Gerald J. Volk

Commissioning of the Argonne Intense Pulsed Neutron Source (IPNS-I) Accelerator

The IPNS-I 500 MeV Rapid Cycling Synchrotron (RCS) was commissioned during March of 1977. It was originally designed as an injection energy booster for the Zero Gradient Synchrotron (ZGS), as well as a source of high intensity proton beams for neutron production. With the termination of the high intensity operation of the ZGS, the accelerator became a dedicated machine for neutron physics. After a period of tuning and improving accelerator components, the accelerator officially began neutron physics experiments on July 1, 1978. The accelerator has achieved a repetition rate of 15 Hz with beams of 1 × 1012 protons delivered on target. Operation at 30 Hz is expected soon. A description of the accelerator is presented. Turn on procedures, operating experience and initial performance problems are also discussed.

Status Report on the Rapid Cycling Synchrotron

The Rapid Cycling Synchrotron (RCS), originally designed as an injection energy booster for the Zero Gradient Synchrotron (ZGS), operated under constraints imposed by ZGS operation until December 1979. Once these restraints were removed, the RCS made rapid strides toward its near term goals of 8 ¿A of protons for Argonne National Laboratorys Intense Pulsed Neutron Source program. Reliable 30 Hz operation was achieved in the spring of 1980 with beams as high as 2 × 1012 protons per pulse and weekly average intensities of over 6 ¿A on target. These gains resulted from better injection matching, more efficient RF turnon and dynamic chromaticity control. A high intensity small diameter synchrotron, such as the RCS, has special problems with loss control which dictate prudence during intensity improvement activities. The studies and equipment leading to the intensity gains are discussed.

Performance of the Intense Pulsed Neutron Source Accelerator System

The Intense Pulsed Neutron Source (IPNS) facility has now been operating in a routine way for outside users since November 1, 1981. From that date through December of 1982, the accelerator system was scheduled for neutron science for 4500 hours. During this time the accelerator achieved its short-term goals by delivering about 380,000,000 pulses of beam totaling over 6 × 1020 protons. The changes in equipment and operating practices that evolved during this period of intense running are described. The intensity related instability threshold was increased by a factor of two and the accelerator beam current has been ion source limited. Plans to increase the accelerator intensity are also described. Initial operating results with a new H- ion source are discussed.

Beam Intensity Increases at the Intense Pulsed Neutron Source Accelerator

The Intense Pulsed Neutron Source (IPNS) accelerator system has managed a 40% increase in time average beam current over the last two years. Currents of up to 15.6 ¿A (3.25 × 1012 protons at 30 Hz) have been successfully accelerated and cleanly extracted. Our high current operation demands low loss beam handling to permit hands-on maintenance. Synchrotron beam handling efficiencies of 90% are routine. A new H- ion source which was installed in March of 1983 offered the opportunity to get above 8 ¿A but an instability caused unacceptable losses when attempting to operate at 10 ¿A and above. Simple techniques to control the instabilities were introduced and have worked well. These techniques are discussed below. Other improvements in the regulation of various power supplies have provided greatly improved low energy orbit stability and contributed substantially to the increased beam current. These improvements are discussed in a paper1 presented at this conference.

Phase Lock of Rapid Cycling Synchrotron and Neutron Choppers

The 500 MeV synchrotron of Argonnes Intense Pulsed Neutron Source operates at 30 Hz. Its beam spill must be locked to neutron choppers with a precision of ± 0.5 ¿s. A chopper and an accelerator have large and different inertias. This makes synchronization by phase lock to the 60 Hz power line extremely difficult. We solved the phasing problem by running both the Ring Magnet Power Supply (RMPS) of the synchrotron and the chopper motors from a common oscillator that is stable to 1 ppm and by controlling five quantities of the RMPS. The quantities controlled by feedback loops are dc current, injection current, ejection current, resonant frequency, and the phase shift between the synchrotron peak field and the chopper window.

Intensity Stability Dmprovements for the Intense Pulsed Neutron Source Accelerator System

The Intense Pulsed Neutron Source (IPNS) accelerator system consists of a 750 keV CockcroftWalton preaccelerator, 50 MeV linear accelerator and a 500 MeV Rapid Cycling Synchrotron (RCS). The accelerator system accelerates over 2.5 X 10/sup 12/ protons per pulse at a 30 Hz rate to strike a depleted uranium target for producing neutrons, which are used for neutron scattering research. Since beginning operation in 1977, the beam intensity has been steadily increasing with improvements in various systems, such as a new H/sup -/ source, improved correction magnet systems, etc. Instabilities created by the higher intensities have also been brought under control.

The Rapid Cycling Synchrotron Extraction Kicker Magnet Drive System

The Rapid Cycling Synchrotron (RCS) accelerator of the Intense Pulsed Neutron Source-I (IPNS-I) at Argonne National Laboratory utilizes a fast kicker magnet to provide single-turn extraction for a 500 MeV proton beam at a 30 Hz rate. The single-turn, 0.89 m long ferrite magnet is broken up into two identical cells with four individual windings. Each winding requires a 4863 A magnetizing current into a 7.0 ¿ load with a rise time of less than 100 ns and a flattop of about 140 ns. Pulse forming network (PFN) charging and switching techniques along with the components used will be described.

Intense Pulsed Neutron Source (IPNS-I) Accelerator 500 MeV Fast Kickers

Two ferrite loaded picture frame magnets with a kick of up to 15 mrad each are used to extract 500 MeV protons from the IPNS-I accelerator to the neutron source target at the Argonne National Laboratory. The magnet aperture is 10 cm wide by 5 cm high and the length is 60 cm. The single bunch extraction requires a magnetic field rise time (0 to 100%) of 90 ns and a flattop of 100 ns. The magnets receive the 3600 A maximum current via an array of 50 ¿ coaxial cables connected in a shunt arrangement. The two legs of each magnet are energized with separate lines to keep the potential to ground to less than 40 kV. The system is designed to run at 30 pulses per second repetition rate. The complete system of control electronics, power supply, deuterium thyratron switch, magnet and resistive load will be described along with some of the problems of stray inductances and the techniques used to reduce them.

Design and simulation of fast pulsed kicker/bumper units for the positron accumulator ring at APS

In the design of fast pulsed kicker/bumper units for a positron accumulator ring at APS, different pulse forming networks were considered and different structures for the magnet were studied and simulated. Some design considerations and computer simulation results of different designs are described.<<ETX>>

Betatron Tune Measurement at the Argonne Rapid Cycling Synchrotron

In the past, betatron tune measurements at the Rapid Cycling Synchrotron (RCS) were made using a spectrum analyzer for betatron frequency analysis and one of the extraction kicker magnets to induce the coherent betatron motion. This method had several severe limitations: poor signal-to-noise ratio, inability to extract the beam after the measurement and dependence on the horizontal kick coupling into the vertical plane for vertical tune measurements. A new system is presently being constructed which will eliminate these problems. The beam will be kicked by independent horizontal and vertical ferrite pinger magnets. The beam positron data will be digitized and then analyzed by an array-processing computer using the Fast Fourier Transform (FFT). The control system will allow for additional improvements.