Bonn Isochronous Cyclotron Research Articles

The new high intensity polarized proton and deuteron source for the Bonn isochronous cyclotron

An atomic-beam polarized ion source for the production of polarized protons and deuterons is described. Beam intensities of 160 μA for polarized protons and deuterons are obtained at an emittance of 9π cm· rad· eV . Within the phase space accepted by the Bonn isochronous cyclotron 50 μA of deuterons and 35 μA of protons were measured. The atomic beam emerging from a liquid nitrogen cooled dissociator nozzle is polarized and focussed by two tapered sextupole magnets. Two radiofrequency transitions can be mounted either before or behind the second sextupole, leading to theoretical values for deuterium vector and tensor polarizations of P z =±1 and P zz =−2, respectively. The polarized atoms are ionized by electron impact inside a cold-cathode Penning ionizer working at a magnetic field of 4 T produced by a superconducting solenoid. The efficiency for this ionizer is estimated to be η=6.2×10 −2.

External Ion Sources and Injection Lines at the Bonn Isochronous Cyclotron

The complex of external ion source facilities at the Bonn Isochronous Cyclotron is described. A universal ion source of the Penning type was developed for the production of intense beams of multiply charged ions. Details of this ion source and performance figures are presented. An atomic beam polarized ion source is used for the production of polarized protons and deuterons. A modified atomic-beam polarized ion source using a superconducting solenoid ionizer is under construction. For the combined installation of the universal ion source and the polarized ion source a compact beam transport system has been developed which allows the optimum matching with the cyclotron. A buncher with triangular shaped pulses is used in order to increase the beam intensities. Ionoptical and technical details of the external beam lines and the axial injection are presented.

Beam Stabilization and Automatic Energy Variation at the Bonn Isochronous Cyclotron

Control systems have been developed for the stabilization of the external cyclotron beam with respect to the horizontal and vertical alignment, the beam energy and the beam intensity. The operating characteristics of the feedback circuits are presented and the joint operation is discussed. The incorporation of the control systems into a microcomputer controlled energy variation program makes it possible to obtain a reliable and convenient system for the automatic measurement of excitation functions with an isochronous cyclotron.

Microcomputer controlled energy variation of an isochronous cyclotron and beam handling system

An automatic 3 MeV variation of a 30 MeV α-beam was performed in 300 steps at the Bonn Isochronous Cyclotron. A microcomputer in connection with a control unit adjusted the cyclotron and the monochromator system parameters. This combination allowed a direct and precise measurement of broad excitation functions. Using fast magnetic field stabilization an energy-shift was accomplished to an accuracy of better than 1 part in 10 5 within 20 s. The stability of the beam position on the target was about 0.05 mm.

Kompakte schachbrett-detektor-elektronik für blocking-experimente

For channeling and blocking experiments at the Bonn Isochronous Cyclotron the electronics and the computer interface for a two-dimensional position sensitive detector were developed and constructed. The X- Y-detector is a “checkerboard counter” BPY 75-300 (Philips). Parts of the electronics are layed out in ECL II technique. Data transmission from the scattering chamber to the experiment electronics and to the computer uses a fast serial transmission system with only three pairs of coax cable.

The polarized proton and deuteron beam at the Bonn isochronous cyclotron

The present state of the polarized proton and deuteron source at the Bonn cyclotron is described. At the end of the source, which is of the atomic beam type, typical ion beam intensities are 2 μA for protons and 3 μA for deutrons. The overall transmission from the source to the first stopper after extraction from thecyclotron is 3%. Target currents with an energy resolution E/ ΔE = 500 are 20 nA for deuterons and 10 nA for protons. For the proton beam a polarization P = −0.71 was measured. For the deuteron beam a pure vector polarization P z = −0.47 or various mixtures of vector and tensor polarization are obtained.

Energy stabilization of an isochronous cyclotron beam with an external monochromator control

A very high energy stability of an isochronous cyclotron beam can be achieved with a feedback control of the Dee-voltage where the feedback signal is taken from the analyzing slit of a monochromator system. The principle of regulating is described with the aid of the energy-phase distribution of the beam pulses. The residual instabilities of the rf-amplitude and/or the rf-frequency are well compensated. A fast response can be achieved. The practical realization of a feedback controlled energy stabilization at the Bonn Isochronous Cyclotron yields a short- and long-term stability of better than 1 × 10 −4. The developed feedback control can be applied to other isochronous cyclotrons, too, especially to the large separated-sector machines.

The beam handling system at the bonn isochronous cyclotron

The lay-out and the ion-optical structure of the beam handling system at the Bonn Isochronous Cyclotron is described. The following beam preparation modes are possible with two double monochromator systems: (1) double dispersive with an extremely high momentum resolution of 30 000; (2) double dispersive with an adjustable dispersion matching with a magnetic spectrograph; (3) nondispersive, nearly isochronous, variable momentum resolution up to 8000, adjustable time of flight resolution below 0.5 ns; (4) achromatic with a transmission of 100%. The practical experiences in operating the system and achieving the design performances are discussed. The results of rigorous test measurements are given.

The polarized proton and deuteron source for the Bonn isochronous cyclotron

An atomic-beam polarized ion source for production of polarized protons and deuterons at the Bonn isochronous cyclotron is described. At the end of the source a proton beam of 1.5 μA or a deuteron beam 2 μA is obtained (typical values). The emittance of the beam corresponds to the acceptance of the cyclotron. A tensor polarization value P zz = 0.8 of the deuteron beam was measured via T(d,n) 4He. For the proton beam a polarization of P ≈ 0.6, for the deuteron beam a vector polarization of P z ≈ 0.5 is to be expected.

Entwicklung eines axialen strahlführungssystems zum einschuβ polarisierter ionen in das isochron-zyklotron der universität bonn

A beam transport system for the axial injection of polarized protons and deuterons was developed at the Bonn isochronous cyclotron. The injection system, whose elements are 3 einzel-lenses and 4 electrostatic quadrupole lenses, brings the beam 225 cm upwards through a hole in the lower yoke of the magnet to the cyclotron median plane. A hyperboloid inflector inflects the beam for further acceleration. Beam adjustment is possible by steering systems and simple monitoring devices. Unpolarized ion beams can be injected into the beam transport system through a second inflector. The transmission of the system was estimated by tests outside of the cyclotron. For proton injection energies (2–4 keV) the transmission between source and inflector is 30–50%, for deuterons (4–8 keV) 60%.

Multi Turn and Single Turn Extraction from the Bonn Isochronous Cyclotron

The isochronous cyclotron at the BONN university is a multi particle variable energy machine. Its basic design is very similar to the Julich Cyclotron. The relatively low maximum energy of approx. 30 MeV deuterons and the high energy gain per turn of 220 keV results in a large turn separation of 3 mm at the extraction radius. The machine operates in the single turn extraction mode as well as in the multi turn extraction mode.