C. Burkhart

ILC Marx modulator development program status

A Marx-topology klystron modulator is under development for the International Linear Collider (ILC) project [1]. It is envisioned as a lower cost, smaller footprint, and higher reliability alternative to the present, bouncer-topology, baseline design. The application requires 120 kV (+/−0.5%), 140 A, 1.6 ms pulses at a rate of 5 Hz. The Marx constructs the high voltage pulse by combining, in series, a number of lower voltage cells. The Marx employs solid state elements; IGBTs and diodes, to control the charge, discharge and isolation of the cells. Active compensation of the output is used to achieve the voltage regulation while minimizing the stored energy. The developmental testing of a first generation prototype, P1, has been completed. This modulator has been integrated into a test stand with a 10 MW L-band klystron, where each is undergoing life testing. Development of a second generation prototype, P2, is underway. The P2 is based the P1 topology but incorporates an alternative cell configuration to increase redundancy and improve availability. Status updates for both prototypes are presented.

A hierarchical control architecture for a PEBB-based ILC Marx modulator

The idea of building power conversion systems around Power Electronic Building Blocks (PEBBs) was initiated by the U.S. Office of Naval Research in the mid 1990s. A PEBB-based design approach is advantageous in terms of power density, modularity, reliability, and serviceability. It is obvious that this approach has much appeal for pulsed power conversion including the International Linear Collider (ILC) klystron modulator application. A hierarchical control architecture has the inherent capability to support the integration of PEBBs. This has already been successfully demonstrated in a number of industrial applications in the recent past. This paper outlines the underlying concepts of a hierarchical control architecture for a PEBB-based Marx-topology ILC klystron modulator. The control in PEBB-based power conversion systems can be functionally partitioned into (three) hierarchical layers; system layer, application layer, and PEBB layer. This has been adopted here. Based on such a hierarchical partition, the interfaces are clearly identified and defined and, consequently, are easily characterised. A conceptual design of the hardware manager, executing low-level hardware oriented tasks, is detailed. In addition, the idea of prognostics is briefly discussed.

All solid-state, switched pulser for air pollution control system

This paper describes an all solid-state switched pulser for an air pollution control system. The proposed pulser can produce 20 kV, 500 A, 100 ns pulses at repetition rates up to 10 kHz, and it is composed of 30 series connections of power circuit card assemblies which contain paralleled MOSFETs, energy storage capacitors and pulse transformer. Higher pulse voltages and currents can easily be obtained by increasing the numbers of series and parallel connections of power circuit cards and MOSFETs, respectively. This paper places emphasis on the overvoltage and the overcurrent protections including short circuit conditions for reliable operation in real situations. Experimental results show that the proposed pulser is very efficient in air pollution control application and could be useful for other applications such as synthesis of nanosize powders and nonthermal food processing.

A vernier regulator for ILC Marx droop compensation

A two-part compensation scheme, Vernier Regulation, has been applied to offset the voltage droop (40% without correction) in a Marx-topology klystron modulator developed for the International Linear Collider (ILC). Coarse regulation, ±5%, is achieved by turning on additional Main Marx cells (Delayed Cells) sequentially as the droop reaches the cell voltage (11 kV). Further regulation to ±0.5% is achieved by adding a small Marx in series with the Main Marx. This Vernier Marx is composed of sixteen, 1.2 kV cells that are assembled as a seventeenth cell in the Main Marx. These Vernier Cells are turned on sequentially to generate a series of discrete corrections to the droop in the Main Marx cells with a step size ≤1% of the output voltage. As the required correction reaches 11 kV, all Vernier Cells are turned off synchronously with the turn on of a Delayed Cell. There are up to five Delayed Cells and six Vernier Marx cycles during each ILC Marx output pulse. The Vernier Marx has a local control system that will detect and respond to over-voltage and over-current errors. In this paper, a detailed description of the design, implementation and testing of the Vernier Marx is presented.

P1-Marx modulator for the ILC

A first generation prototype, P1, Marx-topology klystron modulator has been developed at the SLAC National Accelerator Laboratory for the International Linear Collider (ILC) project[1]. It is envisioned as a lower cost, smaller footprint, and higher reliability alternative to the present, bouncer-topology, baseline design. The application requires 120 kV (+/−0.5%), 140 A, 1.6 ms pulses at a rate of 5 Hz. The Marx constructs the high voltage pulse by combining, in series, a number of lower voltage cells. The Marx employs solid state elements; IGBTs and diodes, to control the charge, discharge and isolation of the cells. Active compensation of the output is used to achieve the voltage regulation while minimizing the stored energy. The P1-Marx has been integrated into a test stand with a 10 MW L-band klystron, where each is undergoing life testing. A review of the P1-Marx design and its operational history in the L-band test stand are presented.

Final design of the SLAC P2 Marx klystron modulator

The SLAC P2 Marx has been under development for two years, and follows on the P1 Marx as an alternative to the baseline klystron modulator for the International Linear Collider. The P2 Marx utilizes a redundant architecture, air-insulation, a control system with abundant diagnostic access, and a novel nested droop correction scheme. This paper is an overview of the design of this modulator.

A prognostic method for scheduling maintenance on the P2-Marx modulator

The SLAC National Accelerator Laboratory is developing a second generation Marx-type modulator for the ILC, the P2-Marx. The modulator is expected to operate reliably in excess of 105 hours with minimum downtime. A prognostic system is being implemented with the development of the P2-Marx to monitor and track the health of key high voltage components. This paper discusses the way in which the prognostic system will be implemented and used to monitor the health of the P2-Marx modulator.

Lifetime tests on a high ohms/square metalized high crystalline polypropylene film capacitor with application to a Marx modulator

This paper presents accelerated lifetime tests on a polypropylene film capacitor. Experimental parameters (20% droop, 5 Hz repetition rate) simulate anticipated operating conditions encountered in the SLAC P2 Marx. Elevated film electric field stress is utilized as the acceleration parameter. Results indicate that, for the particular film of interest, a film stress of ∼290 V/μm corresponds to a 105 hour lifetime. In addition, the voltage scaling exponent for this film is 13.1.

Design considerations for a PEBB-based Marx-topology ILC klystron modulator

The concept of Power Electronic Building Blocks (PEBBs) has its origin in the U.S. Navy during the last decade of the past century. As compared to a more conventional or classical design approach, a PEBB-oriented design approach combines various potential advantages such as increased modularity, high availability, and simplified serviceability. This relatively new design paradigm for power conversion has progressively matured since then and its underlying philosophy has been clearly and successfully demonstrated in a number of real-world applications. Therefore, this approach has been adopted here to design a Marx-topology modulator for an International Linear Collider (ILC) environment where easy serviceability and high availability are crucial. This paper describes various aspects relating to the design of a 32-cell Marx-topology ILC klystron modulator. The concept of nested droop correction is introduced and illustrated. Several design considerations including cosmic ray withstand, power cycling capability, fault tolerance, etc., are discussed. Details of the design of a Marx cell PEBB are included.

The SLAC P2 Marx

A proposed high energy physics accelerator, the International Linear Collider, will require greater than five hundred rf stations. Each station is composed of a klystron driven by a modulator. Recently, the SLAC P2 Marx was designated the baseline modulator for the ILC. This paper describes some key features of this modulator and presents recent experimental results.