Line Type Modulators

Line type modulators are typically developed for driving klystrons, high power RF tubes, and other high voltage loads that require tight pulse shape control (usually a square pulse with minimal rise/fall times and minimal flat-top ripple).

Line type modulator technologies:

  • Low impedance pulse forming networks (PFNs) match users load impedances for optimum energy transfer and pulse shaping
  • Rep-rated high power switching (often with thyratrons) initiates output pulse generation
  • Low leakage inductance, high turns-ratio pulse transformers allow fast output risetime pulses
  • Variety of control system designs to meet user specific requirements

Example Projects:


520 MW Klystron Line Type Modulator Technical Specifications

  • Output voltage: -200 to -600 kV
  • Output current: 870 A @ -600 kV
  • Flat top pulse width: 10 ms
  • Continuous Rep-rate: Up to 50 Hz
  • Rise time: less than 1 ms
  • Pulse flatness: less than +/- 0.5%
  • Pulsed voltage stability: +/- 1200 V
  • Peak power: 522 MW
  • Average power: 380 kW

520 MW Klystron Line Type Modulator Technical Features

  • Center point SCR phase controller with primary side filter inductor and 45 kV, 54 mF filter capacitor bank
    • “Rough” voltage regulation and control
    • Limits input power line harmonics
  • Solid state (SCR), 40 kV command charging switch assembly w fiber optic trigger initiates PFN charging
  • 1 H charging inductor with solid state de-qing switch allows precise regulation of PFN charging voltage
  • 4 parallel Rayleigh Pulse Forming Networks
    • Each 10 ohm, 20 sections
    • Air insulated to 75 kV
    • Tunable inductors provide output pulse shaping for low ripple flat top
  • 2 parallel, ITT F-237 thyratron switches generate output pulse into the1:16 pulse transformer
  • Local, remote, and computer controls (using National Instruments LabView software)
520 MW HPM Line Type Modulator Plan (Overhead View)

520 MW HPM Line Type Modulator Plan (Overhead View)

520 MW Klystron Line Type Modulator Layout showing (left to right) the pulse transformer tank (with 2 thyratrons on top, pulse transformer in the middle, and output diagnostics on the bottom), PFN compartment (with 4 parallel PFNs), and HV power supply / resonant charging compartment. In the HVPS/RC charging compartment, the large rectangular object on the bottom is the Transformer/Rectifier (T/R) set. Eight square components on top of that are the filter capacitors on the output of the T/R set. Above them is the charging inductor tank. To the right of the filter capacitors is the primary side filter inductor tank and the phase controller sub-assembly mounted on the enclosure door panel. The top right corner of the enclosure is a dedicated controls electronics bay separated from the remainder of the enclosure.

520 MW HPM Line Type Modulator Main Enclosure Assembly

520 MW HPM Line Type Modulator Main Enclosure Assembly

520 MW Klystron Line Type Modulator showing (left to right) the pulse transformer tank, PFN compartment, and HV power supply / resonant charging compartment. The large grey tank in the HV power supply compartment is the Transformer/Rectifier (T/R) set that converts 480 Vac input power into 40 kVdc.

520 MW HPM Line Type Modulator Main Enclosure Assembly w Resonant Charging Subsystem (L) and Pulse Forming Networks (PFNs) (R)

520 MW HPM Line Type Modulator Main Enclosure Assembly w Resonant Charging Subsystem (L) and Pulse Forming Networks (PFNs) (R)

520MW Klystron Line Type Modulator showing opposite side with (l-r) resonant charging subsystem, Pulse Forming Network, and pulse transformer tank.  The large blue tank in the resonant charging subsystem compartment is the 1 Henry charging inductor with parallel de-qing winding.  The command charging switch can be seen on top of it to the left and a de-spiking L-R network and the de-qing circuit on the top right side. On the front side of the pulse transformer tank one can see the pump, filter, and heat exchanger for removing heat from the oil along with two “Hoffman” enclosures for containing diagnostic and power feedthrus into the tank.

520 MW HPM Line Type Modulator Main Enclosure Assembly w Voltage Diagnostics and HV Dump Circuit

520 MW HPM Line Type Modulator Main Enclosure Assembly w Voltage Diagnostics and HV Dump Circuit

520 MW Klystron Line Type Modulator HVPS Dump Circuit and Diagnostics  located above the T/R set oil insulated tank. The HVPS dump resistor array and Ross relay are located on the top right side while two high voltage probes are also suspended from the enclosure roof for monitoring the HVPS and PFN voltages. On top of the T/R set tank can be seen the HV output insulator post and the buswork combining multiple power cables from the phase controller.

