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Empirical scaling relations are deduced describing the neutron emission from TFTR supershots using a database that includes all of the supershot plasmas (525) from the 1990 campaign. A physics based scaling for the neutron emission is derived from the dependence of the central plasma parameters on the machine settings and the energy confinement time. This scaling has been used to project the fusion rate for equivalent DT plasmas in TFTR, and to explore the machine operation space that optimizes the fusion rate. Increases in neutron emission are possible by either increasing the toroidal magnetic field or further improving the limiter conditioning

This paper will summarize studies of carbon impurity sources, contamination, and migration developed through JET methane gas injection experiments. These studies were analyzed using the 2D SOL code EDGE2D/NIMBUS. The code is capable of repeating the JET analysis using the ITER geometry and SOL plasma. This allows assessment of whether the physical processes occurring in JET might also occur in ITER, and thus whether the JET results transfer, in any sense, to the ITER plasmas. Certainly, the ITER choice of wall materials (W and Be) is different than for the present JET C studies. So the present status of these studies is to relate JET carbon behavior to carbon in ITER.JET carbon sources were studied spectroscopically and analyzed with atomic physics models in EDGE2D. The carbon sources are dominated by chemical sputtering at rates which are within a factor‐of‐two of the published literature. The JET carbon contamination is dominated by main chamber sources which are ionized in the main chamber SOL about 1–...

Solid lithium and boron pellets have been injected into TFTR plasmas to improve plasma performance by coating the graphite inner wall bumper limiter with a small amount of lower Z pellet material, which reduces the influx of carbon from the walls and reduces the edge electron density. This new wall conditioning technique has been applied successfully when continued He conditioning discharges, which are normally used for wall conditioning, no longer significantly reduce the carbon and deuterium influxes. The results show that both Li and B pellets significantly improve wall conditioning and lead to 15–20% improvements in supershot plasma performance when injected ≥1 s prior to neutral beam injection in supershot target plasmas. Neutral beam penetration calculations indicate that the lower edge densities resulting from Li or B pellet wall conditioning lead to improved beam penetration. Sputtering yield calculations confirm that the addition of small amounts of Li on a graphite target can significantly reduce the C sputtering yield.

Recent research on TFTR has emphasized optimization of performance in deuterium plasmas, transport studies and studies of energetic ion and fusion product physics in preparation for the D-T experiments that will commence in July of 1993. TFTR has achieved full hardware design parameters, and the best TFTR discharges in deuterium are projected to QDT of 0.3 to 0.5.The physics phenomena that will be studied during the D-T phase will include: tritium particle confinement and fueling, ICRF heating with tritium, species scaling with tritium, collective alpha-particle instabilities, alpha heating of the plasma and helium ash buildup. It is important for the fusion program that these physics issues be addressed to identify regimes of benign alpha behavior, and to develop techniques to actively stabilize or control instabilities driver by collective alpha effects.

The 2004 tracer experiment of JET with the injection of 13CH4 into H-mode plasma at the outer divertor has been modelled with the Monte Carlo impurity transport code ERO. EDGE2D solutions for inter-ELM and ELM-peak phases were used as plasma backgrounds. Local two-dimensional (2D) deposition patterns at the vertical outer divertor target plate were obtained for comparison with post-mortem surface analyses. ERO also provides emission profiles for comparison with radially resolved spectroscopic measurements. Modelling indicates that enhanced re-erosion of deposited carbon layers is essential in explaining the amount of local deposition. Assuming negligible effective sticking of hydrocarbons, the measured local deposition of 20–34% is reproduced if re-erosion of deposits is enhanced by a factor of 2.5–7 compared to graphite erosion. If deposits are treated like the substrate, the modelled deposition is 55%. Deposition measurements at the shadowed area around injectors can be well explained by assuming negligible re-erosion but similar sticking behaviour there as on plasma-wetted surfaces.

