T. K. Khoe

Tests on superconducting helix resonators

A niobium helix‐resonator cavity close to the frequency suitable for a heavy‐ion accelerator has been subject to an 8‐week test, including 323 h at full power (axial electric field Eax>2.5 MV/m). The cavity, with an anodically deposited protective film of Nb2O5, had a high Q and supported high fields without deterioration over the whole period during which it was subject to a moderate internally generated x‐ray dose. Properties were found to be stable against considerable thermal cycling and exposure to air. Measurement of emitted x‐ray maximum energy allowed an independent corroboration of the field measurement calibration.

Ultra-Short Pulies of Heavy Ions

The bunching requirements for a heavy-ion tandemlinac accelerator are defined and a bunching system to satisfy these requirenents is outlined. This discussion introduces an experimrent on the bunching of 45 MeV 16O ions by means of a ¿/2 superconducting-helix resonator. The measured ion-bunch width is 64 psec, a value daminated by the resolution width of the ion detector. By correcting for the detector-resolution width one infers that the ion bunch itself is <40 psec wide.

Application of solenoid focusing in a superconducting heavy-ion linear accelerator☆

Abstract When the resonators of a heavy-ion linear accelerator are operated in the phase-stable region, their inherent radial-defocusing property makes external radial focusing elements necessary for preventing beam blow-up. Although quadrupoles are generally chosen for room-temperature ion linacs for reasons of space and power efficiency, solenoid focusing is superior in superconducting heavy-ion linacs in the energy range of present interest. Since power and cooling requirements are low, for equal beam-optical properties, superconducting solenoids are cheaper and simpler focusing elements than the corresponding quadrupoles. Calculations made for a superconducting-helix linac for heavy ions show that with resonators containing five 1 2 λ sections, the solenoids required are small and use magnetic fields readily attainable in commercial construction. Calculations made with the computer code TRIM show that a relatively small iron shield can be built which reduces the leakage field to negligible values in a relatively short space.

Vibration-RF Control of Superconducting-Helix Resonators for Heavy-Ion Acceleration

An electronic system for the control of the effects of RF frequency oscillations caused by mechanical vibrations in a superconducting helix are described. A combination of frequency modulation and amplitude modulation is used to lock the phase of a self-excited accelerating structure to that of a controlling master oscillator. The system has been used successfully during beam acceleration with a superconducting helix.

ASPUN, Design for an Argonne Super Intense Pulsed Neutron Source

Argonne pioneered the pulsed spallation neutron source with the ZING-P and IPNS-I concepts. IPNS-I is now a reliable and actively used source for pulsed spallation neutrons. The accelerator is a 500 MeV, 8-9 ..mu..a, 30 Hz rapid cycling proton synchrotron. Other neutron spallation sources are now in operation or in construction. These include KENS-I at the National Laboratory for High Energy Physics in Japan, the WNR/PSR at Los Alamos National Laboratory, and the SNS at the Rutherford Appleton Laboratory in England. Newer and bolder concepts being developed for more intense pulsed spallation neutron sources include SNQ at the KFA Laboratory in Germany, ASTOR at the Swiss Institute for Nuclear Physics, and ASPUN, the Argonne concept. ASPUN, presented in this paper, is based on the Fixed-Field Alternating Gradient concept. The design goal is to provide a time-averaged beam of 3.5 ma at 1100 MeV on a spallation target in intense bursts, 100-200 nanoseconds long, at a repetition rate of no more than 60 to 85 Hz. Design parameters are given.

A 1500-MeV Fixed-Field Alternating-Gradient Synchrotron for a Pulsed-Spallation Neutron Source

The first conceptual design of the FFAG for ASPUN was an 1100-MeV, 20-sector machine with an injection radius of 17.5 m and an extraction radius of 18.75 m. The conceptual design currently under study has a higher extraction energy, a larger average radius, but still has 20 sectors. The current interest in higher extraction energy is stimulated by calculations that indicate that the useful neutron production per incident proton is still increasing proportionally up to 1500 MeV. The larger radius also matches existing buildings at Argonne that could be made available for the facility. 11 refs., 4 figs., 3 tabs.

The Design of the Zero Gradient Synchrotron Booster-II Lattice

A 500 MeV booster has been designed at the Argonne National Laboratory to increase the beam intensity from the Zero Gradient Synchrotron (ZGS). Many turns of H ions from the 50 MeV lirac will be injected into the booster and stripped to H so that the ring will contain the maximum useful charge in each booster pulse. Several booster pulses will be injected into the ZGS to form one ZGS pulse. This machine is now under construction.

Development and Operation of a Prototype Superconducting Linac for Heavy-Ion Acceleration

A prototype superconducting-helix accelerator is described and design considerations are discussed. The results obtained during 120 hours of beam acceleration are given. These include a wealth of practical engineering experience, the demonstration of stable operation with external phase control, and measurements of various kinds of accelerator-physics data.

Longitudinal and Transverse Space Charge Limitations on Transport of Maximum Power Beams

The maximum transportable beam power is a critical issue in selecting the most favorable approach to generating ignition pulses for inertial fusion with high energy accelerators. Maschke and Courant1 have put forward expressions for the limits on transport power for quadrupole and solenoidal channels. We have included in a more general way the self consistent effect of space charge defocusing on the power limit. The results show that no limits on transmitted power exist in principal. In general, quadrupole transport magnets appear superior to solenoids except for transport of very low energy and highly charged particles. Longitudinal space charge effects are very significant for transport of intense beams.

Acceleration of Polarized Protons in the Zero Gradient Synchrotron (ZGS)

With the advent of high currenr (,6-12 PA) and high polarization (7570) proton sources, It became attractive to consider the acceleration of polarized protons to high energy (12 GeV). Such a source has been procured and a second preaccelerator with a beam transport line to the 50-MeV linac has been installed. A description of this ;ystem will appear in the conference proceedings. Since acceleration of polarized protons to 50 MeV has been previou;ly accomplished at the Rutherford Laboratory linac, we will not go into this topic in the present paper. We will concentrate on explaining those factors which make the ZGS an excpllant accelerator for minimizing the depolarization of an accelerating beam of polarized protons.