Minutes of DRAGON Meeting of July 19, 2005
Present: DH, LF, CV, AO, PM, BG, BW, HC, RL, GR, MH, JDA (recorder)

1. Minutes of the meeting of July 12, 2005 were approved.
2. Business arising
a. The small water leak on Q3 has not yet been looked at.     ACTION: PM will check it.
b. Beam requests were submitted for E989, 811, 1027; E1024 goes in today.
c. The plan to test the DSSSD dead layer will not proceed as data had been taken with attenuated beam.
3. DRAGON Hardware
a. During the TUDA run there seemed to be a problem occasionally with the FCCH slits during beam energy measurements.     ACTION: PM will check it.
4. E989 
a. As mentioned earlier a small organizational meeting was held on Friday, July 22 to discuss aspects of the experiment. Notes of this meeting were circulated earlier (and are attached), and comments below are in addition to these earlier comments. 
b. The 35% variation in the Ge efficiency calibration done before and after the run is of concern. It will be measured again to see if this is consistent.
c. The need for Pb shielding to be replaced at the downstream of the gas target to shield the BGO system. DH will take care of replacing this shielding back.
d. AO will assist CR with some aspects of the GEANT calculations which are related to the energy loss question.
e. LF has started extracting information for the first 300 seconds of the elastic monitor for comparison to FC4 and normalization.
f. Fig. 1 attached shows leaky beam from the second DSSSD. The significant change in resolution and also, mainly, the peak position are now understood. AP will work on this. 
g. AP gave a short outline of his scheduled presentation to ISAC forum on Wednesday.
h. DH talked about the need for a beam cleanup slit just before the gas target. It would be good to reduce or eliminate the tail of the beam at the ~1% level. Four options were discussed, namely, 
i. Attempt to get a different tune from BL and Marco,
ii. Could put in an aperture before FC4,
iii. Could put in an aperture (adjustable IRIS) just before target chamber. (See note from DH below)
iv. Replace the inlet pumping aperture of the gas target with a smaller aperture unit.   
We will proceed with iii. but keep iv. as a possible backup. Option iii. will require design office help and take about 2-3 months.
 
It was noted that an intense beam could damage an IRIS thin material

5. DRAGON Usage
a. TUDA uses MD1 on DRAGON to measure beam energies. While these have gone ok, TUDA is having detector problems with their run.
b. The O16 run will start Aug. 4, 2005. DH will assist.

6. Meeting ended at 12:00

Below I have written down some specs for an iris-type skimmer, with a
view to submitting an REA to have it designed & built by Design Office and
Machine Shop.
  Does this describe what you had in mind?  A mechanical iris could be
like the NT35-111 from Edmund Optic
http://www.edmundoptics.com
            /onlinecatalog/displayproduct.cfm?productID=1461&search=1

I have assumed that positioning could be done by closing the iris down
until it is significantly smaller than the 6-mm aperture of the gas cell,
then back-lighting from IV8 and viewing on the CCD.

Other desiderata?

DaveH

        BEAM HALO SKIMMER FOR DRAGON

  If 1% of a radioactive beam is stopped at the DRAGON gas target, the
resulting background in the surrounding gamma-ray detectors may be
undesirable, or even unacceptable.  We want to add an adjustable iris
upstream of the gas target to skim off beam halo at a place where it can
be shielded from the gamma detectors.

Location: first upstream pumping stage of the windowless gas target.
        * This machined box has an unused port on the underside,
        approximately 6 cm below beam height.  The skimmer mount would
        replace a 6"-diameter tube with flange which currently is attached
        to the box.  
        * The skimmer must fit in a 6-cm gap between pumping tubes on the
        beam axis, leaving at least 15 mm clear towards the downstream
        side.

Skimmer requirements:
        * variable diameter aperture, good approximation to circular
        (e.g. multi-leaf iris diaphragm).  
        * Diameter to be adjustable to 0.25 mm in a range 3 mm to 12 mm
        (or more).
        * skimmer inner edge no thicker than 1 mm to avoid slit-edge
        scattering of the intercepted beam.
        * should tolerate full beam power if beam accidentally steered
        onto the skimmer (worst-case 2 watts in a 3-mm diameter spot.
        * Operates in the milli-Torr region of a multi-stage differential
        pumping system.
        * Left-right and up-down position of skimmer to be adjustable to
        0.25 mm in a range +/- 5 mm with respect to a nominal beam axis.
        * Adjustments to be possible without breaking vacuum.
        * Adjustments can be done manually.