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.
Uniform beam intensity redistribution in the LENS nonlinear transport line
The Low Energy Neutron Source (LENS) at Indiana University is producing neutrons by using a 7 MeV proton beam incident on a Beryllium target. The Proton Delivery System is currently being upgraded [1], [2]. A new AccSys Technology,Inc. DTL section [3] will be added to increase proton beam energy from 7 to 13 MeV. A 3 MeV RFQ and 10 MeV DTL will be powered by two 1.25 MW klystrons. The goal of this upgrade is a 13 MeV,25 mA proton beam with duty factor greater than 3%. At this power level it becomes increasingly important to make a proton beam that is uniformly distributed to prevent excessive thermal stress at the surface of the Be- target. To achieve this goal two octupole magnets are being implemented in each LENS beam transport line. In this paper we discuss the experimental results of the beam intensity redistribution as well as some features inherent in tuning of the nonlinear beamline and our operational experience.
Performance of an AccSys Technology PL-7 Linac as an Injector for the IUCF Cooler Injector Synchrotron
An AccSys Technology Model PL-7 Linac is used to preaccelerate H ions to 7 MeV for strip injection into a new 2.4 T-m injector synchrotron now being commissioned at IUCF. The Cooler Injector Synchrotron (CIS) is designed to inject over 10 polarized protons or deuterons per pulse at 5 Hz into an existing electron cooled synchrotron-storage ring (Cooler) for nuclear research [1]. The linac, a 3 MeV RFQ coupled directly to a 4 MeV Drift Tube Linac, is designed to transmit over 1 mA of 7 MeV H ions to the CIS injection beam line with 85% transmission, 1 π mm mrad normalized emittance and 1% energy spread. Two 350 kW, 425 MHz rf amplifiers power the linac which accelerates variable pulse width H ions at duty factors up to 0.2%. We discuss the beam performance of this unique linac after a year of service as a synchrotron injector, and compare measured beam properties with calculations made during design and fabrication.