MODULATORS terwards awarded two new contracts from ESS ERIC for the manufacture of 9 and 5 additional modulators for the superconducting sections of the ESS LINAC. KLYSTRONS ESS Bilbao is also in charge of the delivery of the power klystrons for the RFQ and DTL tanks. Klystrons are va cuum electron devices (or “tubes”) able to provide huge amounts of RF power. Six pulsed klystrons featuring up to 3 MW peak at 352.21 MHz are required. Three of them have recen tly been acquired from Thales Microwave and Imaging Sub-Systems and delivered to the ESS site. At the same time, three existing klystrons (procured by ESS Bilbao in 2010 from Communications and Power Industries, or CPI, Inc.) have been refurbished following a lengthy reconditioning procedure to accommodate the tubes for the ESS long-pulse operation. As such Courtesy of ESS longer pulses might create increased mechanical stress in the collector parts, a thorough conditioning proce dure was performed to progressively and safely enlarge The pulsed high voltage power converters, also known the pulse length until the nominal operating conditions as modulators, energize the klystrons for the ESS LI were achieved. NAC’s RFQ and DTL tanks. A total amount of 3 modu lators is required for 6 klystrons, i.e.: each modulator powers two klystrons in parallel. These modulators are based on an advanced topology developed by the team led by Carlos Martins at ESS ERIC with the help of Lund University, known as Stacked Multi-Level (SML). This topology is able to provide high quality pulses, out- standing efficiency and low flicker, while exhibiting high power density in a relatively reduced footprint. ESS Bilbao took over the responsibility to procure the first 3 modulators, based on a “built-to-print” stra tegy,where ESS ERIC provided a complete design dossier. The contract was awarded to Jema Energy, S.A., a Basque company specialized in the design and manu facturing of turnkey energy conversion systems. Jema Energy, a lifelong partner of ESS Bilbao, undertook the industrialization of the design and the manufacturing Courtesy of ESS and factory tests of the three modulators. The in-kind contribution was executed on the basis of SSPAS a joint collaboration between the parties (ESS ERIC, As opposed to RFQ and DTL, buncher cavities requi ESS Bilbao and the industrial partner), with shared res re medium power amplifiers (with “only” 30 kW peaks). ponsibilities and due regard to the prime interests of These power levels (and increasingly higher ones) can the ESS project overall. be provided by Solid State Power Amplifiers (SSPAs), It is worth mentioning that JEMA Energy was af based on LDMOS FET transistors. These offer some ad 8