Minutes of A0 photoinjector group meeting
                        Monday September 13th, 2004


     
      minutes at: http://nicadd.niu.edu/fnpl/Operation/Minutes/


* Next meeting: Monday September 20th 10:30 CDT, in WH10


* Plan for next week:

Since there is uncertainty on when the LCW will be back (TeV-related 
shutdown), We will decide about the schedule as soon as the LCW is 
back: the plan are then:
    - resume operation 
    - run beam 1 nC for HOM-based beam alignment
    - test CCD digital camera optics on an OTR screen.
    


Discussions:

* Achievements of last week:

- we did not run for the last two weeks:
   - Week of Aug 30: due to various hardware problem:
      - problem with 200 kW power supply and then 
        problem with a power supply of the 200 kW klystron 
	solenoid; this latter problem seems to be related 
	to the high temperature in the building due to air 
	conditioning shutdown for the full week
   - Week of Sep 6: due to (scheduled) cooling water 
        unavailability (LCW). 

- a great deal of work has been done on the laser:
      - the stepping autocorrelator was re-commissioned 
        and is now operational [Jianliang/Rodion], 
	pulse length of 14.5 ps (FWHM) for a bandwidth of
	19.5 Anstr was measured (measurement in the IR after 
	all amplification + gratings). Note this is consistent 
	with 3.5 ps rms UV measurement using a streak camera. 
	[under linear operation of the frequency doubling crystal 
	we expect the IR pulse length over UV pulse length ratio to 
	be ~ 2]
      - work was done on the CW autocorrelator. A measurement  
        of the IR pulse length at the oscillator was attempted: 
	a signal was observed but there is some alignment problem 
	of the rotating table use in the CW oscillator. Jianliang 
	proposed to replace the two mirrors in the rotating arm of 
	the autocorrelator by a retro-reflector 
	
* Other discussion:

      - N. Baboi of DESY presented the measurement done at TTF-2 
        to try to center the beam in the first TESLA cavity 
	of the first cryomodule. The high-order mode (HOM) excited 
	by the beam due to an offset with respect to the 
	cavity e.m. center. Such a type of measurement is planned 
	to be attempted at FNPL: Tim (Koeth) has been trying to 
	measure the HOM mode using a network analyzer but could 
	not see any signal up to now. 
    
      - Rodion presented the proposal for the laser oscillator upgrade 
        being planned at FNPL, the proposal is available on the www at:
	
	http://beamdocs.fnal.gov/cgi-bin/public/DocDB/ShowDocument?docid=1342&version=2

      - Philippe briefly discussed the resolution measurement of the 
        new digital camera a details on the set-up and measurement is 
	available at:
	
	http://beamdocs.fnal.gov/cgi-bin/public/DocDB/ShowDocument?docid=1346&version=1
	
      - Philippe reported on an e-mail from Brian Degraff about A0 
        cryosystem contamination [included below]:

>	    This holiday weekend, the 500 L liquid helium dewars that supply the South
>	Cave at A0 ran dry for a short period of time before techs came is and put new
>	full dewars online.  As a consequence we drew contamination from the bottom of
>	these dewars into the A0 Cryo System.  We have encountered this problem before
>	and previously we have been able to "break" the contamination up and restore
>	flow.  This latest event has completely plugged the cooldown and 5K shield
>	lines.  I have made several attempts over the last two days to restore flow
>	with no success.  There are several implications you need to be aware of:
>
>	1) For the immediate future, we are still going to be able to operate the
>	South Cave as we always would... batchfilling the cryovessel with liquid
>	helium, pumping down in the morning and letting the system come back to
>	atmosphere at night.  The vacuum pumps have more than enough capacity to
>	handle the loss of the 5K shield.
>
>	2) If we have another contamination event, or even a slow buildup of
>	contamination over time, we now no longer have the 5K shield flow to "expel"
>	this contamination.  The most likely place for the next contamination event is
>	in the tube side of the heat exchanger (even if the plug is somewhere
>	upstream, it would have to be flush out through the tube side of the heat
>	exchanger).  If we plug the heat exchanger, we will not be able to operate the
>	cave and will be force into an emergency warm-up.
>
>	Given the potential problems of attempting an "emergency warmup" whenever it
>	is needed, you should consider allowing the A0 Cryo System to be warmed up in
>	a controlled manner to room temperature.  Please let me know if you have any
>	questions.


ACTION ITEM updated:
SEPT 16, 2004

H8/ calibration of upstream directional coupler and
    insulator (Markus need to speak to Tim and with Kai to
    schedule this STATUS?)
H13/ Pulse stacker, what do we do? (Rodion)
H21/ the laser uniformity problem can this be due to the new (since
     late summer) tight focusing in the doubling crystal area to
     improve conversion efficiency? On going work [Rodion]
H28/ Problem with emittance measurement at X7 (Philippe 04/16/04)
H29/ Need daily monitoring of the laser parameters (Jamie/Rodion 04/23/04)
     [OSCILLATOR BW AT 131.225.136.161:8000/~laser]
H32/ Digital camera from SONY(?): camera sent back waiting for new ones
     [New CAM received/ tested by Markus OK] Optics set-up [Philippe/Yin-e]
     to be TESTED with OTR [Sep 16]
H33/ laser fluctuation since June 1st week [FIXED?]
H34/ Need more work on power supply + devise a way to measure
     the current being put out to the magnet [Jamie]
H35/ A0 cryosystem contamination

from Adrian Melissinos:

NEEDED LASER STUDIES:

1. Study of oscillator bandwidth versus length of
   compressed pulse. Measure IR length using stepping
   autocorrelator [Done week of AUG 23rfd 2004]
2. beam profile (wavefront) studies both in IR and UV
   in laser room and on virtual cathode. Use spatial filters
3. study of doubling and quadrupling efficencies with old
   and new crystal, take a tuning curve

POSSIBLE LASER UPGRADE PROJECTS

1. Measure IR pulse length before compression (use diode?)
   implement cw autocorrelation
2. Install new beamline between multipass and 2-pass --
   install spatial filter, rebalance 2-pass amplifiers
3. Relay imaging UV from laser room to cave
4. _harware_: replacing all coolers with new system IV +
   use existing system III as back-up
5. pulse stacker studies, new pulse stacker R&D