520 MW HPM Line Type Modulator Main Enclosure Assembly w Pulse Forming Networks (PFNs)

520 MW HPM Line Type Modulator Main Enclosure Assembly w Pulse Forming Networks (PFNs)

520 MW Klystron Line Type Modulator PFNs  Two of the four Pulse Forming Networks are shown.  Each is a 75 kV, air-insulated, 20 section, 10 ohm, Rayleigh type PFN with low inductance, plastic case capacitors and tunable, solenoid inductors. One “folded” PFN takes up the top half of the enclosure and one the bottom half. End of line clipper circuits are connected to the left middle terminals while the outputs of the PFNs are tied together in the middle right side with buswork for connections to a feedthru insulator panel into the oil tank.

520 MW HPM Line Type Modulator Oil Tank Assembly with Two Thyratron Switches and Pulse Transformer

520 MW HPM Line Type Modulator Oil Tank Assembly with Two Thyratron Switches and Pulse Transformer

520 MW Klystron Line Type Modulator Thyratrons and Pulse Transformer in Oil Tank  The two parallel, ITT F-237 75 kV thyratrons are located in the top rear with the Stangenes 1:16 pulse transformer in the center.  Connecting buswork and high voltage diagnostics can also be seen in the oil filled tank.

520 MW HPM Line Type Modulator Oil Tank Assembly with Two Thyratron Switches and Pulse Transformer (Prior to Oil Filling)

520 MW HPM Line Type Modulator Oil Tank Assembly with Two Thyratron Switches and Pulse Transformer (Prior to Oil Filling)

520 MW Klystron Line Type Modulator Thyratrons and Pulse Transformer Prior to Oil Fill  Prior to filling with oil, this photo shows another view of the two ITT F-237 thyratrons, the Stangenes 1:16 pulse transformer, and the low inductance buswork.

520 MW HPM Line Type Modulator Main Enclosure With Control Module and Auxiliaries and Remote Control Rack

520 MW HPM Line Type Modulator Main Enclosure With Control Module and Auxiliaries and Remote Control Rack

Remote (left) and Local (right) Control Chassis  Modulator control system allows operation from local, remote, or computer control.  Other auxiliary subsystems are also shown on the right side, including the thyratron heater and reservoir power supplies, the klystron heater power supply, the internal pulse/timing generator, and the computer interface (CAMAC crate).

520 MW HPM Line Type Modulator LabView Computer Control Panel

520 MW HPM Line Type Modulator LabView Computer Control Panel

Computer control monitor screen  allows operation from remote computer (through National Instruments LabVIEW software). This is the top level screen which allows overall control of the modulator. Other screens for viewing interlock status, controlling the trigger generator, and setting up the oscilloscope data acquisition are also available from this screen.

Photos of the power supply system may be seen on the <!A HREF=”phsps.html”>Ness Engineering SCR Phase Control Power Supply Experience<!/A> page.

More detailed photos of the solid state, command charging switch assembly and resonant charging system can be seen on the <!A HREF=”ssmod.html”>Ness Engineering Solid State Switching Experience<!/A>  page.

520 MW HPM Line Type Modulator PFN Charging Current and Voltage Waveforms

520 MW HPM Line Type Modulator PFN Charging Current and Voltage Waveforms

520 MW Klystron Line Type Modulator PFN Charging Current and Voltage Waveforms  shows the half-sinusoidal PFN resonant charging current waveform (terminated somewhat early by the de-qing process) and the typical “1-cos” PFN voltage waveform associated with command resonant charging ending with a voltage of 71.2 kV on the PFN capacitors.

520 MW HPM Line Type Modulator Output Current Waveform

520 MW HPM Line Type Modulator Output Current Waveform

520 MW Klystron Line Type Modulator Output Current Waveform  shows the output pulse shape of the 10 ms flat-top pulse delivered to the load.

More details on the technical design and performance of this line type modulator can be found in the published technical papers on the 520 MW Klystron Modulator System and the Command Resonant Charging System for this modulator.