In the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Fusion 26, 11 (1984)], the highest neutron source strength Sn and D–D fusion power gain QDD are realized in the neutral‐beam‐fueled and heated ‘‘supershot’’ regime that occurs after extensive wall conditioning to minimize recycling. For the best supershots, Sn increases approximately as P1.8b. The highest‐Q shots are characterized by high Te (up to 12 keV), Ti (up to 34 keV), and stored energy (up to 4.7 MJ), highly peaked density profiles, broad Te profiles, and lower Zeff. Replacement of critical areas of the graphite limiter tiles with carbon‐fiber composite tiles and improved alignment with the plasma have mitigated the ‘‘carbon bloom.’’ Wall conditioning by lithium pellet injection prior to the beam pulse reduces carbon influx and particle recycling. Empirically, QDD increases with decreasing pre‐injection carbon radiation, and increases strongly with density peakedness [ne(0)/〈ne〉] during the beam pulse. To date, the best fusion resu...

This paper reports on accurate determinations of fusion neutron yields on the Tokamak Fusion Test Reactor (TFTR) which require that the neutron detectors be absolutely calibrated in situ, using neutron sources of known strengths. For such calibrations, numerical simulations of neutron transport can be powerful tools in the design of experiments and the study of measurement results. On the TFTR, numerical calibration experiments are frequently used to complement actual detector calibrations. Calculational approaches and transport models used in these numerical simulations are presented and the results from a simulation of the calibration of {sup 235}U fission detectors are summarized.

The JET neutron profile monitor was used to study the transport of tritium into a magnetically confined deuterium plasma. Trace amounts of tritium were introduced through a gas valve beyond the plasma edge into a variety of plasma confinement regimes. The d(t,n)α fusion cross section is two orders of magnitude greater than the d(d,n)3He cross section and so a puff of tritium which has a negligible effect on the plasma nevertheless produces a large d–t neutron signal. The profile monitor consists of two cameras each made up of a fan-shaped array of collimated lines of sight. It was used to measure the d–d and d–t neutron profiles simultaneously. This article describes the detection system, its operation and assesses the difficulties due to scattered neutrons. The profiles can be used to determine tritium density and transport coefficients.

JET has performed two dedicated carbon migration experiments on the final run day of separate campaigns (2001 and 2004) using 13CH4 methane injected into repeated discharges. The EDGE2D/NIMBUS code modelled the carbon migration in both experiments. This paper describes this modelling and identifies a number of important migration pathways: (1) deposition and erosion near the injection location, (2) migration through the main chamber SOL, (3) migration through the private flux region (PFR) aided by E × B drifts and (4) neutral migration originating near the strike points. In H-Mode, type I ELMs are calculated to influence the migration by enhancing erosion during the ELM peak and increasing the long-range migration immediately following the ELM. The erosion/re-deposition cycle along the outer target leads to a multistep migration of 13C towards the separatrix which is called ‘walking’. This walking created carbon neutrals at the outer strike point and led to 13C deposition in the PFR. Although several migration pathways have been identified, quantitative analyses are hindered by experimental uncertainty in divertor leakage, and the lack of measurements at locations such as gaps and shadowed regions.

Detached plasmas have been proposed as a means of distributing power losses uniformly on walls in ITER and other reactor scenarios. Ohmically and neutral beam injection (NBI) heated detached plasma studies are being carried out on TFTR in order to help determine the practicality of this concept. NBI heated detached plasmas with up to 8.5 MW of beam power have been maintained detached for up to 300 ms. A confinement related delay in the radiated power is observed at low beam power. H-mode-like events have been observed for several beam heated detached plasmas and radiative emissivities as high as 0.8 MW/m 3 have been realized. These results are especially of interest to ITER and other reactor design studies.

Local ion temperature gradients were measured at two radial positions in the PLT tokamak by counting the escaping d(d,p)t protons on orbits at closely spaced intervals. A single surface barrier detector was used to make each gradient measurement, eliminating relative calibration uncertainties. The ion thermal diffusivities inferred through ion energy balance with the measured temperature gradients are within a factor of two of the Chang-Hinton neoclassical values for the 3He minority ICRH plasmas.

