D. Friesel

Effects of rf voltage modulation on particle motion

Abstract The effects of rf voltage modulation on synchrotron motion were studied experimentally. The experimental data revealed the resonance islands generated by the rf voltage modulation. With electron cooling, beam particles were observed to damp to the basins of these resonance islands or attractors, which were observed to rotate about the origin of the phase space at a half of the modulation frequency. The measured amplitude of the attractors as a function of the modulation frequency agreed very well with the theoretical prediction. The Poincare maps in the resonance rotating frame were obtained from the experimental data and compared with tori of the Hamiltonian flow. Based on our theoretical formulation, slow beam extraction using rf voltage modulation and a bent crystal are also studied.

The Indiana University Cooler injection synchrotron RF cavity

A small 2.2 Tesla-meter booster synchrotron is under construction at the Indiana University Cyclotron Facility to boost polarized beam performance in the electron cooled Indiana University Cooler Synchrotron. Polarized light proton or deuteron beam from a high intensity polarized ion source will be preaccelerated to 7 and 6 MeV respectively by an RFQ/DTL accelerator. The beams are then debunched to reduce the energy spread and strip-injected into the booster synchrotron. The booster RF system must accomplish the tasks of beam capture and acceleration. At the end of the acceleration cycle, the beam phase needs to be aligned to the Cooler synchrotron RF for bucket-to-bucket beam transfer. A single RF cavity in the ring will provide the necessary RF field to accomplish the above tasks.

The Indiana University Cooler injector synchrotron RF system

A 2.2 Tesla-meter synchrotron with 17.4 m circumference is being built at the Indiana University Cyclotron Facility (IUCF). The purpose of the project is to achieve higher luminosity for nuclear physics experiments using electron cooled polarized light ion beams in the IUCF Cooler synchrotron. The injection line for the booster synchrotron consists of an RFQ/DTL linear accelerator delivering a 7 MeV proton beam and a 6 MeV deuteron beam for the booster injection. A debunching system will be installed in the injection beamline to reduce the energy spread of beams out of the linear accelerators. Charge-exchange injection is used for high intensity multiturn beam accumulation. The booster output beams, 200 MeV for protons and 105 MeV for deuterons, will be transferred bucket to bucket to the IUCF Cooler synchrotron. The rf system design for the booster synchrotron is presented in this paper.

Progress in commissioning the IUCF cooler

Some of the techniques used and results observed during the commissioning of the IUCF (Indiana University Cyclotron Facility) electron cooled storage ring are described. Measurements of machine properties and their comparison with design values, methods of closed-orbit corrections, and the methods used in ramping the beam to higher energies are discussed. Plans for enhancing the performance of the ring are described.<<ETX>>

Nonlinear beam dynamics studies at the IUCF cooler ring

The nonlinear beam dynamics of transverse betatron oscillations were studied experimentally at the IUCF Cooler Ring. Particles were kicked onto resonance islands and the properties of these islands were studied. The island tune was determined with high precision by Fourier analyzing the spectrum containing the islands and the properties of these island were studied. The island tune was determined with high precision by Fourier analyzing the spectrum containing the island oscillations. The island width was estimated based on a single resonance model. The Hamiltonian of particle motion near a resonance condition was thus deduced.

Measurement of space charge effect on transverse emittance

The SNS accumulator ring is designed to compress 1.5/spl times/10/sup 14/ 1 GeV protons from a bunch train of 1000 /spl mu/s H/sup -/ to a single proton bunch with bunch length 700 ns. The injection scenario of the SNS is experimentally simulated at the Cooler Injector Synchrotron (CIS) at Indiana University. A 100 /spl mu/s, 7 MeV H/sup -/ bunch train from the RFQ and DTL is compressed into a single proton bunch with bunch length /spl les/ 150 ns. The transverse rms emittance of the 7 MeV beam is measured by the quadrupole tuning method in the CIS extraction line. Measurements are taken at various beam intensities with peak currents ranging from a few mA to hundreds of mA. Results are compared with simulation, and the effects of multiple strip foil transits and space charge are discussed.

Determination of the linear coupling resonance strength using 2D invariant Tori

Experimentally obtained Poincare maps in the resonant precessing frame for particle motion with linear coupling revealed invariant tori of the 2D Hamiltonian. Using these tori, we obtained the linear coupling strength, the tune shift with betatron amplitude coefficient and the proximity parameter to the resonance. The coupling strengh obtained with this method agreed well with that obtained from measuring the betatron tune separation of the normal modes.

Longitudinal phase‐space measurements at IUCF

Synchrotron motion in the IUCF cooler ring was studied using turn‐by‐turn beam tracking on ten‐turn intervals, where the beam phase relative to the rf and the closed‐orbit position in a high‐dispersion region were measured. The synchrotron tune shift with amplitude was measured and is compared with theory. The driven response of the system was also studied using the same techniques, and was found to share many of the same characteristics of other parametric resonant systems. The experimental results did not exhibit any effects of bunch decoherence expected from the tune shift with amplitude.

Betatron coupling correction at the IUCF cooler, leading to improved determination of fourth‐order resonance Hamiltonian

Recently the Hamiltonian of particle motion near a resonance condition was deduced at the Indiana University Cyclotron Facility Cooler Ring. It was found that linear betatron coupling complicated the analysis. A coupling correction scheme is described which reduced the coupling coefficient from 0.03 to 0.0012. When particles were kicked onto resonance islands with the coupling reduced, the island motion was stable for upwards of 1×106 turns. This stable island motion allowed for the determination of higher‐order terms in the Hamiltonian.

Modeling of the IUCF cooler synchrotron

Measurements of lattice parameters for the Indiana University Cyclotron Facility (IUCF) Cooler synchrotron at betatron tunes close to a sum resonance line are discussed. The measured beta functions at 36 quadrupole locations and the dispersion functions at 35 Beam Position Monitor (BPM) locations are compared with calculations. The methods used to make the above measurements and the data analysis are described.