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)

Limits on the experimental simulation of nuclear fuel rod response. [PWR]

The steady-state and transient effects of intrinxic geometric and material property differences between typical nuclear fuel pins and electric fuel pin simulators (FPSs) are identified. The effectiveness of varying the transient power supplied to the FPS in reducing the differences between the transient responses of nuclear fuel pins and FPSs is investigated. This effectiveness is shown to be limited by the heat capacity of the FPS, the allowed range of the power program, and different FPS power requirements at different positions on a full-length FPS

Nuclear pin simulation analysis

The PINSIM-MOD1 computer code has been developed and is being used at ORNL to investigate the relationships between thermal-hydraulic transients involving nuclear fuel pins and similar transients involving electrically-heated fuel pin simulators. PINSIM-MOD1 is currently being used to (1) predict the thermal response of specified nuclear and/or electric pin models to power and/or hydraulic transients; (2) determine transient electric pin power required to simulate a nuclear pin transient; (3) analyze and evaluate electric pin simulator transients; and (4) optimize the design and operation of electric pin simulators. Some differences between electric and nuclear pins are discussed. An overview of the PINSIM-MOD1 computer code, and some typical results from three types of PINSIM-MOD1 problems are presented

Blowdown Heat Transfer Separate-Effects Program. Quarterly progress report, April-June 1980

Two transient film boiling tests were run - one in upflow, the other in downflow. The purpose of these tests was to provide experimental heat transfer data that could be used in an assessment of several film boiling correlations used in current thermal-hydraulic computer codes. The tests were designed to provide accurate posttest calculations of heat fluxes, surface temperatures, and local fluid conditions. THe Upflow Film Boiling Test 3.03.6AR was run on May 21, 1980, in the THTF. This test resulted in single-phase fluid flow at the test section inlet (subcooled) during the time the bundle was in high-flow film boiling. Furthermore, no flow reversal occurred during the test. Preliminary posttest analysis indicates that the calculation of mass flows at the inlet to the test section should result in numbers with relatively small uncertainties. We are optimistic that local fluid conditions can be calculated for this test with an accuracy sufficient for correlation evaluation. 7 figs

Blowdown heat transfer separate-effects program. Quarterly progress report, January-March 1980

Six additional bundle uncovery/recovery tests were performed in the Thermal-Hydraulic Test Facility during January, bringing the total number of these tests to eight. Data taken during the tests were found to be contaminated by numerous spurious spikes. Work to remove the spurious spikes is under way. Posttest analysis of the tests is approx.20% completed. The recovery portion of one of the tests will be analyzed by COBRA/TRAC, currently being developed by Pacific Northwest Laboratories (PNL). Work to debug the code for this application is in progress at PNL. The uncovery/recovery tests apparently caused damage to the 0-rings that form part of the loop pressure boundary. Refurbishment of the 0-ring seal system is being performed concurrently with scheduled loop modifications that include installation of ten in-bundle differential pressure instruments. Design, procurement, and fabrication of the in-bundle gamma densitometer system are continuing on schedule

Performance of the prototype LaBr3 spectrometer developed for the JET gamma-ray camera upgrade

In this work, we describe the solution developed by the gamma ray camera upgrade enhancement project to improve the spectroscopic properties of the existing JET γ-ray camera. Aim of the project is to enable gamma-ray spectroscopy in JET deuterium-tritium plasmas. A dedicated pilot spectrometer based on a LaBr3 crystal coupled to a silicon photo-multiplier has been developed. A proper pole zero cancellation network able to shorten the output signal to a length of 120 ns has been implemented allowing for spectroscopy at MHz count rates. The system has been characterized in the laboratory and shows an energy resolution of 5.5% at Eγ = 0.662 MeV, which extrapolates favorably in the energy range of interest for gamma-ray emission from fast ions in fusion plasmas

Sawtooth pacing with on-axis ICRH modulation in JET-ILW

A novel technique for sawteeth control in tokamak plasmas using ion-cyclotron resonance heating (ICRH) has been developed in the JET-ILW tokamak. Unlike previous ICRH methods, that explored the destabilization of the internal kink mode when the radio-frequency (RF) wave absorption was placed near the q = 1 surface, the technique presented here consists of stabilizing the sawteeth as fast as possible by applying the ICRH power centrally and subsequently induce a sawtooth crash by switching it off at the appropriate instant. The validation of this method in JET-ILW L-mode discharges, including preliminary tests in H-mode plasmas, is presented

Hybrid cancellation of ripple disturbances arising in AC/DC converters

In AC/DC converters, a peculiar periodic nonsmooth waveform arises, the so-called ripple. In this paper we propose a novel model that captures this nonsmoothness by means of a hybrid dynamical system performing state jumps at certain switching instants, and we illustrate its properties with reference to a three phase diode bridge rectifier. As the ripple corrupts an underlying desirable signal, we propound two observer schemes ensuring asymptotic estimation of the ripple, the first with and the second without knowledge of the switching instants. Our theoretical developments are well placed in the context of recent techniques for hybrid regulation and constitute a contribution especially for our second observer, where the switching instants are estimated. Once asymptotic estimation of the ripple is achieved, the ripple can be conveniently canceled from the desirable signal, and thanks to the inherent robustness properties of the proposed hybrid formulation, the two observer schemes require only that the desirable signal is slowly time varying compared to the ripple. Exploiting this fact, we illustrate the effectiveness of our second hybrid observation law on experimental data collected from the Joint European Torus tokamak