A. Rauchas

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.

A Proposed Second Harmonic Acceleration System for the Intense Pulsed Neutron Source Rapid Cycling Synchrotron

The Rapid Cycling Synchrotron (RCS) of the Intense Pulsed Neutron Source (IPNS) operating at Argonne National Laboratory is presently producing intensities of 2 to 2.5 x 10/sup 12/ protons per pulse (ppp) with the addition of a new ion source. This intensity is close to the space charge limit of the machine, estimated at approx.3 x 10/sup 12/ ppp, depending somewhat on the available aperture. With the present good performance in mind, accelerator improvements are being directed at: (1) increasing beam intensities for neutron science; (2) lowering acceleration losses to minimize activation; and (3) gaining better control of the beam so that losses can be made to occur when and where they can be most easily controlled. On the basis of preliminary measurements, we are now proposing a third cavity for the RF systems which would provide control of the longitudinal bunch shape during the cycle which would permit raising the effective space charge limit of the accelerator and reducing losses.

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.

Injected Beam Chopper System for the Intense Pulsed Neutron Source Accelerator System

A new chopper system has been designed and built to allow versatile manipulation of the H- beam for the Intense Pulsed Neutron Source (IPNS) accelerator system. The beam is chopped at an energy of 750 keV, just before injection into the 50 MeV linear accelerator. The system consists of a high speed logic control system, a high power pulse amplifier and a travelling wave beam deflection electrode. The control system allows for up to four concurrently operable functions. The first mode is dedicated to personnel and equipment protection interlocking. The second is for low frequency pulse shaping. The third is a high frequency chop mode for RF synchronized injection of the 50 MeV beam into the Rapid Cycling Synchrotron (RCS). The fourth mode allows width and/or time modulation of the RF synchronized chopping to control the loading of the RF bucket area in the RCS.

Observations and Cure of Head-Tail Effect in the Argonne Rapid Cycling Synchrotron

Radial head-tail effects have been observed in the 500-MeV Rapid Cycling Synchrotron (RCS). The threshold intensity of accelerated beam to induce the instability was 4 × 1011 protons/pulse, and the mode numbers observed were m = 1 and m = 2. Detailed study showed that the radial chromaticity of the lattice at this particular time in the acceleration cycle was positive. This is consistent with theoretical predictions for a machine operating below the transition ¿. In order to prevent the onset of this instability, a set of programmable sextupole magnets has been introduced that can be programmed to vary the chromaticity at any point during the acceleration period. With these sextupoles, the machine intensity has passed 2 × 1012 protons/pulse.

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.

Beam Position Measurement System at the Argonne Rapid Cycling Synchrotron

The position measurement system for the Rapid-Cycling Synchrotron (RCS) was originally designed with a four-plate, combined function, capacitive pickup pi electrode situated in each of the six short straight sections. During subsequent operation, it was discovered that these electrodes were limiting the aperture and, therefore, were being activated by the circulating proton beam. In addition, the activation made it difficult to maintain the active electronic components in the RCS tunnel. The new position measurement system has been designed to eliminate these problems. The electrodes horizontal and vertical dimensions have been increased and the plates reorientated for simpler, separate function signal processing. A passive impedance matching network has replaced the active cathode follower, eliminating maintenance requirements in the accelerator tunnel. The Radio Frequency (RF) beam signals are transmitted directly to the Main Control Room (MCR) for processing.

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.

Conceptual Design of the Argonne 6-GeV Synchrotron Light Source

The Argonne National Laboratory Synchrotron Light Source Storage Ring is designed to have a natural emittance of 6.5 × 10-9 m for circulating 6-GeV positrons. Thirty of the 32 long straight sections, each 6.5-m long, will be available for synchrotron light insertion devices. A circulating positron current of 300 mA can be injected in about 8 min. from a booster synchrotron operating with a repetition time of 1.2 sec. The booster synchrotron will contain two different rf systems. The lower frequency system (38.97 MHz) will accept positrons from a 360-MeV linac and will accelerate them to 2.25 GeV. The higher frequency system (350.76 MHz) will accelerate the positrons to 6 GeV. The positrons will be produced from a 300-MeV electron beam on a tungsten target. A conceptual layout is shown in Fig. 1. Related papers on the Argonne Synchrotron Light Source may be found in references 1-3.