In this paper plans for alpha-particle experiments on the Tokamak Fusion test Reactor and Compact Ignition Tokamak are described. The main physics issue is whether alpha particles are confined long enough to thermalized. Some of the diagnostic methods required to measure alpha-particle confinement are briefly described.

A workshop on 1–3 August 1989 reviewed the techniques, uncertainties, and experiences of neutron calibration on PLT, TFTR, JET, Tore Supra, JT‐60, JIPPT‐IIU, Alcator C‐Mod, ATF, FT, ASDEX, Textor, and DIII‐D. In the summary session, the workshop participants discussed possible consensus neutron calibration techniques appropriate to D‐D plasmas in tokamaks. The application of such techniques would facilitate a more accurate comparison of neutron yields from different devices, and also allow new calibration techniques to relate their precision to a reference value. General agreement was reached on the suitability of two techniques: (1) a 252Cf source calibration of epithermal neutron detectors, and (2) threshold neutron activation of Ni foils placed vertically above or below the plasma. This paper will present details on detector positioning, neutron transport calculations, and interlab normalization needed to accomplish the standardized calibration using a Cf neutron source.

Accurate, absolutely calibrated measurements of the neutron source strength are needed for determining the quality of plasma performance, for constraining transport analysis, and for studying fast ion physics such as triton burnup. Obtaining an accurate calibration involves more than performing in situ source calibrations. Efforts on TFTR illustrate the additional need for careful detector characterization, periodic renormalization, and proper cross calibration of less sensitive detectors. Multiple detector systems have been developed on TFTR to provide redundancy and a range of energy sensitivity and time resolution. Three independently calibrated systems now agree in their determination of source strength within relative uncertainties of 15%–20%. These accurate neutron measurements can be effectively used to constrain transport simulations of neutral beam injection and test the modeling and simulation assumptions.

The 3He neutron spectrometer used for measuring ion temperatures and the NE213 proton recoil spectrometer used for triton burnup measurements were absolutely calibrated for source strength measurements with DT and DD neutron generators placed inside the TFTR vacuum vessel. Details of the detector response and generator calibration are presented. The calibrated accuracy of the NE213 system to the DD neutron source strength is ±30%, to DT neutrons ±20%, and to the ratio ±20%. Background problems made the accuracy of the 3He system calibration ±70% for the DD peak. Strong affects of local attenuation were observed. For both systems the calibrated efficiencies were 10–100 times less than the unattenuated response, consistent with removal cross sections for the intervening material. The relatively high‐energy threshold of these detectors resulted in insensitivity to scattered neutrons. Within the relative calibration uncertainties, the neutron source strengths from these systems are in agreement with the sourc...

We report results of the TFTR fission detector calibration performed in December 1988. A NBS‐traceable, remotely controlled 252Cf neutron source was moved toroidally through the TFTR vacuum vessel. Detection efficiencies for two 235U detectors were measured for 930 locations of the neutron point source in toroidal scans at 16 different major radii and vertical heights. These scans effectively simulated the volume‐distributed plasma neutron source and the volume‐integrated detection efficiency was found to be insensitive to plasma position. The Campbell mode is useful due to its large overlap with the count rate mode and large dynamic range. The resulting absolute plasma neutron source calibration has an uncertainty of ±13%.

In this paper the confinement of the MeV ions that are created by D–D reactions in the TFTR tokamak [in Plasma Physics and Controlled Nuclear Fusion Research 1988 (IAEA, Vienna, 1989), Vol. 1, p. 27] is described. The ions that escape from the plasma are measured by a new type of detector located just outside the plasma edge. Most measurements made with this detector are consistent with the first‐orbit loss of these ions. Exceptions are correlated with strong magnetohydrodynamic activity, and a preliminary explanation is presented.

