W. P. Jones

Non-Linear Beam Transport for the Lens 7 MeV Proton Beam

A beam transport system has been designed to carry a high-intensity low-emittance proton beam from the exit of the RFQ-DTL acceleration system to the neutron production target of the Indiana University Low Energy Neutron Source (LENS). [1] The goal of the design was to provide a beam of uniform density over a 6cm by 6cm area at the target. Two octupole magnets [2] are employed in the beam line to provide the necessary beam phase space manipulations to achieve this goal. First order calculations have been performed using TRANSPORT [3] and second order calculations have been performed using TURTLE. [4] Second Order calculations have been done using both a Gaussian beam distribution and a particle set generated by calculations of beam transport through the RFQ-DTL using PARMILA. [5] Preliminary performance results for the beam transport system will be discussed.

Electron Gun Design Study for the IUCF Beam Cooling System

The design of a low temperature electron beam cooling system for the Indiana University electron-cooled storage ring is in progress. The storage ring, which will accept the light ion beams from the existing k-200, multi-stage cyclotron facility, requires an electron beam variable in energy from about 7 to 275 keV. The electron beam system consists of a high perveance electron gun with Pierce geometry and a flat cathode. The gun and a 28 element accelerating column are immersed in a uniform longitudinal magnetic guide field. A computer modeling study of the system was conducted to determine electron beam density and transverse temperature variations as a function of anode region and accelerator column design parameters. Transverse electron beam temperatures (Et = mc2ß2¿(¿H+¿v)) of less than a few tenths of an electron volt at a maximum current density of 0.4 A/cm2 are desired over the full energy range. This was achieved in the calculations without the use of resonant focusing for a 2 Amp, 275 keV electron beam. Some systematics of the electron beam temperature variations with system design parameters are presented. A short discussion of the mechanical design of the proposed electron beam system is also given.

Isochronism Studies at IUCF

A non-intercepting, charge sensitive, sampling beam phase probe, similar to the design developed for the 15 MeV injector cyclotron, was recently installed on the moveable south valley probe of the Indiana 200 MeV main stage cyclotron. The probe permits continuous measurement of beam phase from inflection to extraction radius at beam intensities as low as 200 nanoamperes. The measured phase histories obtained show that small deviations from the predictions of our field mapping data are required for isochronous acceleration. The characteristics of the phase probe and the results of the beam phase measurements are discussed.

Isochronization Studies of the IUCF 200 MeV Cyclotron

A non-intercepting movable beam phase probe recently installed in the south valley of the IUCF 200 MeV isochronous cyclotron has been used to study the relative beam phase variation during acceleration for the various beams accelerated by the facility. Small differences between the measured phase histories and the predictions of the field map data were observed and explained. Phase compression during acceleration has been measured, and a method for making rapid small energy changes (± 500 keV) while operating on a single RF frequency using trim coil adjustments at large radius has been developed. These and other consequences of the isochronization studies are discussed.

Isochronization Calculations for the Indiana University Cyclotron

A series of calculations using measured magnetic fields has been performed to determine the optimal gradient coil currents for the wide range of operating conditions to be experienced by the Indiana University main stage cyclotron. Depending on the particle type to be accelerated and final energy desired, the required radial field increase varies from 0.5% to 22%. An iterative least squares fitting technique is used to minimize orbit time variations. For the acceleration of 200 MeV protons (330 revolutions, fourth harmonic) the maximum phase excursion is predicted to be less than two rf degrees. The technique used can be adapted to using measured phase histories to predict corrections to gradient coil currents.

The design of an automatically‐tuned beamline

A new 30 m beamline (BL1C) is being assembled to connect the new High Intensity Polarized Ion Source (HIPIOS) to the IUCF cyclotrons. This line is being instrumented for complete automatic optimization of all transverse and longitudinal ion optical elements by providing a unique feedback signal for each controllable device. Transversely, steerers and 4‐quadrant electrostatic pickups are located approximately 90° apart in betatron phase advance along the beamline. Each pickup is instrumented with a single‐board, 4‐layer op‐amp circuit (BPM system) which measures the beam intensity, horizontal (H) and vertical (V) position, and H and V 10 Hz position modulation. The transverse beam ellipse parameters are first automatically determined at the entrance to the beamline by measuring the beam size using a wire scanner as a function of the strength of a quadrupole. The computer then programs the amplitude and phase of four 10 Hz modulators which vary the current in 4 steerers to move the beam centroid around this...

Beam transport system for the new IUCF polarized ion source

Abstract A high-transmission beam transport system has been designed to couple the new High Intensity Polarized Ion Source (HIPIOS) to the injector cyclotron. Longitudinally, a two stage bunching system will compress 70% of the DC beam into a phase width of ± 3° with an energy spread of less than 3 keV, at a beam energy of 620 keV. A wide band hardware phase feedback system will lock the RF systems to the beam, and there will be diagnostics to measure the beam phase width. Transversely, large aperture quadrupole and dipole magnets will maximize beam transmission; with diagnostics for measuring the source emittance, the beam polarization, and the cyclotron acceptance. The beam position will be monitored using a non-intercepting system and automated error correction will be available. The control system will feature software control “combos” which will provide single knob control for a variety of beam focussing properties. The current status of the beam transport system is discussed.