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Klystron Modulators for 1) – the LP-SPL and for 2) – the HP-SPL

Klystron Modulators for 1) – the LP-SPL and for 2) – the HP-SPL. Carlos DE ALMEIDA MARTINS CERN – AB / PO Pulsed and High Voltage Power Converters Section. 11 Dec 2008. Summary. 1 – Modulators for the LP-SPL @ 2 Hz Selected topology. Advantages 2 – Modulators for the HP-SPL @ 50 Hz

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Klystron Modulators for 1) – the LP-SPL and for 2) – the HP-SPL

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  1. Klystron Modulators for1) – the LP-SPLand for2) – the HP-SPL Carlos DE ALMEIDA MARTINS CERN – AB / PO Pulsed and High Voltage Power Converters Section Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 11 Dec 2008

  2. Summary • 1 – Modulators for the LP-SPL @ 2 Hz • Selected topology. Advantages • 2 – Modulators for the HP-SPL @ 50 Hz • Why not the same topology as the LP-SPL ? • The SNS modulator, by LANL. Design key points • Proposed topology. Advantages • Preliminary theoretical studies Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 11 Dec 2008

  3. 1. Modulators for the LP-SPLMain parameters Rise time fall time time Flat-top Pulse width • Cathode power supply • Pulse width: 2.3 ms • Flat-top duration 2 ms • Precision at flat-top: < 1% • HF ripple at flat-top: < 0.1% • Repetition rate: 2 Hz • Nominal voltage: 110 kV (*) • Nominal current: 91 A (*) • Nominal power (peak): 10 MW (*) • Rise/fall times (99% / 1%): 300µs • Cooling: Air (natural or forced) • Maximum energy in case of arc: < 20 J • No Anode Mode terminal (*) to be confirmed, taking the new klystrons design into consideration Klystron modulators for: 1) LP-SPL ; 2) HP-SPL

  4. 1. Modulators for the LP-SPLSelected topology. Same as Linac 4 and ~same as 3 MeV Test Stand Simplified schematics • Description • Capacitor bank charged via a standard commercial power converter, PS1; • Pulses formed by solid state medium-voltage switches; • Step-up pulse transformer with oil insulation; • Droop compensation system, PS2; • Commercial filament power converters, PS4; • No CROWBAR needed in the HV line for klystron arc protection Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 11 Dec 2008

  5. Prototype for the 3 MeV Test Stand. Cathode ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 ms Flat-top width: 30% of the LP-SPL; Peak power: 20% of the LP-SPL; Average power: 16 % of the LP-SPL; A global klystron supply solution: ( Cathode, Anode, Filament power supplies in one system ) Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 11 Dec 2008

  6. Test of the prototype in a dummy load Cathode voltage Thyratron Firing 200µs Earc (65kV)=0.44J Earc (100kV)~1J Cathode Current (4A/div) Cathode voltage (zoom at flat-top) Cathode Voltage (20kV/div) Without bouncer < 1% With bouncer Cathode ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 ms Normal Operation Arc protection (short circuit with Thyratron) Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 6 11 Dec 2008

  7. Test of the prototype with the LEP klystron Ch2: Cathode Voltage to ground (20 kV/div) Ch2: Cathode Voltage to ground (2 kV/div) < 1% Ch3: Cathode Current (4A/div) Ch3: Cathode Current (0.8A/div) 1% 1.2% Ch4: Anode Voltage to ground (10 kV/div) Ch4: Anode Voltage to ground (1 kV/div) Cathode ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 ms Normal Operation at nominal Zoom at flat-tops Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 7 11 Dec 2008

  8. 1. Modulators for the LP-SPLAdvantages of this topology. • Advantages • Simple and reliable; • All active electronic components on transformer primary side (medium voltage); • Easy to control and interlock; • Straightforward path from design to practical results; Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 11 Dec 2008