JET plasmas with reverse magnetic field feature a different SOL flow than those with normal field. The observed carbon fuelling efficiency from injecting methane gas was similar in reverse and normal field. EDGE2D modeling used an externally applied force to create the SOL flows, without specifying the origin of the force. The resulting flow agreed reasonably with the experimental values between the separatrix and 4 cm mid-plane depth in the SOL. The effect of the flow on the calculated carbon screening was 5-15% higher carbon fuelling efficiency for the low flow velocity with reverse field. (c) 2004 Elsevier B.V. All rights reserved.

Plasma impurity content depends upon the impurity sources, fueling efficiency, and confinement. In JET [Joint European Torus], carbon is the primary impurity, and its fueling efficiency has been studied using methane gas injection and modeled with the SOL [scrape-off layer] codes: DIVIMP and EDGE2D. In this paper, EDGE2D modeling of similar AUG [ASDEX-Upgrade] experiments and projections to ITER are described. The parameters have been identified which govern the size scaling of carbon screening. Size scaling is complex. For carbon injected from the main chamber, the important factors include: the SOL temperature, the magnitude of the thermal force at the divertor entrance, and the parallel distance to the divertor. For carbon injected at the strike points, the intersection of the carbon ionization region with the region of strong thermal force determines the carbon fueling efficiency ITER projects to have much better carbon screening than JET. The ITER SOL is hotter so that main chamber carbon is ionized further from the separatrix making the calculated carbon fueling efficiency lower. Also, the carbon originating near the strike point has less chance of escaping the divertor by factors of about 100. The carbon sputtering is projected to be larger by similar factors, making the projected ITER core contamination similar to JET. However, that result is based upon the assumption that the wall materials have similar composition and behavior as observed on JET. A general result is that the core contamination at fixed total sputtering rate and core impurity confinement increases when the fraction of carbon ionized in the main chamber SOL increases, and decreases for larger machine size and higher density operation.

ELMy H-modes in helium-4 plasmas provide valuable information on ELMy H-mode physics as well as a possible early low activation operational phase for next-step tokamaks, such as ITER. With this in mind, a series of helium-4 H-mode experiments were performed on JET with pure helium-4 NBI auxiliary heating (up to 12 MW). A set of ELMy H-mode plasmas were produced, in both the Type I ELM regime and a second regime, which showed characteristics similar to the deuterium Type III regime, but with a reverse ELM frequency dependence on power. Sawteeth were also observed, and had similar behaviour to those seen in deuterium. Compared with deuterium plasmas, Type I ELMy H-mode confinement is seen to be 28 +/- 6% poorer in helium-4 plasmas and the L-H power threshold 42 +/- 10% larger. This is the opposite of the behaviour predicted by experimental isotope mass scalings from hydrogenic plasmas.Comparison with a wider hydrogenic database, enables the effects of isotopic charge and mass to be studied independently.

ELMy H-mode experiments at JET in 2000/mid-2002 have focused on discharges with normalized parameters for plasma density, energy confinement and beta similar to those of the ITER Q(DT) = 10 reference regime (n/n(GW) similar to 0.85, H-98(y,H-2) similar to 1, beta(N) similar to 1.8). ELMy H-mode plasmas have been realized reaching or even exceeding those parameters in steady-state conditions (up to similar to5 s or 12tau(epsilon)) in a reproducible way and only limited by the duration of the additional heating phase. These results have been obtained (a) in highly triangular plasmas, by increasing the average triangularity delta towards the ITER reference value (delta similar to 0.5), and (b) in plasmas at low triangularity (delta similar to 0.2) by seeding of Ar and placing the X-point of the plasma on the top of the septum. Pellet injection from the high field side is a third method yielding high density and high confinement, albeit not yet under steady-state conditions. In highly triangular plasmas the influence of input power, plasma triangularity and impurity seeding with noble gases has been studied. Density profile peaking at high densities has been obtained in (a) impurity seeded low triangularity discharges, (b) ELMy H-modes with low levels of input power and (c) discharges fuelled with pellet injection from the high field side. New ELM behaviour has been observed in high triangularity discharges at high density, opening a possible route to ELM heat load mitigation, which can be further amplified by Ar impurity seeding. Current extrapolations of the ELM heat load to ITER show possibly a window for Type I ELM operation. Confinement scaling studies indicate an increase in confinement with triangularity and density peaking, and a decrease in confinement with the Greenwald number. In addition, experiments in H isotope and He indicate tau(E) proportional to M(0.19)Z(-0.59). The threshold power for the L-H transition in He plasmas shows the same parametric dependence as in D plasmas, but with a 50% higher absolute value.

