K. Brand

Low-energy fusion cross sections of D + D and D + 3He reactions

Abstract The D(d, n) 3 He and D(d, p)T reactions have been investigated at E c.m = 2.98 to 162.5 keV and the 3 He(d, p) 4 He reaction at E c.m. = 6.95 to 141.8 keV. The studies involved high-current accelerators with well-known beam characteristics and windowless gas target systems of the extended and quasi-point supersonic jet type. The measurement of absolute cross sections, angular distributions and excitation functions is reported. The data extend into the thermal energy region of future fusion reactors. The results for the D(d, n) 3 He and D(d, p)T reactions are in good agreement with previous work, while substantial differences are found for 3 He(d, p) 4 He.

Energy determination of heavy-ion beams☆

Abstract The energy calibration of the beam analyzing magnet at the 4 MV Dynamitron tandem accelerator in Bochum has been carried out over a wide magnetic field range ( B =2.4–12.4 kG) using the well-known energies of several proton induced resonance reactions. The roles of projectile and target nuclei have been exchanged in these reactions, i.e. a hydrogen gas target has been bombarded with the corresponding heavy ions. In this way, the necessary high energies of the heavy ion beams were accurately defined and used in the calibration of the beam analyzing magnet at high field strengths. For the field range investigated, the magnet calibration factor K was observed to be constant within experimental uncertainties ( ΔK =±0.2%). Atomic effects in the measurement of nuclear energies are discussed.

The reflected beam sputter source

Abstract The cesium beam of a General Ionex 834 sputter source is steered through an off-axis molybdenum cone, reflected by the negative ion extraction electrode and sharply focused on a pill of target material located on the back of the molybdenum cone. This improves the emittance of the negative ion beam and eliminates two disadvantages of this type of sputter source: (1) the complicated form of the target and (2) ionizer damage from backstreaming negative ions.

Operation results of the dynamitron tandem at Bochum

The performance of the Dynamitron-Tandem accelerator at Bochum with respect to beam energy resolution, stability and reproducibility, and beam intensity is reported. The energy resolution has been determined by measuring with thin targets (i) the shape of the neutron threshold in 7Li(p, n) at Ep = 1.88 MeV and the width of a single isolated resonance in the reaction 28Si(p, p1) at Ep = 5.197 MeV, (ii) the fine structure distribution of the lowest 12+ isobaric analogue resonance in the reaction 92Mo(p, p0) near Ep = 5.3 MeV, and (iii) the mean level width of the fluctuating excitation function near the lowest 12+ isobaric analogue resonance in the reaction 88Sr(p, p0) near Ep = 6 MeV. These measurements yield ΔE<1.2keV at Ep = 1.88 MeV and ΔE = (1.5±0.2) keV at Ep < 5.2 MeV. The beam energy stability obtained from the resonance yield of 28Si(p, p1) at 5.2 MeV was better than 120 eV and the absolute beam energy is reproducible to better than 3 × 10−4. Energy analyzed maximum beam currents so far are 125 μA for protons at 8 MeV and 27 μA for 16O(4+) at 20 MeV. Operational experience of the tandem and its associated parts (high voltage generator, injector, beam handling system) over a period of about nine months has demonstrated the high reliability of the whole system. A major advantage compared to most accelerators is the extremely easy way to operate the machine.

A recoil separator for the measurement of radiative capture reactions

A recoil separator in combination with a windowless gas target has been designed for the measurement of the radiative capture reaction p(7Be, γ)8B. The separator consists of momentum and velocity filters and a ΔE−E detector telescope. The setup was tested quantitatively using the p(12C, γ)13N reaction at the effective energy Ecm = 841 keV. Projectile fluxes were measured directly with Faraday cups and indirectly with elastic backscattering into Si detectors, while the 13N recoil flux was measured directly with the ΔE−E telescope. A suppression of the 12C beam particles by a factor 2 × 10−10 was observed when the system was tuned for the recoil 13Ns. Special emphasis was given to the charge state probabilities of the 13N recoils. Possible improvements of the system for the measurement of other capture reactions are discussed.

Technical developments for ion beams with high energy resolution

Abstract Efforts are underway to investigate the various sources of the energy spread of ion beams from the 4 MV Dynamitron tandem accelerator at Bochum and to minimize their contributions. As part of this program the influence of the 120 kHz oscillator frequency has been studied. The long term stability of the ion beam energy was also investigated. In addition, techniques are described to vary the ion beam energy in very small steps with minimal changes in beam optics.

Improvement of the reflected beam sputter source

Abstract By using cesium collection techniques the output of the source is increased by a factor of 10 and more for some ion species.

Absolute energy calibration of a low-energy accelerator by the time-of-flight technique

Abstract The absolute energy of the proton beam from the 100 kV accelerator in Bochum has been measured using electrostatic deflection plates and a microchannel-plate detector as start and stop devices in a time-of-flight setup, respectively. The measurements confirm the absolute energy determinations made by a calibrated resistor chain, within a mean deviation of ± 26 eV.

Intense low energy heavy ion beams from a tandem dynamitron

Abstract A second injector has been installed in front of the established one to be used mainly for heavy ion beams. The high resolution 90° analyzing magnet ( M / ΔM = 100) is mounted on a rotary mount to allow for the simultaneous installation of different types of ion sources. Better ion optics of the new injector together with terminal cryopumping lead to improved transmission through the accelerator system.

A tanked tube for open air accelerators

Abstract A standard 60 cm beam tube section designed for pressurized accelerators has been encapsulated and insulated by SF 6 gas to be used on a 400 kV open air accelerator.