ILS

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Effects of coupling in a poloidal/toroidal array I) Coupling between elements in an array fed by different RF sources has in general no effect on load resilience. However, inter-element coupling has important effects on both the location of the match point in the parameter space and on match acquisition if the RF sources introduce electrical asymmetries in the system. For cases having practical relevance, the array elements behave as they were independent, if adjacent currents in the array are equal in module and in- or out- of phase If not, number and location of match points degenerates in a way depending on both load and source (in particular on load power factor) matching some element of the array becomes impossible with pure reactances This behaviour is true for any array with multiple sources

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Effect of poloidal septum on toroidal coupling Retracted septum Full septum

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Effects of coupling in a poloidal/toroidal array II) K = 2.3 % K = 3,7 % K = 1 % K = 5 % Critical angle in ITER Proto (amplitude ratio = 1) R s3 X s1 VaVa X C1 X s3 IaIa I1I1 I3I3 X C3 R s2 R s4 X s2 VbVb X s4 IbIb I2I2 I4I4 X C4 kpkp kpkp ktkt X C2 R s1 ktkt At high circuit power factor, for amplitude ratios different from 1 and phasing differing from 0 and p by a critical ratio/angle, a parasitic current circulation between RF sources would take place if not prevented by the protection systems It becomes impossible to match some array element with pure reactances R s3 X s1 VaVa X C1 X s3 IaIa I1I1 I3I3 X C3 R s2 R s4 X s2 VbVb X s4 IbIb I2I2 I4I4 X C4 kpkp kpkp ktkt X C2 R s1 ktkt

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Recepy for perfect match and load resilience for a single ITER-like structure Condition 1 implies: 1)a structure geometrically symmetric 2)an active control of the currents in the two half sections I in Z 11 I 1 X C1 Z 22 I 2 X C2 Z 12, Z 21 Load resilience relies on zeroing of the input reactance by means of phase compensation 1.The currents in the two half sections should be complex conjuate (with I in as phase reference) 2.The input resistance must be of the same order as the load resistance.

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Recepy for perfect match and load resilience for an array of ITER-like structures 1.The currents in all half sections should be kept complex conjugate (with I in as phase reference). This implies: 1)an array structure geometrically symmetric 2)active control of the currents in the two half sections 2.Each ILS should be kept matched at Z in = R 0 + i k p X for maximum load resilience. 3.Currents in adjacent half sections should be kept in- or out- of phase. I1I1 I2I2 I3I3 I4I4

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Detection of monitoring, control, and protection signals Relative detection error : Control signals Module : < 5% Phase : < 5 ° BP : DC – 100 Hz Monitoring signals Module : < 10% Phase : < 10 ° BP : DC –10 kHz Protection signalsOn/Off BP DC – 1 MHz To properly operate, a large array needs an integrated control (of frequency, power and phase ) and protection system which relies on the vectorial monitoring of some circuit parameters. The control system proposed here relies on the vectorial measurement of the input currents in each half section and of the input voltage. In a next step device, the monitors are exposed to high temperatures and to neutron radiation field. They should therefore be rugged, reasonably insensitive to mechanical, thermal and nuclear loads and not require maintenance and/or recalibration

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Position of the vectorial probe Impedance probe The vectorial probe should be ideally located at the T-junction input plane. However, for impedance matching purposes the currents can be measured anywhere in symmetric position along the sections, provided they are related of the total current rather than to the local current density.

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Sketch of impedance monitor and equivalent circuit V 0 I 1 I 2 V0V0 C1C1 C2C2 i*k*I 1 C2C2 L i*k*I 2 L R RLRL V V1V1 R V2V2

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Circuit equations Z =R +i (wL-1/wC 2 ) R<< wL<<1/wC 2 i.e. for C1/C2<<1

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Detection V1V1 V 2 -V V 1 -V V V2V2 V 1 +V X X Z1Z1 Z2Z2 From the basic RF signals V, V1 et V2 all circuit parameters can be computed by simple linear combinations and mixing

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Automatic matching for a single ILS 5. The same matching algorithms used for a single ILS are also used (with additional phase and power control) to match an array of ILS. 1.The proposed automatic matching methods seeks implicit solutions of the match equations. 2.It relies on the operation of two feedback loops operating on the two tuning elements, driven by the error signals constructed as described above. The two loops operate with different time constants, ( FL -> fast loop, SL -> slow loop) so that the FL tracks the SL 3.The module of the input reflection coefficient Ι  in Ι, often used for manual match, is not a convenient intelligence for automatic control. 4. Convenient error signals are: Re(  in ) and Im(  in ) = 0 or equivalent for a straight perfect match (if effects of coupling negligible) Arg(Y1) + Arg(Y2)= 0 and Re(Z 0 ) - R 0 =0 for matching to a complex impedance

