The klystron RF systems for the indiana university lens accelerator
This paper describes the Klystron RF systems for the Indiana University Low Energy Neutron Source (LENS) accelerator 425 MHz radiofrequency quadrupole (RFQ) and drift tube linac (DTL) systems. Of interest in the power conditioning system is the design of the totem-pole grid-catch modulator for the mod-anode klystrons. This topology provides a fast rise and fall and closed loop regulation for the klystron mod-anode to cathode voltage, which minimizes RF amplitude and phase droop while maximizing efficiency. Another advantage is that short pulse high rep-rate operation is viable within the average power capabilities of the klystron. The 425 MHz, 1.25 MW klystron amplifier chain will also be detailed. Of final interest, is the digital low level RF system. This provides vector control of the cavity field using direct conversion, non-I/Q sampling architecture, at a sampling rate of 132 MHz with a 12-bit analog-to-digital converter (ADC). Four input and two output channels are integrated into a 6 unit (6U) VME module, with all DSP functions performed in Xilinx Spartan-3 field-programmable gate arrays. The design and implementation of these systems, coupled with LENS operational results, will be presented.
Upgrade of the LENS Proton LINAC: Commissioning and results
The Indiana University Cyclotron Facility is operating a low energy neutron source which provides cold neutrons for material research and neutron physics as well as neutrons in the MeV energy range for the neutron radiation effects studies. Neutrons are being produced by a 7 MeV proton beam incident on a beryllium target. Since the first commissioning of the LENS Proton Delivery System (PDS) in December 2004 its performance has been significantly improved. The RF system of the accelerator has been upgraded by replacing 350 kW 425 MHz 12 tube amplifiers with two Litton 5773 klystron RF tubes capable of running at 425 MHz and 1.25 MW. Since the commissioning of the klystrons, a proton current of 25 mA at 7 MeV and 0.6% duty factor has been successfully delivered to the beryllium target. A future part of this upgrade will introduce a new 6 MeV DTL section to increase proton beam energy from 7 to 13 MeV. The 3 MeV RFQ and 4 MeV DTL will be powered by one klystron and the 6 MeV DTL will be powered by the second klystron. The expected output is 25 mA and 13 MeV of proton current at 0.6% duty factor. A second target station has been added to allow separate source optimization for the two primary research programs (cold neutrons and radiation effects). Other upgrades include increasing the RF duty factor to 3% through the installation of a new power supply for the klystrons. In this contribution we discuss the results of the commissioning of the new RF system, second beamline and second target station, as well as improvement in the beam parameters after these upgrades. The future plans will also be outlined.
An analytical approach to the design of electrodes in high-power, fast-transverse-flow CO2 lasers
Abstract Usually, the design of the electrodes of fast-transverse-flow CO 2 lasers relies more on experimental data than on theoretical analysis. Traditional systems sustain a stable, high-power discharge but the current distribution generates a peaked, non-uniform small-signal-gain pattern. We present a theoretical model suitable for the design of electrodes that achieves a quasi uniform gain distribution. The analysis, based on a two-temperature model and the gas-transport equations, computes the electron density that supports a flat gain pattern. Combining the desired electron density with the electron-balance equations, the model determines the required electric field. The results were used to design a new set of electrodes for a home-made fast transverse flow CO 2 laser. A stable, large volume discharge ( 4 × 8 × 90 cm 3 ) with very good uniformity was obtained. The resulting gain distribution was registered in a bi-dimensional map. The peak gain rose from 1.2 m - 1 , attained with the old electrode set, to 1.6 m - 1 with the new one and the gain showed a homogeneous profile.