  9. 2. Modulators for the HP-SPLWhy not the same topology as LP-SPL? • Cathode power supply LP-SPL HP-SPL • Pulse width: …………………… 2.3 ms …………………. 2.3 ms • Flat-top duration ………………… 2 ms ……………………….. 2 ms • Precision at flat-top: ……………. < 1% ……………………….. < 1% • HF ripple at flat-top: ……………. < 0.1% ……………………… < 0.1% • Repetition rate: ………………… 2 Hz ………………………... 50 Hz • Nominal voltage: ………………… 110 kV ……………………... 110 kV • Nominal current: ………………... 91 A ………………………… 91 A • Nominal peak power: ………….. 10 MW ……………………… 10 MW • Nominal average power: ……. 46 kW ……………………… 1.15 MW • Rise/fall times (99% / 1%): …….. 300µs ……………………… 300µs • Cooling: …………………………… Air (natural or forced) ……. Water • Maximum energy in case of arc: .. < 20 J ……………………… < 20 J • Practical limitations of the LP-SPL topology • Relies on two SPECIAL components (solid state HV switch and pulse transformer); • The whole power has to pass through these two crucial components; • A pulse transformer for 1.2 MW average power, 50Hz, has never been built: -demagnetization of the core during “off-time” requires high negative voltages; • A HV solid state switch for 1.2 MW average power has never been built; • A modular approach, by placing several LP-SPL systems in parallel to increase power is possible, however very expensive and less reliable for klystron protection in case of arc; Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 11 Dec 2008

  10. The SNS modulator, by LANL The Oak Ridge Nat Lab (SNS) type modulator, Bill Reass and Al. Los Alamos Lab AC/DC input converter not shown 140 kV, 70A, 1.6ms, 60 Hz (9.8 MWpk, 940 kWav) Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 11 Dec 2008

  11. The SNS modulator, by LANLAdvantages • Advantages • All active electronic components on transformer primary side (medium voltage); • Semiconductor switches of standard commercial types (multisource); • Transformers are not of “pulsed type”. Traditional High Frequency transformer design and construction techniques can be applied; • Flat-top closed loop regulation through the IGBT controls; • Intrinsic voltage shut-down in case of klystron arc, due to the resonance technique (De-Qing); Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 11 11 Dec 2008

  12. The SNS modulator, by LANLDesign keypoints • Hard points • Construction of the HF transformers: • Mechanical stress due to pulsed operation; • High Frequency (20 kHz) bandwidth with High Voltage insulation (110 kV at worst point); • Assure “soft-switching” of the IGBT’s in all operating points -> safe interlocking if not; • Thermal management; • Mechanical layout (reliability); Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 12 11 Dec 2008

  13. 2. Proposed topology for the HP-SPL Capacitor charger: In surface building Pulse former: In the tunnel + AC - DC 110 kV, 91A, 2.3ms, 50 Hz (10 MWpk, 1.15 MWav) • Pulse former: • Modular topology (4 or 5 independent modules in parallel/series); • Easier imposition of “soft switching” in all operating points (no coupling between modules); • However, former hard points related to the transformers, thermal management and mechanical layout remain. Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 11 Dec 2008

  14. Studies based on simulation(Jonas BAKKEN, Tech. Univ. Trondheim, NO) Simulated circuit Soft switching Cathode pulse Intrinsic current limitation in case of arc zoom Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 14 11 Dec 2008

  15. Conclusions • The acronym SPL is meaningless for modulator discussions. Always specify: LP-SPL or HP-SPL; • The LP-SPL topology will be the same as the Linac 4 one. New design and prototyping needed for higher ratings (longer flat-top and peak power); • The HP-SPL modulator project will be a unique project in this domain, at the ultimate technology frontier: • Only one (known) realization in solid state was done worldwide; • Several difficulties to get it working at nominal ratings; • A new topology has been studied (simulation), based on a modular approach. It solves some of the former difficulties but others remain; • A prototype construction and validation at CERN is possible in the medium term only and requires advanced preparation. Klystron modulators for: 1) LP-SPL ; 2) HP-SPL 15 11 Dec 2008

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