Week of February 14th, 2000

Hi All - We've been extremely busy out here in cow country....

Wednesday - 16 February 2000

Reinstalled the SBL and analyzer. We encountered only a few minor
problems and had both installed within the day.

Thursday - 17 February 200

The run day was Gennady Fiksel's, but he had some setting up to do. During
that period of time, we leak checked the SBL and analyzer, situated
control racks and reconnected all PBL and SBL control and readback
cabling.

During Gennady's run, we ran in the background and conditioned the PBL
sweeps. We drove all four sets of plates and digitized the readback
voltage from each supply.

The three upper sets of plates all held voltage; there were occasional
discharges during which they were occasionally loaded down, but for the
most part, they opperated well. The 20kV pair did not do as well, but was
able to hold both positive and negative voltages during some discharges.

I will e-mail the run log and fax some representative data at a later
time.

Friday - 18 February 2000

Again, Gennady's run day. We continued with conditioning the 20kV sweep
plates in the PBL and all three pairs in the SBL. The radial plates in
the SBL were not able to hold voltage on the positive side. The toroidal
SBL plates were better, with the third set of plates operating the best.

Week of February 21st, 2000

Monday - 21 February 2000

Our run day. The objective of the run was to estimate beam size at the
BPM and shutter and work on beam focus.

We were working with a 44keV beam.

To measure beam size we biased the shutter positive and measured the
current detected on the grey wire. Using Lei's [sweep V] vs [beam motion
at the entrance port] chart, we determined that the beam size at the
shutter is very comparable to the beam size at the BPM.

During the focusing effort - we noticed that higher filament currents tend
to broaden the beam, but not raise the localized amplitude of the detected
current.

We have been using a new method of measuring primary beam current. We run
the primary beam into the shutter with the shutter closed. Externally
connected to the shutter we have in series a resistor (I'm not sure, but I
think it's 1Mohm) and a current meter. With this setup, the shutter
naturally biases itself, thus reattracting secondary electrons, giving us
a true beam current measurement. In addition, by putting a multimeter in
parallel with the resistor, we are able to measure the bias voltage of the
shutter. We have confirmed that the bias voltage is a function of
incident beam current. Lei has measured the secondary electron emission
factors for a variety of beam energies. For a 45keV beam the secondary
electron emission factor is approximately a factor of 3-4. Lei, please
send an e-mail summary of the primary current and focusing tests that you
ran. Assuming the secondary electron emission factor of 3-4, we confirmed
the detected primary beam current using an I/V.

The source used during the day's run was the source that had been in the
accelerator for the last month+. During beam current measurement on the
shutter, we were able to detect less than 10uA. Despite the
low beam current, in light of the changes made to the PBL, we decided to
try and detect secondaries with the analyzer. We were unable to detect
secondaries. In addition, the extracted current levels were not improved
by the pulsing of the filament.

Since we had a run day the following day, we decided to change the ion
source in the hopes that it would increase our primary current.

Changed the ion source - installed a new Na+, four turn source.

Tuesday - 22 February 2000

Our hopes were high that with the new source installed, we would have high
primary beam currents. Over the course of 1 1/2 hours, we
slowly brought the filament current up on the
source. At the four amp range where we expected to see some emission, we
saw none. The source did not beginning emitting until we reached the
5.5-6amp range. Extracted current was very low - on the order of 1-2uA,
despite our raising the filament current to 8A. At 11:45, we changed the
source once again. Inspection of the source revealed that the filament
was recessed approximately 2 - 2.5 mm from the front of the source cup.
All else seemed fine with the source.

We installed another source being extremely gentle with the the filaments
and the source. Pumped down - once on the 10E(-6) scale we applied .5A to
the filament and went to lunch. Again, slowly raised the filament current
to 4-5A. We had emission at these filament current levels, but again the
beam current was small. The beam was being run in the energy range of
40keV. At 6.5A filament current, the current measured on the shutter was
approx 6-8uA. Three sections of the column were not shorted during this
experiment.

We turned our attention to injecting the beam into MST and detecting on
the PBL detectors in the machine (without plasma). We were able to hit
three radially displaced detectors. We detected 4uA (no biasing) on a
pin. It was necessary to adjust the toroidal position of the beam by
applying a toroidal offset voltage to detect maximum current levels on the
pin. This test was interesting and should be persued further. A more
detailed test will help to confirm/determine sweep angle vs sweep voltage
for a given beam energy.

The day was getting a little long in the tooth so we decided to try once
again to detect secondaries. My notes are incomplete and I can not say
what our actualy primary current was for these shots. Although, the bpm
signal was being digitized so we can get an idea from that. Running a
40keV beam we scanned many parameters over approximately 32 shots. While
holding all parameters at their nominal values, we tried varying each of
the follwing; we tried dropping and then raising the analyzer voltage,
tried varying F from -.18 to -.24 ( with the nominaly value of -.2),
current scan from 265kA to 363kA (nominal 300kA). We tried fixing one
sweep voltage while sweeping in the orthogonal direction and vice versa.
During all of this we incrementally increased the filament current to 8A,
and continued to see poor ion extraction levels.

At the end of the day extraced beam current was very low.

Wednesday - 23 February 2000

MST Meeting - able to get Thursday and Friday as run days.

Lei and I met for 1-2hrs and discussed a number of things (more about
this in a separate e-mail).
We have decided to temporarily abandon trying to detect secondaries, and
instead work on getting consistently high current, focused beams.

