On the mechanisms governing gas penetration into a tokamak plasma during a massive gas injection

A new 1D radial fluid code, IMAGINE, is used to simulate the penetration of gas into a tokamak plasma during a massive gas injection (MGI). The main result is that the gas is in general strongly braked as it reaches the plasma, due to mechanisms related to charge exchange and (to a smaller extent) recombination. As a result, only a fraction of the gas penetrates into the plasma. Also, a shock wave is created in the gas which propagates away from the plasma, braking and compressing the incoming gas. Simulation results are quantitatively consistent, at least in terms of orders of magnitude, with experimental data for a D 2 MGI into a JET Ohmic plasma. Simulations of MGI into the background plasma surrounding a runaway electron beam show that if the background electron density is too high, the gas may not penetrate, suggesting a possible explanation for the recent results of Reux et al in JET (2015 Nucl. Fusion 55 093013)

Coffeeshops en cannabis

The Dutch tolerance policy on soft drugs is still unique in Europe and across the world. While combating the use of and trade in soft drugs may not be a priority of judicial authorities and police everywhere, the policy of tolerance will not be adopted by other countries. The liberal soft drugs policy still seems to command ample support in the Netherlands. It is generally regarded as the most suitable way to regulate the use of soft drugs and limit health risks for users. However, the issue of whether the assumptions on which the tolerance policy is based are in fact correct is indeed a valid question, which is discussed from broadly differing viewpoints in this issue by authors from a wide range of fields

JET experience on managing radioactive waste and implications for ITER

The reduced radiotoxicity and half-life of radioactive waste arisings from nuclear fusion reactors as compared to current fission reactors is one of the key benefits of nuclear fusion. As a result of the research programme at the Joint European Torus (JET), significant experience on the management of radioactive waste has been gained which will be of benefit to ITER and the nuclear fusion community.The successful management of radioactive waste is dependent on accurate and efficient tracking and characterisation of waste streams. To accomplish this all items at JET which are removed from radiological areas are identified and pre-characterised, by recording the radiological history, before being removed from or moved between radiological areas. This system ensures a history of each item is available when it is finally consigned as radioactive waste and also allows detailed forecasting of future arisings. All radioactive waste generated as part of JET operations is transferred to dedicated, on-site, handling facilities for further sorting, sampling and final streaming for off-site disposal. Tritium extraction techniques including leaching, combustion and thermal treatment followed by liquid scintillation counting are used to determine tritium content.Recent changes to government legislation and Culham specific disposal permit conditions have allowed CCFE to adopt additional disposal routes for fusion wastes requiring new treatment and analysis techniques. Facilities currently under construction include a water de-tritiation facility and a materials de-tritiation facility, both of which are relevant for ITER. The procedures used to manage radioactive waste from generation to off-site disposal have been assessed for relevance to ITER and a number have been shown to be significant. The procedures and de-tritiation factors demonstrated by radioactive waste treatment plants currently under construction will be important to tritium recovery and waste minimisation in ITER and DEMO