Beams Document 3934-v2

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Design and Operating Results for a New 201 MHz Radio Frequency Power System for LANSCE

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Submitted by:
Fernanda G Garcia
Updated by:
Camille M. Ginsburg
Document Created:
01 Sep 2011, 12:03
Contents Revised:
09 Sep 2011, 11:00
Metadata Revised:
09 Sep 2011, 11:01
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01 Sep 2011, 12:03
A prototype 201.25 MHz RF Power Amplifier for Los Alamos Neutron Science Center (LANSCE) has been designed, fabricated, and tested. The amplifier has exceeded our goal of producing 2 MW peak at 12% duty factor (240 kW of average power) at an elevation of 2.1 km above sea level. It has been designed to use a Thales TH628 Diacrode®, a state-of-art tetrode power tube that is double-ended, providing twice the power of a similar-sized conventional tetrode. The amplifier is designed with tunable input and output transmission line cavity circuits, a grid decoupling circuit, an adjustable output coupler, high-order mode suppressors, blocking, bypassing and decoupling capacitors, and a cooling system. The tube is connected in a full wavelength output resonator, with the lower main tuner situated ¾ of a wavelength from the central electron beam region in the tube and the upper slave tuner ¼ of a wavelength from the same point. The amplifier avoids use of a high-level anode modulator by leaving DC power on the tube, even between pulses. Field control for beam loading is handled by digital low level RF electronics, as the amplifier chain is linear. In addition to the ampifier, a new test facility was designed and constructed with a capacitor bank and charging power supply to supply up to 30 kV DC to the tube with 1500 uS RF pulses. A new fast protection/power monitoring system was developed to take samples of RF reflected power, anode HV, and various tube currents, with outputs to quench the HV charging supply, remove RF drive and disable the conduction bias pulse to the grid of the tube during fault events. The test stand is controlled with a programmable logic controller, for normal startup sequencing and timing, protection against loss of cooling, and operator GUI. A pair of production amplifiers are planned to be power-combined and installed for each of three DTL tanks at LANSCE to return operation to >10% duty factor.
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