The two most sensitive TFTR fission‐chamber detectors were absolutely calibrated in situ by a D‐T neutron generator (∼5×107 n/s) rotated once around the torus in each direction, with data taken at about 45 positions. The combined uncertainty for determining fusion neutron rates, including the uncertainty in the total neutron generator output (±9%), counting statistics, the effect of coil coolant, detector stability, cross calibration to the current mode or log Campbell mode and to other fission chambers, and plasma position variation, is about ±13%. The NE‐451 (ZnS) scintillators and 4He proportional counters that view the plasma in up to 10 collimated sightlines were calibrated by scanning the neutron generator radially and toroidally in the horizontal midplane across the flight tubes of 7 cm diam. Spatial integration of the detector responses using the calibrated signal per unit chord‐integrated neutron emission gives the global neutron source strength with an overall uncertainty of ±14% for the scintillators and ±15% for the 4He counters.

During the initial deuterium-tritium experiments on TFTR, neutron emission was measured with {sup 235}U and {sup 238}U fission chambers, silicon surface barrier diodes, spatially collimated {sup 4}He proportional counters and ZnS scintillators, and a variety of elemental activation foils. The activation foils, {sup 4}He counters and silicon diodes can discriminate between 14 MeV and 2.5 MeV neutrons. The other detectors respond to both DD and DT neutrons but are more sensitive to the latter. The proportional counters, scintillators, and some of the fission chambers were calibrated absolutely, using a 14-MeV neutron generator positioned at numerous locations inside the TFTR vacuum vessel. Although the directly calibrated systems were saturated during the highest power deuterium-tritium operation, they allowed cross-calibration of less sensitive fission chambers and silicon diodes. The estimated absolute accuracy of the uncertainty-weighted mean of these cross-calibrations, combined with an independent calibration derived from activation foil determinations of total neutron yield, is {plus_minus}7%.

A detector system based on partially depleted silicon surface barrier detectors and fast front‐end electronics has been built and cross calibrated to a set of absolutely calibrated 4He recoil detectors. The cross‐calibration factor for the channel with the widest dynamic range is 2.5×10−13 counts per 14 MeV source neutron. These data agree well with the independent neutron activation data. The new detector system covers a large dynamic range (corresponding to 1013–1018 neutrons/s). The response is linear, except at the highest count rates where the detector dead time (∼200 ns) causes departure from linearity. The noise discrimination against 2.5 MeV neutrons and γ pileup is excellent. Measurements of D‐T neutrons from a tritium gas puff experiment as well as from a high‐power D‐T discharge in the TFTR tokamak are presented.

TFTR will soon enter its D-T phase with the introduction of tritium. This will result in the production of neutrons having 14 MeV energy which is significantly greater than the 2.5-MeV neutrons encountered during D-D operation. In preparation for the D-T phase, a calibration of the four neutron detection systems was performed using a 14-MeV neutron generator producing 10/sup 8/ n/sec. To account for the spatial extent of the toroidally shaped plasma and for neutrons scattered from surrounding structures, detector responses were determined with the source positioned at many locations inside the vacuum vessel. Before the generator could be used as a calibration source, a characterization of its total yield and angular emission properties was obtained. The total yield was determined by aluminum activation methods to within /spl plusmn/6%, while the angular emission was found to be anisotropic in the forward and reverse cones along the generator axis. After the characterization was performed, the generator was mounted on a moveable track inside the vacuum vessel, where it could be remotely moved across the view of each detector. This paper presents details of the methods and results of the source characterization, together with initial results of the in-vessel D-T neutron calibration.