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46 MW Klystron Line Type Modulator Technical Specifications

  • Output voltage: -230 kV
  • Output current: 200 A
  • Flat top pulse width: 60 ms
  • Maximum pulse width: 75 ms
  • Continuous rep-rate: Up to 10 Hz
  • Pulse flatness: less than +/- 0.25%
  • Pulsed voltage stability: less than +/- 0.2%
  • Peak power: 46 MW
  • Average power: 34.5 kW

46 MW Klystron Line Type Line Type Modulators Technical Features

  • Coupled cavity linac (CCL) portion of Superconducting Super Collider (SSC)
    • Eleven 46 MW klystron modulators required
    • Thomson CSF TH-2143 klystron
  • Five Maxwell CCDS capacitor charging power supplies operate in parallel
    • Each power supply rated 35 kV, 8 kJ/s
    • Charge Pulse Forming Network directly to highly regulated voltage without resonant charging and de-qing
    • Diode isolation / protection circuits to allow continued operation if one unit fails
  • 20 Section Rayleigh PFN
    • Air insulated and charged to 35 kV
    • Tunable inductors provides pulse shaping for low ripple (less than +/-0.25%) output pulse
  • ITT F-331 thyratron generates long (60-75 ms) output pulse into pulse transformer
  • VME based computer controls system allows control and monitoring of over 150 analog and digital input and output signals
46 MW SSC CCL Line Type Modulator Overall Assembly

46 MW SSC CCL Line Type Modulator Overall Assembly

46 MW Klystron Line Type Modulator for SSC (Left to right) Pulse transformer tank with klystron (and lead shielding) installed on top, thyratron and Pulse Forming Network section, and controls and power supply compartment.

46 MW SSC CCL Line Type Modulator Pulse Forming Network (PFN) and Thyratron Assembly

46 MW SSC CCL Line Type Modulator Pulse Forming Network (PFN) and Thyratron Assembly

46 MW Klystron Line Type Modulator PFN and Thyratron Front View  Front view of Pulse Forming Network and thyratron compartment.  Thyratron and auxiliary circuit is located in lower left of photo with PFN in center and End of Line Clipper assembly in lower right.

46 MW SSC CCL Line Type Modulator Pulse Forming Network (PFN

46 MW SSC CCL Line Type Modulator Pulse Forming Network (PFN)

46 MW Klystron Line Type Modulator PFN and Thyratron Rear View  Rear view of 20 Section, air insulated, Rayleigh Pulse Forming Network with low inductance, metal case capacitors and tunable, solenoid inductors. The charging power supply isolation diode network can be seen at left with PFN assembly in the middle and thyratron assembly in the bottom right.

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8 MW Klystron Line Type Modulator Technical Specifications

  • Output voltage: -125 kV
  • Output current: 64 A
  • Flat top pulse width: 90 ms
  • Maximum pulse width: 105 ms
  • Continuous rep-rate: Up to 10 Hz
  • Pulse flatness: less than +/- 0.25%
  • Pulsed voltage stability: less than +/- 0.2%
  • Peak power: 8 MW
  • Average power: 8.4 kW

8 MW Klystron Line Type Modulators Technical Features

  • Drift tube linac (DTL) portion of Superconducting Super Collider (SSC)
    • Five 8 MW klystron modulators required
    • Thomson CSF TH-2140 klystron
  • Two Maxwell CCDS capacitor charging power supplies operate in parallel
    • Each power supply rated 35 kV, 8 kJ/s
    • Charge Pulse Forming Network directly to highly regulated voltage without resonant charging and de-qing
    • Diode isolation / protection circuits to allow continued operation if one unit fails
  • 20 Section Rayleigh PFN
    • Air insulated and charged to 35 kV
    • Tunable inductors provides pulse shaping for low ripple (less than +/-0.25%) output pulse
  • ITT F-307 thyratron generates long (90-105 ms) output pulse into pulse transformer
  • VME based computer controls system allows control and monitoring of over 150 analog and digital input and output signals
8 MW SSC DTL Line Type Modulator Overall Assembly

8 MW SSC DTL Line Type Modulator Overall Assembly

8 MW Klystron Line Type Modulator w Klystron Installed (Left to right) Pulse transformer tank with klystron mounted on top, thyratron and PFN section, and controls and power supply compartment.

8 MW SSC DTL Line Type Modulator Pulse Forming Network (PFN)

8 MW SSC DTL Line Type Modulator Pulse Forming Network (PFN)

8 MW Klystron Line Type Modulator PFN and Thyratron Thyratron and auxiliaries are located in the front left with the 22 section, air insulated, Rayleigh Pulse Forming Network in the center using low inductance, plastic case capacitors and tunable, solenoid inductors.  The two parallel HV power supplies and klystron and thyratron auxiliary power supplies can also be seen on the far right.

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 Send consulting inquiries, comments, and suggestions to nessengr@san.rr.com