Design of the ZT-1 toroidal pinch experiment

The improved stability period of a reversed-field-pinch (RFP) configuration with high current density (500 A*cm" 2 , on average) is well understood on TPE-IR(M) with a metal liner whose size is the smallest among the RFP experimental devices being operated at present (r/R = 9/50 cm unit). Plasma parameters of I p = 130 kA (duration time about 1 ms),n e o=6X 10 13 cm" 3 , T e 0 *600 eV, and |3 p «s 10% are obtained. The improved stability period is characterized by a remarkably reduced fluctuation level (5B p /B p « 1%) and a steady improvement of plasma confinement. Possible explanations for the interesting phenomena in the setting-up phase and the improved stability period of TPE-IR(M) are given, i.e. relaxation phenomena, toroidalflux enhancement within the plasma, and current disruption. The scaling of electron temperature and density, depending on the plasma current in the improved stability period, are described with a discussion of the energy confinement time. The entire performance of TPE-1 R(M) is discussed in relation to that of other RFP machines.

Section: Introductionmentioning

confidence: 99%

Improved stability period in high-current-density operation of reversed-field pinch on ETL-TPE-1R(M)

Hirano¹,

Shimada²,

Maejima³

et al. 1982

“…The secondary wall breakdown problem was avoided by removing the high voltage after pinch formation. These results encouraged the construction of the reversed-field toroidal Z-pinch experiment ZT-1 [12] in 1970. Advances had also been made by then in the understanding of pinch formation with plasma heating and field diffusion [13], and in analytic RFP stability theory [14].…”

Section: Zt-40mentioning

confidence: 86%

Development of the reversed-field pinch experimental programme at Los Alamos

Phillips¹,

Baker²,

Massey³

1985

“…Our main purpose is to develop a model for the evolution of slow RFP devices during the sustainment Phase B based on 1DMHD computer calculations similar to those for tokamaks [4]. Recent results in experimental RFP research are given in Refs [5] and include measurements on ZT1 (minor radius a = 0.10 m) and ZTS (a = 0.15 m) at Los Alamos, TPE (a = 0.058 m) at Tanashi, Eta-Beta (a = 0.0485 m) at Padua and HBTX1 (a = 0.06 m) at Culham. Previous work on these devices is described in Refs [6].…”

Section: Introductionmentioning

confidence: 99%

“…To predict the performance of future large devices it is therefore appropriate to start from the earlier experimental results obtained on ZETA. Both phases A and B in ZETA occupied a period equivalent to many instability growth times, so leading to a quasistationary level of turbulence [7] rather than a behaviour dominated by a single non-linear mode or a few such modes as in the smaller fast devices [5,8].…”

Section: Introductionmentioning

confidence: 99%

“…Subsequent theoretical predictions by Taylor [17] and Kadomtsev [18] suggest that a force-free RFP configuration develops spontaneously during the unstable setting-up phase A as the plasma tries to relax towards a minimum energy state, and although the details of the formation of the RFP in this way are not yet understood these theories do help to explain why it should occur. Self-reversal is observed in the fast RFP devices referred to above [5], which also offer an alternative method for generating RFP discharges by fast programming of the currents [5,6,8].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Evolution of the reversed-field pinch

Christiansen

Roberts

1978

This paper discusses the time evolution of a slow Reversed-Field Pinch during the sustainment phase, starting from an initial low-β configuration at the end of the setting-up phase which corresponds approximately to a Taylor Reversed-Field Bessel-function state. Calculations are made with a one-dimensional MHD (1DMHD) equilibrium and diffusion code. Because of local overheating and consequent rise of plasma pressure the central region of low shear becomes Suydam-unstable, and it is assumed that this results in local MHD turbulence, so flattening out the central density and temperature profiles and leading to a quasi-steady state which gradually evolves in time. The pinch then consists of two main zones, a central Suydam-unstable core I and an outer MHD-stable layer II which is responsible for confinement. An external zone III may exist near the wall but is not studied here. The configuration time τc depends on the time for which the trapped positive Bz flux ψ+ can persist against resistive diffusion. This in turn depends on the electron temperature in zone II and hence on the anomalous electron thermal conductivity that is assumed in the model. Some information can be obtained by normalizing the phenomenological transport coefficients used in the code to the measurements made on ZETA but this does not provide a very sensitive check. Further information can be obtained from empirical tokamak scaling laws. Then the performance of the proposed device RFX is predicted. A significant difference between ZETA and RFX is that in ZETA it was the disappearance of the negative flux ψ− that terminated the quiescent period, while in RFX it is the positive flux ψ+ that controls the configuration time. This leads to a substantial improvement in predicted performance.