[en] In neutron-antineutron oscillation experiments the quasifree condition defines the tolerable size of the residual magnetic field along the neutron beam. The best way to ensure that the quasifree condition is met during a neutron oscillation search is to use neutrons themselves for the measurement of the residual magnetic field, by observing neutron spin rotation along the neutron path of flight. We have tested such a neutron spin magnetometer, using a polarized neutron beam. A combined active plus passive shielding setup was developed for the magnetic shielding of the neutron beam. (orig.)

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[en] A beam of fully polarized cold neutrons was transported through a zero magnetic field region of 70 m length without loss of polarization. The purpose of this exercise was twofold: Firstly, to demonstrate that the new zero-field neutron spin-echo method will work also for very long neutron flight paths; secondly, to prove in the most direct way that the neutron free-flight region of the ILL neutron-antineutron oscillation experiment was indeed sufficiently field-free ('quasifree condition') by using the neutrons themselves as a magnetometer. To this purpose the residual magnetic field integrals in the long 'zero-field' region were measured with a conventional neutron spin-echo method. The overall spin precession angle of the neutrons during their flight through the long zero-field region was found to be less than 2⁰. (orig.)

[en] We describe the magnetic shielding system of the neutron-antineutron oscillation experiment at the ILL, Grenoble. It shields the cold neutron free flight path over a volume of 75 m length and 1 m diameter against external magnetic fields. With a field suppression factor of ≅ 10⁴, the mean residual magnetic field along the beam is well below 10 nT, which corresponds to a quasi-free neutron propagation efficiency of better than 99%. (orig.)

[en] In the neutron-antineutron oscillation experiment at ILL the divergence of the free flying cold neutron beam was strongly reduced without loss of intensity by the use of a 34 m long neutron-optical horn system. The divergence reduction was accurately studied in order to maintain the total width of the neutron beam below 1.1 m after a neutron free flight distance of about 80 m. The fabrication and performance of this system are described. (orig.)

[en] The search for neutron-antineutron (nanti n) oscillations conducted by a Heidelberg-ILL-Padova-Pavia collaboration at the European slow neutron facility at Grenoble requires a very strong cold neutron beam, but an extremely low neutron-induced radiation background. This article describes the analysis and suppression of neutron-beam-related background in the nanti n experiment. In particular, the fabrication of a 20 m² shield of isotopically pure sintered ⁶LiF ceramics which protects the annihilation detector from the inside against neutrons scattered from the annihilation target is described. (orig.)

[en] The National Spherical Torus Experiment (NSTX) is a proof-of-principle experiment designed to study the physics of Spherical Tori (ST), i.e., low-aspect-ratio toroidal plasmas. Important issues for ST research are whether the high-eta stability and reduced transport theoretically predicted for this configuration can be realized experimentally. In NSTX, the commissioning of a digital real-time plasma control system, the provision of flexible heating systems, and the application of wall conditioning techniques were instrumental in achieving routine operation with good confinement. NSTX has produced plasmas with R/a(approx) 0.85 m/0.68 m, A(approx) 1.25, Ip* 1.1 MA, BT= 0.3-0.45 T, k* 2.2, d* 0.5, with auxiliary heating by up to 4 MW of High Harmonic Fast Waves, and 5 MW of 80 keV D0 Neutral Beam Injection (NBI). The energy confinement time in plasmas heated by NBI has exceeded 100 ms and a toroidal beta (bT= 2m0 and lt;p and gt;/BT02, where BT0 is the central vacuum toroidal magnetic field) up to 22% has be en achieved. HHFW power of 2.3 MW has increased the electron temperature from an initial 0.4 keV to 0.9 keV both with and without producing a significant density rise in the plasma. The early application of both NBI and HHFW heating has slowed the penetration of the inductively produced plasma current, modifying the current profile and, thereby, the observed MHD stability

[en] The experimental search for neutron-antineutron oscillations has been completed at the ILL high flux reactor at Grenoble. A neutron beam of intensity 10¹¹ n s^-1 was propagated for a time t ≅ 0.1 s in vacuum in a region shielded against the external magnetic field. No antineutron was detected in 2.4.10⁷ s running time. The lower limit τ_n anti n ≥ 0.86.10⁸ s for n anti n transitions was established at 90% C.L. (orig.)

[en] An experiment has been set up at the Institut Laue-Langevin in Grenoble to search for free neutron-antineutron oscillations. No candidate events were observed in the first run of the experiment, providing a lower limit in the oscillation time τ_nsub(anti n)>10⁷ s at 90% CL, which improves the previous experimental limit by an order of magnitude. (orig.)