Hi,

The following is my summary of a meeting on graphite targets at
TRIUMF, held at Nate's urging to try to initiate some action to solve
the problems. The .pdf attachment (867 kB) is some 20 pages of memos
and a technical summary of the general problem of brazing graphite.

Glen
-- 
 Glen Marshall                mailto:Glen.Marshall@triumf.ca
 TRIUMF, 4004 Wesbrook Mall   phone: 604-222-7466
 VANCOUVER, BC V6T 2A3        fax:   604-222-1074



	     Summary of meeting on graphite targets

			  June 6, 2000

Chair: R. Helmer
Present: G. Dutto, S. Kreitzman, T. Lyth, G. Marshall, R. Ruegg,
G. Stinson, and J. Yandon

Rich Helmer had distributed some memos dating as far back as
1994, which summarized the efforts to maintain and improve
graphite target fabrication at TRIUMF during that period. A short
article on brazing of carbon and graphite was appended.

In brief, TRIUMF had routinely used 10 mm graphite production
targets at 1AT1. They would eventually deteriorate via
exfoliation of the pyrolytic graphite layers. However, two or
sometimes more targets would be sufficient for a typical running
period of several months at currents below 130 microamps. The
targets were produced in Victoria by a technician, Peter
Verstraaten, under the supervision of Terry Hodges, TRIUMF's
production target design expert.

Prior to 1994, target production was transferred to TRIUMF,
following the retirement of Peter Verstraaten. Tom Lyth attempted
to make targets at TRIUMF for both 1AT1 and 1AT2. At 1AT2, the
stresses on the target are more severe due to higher power
deposition. However, even the targets made for 1AT1 had poor
survival times of only a few days, and the failure mode was not
exfoliation, but rather that the brazed bond between the
quarter-round-shaped graphite and the target holder or saddle
(brazed to the curved surface at the lower right quadrant as seen
by the proton beam) failed and the target fell from the holder.

The discussion soon revealed an essential difference in technique
between the Victoria production and TRIUMF production. Victoria
targets were heated in a vacuum oven. The oven was brought to
TRIUMF but had not been used due to lack of a power supply, and
another oven using RF induction heating was used for the
unsuccessful targets.

The conclusion of the meeting was that we should first try to
reestablish the fabrication of 1AT1 targets with the original
oven and heating procedures, after finding (borrowing or buying)
an appropriate power supply. The supply specifications were not
too clear at the meeting. We should try to make two targets for
the ladder to be used in the fall running period. The targets
should be run at limited currents until it is shown that they
survive reasonably well; this requires cooperation of other
groups in the TRIUMF meson hall, but at least the muSR and E614
groups have strong motivation to accept this.

Gerardo Dutto agreed to ask Terry Hodges (who retires soon) to
consult, and if he agrees, Glen Marshall will act as TRIUMF
liaison in the production of the first targets for 1AT1. For it
to be successful, there must be and adequate level of priority
given in order that Tom Lyth and/or other technical personnel can
participate.

Filename: graphite.pdf

Created for the The Center for Subatomic Research E614 Project Projects Page.

Created by The CoCoBoard.