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Automatic matching for a single ILS: Match trim This is the case when the settings of the tuning reactances are known at the same frequency but at another load value. This is the case for two similar plasma pulses or for vacuum and plasma. Plasma load R L =1  C 2 (pF) C 1 (pF) 42 Vacuum match : R L = 0.1  C 2 (pF) C 1 (pF) 42 k p = 0

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Match trim with coupling (k p = 2%) C 1 (pF) C 2 (pF) C 1 (pF) C 2 (pF) 42 Vacuum match : R L = 0.1  Plasma load R L =1 

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Match trim to real input impedance (Z in = R 0 : k p X s << R 0 ) Im(  in ) = 0 Re(  in ) = C 1 (pF) C 2 (pF) 42

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Matching at Y in = 1/R 0 and Y in = 1/(R 0 -k p X) (kp = 0.02) Arg(Y 1 ) + Arg(Y 2 )= 0Re(Z 0 ) = R C1 (pF) C2 (pF) 43.8 Re(G in ) = 0Im(G in ) = 0

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Matching at Y in =1/(R 0 -k p X) kp = 0.0 kp =0.04

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Automatic matching for a single ILS: Match acquisition C 1 (pF) C 2 (pF) C 1 (pF) C 2 (pF) 49 To get into the area of the match It is useful to seek for the (unique) series resonance of the defined by the condition Im(Y 1 ) = Im(Y 2 ) = 0 and Im(V in ) = 0 ( Phase Ref: I in =I 1 +I 2 ) Series resonance In this case no reactance settings are available at the operating frequency The reflection coefficient is not a convenient control variable for match acquisition since the module is flat in most of the parameter space

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Automatic matching for a single ILS: Match acquisition In this case no reactance settings are available at the operating frequency 1 ) The two capacitors are set at the same value by imposing  X C = (X C1 -X C2 ) = 0 by a loop conrolled by Im (I 1 ) - Im(I 2 ) = 0 Im (I 1 ) - Im(I 2 ) = 0 2) The series resonance is tracked by imposing X C = (X C1 +X C2 )/2 = X s by a loop controlled by Im (I in ) – Im(V in ) =0 3) The match point is reached from the series resonance point as described above Series resonance C1 (pF) C2 (pF) 58

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Match acquisition path C1C1 C2C2 Series resonance point

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Matching an array of ILS Matching an array of ILS is performed in the same way as for the single ILS. 1.The array elements are sequentially set to the array (single) series resonance at the desired frequency ( the array is mismatched). 2. All elements are powered at equal power and in or out of phase (the array is mismatched ) 3. The the match condition to real or complex impedance is applied with similar time constants. Convergence to match is not critical because the array elements are virtually decoupled by the phase/module condition. 4. As for a single ILS, step 1 and 2 are necessary only if no previous settings of the tuning reactances are known at the same frequency but at another load value (like the vacuum match Match acquisition Match trim

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Conclusions A ITER-like array can be in principle be automatically matched for most foreseable load conditions, and in condition of “load resilience”, by using two capacitive tuning elements and an inductive trim located in the transmission line.. To obtain this result, the vectorial control of the currents in each half section of the array, as well as of all input voltage(s) are necessary. These can be implemented by an integrated, power, phase and match control system, (which can also provide array protection against voltage breakdown) by a set of 3N control loops, acting on the 2N capacitive elements and N inductive trims, driven by 3 N vectorial measurements. This proposal needs an experimental validation and probably some improvement. It is our intention to build this control system and to test it on the Tore Supra ITER Prototype next year.

Euratom TORE SUPRA G. Bosia “Automatic control of ITER-like structures” Venice, 21 – Match trim to complex input impedance (Z in = R 0 + k p X s ) C 1 (pF) C 2 (pF) 42 DCDC C C DCDC Im(Y 1 )+ Im(Y 2 ) = 0 Re(Y 1 )+ Re(Y 2 ) = 1/R 0 Im(Y 1 )+ Im(Y 2 ) = 0 Re(Y 1 )+ Re(Y 2 ) = 1/R 0