FUSION DEPARTMENT 1986 ANNUAL REPORT ITALIAN COMMISSION FOR NUCLEAR AND ALTERNATIVE ENERGY SOURCES FRASCATI ENERGY RESEARCH CENTER FUSION DEPARTMENT 1986 ANNUAL REPORT ACTIVITIES CARRIED OUT IN THE FRAME OF THE EURATOM-ENEA ASSOCIATION ON FUSION RESEARCH SUMMARY Preface 1. Fusion Physics 9 1.1 Introduction 11 1.2 Experiments on the Frascati tokamak (FT) 11 1.3 The 8 GHz RF experiments 31 1.4 Diagnostics 32 1.5 Plasma theory 46 1.6 Participation in Jet 53 1.7 Collaboration with Garching and Princeton 60 1.8 The joint proposal with CNR Milano on ECRH for FTU 61 References 63 2. Inertial Confinement 65 2.1 Introduction 67 2.2 Diagnostics 67 2.3 Target positioning and replacing system 71 2.4 Target alignment procedures 76 References 79 3. Frascati Tokamak Upgrade 81 3.1 Introduction 83 3.2 Status of the project and time schedule 83 3.3 Load assembly 85 3.4 Electrical power supplies 98 3.5 Lower hybrid, electron mode RF system 104 3.6 Control system 110 3.7 Radiological hazards and safety 119 3.8 Infrastructures 121 References 124 4. Fusion Reactor Engineering 125 4.1 Introduction 127 4.2 Conceptual studies 127 4.3 Applied neutronics 152 4.4 Superconducting magnets 156 4.5 Ceramic breeder materials 166 4.6 Safety and environment 170 4.7 Remote maintenance 173 References 175 Organization Chart 179 List of Reports and Publications 181 77?/s report has been prepared by the Study and Documentation Service (STUDOC-AFUD-FUS), mainly on the basis of contributions provided by the scientific and technical staff of ENEA's Fusion Department (Main STUDOC collaborators in the preparation of this issue: Lucilia Crescentini, Marisa Cecchini and Peter Riske for text-composition, graphics, and overall coordination; Sergio Ciarlo and Fiorenzo Pepi for photographic work). PREFACE This annual report describes the research activity carried out during 1986 by the Fusion Department of the Italian Commission for Nuclear and Alternative Energy Sources (ENEA). The report outlines the main results obtained by the three major projects of the Fusion Department (Fusion Physics, Frascati To- kamak Upgrade, and Fusion Reactor Engineering), plus the divi- sional project Inertial Confinement mentioned separately be- cause of its particular scientific content. Most of the research work was performed by the Fusion Depart- ment at its location at the ENEA Frascati Energy Research Center, but some work was also done elsewhere, or with re- course to other ENEA departments. The research activity described in this annual report was carried out within the frame of the Association Euratom-ENEA on Fu- sion, with the exception of some minor activities described in sections 4.3.1 and 4.4.5. Fusion Physics B6 ANNUAL HhPOR1 •••••1HH 1 r *.,<: 1 1 / 1 r i 1 ir i ; :: Li i•rf •n r/- - h . * ;K ^ -1 W •" 4a t . - -* p-* •• w • •- * t to the 8 GHz experiment in FT •Waveguides • 10 1986 ANNUAL REPORT 1. Fusion Physics 1.1 INTRODUCTION The Fusion Physics Project is concerned with the following main activities: • Experimentation of the high-field Frascati Tokamak (FT); • Development of new diagnostics, also in view of the new Frascati Tokamak Upgrade (FTU) which is under construction; • Participation in the European Community experiment JET. These subjects are described in the following sections. 1.2 EXPERIMENTS ON THE FRASCA Tl TOKAMAK (FT) During 1986 the experimental program on FT was devoted to new research, especially in the fields of confinement and thermal transport and of RF heating. Important results obtained were • the consistency of thermal transport coefficients obtained from energy balance and thermal pulse diffusion measurements; • the absence of confinement degradation during RF heating at 2.45 GHz (at the plasma parameters of FT operation). 1.2.1 Thermal Diffusion in Ohmic Discharges The sawtooth disruptions are due to an MHD internal instability that flattens the temperature profile within a certain radius rs in a very short time. i-y FUSION PHYSICS Inside the radius rs the plasma is suddenly perturbed, whilst outside rs everything remains unchanged. Later on, the perturbation propagates outside due to the finite thermal conductivity of the plasma The analysis of the time evolution of the temperature at radii greater than rs allows the coefficient of electron thermal diffusion \e to be determined. Under some limitations, the same coefficient can be obtained by a detailed energy balance of the plasma during a steady state. The fact that these two coefficients are the same is not trivial, and it is interesting to compare them over a large range of plasma -parameters. A fairly extensive experimental campaign on FT has been devoted to HP ar) measuring \e