Use of ICRH for startup and initial heating of the TMX-U central cell

A study, using a Monte-Carlo simulation code, of ICRF-sustained mode operation in tandem mirrors by way of ICRF end-cell fuelling and heating is described. Although the basic parameter space considered corresponds to the Phaedrus experiment, the central-cell density and temperatures are extended towards the reactor regime. It is found that significant end cell ion potential barriers can be generated with ICRF, but that, owing to choking of the central-cell ion source stream by the plugging potential, saturation occurs and power requirements rapidly increase, so that the potential rise is limited to about twice the central-cell ion temperature. Although performance is improved as the ion cyclotron resonance approaches the end-cell mid-plane, no significant difference is found between inboard, outboard or double resonance location. As the central-cell density and temperatures are increased, the RF power requirement is found to increase dramatically. Optimum performance for end cell fuelling results when the central-cell electron temperature is higher than the ion temperature, but the magnitude of this ratio is limited by an increase in threshold power level with electron temperature.

“…For example, the highest power point shown in Fig. 4 corresponds to E + = 1500 V'rrf 1 and gives rise to an n c = 2.0X10 1 8 nf 3 .…”

Section: Rf-sustained Mode Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Monte-Carlo study of ICRF-sustained mode operation in tandem mirrors

Todd

1984

“…Here, n ^ is a convenient measure of the passing ion density. In TMX-U, barrier pumping is performed by charge exchange on neutral beams at a rate proportional to the beam current, I B «s 100 A. Equating these pumping and trapping rates for the TMX-U configuration, the equilibrium condition becomes [21] n m i r (cm" 3 )/T 3 / 2 (eV) < 6 X 10 6 I B (a) * 6 X 10 8 (15) For typical values of T p ~ 100 eV measured during unplugged conditions, Eq. ( 15) predicts that the neutral beam systems on TMX-U can pump adequately only for densities <10 1 2 cm" 3 , which is consistent with Fig.…”

Section: Axial Plugging and Passing Ion Collisionalitymentioning

confidence: 99%

Ion cyclotron heating in TMX-U

Dimonte¹,

Molvik

Barter³

et al. 1987

Self Cite

Ion cyclotron heating (ICH) is applied to TMX-U to improve the thermal barrier performance by reducing the passing ion collisionality. During its development, measurements of the antenna loading resistance, R , and the absorption efficiency, rj, were compared with calculations with the antenna design code ANTENA over a wide range of densities and frequencies. Good agreement in R was obtained in the short wavelength slow wave regime but not for long wavelength fast waves because the experimental magnetic field gradients are not modelled in ANTENA. Similarly, r) is much larger experimentally (40%) than in ANTENA (10%) due to the magnetic beach in TMX-U. In its application, ICH successfully decreased the passing ion collisionality tenfold but did not extend thermal barrier plugging to higher density, indicating that collisional barrier filling is not currently limiting TMX-U performance.

“…The time evolution of the transition region density is given by d__ dt " v cx,t '"ictt* (17) 1pxo ~ n exo (16) The first term on the right-hand side gives the trapping rate [13] of passing ions which scatter into the potential depression per unit volume. The second term represents the loss rate due to charge exchange with neutral beams injected into the transition region.…”

Section: Transition Regionmentioning

confidence: 99%

Time-dependent studies of a tandem mirror with thermal barriers

Montalvo

Emmert

1986

The time evolution of a plasma confined in a tandem mirror with thermal barriers has been studied. A physics model is given which describes the kinetic interactions in velocity space between the particles of the various plasma species that exist in each spatial region of the confinement, and the effects of a variety of particle and energy sources applied to the plasma. The analysis includes particle and energy rate equations for the various species determining the plasma confinement. The analysis also includes quasineutrality and ambipolarity conditions which define the ambipolar potential profile along the axis of the device as well as expressions for the passing particle densities in each region. This model describes in a self-consistent manner the time evolution of tandem mirror confinement with thermal barriers including the steady-state phase of operation. The resulting system of equations is solved numerically. The axicell MFTF-B configuration has been studied specifically. A possible startup scenario has been obtained. The results show the time sequence that must be followed to build up a plasma from given initial conditions to the steady-state phase by means of appropriately programmed particle and energy sources applied to the plasma.