Minutes of DRAGON meeting April 23, 2002

Present: MC, DH (recorder), SB, LB, SE, FS, AC, AO, JR, CW, CJ, DO

1. Minutes of previous meeting
	No corrections.

2. Review of the past week's running
	- 21Ne beams at 275 keV/u (leaky beam studies) and at
	215 keV/u (prep. for 21Na beam).
	- 24Mg beam at 425 keV/u
	  * leaky beam study (AO):
	    o Y-steering by 13 strips at the DSSSD showed the same
	      deflection of recoils and beam (to within 1/2 strip)
	      so leaky beam ends up with same q as recoils
	    o trimming beam using the slits between the HEBT2 22-deg
	      benders did not reduce leaky beam
	    o the charge state distribution of leakies peaked at the
	      same charge as recoils, but was narrower.
	  * omega-gamma comparison: again is lower than the most recent
	    measurement in non-inverse kinematics, using provisional
	    online values.
	- 21Na at 215 keV/u
	  * beam delivered just before 24:00 Monday, at good intensity
	  (up to 6 x 10^8 /sec) but with losses due to cyclotron rf
	  sparking and trips of the HV on the RIB ion source.
	  * tuning for spill reduction went quickly, achieving 0.8 MHz
	  with BGO thresholds < 0.5 MeV and ~250 Hz for 2 MeV threshold
	  (but with excursions above 1000 Hz later in the night).
	  * the Beta monitor was calibrated against FCCH current and
	  appeared to give a good estimate of beam current fluctuations
	  * beam energy loss was 15 keV/u for 4.5 Torr
	  * acquired 8 coincidence events in about 6 hours, approximately
	  consistent with the yield measured last winter.
	  * Elastic Monitor was not giving proton counts visible above
	  a low-pulse-height, random-vs-rf background.  Without beam
	  JR had observed noise which increased and decreased by a 
	  factor 10 with nothing changed.  He has added a "lower 
	  fraction" CFD to make a time difference measurement (TDC-27)
	  which is sensitive to risetime differences between noise and
	  a pulser simulation of protons (see figures).  When the CFD
	  Monitor output is viewed on the scope (see figure), the
	  difference between the noise and normal signals is evident.
	  On a longer timescale, the noise is associated with ringing
	  which takes hundreds of ns to damp down.  It appears to be
	  associated with turbos (2000 Hz = 3 x 38000/60 ?).
	  Suggestions (AO) for distinguishing the noise from proton signals
	  included Pile-up Gate (or equivalent in multi-hit TDCs) to
	  respond to the feature of noise-induced ringing.  SB noted
	  that the lousy t signal out of the pre-amp might be improved
	  dramatically by adjusting an internal pot.

3. Future run plans
	We may get beam overnight Tuesday-Wednesday, if Cyclotron RF
	tip-tuning can't go ahead this afternoon.  Should beam be
	available, the plan will be to run more at 215 keV/u, we hope
	with good Elastic Monitor, but in any case to get better
	statistics than the present 8 counts.
	When beam returns Wednesday night we will continue the 
	running at 212.5/210 keV/u, and expect to switch to the
	822 keV resonance 1-2 days later.  The "ITW" access time
	on Thursday morning may become beam delivery.

4. AOB
	SE: on Friday Falk Herwig from UVic will be visiting TRIUMF
	and giving an informal seminar at 11:00 in the Conference
	Room.  He is working on a Monte Carlo approach to the problem
	of network calculations in nuclear astrophysics.