Torus Configuration Research Articles

Fusion Engineering and Plasma Science Conditions of Spherical Torus Component Test Facility

A broadly based study of the fusion engineering and plasma science conditions of a Component Test Facility (CTF), using the Spherical Torus or Spherical Tokamak (ST) configuration, have been carried out. The chamber systems testing conditions in a CTF are characterized by high fusion neutron fluxes Γn > 4.4 × 1013 n/s/cm2, over size scales > 105 cm2 and depth scales > 50 cm, delivering > 3 accumulated displacement per atom (dpa) per year. The desired chamber conditions can be provided by a CTF with R0 = 1.2 m, A = 1.5, elongation ~ 3, Ip ~ 9 MA, BT ~ 2.5 T, producing a driven fusion burn using 36 MW of combined neutral beam and RF power. Relatively robust ST plasma conditions are adequate, which have been shown achievable4 without active feedback manipulation of the MHD modes. The ST CTF will test the single-turn, copper alloy center leg for the toroidal field coil without an induction solenoid and neutron shielding, and require physics data on solenoid-free plasma current initiation, ramp-up, and sustainment to multiple MA level. A new systems code that combines the key required plasma and engineering science conditions of CTF has been prepared and utilized as part of this study. The results show high potential for a family of lower-cost CTF devices to suit a variety of fusion engineering science test missions.

Consideration of magnetic field fluctuation measurements in torus plasma with a heavy ion beam probe

The article proposes a method of magnetic fluctuation measurement using a heavy ion beam probe (HIBP) in an axisymmetric torus configuration. The method is based on the detection of the toroidal position (not velocity) of the secondary beam in the analyzer. However, the method needs careful consideration with respect to path integral fluctuations along the probing beam orbit to evaluate local magnetic fluctuation, similarly to density fluctuation measurements with a HIBP. Here, we present an analytic formula to estimate and calculate the path integral effects for different fluctuation patterns in the profile, the correlation length, the radial wavelength, and the poloidal mode number. As a result, it is found that a large distance between the plasma and the detector lessens the importance of the path integral effect, and that local fluctuation of the magnetic field can be properly detected with a HIBP.

General equilibrium property of spherical torus configurations with large triangularity

The general equilibrium properties of the spherical torus configuration can be analysed by a simple version of the solution of the Grad–Shafranov equation, i.e. the so-called Solov'ev configuration which involves only four parameters for the magnetic surfaces with both large elongation and triangularity. The safety factor q-profile and the shear -profile can be determined analytically and it is found that both of them increase rapidly near the edge region. It is also noted that the length of the magnetic field line in the favourable curvature part is much greater than that in the unfavourable curvature part near the edge region. There is a substantial magnetic well in this kind of configuration as well. The trapped particle fraction on different magnetic surfaces as a function of relevant parameters is also given.

National Spherical Torus Experiment: engineering overview and research results 1999–2000

The National Spherical Torus Experiment (NSTX) is a new US facility for the study of plasma confinement, heating, and current drive in a low aspect ratio, spherical torus (ST) configuration. The ST configuration is an alternate magnetic confinement concept which is characterized by high β (ratio plasma pressure to magnetic field pressure) and low toroidal field compared to conventional tokamaks, and could provide a pathway to the realization of a practical fusion power source. NSTX achieved first plasma in February 1999, and since that time has completed and commissioned all components and systems within the machine proper. Routine operation with inductively driven plasma current ≤1 MA and flat top ≤0.3 s has been established, and the ohmic characterization phase of the research program is underway. Radio frequency (RF) and neutral beam injection (NBI) systems have been installed and are presently being commissioned. This paper describes the NSTX mission, gives an overview of the engineering design, and summarizes the research results obtained thus far.

National Spherical Torus Experiment (NSTX) Engineering Overview & Research Results 1999-2000

The NSTX is a new US facility for the study of plasma confinement, heating, and current drive in a low aspect ratio, spherical torus (ST) configuration. The ST configuration is an alternate magnetic confinement concept which is characterized by high β (ratio plasma pressure to magnetic field pressure) and low toroidal field compared to conventional tokamaks, and could provide a pathway to the realization of a practical fusion power source. NSTX achieved first plasma in February 1999, and since that time has completed and commissioned all components and systems within the machine proper. Routine operation with inductively driven plasma current ≤ IMA and flat top ≤ 0.3 seconds has been established, and the ohmic characterization phase of the research program is underway. Radio Frequency (RF) and Neutral Beam Injection (NBI) systems have been installed and the first heating experiments are now underway. This paper describes the NSTX mission, gives an overview of the engineering design, and summarizes the research results obtained thus far.

