DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING High Power RF Amplifiers Development at LNL Fabio Scarpa - INFN LNL

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING Introduction A new program for modular High Power RF Amplifier has started at LNL in 2000 in collaboration with LURE. The goal was to build a low-cost, high reliability device capable of working even in completely mismatched conditions with SC resonators. A 2.5 kW prototype and a 5 kW one have been successfully built and tested, confirming the design expectations. The next step will be the project of two 10 kW amplifiers that can be used separately or coupled together to obtain a 20 kW unit.

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING In designing the high power RF amplifier the solid-state MOSFET technology has been chosen because it can give several advantages over both the electron tubes and the bipolar transistors: With respect to the electron tubes: No high voltages No periodic replacements With respect to the bipolar transistors: No thermal runaway No secondary breakdown

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING Description of the Amplifier The amplifier is built using a set of eight modules connected in parallel by means of an eight- way power combiner. Each module must provide a RF power of at least 315 W, with a minimum power gain of 9 dB. Taking into account some power losses in the cables and in the combiner, a total power of 2.5 kW can be obtained at the output. Another module as preamplifier is connected to this set as by means of an eight-way power splitter. In order to save space the water cooling has been chosen so the complete amplifier could be mounted inside a 19” rack 1.2 m high and 80 cm deep Block diagram

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING The 315 W Amplifier Module Each module uses one double power MOSFET type D1029UK produced by Semelab mounted in a push-pull circuit working in class AB. A low cost 300 W circulator and a 500 W RF termination is mounted inside any module in order to protect it against the reflected power.

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING Frequency352.2 MHz Output power315 Watt CW Minimum gain10 dB +1.5 dB at 315 W Phase difference+/- 7.5 deg Output impedance50 Ohm Input impedance50 Ohm StabilityUnconditional Module specifications

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING Gain Phase During modules have been built, adjusted and tested at LNL obtaining optimum compliance to the specifications. A maximum power of 330 W could be obtained for all modules with a minimum gain of 11 dB at 330 W. During modules have been built by an external company following our design. We have found they were compliant to our specifications. Module Test Results Particular care had to be taken in adjusting the modules in order to minimize the gain and phase differences and to reach the correct stability margin.

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING The 8-way Splitter/Combiner In order to connect the modules, a simple 8-way Star-Point Combiner has been built at LNL. Being a bidirectional device, it can be used as a Splitter too. It has N connectors at the low power side, and an EIA 7/8” flange at the high power side.

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING The 2-way High Power Combiner

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING The Directional Coupler

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING The High Power Directional Coupler

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING 2.5 kW Amplifier test results Gain and Efficiency After the assembling of the amplifier, no adjusting were necessary and it immediately started to work. A power of 2.5 kW could be reached with 1.5 dB gain compression. Long Test An 8-hour long test has been done at 2kW and 2.4 kW showing a good behavior in both conditions. A 60-days long test has been done at 2 kW and 2.4 kW

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING 2.5 kW Amplifier test results Test1: just after assembly Test2: after 4 months Test3: after further 16 months Test4: after first 30 days of the long test Test5: at the end of 60-day long test After replacing some components, the gain has recovered but not completely. We believe it is due to insufficient cooling. However we believe that a maximum power of 2 kW must be chosen for a safe and reliable long term working. As time passed we could realize that problems of gain degradation occurred.

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING Second harmonic704 MHz-55.8 dB Third harmonic1056 MHz-65.1 dB A spectrum measurement was done at the output of the amplifier at 2.4 kW in order to know the harmonic content of the radio frequency power. Harmonic content

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING Photos of the 2.5 kW 352 MHz amplifier

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING The 5 kW amplifier In this case the amplifier is built using 2 sets of 2.5 kW blocks connected in parallel. Now 18 modules are necessary, plus a preamplifier, a low-power 2-way splitter, a high power 2-way combiner and an output directional coupler. All these components except the preamplifier have been designed and built at LNL. This amplifier is still water cooled and could be mounted inside a 0.8m x 0.8m x 2 m rack.

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING 5 kW Amplifier test results Several tests were done on our 5 kW Amplifier An 8-hour long test at 4.7 kW. A 7-days long test in matched condition at 4 kW and 4.6 kW. A 4-days long test in full mismatched condition at 2.5 kW, 4 kW and 5 kW. Many power sweep tests.

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING 5 kW Amplifier test results As happened for the 2.5 kW amplifier, no adjusting were necessary and it immediately started to work. A power of 5 kW could be reached with 1 dB gain compression. The gain degradation is still present but it is less than before. Test1: Just after assembling Test2: After 8-hour long test Test3: After 7-days long test

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING 5 kW Amplifier long test results Matched conditionFull mismatch condition

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING Photos of the 5 kW 352 MHz amplifier

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING The 10 kW amplifier The next step is to build a 10 kW amplifier. Again this amplifier uses the 2.5 kW block, and in this case they will be four. A low power 4-way splitter and a high power 4-way combiner are under development.

DESIGN STUDY November 28 th - 30 th 2005First EURISOL Design Study TOWN MEETING Conclusions Two solid-state high power RF amplifiers were constructed and tested at Laboratori Nazionali di Legnaro. The devices have shown very good characteristics of efficiency, stability, harmonics and low cost. These amplifiers are a prototypes for medium intensity proton and ion accelerators based on superconducting resonators. The amplifier design is modular; higher RF output power can be obtained by combining a larger number of units.