Newsgroups: sci.physics.plasma
From daemon@pppl.gov Tue Jan 31 21:12:23 1995
From: rhawryluk@pppl.gov (Rich Hawryluk)
Organization: Princeton Plasma Physics Laboratory
Subject: TFTR Update January 31, 1995

TFTF Update for January 31, 1995

Operations were resumed on Tuesday, January 3, 1995 after the completion of
an extended maintenance/holiday period which began on December 9, 1994. All
systems were returned to operational status during the first shift and
the week was devoted to discharge target development with neutral beam
injection and ICRF.

An ICRF D-T experiment was carried out on Monday Jan. 9th to
study ICRF-induced changes in the rate of alpha particle loss as a function
of toroidal field current. There were 8 DT shots. The ICRF-induced loss
was seen in three out of the four toroidal field cases.

Experiments on mode conversion current drive produced an estimated 100 -
150 kA of noninductively driven current with 2-2.5 MW of applied ICRF
power. These experiments were performed with a He3-He4 ohmic target
plasma.

The week of Jan. 16th was scheduled as an ICRF run week with some
operations in advanced tokamak regime. Up to 4 MW of power was coupled
into the plasma at 90 and 270 degree phasings. A comparison of the plasma
loop voltage with tritium injection during mode conversion current drive
indicates non inductively driven currents on the order of 100 kA were
obtained in mode conversion current drive experiments. Further analysis of
these experiments is on-going.

Early in the run, H-minority resonance heating was performed in an attempt
to condition the outboard limiters. Toroidal field currents of 48, 42, and
38 kA were utilized. The role of TAE instabilities in expelling fast ions
is being further investigated.

A number of D-3He shots during ICRF mode conversion experiments showed
evidence of additional loss of high energy fusion products. These were
with 180 degree phasing of the antenna. Two DT shots were taken, also with
180 degree phasing in an ICRF mode conversion experiment, but the loss
appeared to be only normal first orbit loss. These results are being
analyzed further.

Experiments were started that are aimed at producing a q profile with a
significant region of negative magnetic shear in the plasma core and study
its effects on the local transport. After conditioning at R=2.60 m, a puff
of helium gas at t= 0.25 seconds helped to control the MHD activity. After
this, the neutral beam start timing was varied from 2.0, 1.5, to 1.1
seconds. As the start of neutral beam injection was moved earlier in the
pulse, q(0) rose to 1.8 from 1.4. Motivated by this success, the startup
was modified to inject as early as 0.6 seconds. With NBI starting at 1.0
or 0.6 seconds, q(0) was ~2.3 and ~2.5 respectively. The addition of an Ip
ramp to increase the plasma current from 1.0 -> 1.8 MA resulted in
considerable MHD activity which caused a minor disruption. Nonetheless,
this startup scenario looks attractive for reversed shear, but needs
further work on ramping the current up to 1.5-2.0 MA.

On Tuesday, 24-Jan-1995 experiments began to examine the differences in the
thermalization of alpha particles as helium ash in sawtoothing and
non-sawtoothing plasmas. Ash buildup was clearly seen during 2 seconds of
neutral beam injection in the sawtoothing case. In the next phase of the
experiment, a non-sawtoothing version of an otherwise similar plasma will
be explored.


Future Activities

Maintenance activities are going on this week. Deuterium-tritium
experiments will resume next week.
_________________________________________________________________________
R. J. Hawryluk
rhawryluk@pppl.gov
PPPL - LOB 325
Phone: (609) 243-3306
Fax: (609) 243-3248