A review of rotating magnetic field current drive and the operation of the rotamak as a field-reversed configuration (Rotamak-FRC) and a spherical tokamak (Rotamak-ST)

The physics underlying the rotating magnetic field current drive technique is presented. The rotamak is a compact torus configuration having the unique and distinctive feature that the toroidal plasma current is driven in a steady-state, noninductive fashion by means of the application of a rotating magnetic field. In its basic form, the rotamak is operated as a field-reversed configuration (Rotamak-FRC). However, by means of a simple modification, a steady toroidal magnetic field can be added to the basic rotamak apparatus and the configuration then becomes that of a spherical tokamak (Rotamak-ST). The performance of a 50-liter rotamak device, both as an FRC and as an ST, is described. Toroidal currents of over 10.5 kA have been achieved with input powers of 300 kW (at 0.5 MHz). Hydrogen plasmas with ne≈7×1018 m−3 and Te≈35 eV have been obtained. The noteworthy reproducibility of the rotamak discharge has enabled the magnetic field lines of an ST to be directly reconstructed from experimental data for the first time. Attention is drawn to the fact that a fair evaluation of the rotamak concept requires experimentation at higher radio-frequency power levels than are presently available.

Improved tokamak concept focusing on easy maintenance

Maintainability improvement on tokamak fusion reactor may prove to be a critical path in order to launch the fusion energy into commercial use. The more the development of tokamak device progresses from an experimental reactor to a commercial reactor, the more important the maintenance issue becomes. The maintenance difficulty of tokamak system is due to its configuration complexity, enormous electromagnetic loads and material radioactivation. In order to mitigate the difficulty, a very low activation material of SiC/SiC composite and a torus configuration with high aspect ratio of eight are introduced. The torus system is radially divided into equal sectors and each sector forms an assembly unit. All the piping and feeder systems are extracted to the spacious torus central region. The new concept is called `DREAM' tokamak reactor, which stands for DRastically EAsy Maintenance. The maximum toroidal field strength of 20 T and the plasma major and minor radii of 16 m and 2 m lead to high fusion power of 5.5 GW under the moderate physics constraints such as a `non-reversed shear profile' with the MHD safety factor of 3, Troyon factor of 3 for the beta limit and the energy confinement time enhancement factor of 2.

Precessional Light Curves of SS 433

We have calculated theoretical light curves of SS 433 during precession, using a model in which SS 433 consists of a geometrically thick torus around a compact star and a companion star filling the Roche lobe. In order to interpret a bright hump at the precession phase of 0 (the torus is seen from the “bottomside”), the configuration of the torus is not very thick, but should be rather thin (at least mildly thin). Combinations of light curves during eclipse and precession impose several constraints on the physical parameters: the binary mass ratio, torus configuration, and surface temperature of the companion. The favorite combination is a mass ratio of about 2 (a compact star is a black hole) and a surface temperature of the companion of around 17000 K.

Dibaryons as axially symmetric skyrmions

Dibaryon configurations are studied in the framework of the bound-state soliton model. A generalized axially symmetric ansatz is used to determine the soliton background. We show that once the constraints imposed by the symmetries of the lowest-energy torus configuration are satisfied, all spurious states are removed from the dibaryon spectrum. In particular, we show that the lowest allowed state in the S = −2 channel carries the quantum numbers of the H-particle. We find that, within our approximations, this particle is slightly bound in the model. We discuss, however, that vacuum effects neglected in the present calculation are very likely to unbind the H.

Numerical simulation of torus‐driven plasma transport in the Jovian magnetosphere

The Rice convection model has been modified for application to the transport of Io‐generated plasma through the Jovian magnetosphere. The new code, called the RCM‐J, has been used for several ideal‐MHD numerical simulations to study how interchange instability causes an initially assumed torus configuration to break up. In simulations that start from a realistic torus configuration but include no energetic particles, the torus disintegrates too quickly (∼50 hours). By adding an impounding distribution of energetic particles to suppress the interchange instability, reasonable lifetimes were obtained. For cases in which impoundment is insufficient to produce ideal‐MHD stability, the torus breaks up predominantly into long fingers, unless the initial condition strongly favors some other geometrical form. If the initial torus has more mass on one side of the planet than the other, fingers form predominantly on the heavy side (which we associate with the active sector). Coriolis force bends the fingers to lag corotation. The simulation results are consistent with the idea that the fingers are formed with a longitudinal thickness that is roughly equal to the latitudinal distance over which the invariant density declines at the outer edges of the initial torus. Our calculations give an average longitudinal distance between plasma fingers of about 15°, which corresponds to 20 to 30 minutes of rotation of the torus. We point to some Voyager and Ulysses data that are consistent with this scale of torus longitudinal irregularity.