from both the heat pulse propagation (\e ) d from the power PB balance (\( ) This campaign covered nearly all the operation region of FT. The temperature profiles of each series of shots are shown in Fig. 1.1 where they are ordered according to their parameters in the Hugill-Murakami plot. The sawtooth heat pulse propagation can be observed in a radial region n<r<r2, which has been shadowed in Fig. 1.1, for each shot series. This region corresponds in all cases to the inflection of the election temperature profile, which is the most relevant region for energy confinement (1<q<2). Figure 1.2 shows a typical evolution of the temperature perturbation at radii greather than rs during a sawtooth event. From an observation of the time elapsed tp(r) until the heat pulse induced by the sawtooth activity reaches its maximum, it is possible to deduce the average xeHP in the plasma region where the temperature perturbation diffuses.This can be summarized by the expression A(r2l At = ax"" It has been applied to all the shot series discussed here using both soft x-ray (SXR) and electron cyclotron (2 cjce) emission signals. The electron thermal conductivity (xePB) from the power balance, assuming a steady state, has been derived for the same shots. The electron heat diffusive coefficient xeBPis given by r 2 x'," = i 0 I* (r) dV/4n rK n (rlVT (r) 12 FUSION PHYSICS where P\ is the power loss due to the thermal profile, which is obta«ned by solving the power balance equations F:gure 1.3 gives an example of comparison between the averaged xeHP and the radial profile of xePB in the heat pulse observation region (n<r<r2) which is defined as A - 1/qL Fig. 1.1 - Radial temperature profiles of a series of discharges ordered in a Hugill-Murakami plot 13 FUSION PHYSICS 20 Te(eV) 10 0 12 T (eV) e 8 0 5 Te(eV) 0 Te(eV) 3 0 t/xR Fig. 1.2 - Time evolution at different radial positions of the electron temperature -perturbation during a sawtooth event 14 FUSION PHYSICS 101 - -HP yf. x (m2/s) '- \^^ '- 1 r «? ^^ -=. 10-1 r NC — * • . * X 10-2 I () 10 2() r(cm) Fig. 1.3 - Comparison of the electron thermal conductivities determined from power balance (xep8) and from heat pulse diffusion (xe*""1)" ^or two different discharges 3 x"P (SXR) 2 - I / /A Y 1 V 1 1 0 1 2 3 Fig. 1.4 -Comparison between the electron thermal conductivities XePB and XeHP«tr|e latter determined by the measured electron cyclotron emission 15 FUSION PHYSICS HP Figure 1.4 summarizes the comparison between x* as deduced from 2o)ce emission and the corresponding x/B fOr all the shot series. The same has been done for s^1"' deduced from SXR signals; it is displayed in Kig. 1.5. The conclusion of such a comparison is that for all the ranges of parameters considered in the ohmic heated, experimental campaign of FT. This agreement seems even better than one could expect due to the simplifying assumptions underlying the analysis of the heat pulse propagation and the considerable uncertainties in the power balance. In order to check the previous results, obtained from simple observation of the heat pulse delay, a more complete comparison of the electron temperature fluctuation measured by the 2o)Ce emission has been performed with a full transport and sawtooth reconnection code that runs on the results of the power balance (see Sec. 1.5.3). This code uses the Kadomtsev reconnection model to simulate the sawtooth disruption. The results of the code simulations have been compared with the experimental measurements of temperature fluctuation 3 P HP PB / HP_ e (SXR) = 2xc / xe — / 2 - / / / A / / A 1 A / A /^ 1 >£B(m2/s) Fig.1.5 Comparison between the electron thermal conductivities XePB asnd XeHP. the latter determined by the measured soft x- ray emission 16 FUSION PHYSICS Te (eV) 1 r = 13.3cm 8 — \A^ 1 LkAAv 4 Z' ^< 1 n 1 1 i V Fig. 1.6- Comparison of the electron temperature fluctuation as determined experimentally by the electron cyclotron emission and theoretically by a simulation code (broken line) evolution by 2o>ce emission at different radii. The agreement between measurements and calculations is quite good, both in fluctuation amplitude and in time delay of the maximum, except for those radii which are close to the sawtooth inversion radius (see Fig. 1.6). This comparison confirms more clearly that the sawtooth heat pulse diffusion is ruled by the same thermal diffusion coefficient L xe(r) which rules the energy economy of the plasma. 17 FUSION PHYSICS 1.2.2 RF Experiments In 1986 the 2.45 GHz lower hybrid (LH) heating experiment utilized two waveguide grills: a 4x2 grill with the possibility of changing the relative phase of the field; and a 2 x 2 grill with fixed phasing.