Davide Aguglia

Klystron modulator technology challenges for the Compact Linear Collider (CLIC)

This paper presents the research and development challenges foreseen for the klystron modulators design for a new accelerator complex, the Compact Linear Collider (CLIC). This huge electron-positron accelerator needs roughly 300MW of average power for feeding the 1638 required klystron modulators. The main challenges for designing theses new pulsed klystron modulators are described. Considering the state of the art in several domain such as converters topologies, voltage measurements precision, pulse-to-pulse reproducibility, AC power quality issues, efficiency maximization, accelerator reliability & availability, this paper illustrates the most challenging future developments directions and the need for an international and coordinated R&D program.

Status and operation of the Linac4 ion source prototypes.

CERNs Linac4 45 kV H(-) ion sources prototypes are installed at a dedicated ion source test stand and in the Linac4 tunnel. The operation of the pulsed hydrogen injection, RF sustained plasma, and pulsed high voltages are described. The first experimental results of two prototypes relying on 2 MHz RF-plasma heating are presented. The plasma is ignited via capacitive coupling, and sustained by inductive coupling. The light emitted from the plasma is collected by viewports pointing to the plasma chamber wall in the middle of the RF solenoid and to the plasma chamber axis. Preliminary measurements of optical emission spectroscopy and photometry of the plasma have been performed. The design of a cesiated ion source is presented. The volume source has produced a 45 keV H(-) beam of 16-22 mA which has successfully been used for the commissioning of the Low Energy Beam Transport (LEBT), Radio Frequency Quadrupole (RFQ) accelerator, and chopper of Linac4.

H- Ion Sources For CERN’s Linac4

The specifications set to the Linac4 ion source are: H− ion pulses of 0.5 ms duration, 80 mA intensity and 45 keV energy within a normalized emittance of 0.25 mmmrad RMS at a repetition rate of 2 Hz. In 2010, during the commissioning of a prototype based on H− production from the plasma volume, it was observed that the powerful co-extracted electron beam inherent to this type of ion source could destroy its electron beam dump well before reaching nominal parameters. However, the same source was able to provide 80 mA of protons mixed with a small fraction of H2+ and H3+ molecular ions. The commissioning of the radio frequency quadrupole accelerator (RFQ), beam chopper and H− beam diagnostics of the Linac4 are scheduled for 2012 and its final installation in the underground building is to start in 2013. Therefore, a crash program was launched in 2010 and reviewed in 2011 aiming at keeping the original Linac4 schedule with the following deliverables: Design and production of a volume ion source prototype sui...

Two-Step Method for Identification of Nonlinear Model of Induction Machine

A two-step method is applied for parameter identification of a saturated electromechanical model of an induction machine (IM). The k-factor cross saturation technique is used to account for iron saturation. Balanced and unbalanced short-circuits armature current waveforms of this machine are less sensitive to variations in the mechanical parameters. Conversely, any change in these parameters has a strong impact on the start-up test. Accordingly, in the proposed estimation method, the online double-line-to-neutral short-circuit test is performed to estimate the electrical parameters of the machine and the results obtained are then used to compute the mechanical parameters from the starting test. The good agreement of the estimated results with actual data attests to the effectiveness and suitability of the proposed algorithm in computing the electromechanical parameters of these machines.

Linac4 H⁻ ion sources.

CERNs 160 MeV H(-) linear accelerator (Linac4) is a key constituent of the injector chain upgrade of the Large Hadron Collider that is being installed and commissioned. A cesiated surface ion source prototype is being tested and has delivered a beam intensity of 45 mA within an emittance of 0.3 π ⋅ mm ⋅ mrad. The optimum ratio of the co-extracted electron- to ion-current is below 1 and the best production efficiency, defined as the ratio of the beam current to the 2 MHz RF-power transmitted to the plasma, reached 1.1 mA/kW. The H(-) source prototype and the first tests of the new ion source optics, electron-dump, and front end developed to minimize the beam emittance are presented. A temperature regulated magnetron H(-) source developed by the Brookhaven National Laboratory was built at CERN. The first tests of the magnetron operated at 0.8 Hz repetition rate are described.