‘TORUS’: a slotless, toroidal-stator, permanent-magnet generator

Indexing term: Electrical machines Abstract: TORUS is a compact electrical machine particularly suitable for use as an engine-driven generator and which, when supplied via suitable switching circuits, can operate as a brushless DC motor to start the engine. The machine is of simple and cheap construction and gives high effi- ciency. The use of Neodymium-Iron-Boron per- manent magnets gives good utilisation and small overall size and weight. Several 2.5 kW prototype machines have been built and tested, and have demonstrated all aspects of performance and capability of the TORUS configuration in the gen- erating mode.

The magnetic structure of a Rotamak discharge produced in a metal-walled vessel

An experimental investigation of the magnetic field structure of a Rotamak discharge, generated and maintained in a metal vessel by means of a rotating magnetic field, is described. The rotating magnetic field is produced by feeding r.f. (1 MHz) current pulses, of 40 ms duration and 90 degrees phase difference, through two orthogonal coils located inside the metal chamber. With a total r.f. power input of 30 kW, a plasma/field configuration is generated which consists, firstly, of a compact torus configuration lying within the r.f. coil structure and well away from the vessel wall. The (positive) current ring associated with this inner structure is approximately 250 A. Secondly, an extra two positive current rings, each carrying approximately 150 A, are observed in the outer region between the coil structure and the vessel wall. Finally, a fourth, and unexpected, ring of negative current ( approximately 15 A) is detected which lies between the three positive current rings. It is speculated that this negative current ring arises from a continuous flow of plasma.

Investigations of the magnetic field structure of high-power, short-duration rotamak discharges

In this paper, the application of the rotating magnetic field method of driving plasma current to the generation of a compact torus configuration known as the rotamak is described. The results obtained in a high-power (few MW), short-duration (∼80 μsec) rotamak experiment are presented [Phys. Rev. Lett. 44, 1676 (1980)]. In particular, the magnetic structure of the stable, oblate, compact torus configuration that is produced in the experiment is described in detail.

Experimental Observations of Rotamak Equilibria

Some experimental observations of rotamak equilibria made in a high-power, short-duration (\ensuremath{\sim}80-\ensuremath{\mu}s) experiment and a complementary low-power, long-duration experiment are summarized. In the high-power experiment two possible equilibrium phases have been identified: an oblate, compact torus configuration and a $\ensuremath{\beta}=1$, mirrorlike configuration. In the low-power experiment toroidal plasma current has been driven, and a compact torus configuration has been maintained, for several milliseconds.

Microwave heating of the ELMO Bumpy Torus relativistic electron ring

A model for microwave heating of electron rings in the ELMO Bumpy Torus configuration is analyzed using a relativistically correct quasi-linear formulation. The spatial locations of heating by the different electron-cyclotron harmonics are calculated. The steady-state ring energy and the microwave power required to sustain the rings are determined by balancing the line-averaged heating rate against classical collisional and radiative energy loss processes. Although ring formation is generally attributed to the second harmonic electron-cyclotron resonance, the calculations show that fundamental heating also plays a critical role in ring start-up and steady state. The model predicts ring power requirements for EBT which are consistent with previous estimates.

Compact Torus Configuration Generated by a Rotating Magnetic Field: The Rotamak

Compact Torus Configuration Generated by a Rotating Magnetic Field: The Rotamak

Compact Torus Configuration Generated by a Rotating Magnetic Field: The Rotamak

In the rotamak concept, a rotating magnetic field is used to drive the toroidal current in a compact torus device. A rotamak device is described and initial experimental results are presented. Toroidal currents in the range 6-10 kA have been produced. Magnetic probe and power measurements, together with zero-dimensional, time-dependent plasma model calculations, indicate that a compact torus configuration has been generated for which the Ohmic power input is balanced by line radiation.

Toroidal MHD equilibrium of the Elmo Bumpy Torus

Analytic toroidal equilibria of the Elmo Bumpy Torus configuration are calculated by means of an asymptotic expansion in the amplitude of the bumpiness. Equilibria containing a magnetic well are found where β is smaller than that in a high-β stellarator but comparable to or higher than that in a high-β tokamak or conventional stellarator. It is shown that the plasma shifts inward in a torus and that the magnetic well exists even if the mirror ratio is small and the aspect ratio is infinite.