Impurity seeding in both the Joint European Torus (JET) and DIII-D tokamaks has produced L-mode discharges with confinement enhancements comparable to H-mode and a near doubling of the core ion temperature when compared,to similar unseeded discharges. Although Z(eff) increases with the neon injection, the total neutron rate is as high, or higher, than reference discharges and the calculated thermal neutron rate increases dramatically in both devices. Modelling with the gyrokinetic simulation code shows a reduction in low k turbulence growth rates with neon injection decreasing to less than the E x B shearing rate, consistent with stabilization of ion temperature gradient modes in both JET and DIII-D. Reductions in ion thermal diffusivity are also observed with impurity seeding. Neoclassical m/n = 3/2 tearing modes limit the duration of best performance in DIII-D with neon injection, while n = 1 and n = 2 magnetohydrodynamic modes limit the performance in JET.

Recent experiments at the Joint European Torus [Rebut , Fusion Eng. Des. 22, 7 (1993)] aim to improve confinement quality in high-confinement-mode (H-mode) plasmas at high densities. Energy confinement time as predicted by the International Thermonuclear Experimental Reactor ITER-H98(y,2) scaling at densities near or in excess of 85% of the Greenwald density limit scaling has been obtained by (i) strong plasma shaping (triangularity 0.35

The DT neutron emission from Triton Burnup has been measured with four helium‐4 proportional counters in TFTR’s Multichannel Neutron Collimator. The operating characteristics of an ‘‘alpha’’ recoil proportional counter are presented. The theoretical response function of these detectors, which is complicated by the strong anisotropy of the (n,α) reaction, is compared with the measured response of these detectors from TFTR. A computer simulation predicts wall and end effects. The frequency responses of the detector and electronics have also been tested. A model predicts the saturation effects seen during high‐power plasmas. The calibration techniques for this detector array will be discussed. The detectors have been used to measure the radial profile of the 1 MeV tritons produced by the d(d,p)t fusion reaction. The burnup produces 14 MeV neutrons in the d(t,n)α fusion reaction.

The TFTR multichannel neutron collimator provides time‐resolved neutron emission profiles from ten vertical chords spaced in major radius across the vacuum vessel. An in situ calibration of the system has been made using a 120 mCi 252Cf source scanned inside the vacuum vessel. A mapping of the effective neutron acceptance aperture was performed and showed reasonable agreement with the optical predictions testifying to the effectiveness of the interstitial shielding material. Crosstalk between channels was evaluated and found to be negligible. Periodic renormalization of the system has shown a standard deviation among the sensitivities of only 2.0% over the first seven months of operation.

The authors report a study of the fueling of the plasma core by recycling in the Tokamak Fusion Test Reactor (TFTR). They have analyzed discharges fueled by deuterium recycled from the limiter and tritium-only neutral beam injection. In these plasmas, the DT neutron rate provides a measure of the deuterium influx into the core plasma. They find a reduced influx with plasmas using lithium pellet conditioning and with plasmas of reduced major (and minor) radius. Modeling with the DEGAS neutrals code shows that the dependence on radius can be related to the penetration of neutrals through the scrape-off layer.

During deuterim-only neutral-beam-injected discharges, tritium from earlier deuterium-tritium discharges is released from the vessel limiters and walls to cause a deuterium-tritium neutron count rate comparable to the deuterium-deuterium neutron count rate. A measure of the tritium density in the plasma based on neutron rate measurements is defined and used to determine which parameters influence tritium influx to the plasma core. The tritium density is observed to decrease in a sequence of deuterium-only supershots and to depend on the amount of tritium injected in prior DT shots and the amount of tritium present in the limiter. A weak correlation is also observed with the plasma current, but not with beam power, hydrogen influx, carbon influx, visible bremsstrahlung, lithium pellet injection, blooms, nor disruptions.

