Free Electron Laser Commissioning Meeting

Friday, 30 Oct 98
Recorder: C. Bohn

Next Meeting


Date: 6 Nov 98
Time: "0845"-0945
Place: FEL Facility Break Room

Agenda for Next Meeting


Item Person Responsible Time ---- ------------------ -------- Status of Open Action Items All 5 min Status of Gun/Injector Siggins/Biallas 10 min Status of Commissioning Bohn 20 min Commissioning Schedule Bohn 10 min New Issues All 5 min

This Week's Attendees


J. Bennett, S. Benson, G. Biallas, C. Bohn, D. Douglas, F. Dylla, A. Grippo, K. Jordan, G. Krafft, L. Merminga, P. Michel, P. Piot, C. Rode, M. Shinn, T. Siggins, B. Yunn

Closed Action Items


New Action Items


None.

Old Action Items


Items of Discussion


T. Siggins indicated that sometime late Monday afternoon the gun should be ready for an attempt to extract an electron beam.

Monday this week the gun was taken to 460 kV to obtain quiescent behavior at 420 kV on the cathode, during which time the audit of the Machine Protection System was also successfully completed. Subsequent activities have been slow and methodical in a concerted effort to diagnose the causes of field emission and cathode nonperformance. One idea was that the thermocouple of the cathode heater was defective so that the cathode was not being heat-cleaned and therefore was remaining contaminated. The idea was motivated by observation of unusually good (~10^-10 torr) vacuum conditions during a heat-clean of the cathode this week. The thermocouple was therefore replaced; however, vacuum remained good on a follow-on heat clean, and so it is now thought that the heater was behaving properly. The most likely problem appears to be a defective cesiator because William & Mary reported Monday that they see no cesium from auger analysis of the previous cathode. The cesiator is therefore in the process of being rebuilt and recharged, a procedure that was slowed by difficulties turning on an ancillary ion pump after it had lay dormant for so long. At this writing (1045 Friday, 30 Oct 98), plans are to finish rebuilding the cesiator today and begin baking it this afternoon. A post-heat-treatment, pre-cesiation high-voltage check is slated for this afternoon. High-voltage checks are also planned for Monday during the process of cesiating the cathode (and electrodes, by default).

Taking advantage of the coincidental timing of Halloween, Siggins plans to come in tomorrow night to perform an exorcism on the gun. If successful, we should have electron beam on Monday, after which we will turn to checking out the injector, then the straight-ahead linac and FEL systems, and then turn to recirculation, etc., per the High-Power Setup Procedure. Please consult the scheduling board and/or the www posting thereof to stay abreast of shift assignments.

B. Yunn gave a very nice and clear presentation on the considerable progress he has made toward modeling the full machine with PARMELA. He now has a complete lattice from photocathode to energy-recovery dump, including the wiggler, and he has run a series of 500-particle simulations, with the space-charge force in the post-cryomodule beam turned both on and off (keeping space charge active in the injector in both cases). In the former case, a run takes ~1 hour CPU time on the Cray, as compares to ~5 minutes in the latter case. Roughly speaking, the beta-function profiles and bunch lengths are larger by a factor of two in the recirculation arcs and after deceleration with space charge turned on, compared to with it turned off. Otherwise the profiles are quantitatively similar. With space charge off, the PARMELA results are in reasonable agreement with the results of optics (DIMAD) simulations, though some refinement remains to be done. Yunn also simulated a saved set of machine settings from August and found (not surprisingly) that the beam was not well matched through the recirculation loop. The tool he has developed should be very helpful toward, at the very least, refining the machine settings in the latter stages of commissioning, including setting up the energy-recovery dump line.

As a final note: P. Michel, P. Piot, and K. Jordan found and corrected a polarity reversal in the electronics of Happek #1. Perhaps it is the reason why no signal had been seen on this bunch-length monitor. Another try will take place in conjunction with the injector check once beam is available.

New Issues


None.

Procedures in Work



Unfinished Subsidiary Tasks for Phase Space Metaprocedure


Task                                                           Principal
----                                                           ---------
I.      Stabilize Drifts in Drive-Laser RF Phase               Walker/Fugitt

II.     Calibrate RF Gradients
        A.      Buncher                                        Yunn    
        B.      Cryounit Cavities (fix control screen)         Merminga/Krafft/Yunn
        C.      Cryomodule Cavities                            Merminga/Krafft/Yunn

III.    Reconcile Methods for Setting RF Phase                 Merminga/Krafft/Yunn
        A.      Buncher Cavities
                2.      Minimum bunch length/time of flight
                
        B.      Cryounit Cavities
                1.      Transient phasing
                2.      Cresting
                3.      Time of flight

IX.     Complete Diagnostics Procedures and  Users' Guide      Krafft/Piot
        A.      M_55 #1, #2
        B.      Happek #1, #2
        C.      BPMs
                1.      button calibration factors 
                2.      rotated MEDM spike charts
                3.      difference orbit data acquisition script
        D.      Multislit #1, #2
        E.      Quad/Viewer (at Wiggler, after Wiggler)
        F.      Multimonitor (at Wiggler)
        G.      SLM/CSR
        H.      Zero Phasing
        I.      Momentum Spread (Injector, Linac Pre-Wiggler, Linac Post-Wiggler)
        J.      Energy

XIV.    Laser Turn-On Procedure                                Benson