Neutron emission from TFTR supershots

Abstract

Empirical scaling relations are deduced describing the neutron emission from TFTR• supershots using a data base 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 machine settings and the energy confinement time. Thi:.scaling has been used to project the fusion rate for equivalent DT plasmas in TFTR, aad to explore machine operation space which optimizes the fusion rate. Increases in neutron emission are possible by either increasing the toroidal magnetic field or further improving the limiter conditioning.. 1MIT Plasma Fusion Center, Cambridge, MA 02139 I. INTRODUCTION '4,One goal of the TFTR experimental research program is to achieve scientific breakeven wherein the fusion power produced equals the power required to heat the plasma. Presently, the highest performance TFTR deuterium plasmas are the supershot plasmas [1] which have produced equivalent QDT values _ 1/3 [2] (where "equivalent" is a projection that is defined in Sec. 8). Clearly, there is a need to operate the supershot plasma in a manner that will further optimize its fusion performance.This paper evaluates the statistical dependence of the d(d,n)ZHe fusion neutron emission from TFTR deuterium supershots upon the TFTR machine settings (e.g., plasma current, toroidal magnetic field, neutral beam power, etc.). Empirical and physics-based scaling relations are derived and compared to the neutron emission as well as to that predicted by Q one-dimensional transport codes. The supershot neutron emission is described in terms of a zero-dimensional model which identifies the variables related to the underlying physics of the fusion reactions. This model was used to evaluate equivalent fusion rates for DT plasmas and to suggest machine conditions for optimal performance.The analysis indicates that the primary limitation of the TFTR supershots is the apparent f3-1imit of the supershots when the plasma energy content is about 0.S of the Troyon value [3].Above this limit, TFTR supershots experience some disruptions. Even sporadic disruptions make experiments in the supershot regime difficult due to the sensitivity of supershots to the wall conditions. Another conclusion from the statistical analysis is that the deuterium neutron emission was independent of the neutral beam voltage (from 85 kV to 105 kV).However, considerable improyement was achieved by conditioning the walls with lithium pellet injection. A further improvement is projected by increasing the toroidal magnetic 2 field.The organization of this paper is first to describe the database. Scaling relations are then derived for the neutron emission based upon entirely empirical regression analysis.The measured neutron rates are then compared with those predicted by one-dimensional transport calculations.A zero-dimensional model for the neutron emission is then derived.TFTR supershot scaling for the relevant plasma parameters that describe the classical physics o...

Scenario development for the observation of alpha-driven instabilities in JET DT plasmas

“…8 is plotted the measured neutron rate versus n D P N BI τ s,e with n D the deuterium density (deduced from the electron density and Z ef f measurement), and τ s,e the electron slowing-down time. The beam-target reaction rate computed with the pencil code [31] using the measured kinetic profiles is found to scale linearly with this quantity, as it should [32], and to agree well with the experimental measurement for low to medium NBI power. It is observed that at high NBI power, there is a significant departure of the measured neutron rate from that calculated using pencil, which results from thermonuclear and beam-beam contributions to the neutron rate, although the latter is found not to exceed 10% in these pulses.…”

Studies of global energy confinement in TFTR supershots

“…For these cases, the calculated neutron emission and energy content agreed with the measurements. {[,SNAP/T_ = 0.90 :i: 0.i0 and ESNAp/E "-0.99 =t=0.04) [4] indicating that the plasma measurements were all consistent with each other.…”

“…The approach taken in this paper has been to examine all of the supershot plasmas that were obtained during the extensive 1990 run campaign [4]. The data are intended to encompass the full range of plasma behavior encountered in 1990 when TFTR was operated in the supershot mode [5].…”

“…Recently, a different TFTR supershot scaling for the energy confinement time at peak . neutron emission was found [4] "rE ox. B l.or/.0.22 iv/_o.s6 po.a0 C 1I-°'32…”

Experiments on TFTR supershot plasmas

“…The evolution of the supershot confinement time during the entire CY90 run (aBout 7000 pia.smas) ( Fig. 12)indicates that events such as boronization [18]/rod a disruptive discharge cleaning [19] [15] when tritium is introduced into TFTR supershots. The (x) points did not have blooms, the (r_) points did ha.ve bloom,s.…”