Through semi-independent absolute calibrations of multiply redundant neutron detector systems, the Tokamak Fusion Test Reactor (TFIR) has achieved {+-}7% (one-sigma) accuracy in its fusion power measurements. This has required careful attention to the linearity of detectors up to the present highest fusion power levels achieved on TFTR of over 10 MW. The extended duration of the DT program on TFTR has also tested the stability of the detector systems. These issues of calibration, linearity, and stability are reviewed for the TFTR experience and how it can be applied to plans for ITER.

Current mode operation of the NE451 ZnS Scintillation Detectors of the TFTR Neutron Collimator has enabled us to record the development of radial neutron emission profiles with much faster speed and higher accuracy than in the pulse counting mode. During high-power DT operation, the intrinsic shot noise on the detector traces was so low that the authors could observe sawtooth instabilities and disruptions with good precision and, in addition, were able to identify precursor MHD activity and fishbone instabilities. These results demonstrate that in future tritium burning machines like ITER or TPX, the neutron collimator should be designed not only as a monitor of radial fusion power profiles but also as a wave detector for MHD activity.

The {ital t}({ital d},{ital n}){alpha} and {ital d}({ital d},{ital n}){sup 3}He neutron emissivity profiles are measured in a deuterium neutral-beam--heated plasma where a small amount of tritium (T) gas has been puffed. The tritium density is inferred from the neutron emissivities, and transport coefficients ({ital D},{ital V}) are determined. The particle diffusivities of T and {sup 4}He and the thermal diffusivity are similar in magnitude and profile shape. The convective velocity is small for {ital r}/{ital a}{lt}0.6, and is anomalous for {ital r}/{ital a}{gt}0.6. These are the first measurements of {ital D} and {ital V} for a hydrogen isotope in a tokamak plasma.

Three campaigns, prior to July 1994, attempted to increase the fusion power in DT plasmas on the Tokamak Fusion Test Reactor (TFTR). The first campaign was dedicated to obtaining >5 MW of fusion power while avoiding MHD events similar to the JET X-event. The second was aimed at producing maximum fusion power irrespective of proximity to MHD limits, and achieved 9 MW limited by a disruption. The third campaign increased the energy confinement time using lithium pellet conditioning while raising the ratio of alpha heating to beam heating.

The Tokamak Fusion Test Reactor (TFTR) has performed initial high-power experiments with the plasma fueled by deuterium and tritium to nominally equal densities. Compared to pure deuterium plasmas, the energy stored in the electron and ions increased by ~20%. These increases indicate improvements in confinement associated with the use of tritium and possibly heating of electrons by α-particles.

Short duration (20 msec) neutral deuterium beams are injected into the TFTR tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. I, p. 51]. The subsequent confinement, thermalization, and diffusion of the beam ions are studied with multichannel neutron and charge exchange diagnostics. The central fast-ion diffusion (

The TFTR helium proportional counters are located in the central five (5) channels of the TFTR multichannel neutron collimator. These detectors were absolutely calibrated using a 14 MeV neutron generator positioned at the horizontal midplane of the TFTR vacuum vessel. The neutron generator position was scanned in centimeter steps to determine the collimator aperture width to 14 MeV neutrons and the absolute sensitivity of each channel. Neutron profiles were measured for TFTR plasmas with time resolution between 5 and 50 ms depending upon count rates. The He detectors were used to measure the burnup of 1 MeV tritons in deuterium plasmas, the transport of tritium in trace tritium experiments, and the residual tritium levels in plasmas following 50:50 DT experiments.

Several modifications to existing escaping alpha scintillation detectors in TFTR will be needed before they could be used on ignited tokamaks such as CIT or ITER. The main difficulties are the large heat flux at the desired detector locations and the accumulated radiation damage to the scintillator itself. Constraints imposed by these problems can probably be overcome by using remotely movable (and removable) detectors.

