[en] A status report of the Dortmund ELectron Test Accelerator (DELTA), now under construction, is presented. This low-emittance storage ring is dedicated to FEL and accelerator-physics R and D. Preacceleration will be performed with a 100 MeV LINAC which is presently rebuilt from the old Mainz LINAC. Lattice designs of the 1.5 GeV booster (FODO structure) and storage ring (triplet structure) are completed and prototypes of magnets and vacuum vessels, identical for both cyclic machines, are to be delivered end of 1991. A monitor development has been performed. Commissioning of the machines is planned for end of 1993. An overall description of the vacuum system is given with the design goal of achieving beam life times of > 10 h at high currents. Low-independence vacuum chambers made of 33 mm thick 316LN stainless steel have been designed. They consist of a small-aperture beam channel separated by a continuous slot from an antechamber equipped with DIP's and NEG pumps

[en] A status report of the Dortmund Electron Test Accelerator DELTA in its final phase of construction is presented. DELTA is a 1.5 GeV 3rd generation synchrotron light source designed for low emittance (10^-8 m rad), high currents (500 mA for ≥ 12 bunches) and beam life times of ≥ 10 hours, which is dedicated to free-electron-laser (FEL) and accelerator-physics research and development. With the first FEL experiment, already funded and to be installed in one of the two long straight sections of the racetrack-shaped storage ring, DELTA represents a new Storage-Ring-FEL facility. After first oscillator operation in the visible (planned for end of 1994), FEL experiments in the VUV clearly below 100 nm are foreseen. In the second long straight section an asymmetric superconducting wiggler, providing 1 Angstrom radiation, will be installed in the future and used as wave-length shifter. A predesign study of this second insertion device has been performed already. Details of the construction of DELTA and present status of most hardware components of 100 MeV LINAC, booster synchrotron, storage ring, vacuum system, beam lines and first FEL experiment will be discussed

[en] The third-generation 1.5 GeV electron storage ring DELTA, dedicated to synchrotron-radiation experiments, accelerator technology and UV FEL operation, was commissioned about 2 years ago at the Dortmund University. After the first successful lasing in the visible region (470 nm) beginning of this year, it is planned to obtain lasing also in the UV near 200 nm and then later to use the high average intracavity power and natural synchronization of electron and optical pulses to produce intense beams of high-energy γ-rays by Compton backscattering. Applying these γ-rays, a photo-fission experiment of importance for nuclear astrophysics is described. Since the time resolution of high-brightness synchrotron light sources is limited to more than 10 ps, it is envisioned to test a novel technique for generating sub-picosecond X-ray pulses based on the interaction of the electrons with a co-propagating beam of femtosecond photon pulses from an external TW-laser. This technique will be applied at DELTA by using its superconducting wiggler and a permanent-magnet undulator. Simulations show that a brilliance of 10⁸ photons/(s mm² mrad² 0.1% bandwidth) with pulse durations of the order of 100 fs can be achieved. Using the magnetic insertions of DELTA and an external TW-laser will further allow measurements for testing laser acceleration in the ultra-high vacuum of a storage ring and of radiation damping of the beam emittance on a fast time scale. First, results of laser-beam monitoring at the stretcher ring AmPS to determine the transverse beam emittance are presented and are intended to be performed also at DELTA. For these investigations the electron beam has been scanned at 90 deg. with a high-power laser beam, and forward-scattered Compton photons were detected to derive the beam profile

No abstract available

[en] Several experimental facts will be discussed which indicate that there exists a common configuration inherent to all quasimolecular resonances so far observed in heavy-ion reactions. A comparison of the moments of inertia of the nuclear rotational bands seen as series of resonances in different systems of composite mass A <= 44 and of partial and total widths of the corresponding intermediate structures reveals evidence for a structural similarity of these resonance phenomena. With very few exceptions, resonances have been observed only in reactions where ¹⁶O is one of the interacting particles of where the resonant ¹⁶O reduced partial width is large. (orig./HSI)

No abstract available

[en] A differentially pumped, supersonic jet gas target has been constructed for use in low-energy nuclear reaction experiments with beams of light and heavy ions. The total target thickness as well as the density profile have been determined for various geometrical configurations of the nozzle-skimmer system and as a function of the reservoir pressure. The very compact system has some special properties which allow high energy resolution measurements of differential cross sections at angles close to the beam direction. In particular, the identification of low-energy heavy-ion reaction products at small angles has been achieved using the gas jet in connection with a specially designed ΔE-E annular detector telescope mounted very close to the target center. Different experiments have been performed and typical results are presented. (orig.)

[en] Evidence is presented for populating the 12⁺ and 14⁺ members of the excited ¹²C + ¹²C rotational band in ²⁴Mg by the ¹⁰B + ¹⁴N entrance channel. Excitation functions of the ¹⁰B(¹⁴N,α)²⁰Ne reaction close to 0⁰ and 180⁰ near the Coulomb barrier exhibit pronounced resonances and forward-backward cross-section asymmetries at the energies of these two ¹²C + ¹²C resonances

[en] Excitation functions have been measured at angles close to 0⁰ and 180⁰ for the reactions ¹⁰B(¹⁰B,α)¹⁶O, ¹⁰B(¹⁴N,α)²⁰Ne and ¹²C(¹²C,α)²⁰Ne near the respective Coulomb barriers. The high beam currents of the Bochum Dynamitron Tandem allowed absolute cross sections as low as a few hundred picobarn/sr to be measured. Some α transitions to low-excited residual states of the first two reactions show correlated resonances with intermediate widths of 500-600 keV. This proves for the first time that the observations of intermediate resonances is not restricted to particular entrance channels consisting of α-particle nuclei or to low level densities of the compound system. (Auth.)

[en] The main results of further investigations of resonance-like structures in ¹⁰B(¹⁰B,α) excitation functions performed by measuring the proton, deuteron and ⁸Be channels, and the alpha + ¹⁶O excitation functions are presented. Qualitative evidence is thus provided for the existence of intermediate resonances of probably quasimolecular alpha-particle structure in ²⁰Ne, similar to those observed at lower excitations by alpha + ¹⁶O elastic scattering. 1 reference