JLab FEL Gun Test Stand status

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JLab FEL Gun Test Standstatus

• C. Hernandez-Garcia
• May 1 2007

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Single pulse beam is expected this fall in the
Gun Test Stand housing the second version of the
Upgrade FEL photocathode gun. It will serve as
the test bed for

• 500 kV operation with field emission suppression
  coated electrodes
• High charge (1-2 nC) single pulse beam
  characterization
• NEG coated chamber for improved vacuum
  conditions, and
• A semi-load lock system for increased
  productivity during cathode change-out and for
  testing different cathode materials
• Drive Laser RD

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GTS status

• The gun assembly with coated electrodes for field
  emission suppression was completed in mid
  September 2006.

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GTS status cont

• The assembly was moved to the GTS in September
  2006 and is currently under vacuum in a temporary
  chamber while the latest version is completed.

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GTS status cont

• The latest version of the gun chamber has been
  machined out from a single bead of vacuum arc
  re-melt, cross forged 316 LN Stainless Steel. The
  chamber is awaiting vacuum firing for hydrogen
  desorption before completion. This chamber will
  be NEG coated using a process tested successfully
  on the gun temporary chamber.

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GTS status cont

• The anode plate will be used as a mirror instead
  of a ligthbox further downstream for illuminating
  the photocathode with the drive laser. This new
  anode has been fabricated from a solid Molybdenum
  block and is currently being polished by hand to
  better than 1 micron surface finish. Brewster
  windows are being manufactured.

Electron beam
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GTS status cont

• A design of a semi-load lock system for replacing
  cathodes without perturbing the gun chamber
  vacuum has been completed and fabrication awarded
  to McAllister Inc. This system will also allow
  re-cesiation without opening the SF6 tank,
  shortening the process from 3.5 to 0.5 hours.

Bellows
The bellows are extended to retract the cathode
stalk and the valve is closed
Valve
The bellows are compressed to insert the cathode
stalk with the valve open. The compressed
bellows fit within the corona shield
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GTS status cont

• The old IR Demo 500 kV, 5 mA DC high voltage
  power supply (HVPS) will power up the
  photocathode gun. The SF6 pressurized tank has
  been refurbished and hydro-tested. It is
  installed and being fitted with components.

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GTS status cont

• The GTS vault has been surveyed and the anchoring
  locations for the gun stand and the HVPS have
  been marked down. The layout below shows the
  proposed beam line

Gun SF6 can
Diagnostic beam line
500 kV DC HVPS tank
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To produce 1.35 nC bunches with 2 cathode QE, we
need 200nJ per pulse at 527 nm and 50 ps FWHM

• Use existing FEL drive laser Antares. It will be
  replaced by the Advanced Drive Laser.
• But need to boost the pulse energy of the
  existing Antares laser