A workshop on 1–3 August 1989 reviewed the techniques, uncertainties, and experiences of neutron calibration on PLT, TFTR, JET, Tore Supra, JT‐60, JIPPT‐IIU, Alcator C‐Mod, ATF, FT, ASDEX, Textor, and DIII‐D. In the summary session, the workshop participants discussed possible consensus neutron calibration techniques appropriate to D‐D plasmas in tokamaks. The application of such techniques would facilitate a more accurate comparison of neutron yields from different devices, and also allow new calibration techniques to relate their precision to a reference value. General agreement was reached on the suitability of two techniques: (1) a 252Cf source calibration of epithermal neutron detectors, and (2) threshold neutron activation of Ni foils placed vertically above or below the plasma. This paper will present details on detector positioning, neutron transport calculations, and interlab normalization needed to accomplish the standardized calibration using a Cf neutron source.

The pending approach of significant alpha particle populations in D‐T plasmas in TFTR and JET and in the burning plasma devices, CIT and ITER, has led to detailed study of the measurement of the alpha particles both directly and through their potential effects on the plasma. The possible diagnostics of alpha particles, previously reviewed, for example, by Zweben [S. J. Zweben, Rev. Sci. Instrum. 57, 1723 (1986)], for use on such devices have been narrowed down to a relatively small number of possibilities. Small scintillator detectors at the wall have proven very effective in detecting the escaping T and p fusion products from the D‐D reaction and hence mocking‐up the relevant studies of loss required by ITER. Development of high‐power pulsed microwave scattering systems for investigating the fast confined alphas is in progress for TFTR and JET. Selection of the right frequency and mode will be needed for CIT and ITER but this technique has the major advantage of being able to conform to readily available...

A gridded 3He ionization chamber had about 1–2% energy resolution, and was suitable for neutron spectroscopy of DD neutrons to measure the ion temperature. The gridded 3He ionization chamber was used to measure the neutron spectra on the tokamak fusion test reactor (TETR) during 1987. The ion temperature was deduced for one set of ohmically heated plasmas and agreed within 20% with that measured by other diagnostics. The deuterium concentration n d/n e and Z eff were estimated with 40% uncertainty from the ion temperature measured with the neutron spectroscopy and the neutron source strength measured with fission chambers.

A particle scoop limiter with a graphite face backed by a 50 liter volume for collecting particles was used in PDX. Experiments were performed to test its particle control and power handling capabilities with up to 5 MW of D° power injected into D+ plasmas. Line average plasma densities of up to 8 × 1013 cm−3 and currents up to 450 kA were obtained. Plasma densities in the scoop channels greater than 2 × 1013 cm−3 and neutral densities in the scoop volume greater than 5 × 1014 cm−3 were observed. There is evidence that recycling may have occurred in the scoop channels for several discharges with large line-averaged plasma density. At beam powers up to 2.5 MW, energy confinement times above 40 ms were deduced from magnetics measurements and from transport analysis. Pressures in the vacuum vessel were in the 10 −5 Torr range, and recycling source neutral densities in the central plasma were low.

Radial profiles of the ion temperature have been measured on PLT by using neutron flux Doppler broadening of oxygen, carbon and helium line radiations, and charge exchange. The ion temperature ( 1.2 keV) is consistent with Hinton-Rosenbluth neoclassical heat conduction in the plateau regime as the dominant energy loss from the plasma with central ion energy confinement times 0.1 s.

The magnitude of a fusion reaction rate in a plasma depends strongly on the relative energy of the reacting plasma ions and less strongly on the ion number density. The ratio of two reaction rates, however, is less dependent on the relative velocities while retaining the linear dependence on the relative densities of the plasma ion species. In this manner, the ratio of t (d,n )a to d (d,n)3He fusion reactions depends only on the ratio nt/ndso that tritium levels in a deuterium plasma can be determined from the d-t/d-d reaction ratio [nd≃ne. Similarly, the density of3He can be determined in a deuterium plasma from the ratio of3He (d, p]α to d (d,n)3He fusion reactions. Such measurements of the3He density are of interest since they relate to the alpha ash removal problem expected on a tokamak reactor. © 1983, American Vacuum Society. All rights reserved.