Thursday - 24 February 2000

We spent the day aligning the accelerator by adjusting the length of the
threaded rods used to support the bellows that is mounted at the base of
the accelerator tank. Using the upper set of toroidal plates, we swept
the beam onto the lower set of toroidal plates. We then adjusted the
accelerator angle, such that the sweep voltage needed to hit each of the
lower toroidal plates was approximately equal and opposite. We repeated
the process for the radial plates and then reiterated the process on both
radial and toroidal plates.

It was troubling to note that the fiducials on the BPM, did not move much
relative to the beam profiles. In hindsight, the motion of the beam at
the BPM was probably on the order of millimeters - a motion that we may
not have noticed when viewing the BPM traces and fiducials.

We then double checked the alignment using the grey wire on the shutter.
We estimated that the shutter should be offset 2.7degrees to center the
grey wire over the port. Due to the five degree slop in the shutter
rotation, we set the shutter to 7.7 degrees. The results without sweep
were poor - the beam did not appear to center on the wire. We then
released the rotatable feed-thru set screw and let the shutter hang free.
The beam then seemed to center nicely on the wire.

We then ran the beam (radial direction) along the wire. If all is
aligned, we would expect the beam to remain on the wire as we sweep
radially. I don't have a note on the result of this test, but I think the
beam stayed on the wire. The signal was a bit hard to measure since we
were watching for a constant offset.

We then swept the beam in the toroidal direction, and measured the beam
current on the shutter. The detected current was not what I was
expecting. I speculated that we were scraping off on the 20kV sweep
plates. While biasing the shutter, we repeated the toroidal sweep test
with I/Vs connected to the 20kV plates. We saw scrapeoff on P20NW, but no
scrapeoff on P20SE. We think that the accelerator probably shifted a bit
when Lei and I and Bill were working near the accelerator after having
aligned it.

Friday - 25 March 2000

Recheck of accelerator alignment due to scrapeoff on P20NW plate.
Alignment was off. We redid all of the alignment that was done yesterday.
I should note at this point that there are some threaded rods with
mounting brackets and setscrews that stabilize the accelerator and mount
from the bridge to a midline flange on the accelerator shielding chamber.
We believe that it was the release of the torque on one of these
stabilizing rods that jolted the accelerator out of alignment. They have
since been reattached and the accelerator is stable.
We then began various voltage differences between the HV electrodes in an
effort to extract more ion current. At 50kV between the extractor and
accelerator, we appeared to extract more current, but it was a very
unstable operating regime and we tripped the controller.

A final measurement that afternoon was with 8.8A on the filament, we
detected 3uA actual beam current (natural biasing of the shutter).
Without the biasing, we measured 6uA. Again, I should note that pulsing
the filament did little to improve primary ion current levels.

We then vented the PBL to nitrogen and visually inspected the beamline.
The 1" stainless aperture that we installed on the BPM appears to be
centerd within the beamline when viewed from the accelerator. From that
angle and position it is difficult to see if there is any discoloration on
the stainless aperture which might indicate scrape-off. We noticed
a hole burned in the screen the extends across the tube that extends down
from the accelerator tube HV flange (see J. Matthew's thesis for a
diagram).

Before removing the source (but with the HV flange on the bench), we
inspected it as viewed down the extractor tube, through both extractor and
pierce electrodes. An edge of the source cup was visible through the
aperture of the pierce. If the source had been aligned, the source cup
would not have been visible. While removing the source cup, we noted that
when the source cup is installed, there is a bit of free-play in the
mounting location at the emitting end of the cup. Clearly, this will allow
for a misaligned source and should be fixed.

We then measured the spacing of the pierce electrode from the HV flange.
The pierce electrode was not parallel to the flange, nor was the extractor
electrode parallel to the pierce electrode. Using a micrometer, we
paralleled the pierce with the accelerator flange and the extractor
electrode with the pierce electrode.

During installation of the source, we viewed the cup through the extractor
tube, trying to ensure that the source was centered behind the pierce
aperture. We then reinstalled the flange and pumped down. I should note
that it was a very humid day.

Saturday - 26 February 2000

Realigned the accelerator due to the realignment of the pierce and
extractor electrodes.

We still see the same funny beam shape on the shutter when sweeping the
beam toroidally.

This ion source is operating better than either of the previous two
sources, but not as good as the source that was in for over a month.

Our efforts are now turned toward trying to get higher beam current and a
focused beam - these two seem to go hand in hand.

5 Major electrodes shorted from bottom-up on accelerator column. The two
top electrodes and the accelerator flange are unshorted. With natural
(beam hitting the shutter and biasing the shutter due to the external
resistor connected to the shutter) biasing, with a filament current of 5A,
measured a maximum of .75uA on the shutter.

We then changed the beam energy, with no bias we measured 10uA on the
shutter (assume and electron emission factor of 3 = 3.3ua) - approx 7uA
read from the pierce meter.

Decided to try shorting out even more of the accelerator column.
Grounded the major electrode that is at the same level as the bottom of
the tube that extends from the accelerator flange. Apparently, the
voltage between this electrode and the bottom of the tube was too large.
We arced and took out Lei's HV controller.

Week of February 28th, 2000

Called it a day!

Monday - Wednesday - February 28 - March 1, 2000
RFP Workshop, Madison, WI

Wednesday - 1 March 2000

Spoke with Steve Aceto regarding operation of the accelerator on ATF.
Will send a summary of that conversation at a later time.

Thursday - 2 March 2000

Spoke with Jim Adney about ion optics, electrode configuration and
mounting of the source. Mildly helpful discussion.
_____________________

There are more details that I could include in this e-mail, but I am sure
you're pretty sick of reading this by now, so I will send them in a later
post.

Diane