Dual laser interferometer for plasma density measurements on large tokamaks.
A two-wavelength plasma density interferometer utilizing a CO(2) laser and an HeNe laser is described. The interferometer is being designed for use on Doublet III, a large noncircular cross-section tokamak. The use of the two wavelengths allows the distinction between fringe shifts due to plasma density and fringe shifts due to mirror vibrations. Plasma density fringe shifts of 1/10 of a fringe shift can be measured in the presence of mirror vibrations which cause several fringe shifts. A simple digital phase comparing electronic system is used.
Heterodyne interferometer with unequal path lengths
Laser interferometry is an extensively used diagnostic for plasma experiments. Existing plasma interferometers are designed on the presumption that the scene and reference beam path lengths have to be equal, a requirement that is costly in both the number of optical components and the alignment complexity. It is shown here that having equal path lengths is not necessary, instead, what is required is that the path length difference be an even multiple of the laser cavity length. This assertion has been verified in a heterodyne laser interferometer that measures typical line-average densities of ∼1021∕m2 with an error of ∼1019∕m2.
The REX-ISOLDE project
The Radioactive Beam Experiment REX-ISOLDE [1–3] is a pilot experiment at ISOLDE (CERN) testing the new concept of post acceleration of radioactive ion beams by using charge breeding of the ions in a high charge state ion source and the efficient acceleration of the highly charged ions in a short LINAC using modern ion accelerator structures. In order to prepare the ions for the experiments singly charged radioactive ions from the on-line mass separator ISOLDE will be cooled and bunched in a Penning trap, charge bred in an electron beam ion source (EBIS) and finally accelerated in the LINAC. The LINAC consists of a radiofrequency quadrupole (RFQ) accelerator, which accelerates the ions up to 0.3 MeV/u, an interdigital H-type (IH) structure with a final energy between 1.1 and 1.2 MeV/u and three seven gap resonators, which allow the variation of the final energy. With an energy of the radioactive beams between 0.8 MeV/u and 2.2 MeV/u a wide range of experiments in the field of nuclear spectroscopy, astrophysics and solid state physics will be addressed by REX-ISOLDE.