A novel active bouncer system for klystron modulators with constant AC power consumption

A new linear accelerator under study at CERN (CLIC-Compact Linear Collider) [1] requires the design of a new klystron modulator capable of producing 150 KV and 160 A square shaped pulses with a repetition rate of 50 Hz and a flat-top length of 140 μs. The whole complex will include more than 1600 modulators of 24MW each, synchronously operated. With this operating mode, a total pulsed peak power of 37 GW must be produced, equivalent to 300 MW of average power consumption. The utility grid can tolerate a few percent of power fluctuation, and the klystron modulators system must be designed such that a constant power (300 MW) only is withdrawn from the AC network. This power fluctuation can be reduced either by passive or active solutions. Typical capacitor discharge based klystron modulators are already attenuating this effect by a considerable amount (typically ~90% of power fluctuation attenuation). However, because of design constraints, the capacitor bank cannot ensure a perfect attenuation of the power consumption fluctuation from the AC network. Therefore, additional active or passive solutions must be foreseen in order to resolve the power fluctuation issue.

Finite-Element-Based Optimal Design Approach for High-Voltage Pulse Transformers

This paper presents an optimal design methodology of monolithic high voltage pulse transformers based on the direct 2D FEA identification of the electrical equivalent circuit parameters. This method is applied to the preliminary optimal design of the monolithic high voltage pulse transformer for the future CLIC modulators under study at CERN. The feasibility of such a transformer with tight specifications is demonstrated. The predicted performances obtained with the direct 2D FEA optimization process is validated by 3D FEA simulation.

CERN’s Linac4 H− sources: Status and operational results

Two volume sources equipped with DESY and CERN plasma generators and a low voltage electron dump were operated at 45 kV in the Linac4 tunnel and on a dedicated test stand. These volume sources delivered approximately 20 mA and ensured the commissioning of the Radio Frequency Quadrupole accelerator and of the first section of the Drift Tube Linac. CERN’s prototype of a cesiated surface source equipped with this electron dump was operated continuously from November 2013 to April 2014 on the ion source test stand and is being commissioned in the Linac4 tunnel. Before cesiation, the prototype conditioned in volume mode provided up to 30 mA H− beam. Short cesiations, of the order of 10 mg effectively reduced the intensity of co-extracted electrons down to 2 - 8 times the H− current; this cesiated surface operation mode delivered up to 60 mA H− beam. An H− beam of the order of 40 mA was sustained up to four weeks operation with 500 μs pulses at 1.2s spacing. A new extraction was designed to match these beam pro...

Klystron modulators capacitor chargers design compromises for ac power quality increase of the Compact Linear Collider (CLIC)

This paper presents design compromises for the capacitor bank chargers needed for klystron modulators of a new 50km long linear collider under study at CERN. The problematic consists in a utility grid power fluctuation resulting from more than 1600 capacitor discharge power converters operating simultaneously. The objective is to supply all klystron modulators with a constant power of 300MW. The utility grid configuration and capacitor chargers design compromises are analyzed from topological and control point of view. Integration issues (volumes) and multi objective control strategies to meet tight specifications in terms of pulse-to-pulse reproducibility and utility grid power fluctuation are evaluated and discussed.

Review of design solutions for high performance pulsed power converters

This paper presents a review of topological and control design solutions for improving the performance of pulsed power converters. High bandwidth, low ripple and high efficiency square pulse voltage generators are typical specification requirements for the new generation of power converters for physics and medical research domains. The first part of the paper presents the state of the art of relevant literature on design solutions, optimized for different industrial applications, which can be useful for the pulsed power domain. The second part discusses their pertinence and efficiency implications for pulsed power designs.