Photoinjector for the ILC test facility at Fermilab

1
Photoinjector for the ILC test facility at
Fermilab

• Sergei Nagaitsev
• Fermilab
• May 24, 2007

2
Fermilab NML plans

• Fermilab is constructing the NML facility at the
  existing building (called New Muon Lab) for the
  ILC tests and generic accelerator research
• The NML is being constructed to address primarily
  the ILC S2 RD list
• However, our plans go beyond S2. We would like
  to include elements of S4 RD tasks
  (crab-cavities), diagnostics development,
  personnel training, and accelerator RD.
• The NML facility is staged (1 CM, 2 CMs etc)
  when complete, it would include 1 (or 2) rf units
  running ILC-like beam at 5 Hz.
• 1 rf unit with beam requires building an
  extension tunnel and a new cryo-plant
• The progress is resource limited

3
NML inside (now)
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Outline of our plans

• Cryomodule delivery
• 1st (Type 3) cryomodule is planned to be
  delivered in fall, 2007
• 2nd (Type 3) CM summer 2008
• 3rd (ILC Type 4) CM Mid FY09
• Replace all three CMs with ILC Type 4 in FY2010
• The NML facility will start as a Cryomodule Test
  Stand in FY07-08
• FY08 add beam start civil construction of the
  building extension
• Convert to an ILC RF Unit beam test facility in
  FY11

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NML Schedule (Phase-1)

• Phase - 1 (FY07 thru early FY08)
• Prepare Facility for Testing of Capture Cavity II
  (CCII) and 1st Cryomodule (CM1) without Beam
• Building Infrastructure (AC Power, Water, Air,
  Mechanical)
• Electrical Infrastructure (Racks, Trays, Cables)
• Build Cave to Test these Devices ( 3/4 of Full
  Cave)
• RF Systems (3MW for CM and 300kW for CCII)
• Cryogenic System (1st Refrigerator, Feed Can,
  Feed Cap, End Cap, Distribution)
• Control Room
• LLRF, Controls, Safety Systems, Instrumentation
  (non-beam)
• Move CCII from Meson Detector Building (MDB) to
  NML
• Cool-down and Power Testing

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Phase 1 1st CM (end of CY07)
A used 3-MW Klystron, 10-MW, 1.5-ms modulator
CC2 RF system
Capture cavity 2 in its final location for the
injector
Type 3 cryomodule
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NML Schedule (Phase-2 3)

• Phase - 2 (FY08)
• Testing of 1st and 2nd Cryomodule without Beam,
  Prepare Facility for Beam
• Receive, Install, Power, Cool-down 1st Cryomodule
• Install New Gun and Relocate Injector to NML
• Extend Cave
• Install Beam Lines and Dumps
• Install Additional RF Systems needed for CCI and
  Gun
• Receive, Install, Power, Cool-down 2nd Cryomodule
• Begin Building Extension needed for Phase-3
• Phase - 3 (FY09)
• Testing of Full RF Unit with Beam
• Complete Building Extension
• Begin Testing with Beam
• Install 3rd Cryomodule
• Upgrade Cryomodule RF system to 10 MW

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Two CMs with beam
The existing building is perfect for testing two
cryomodules with ILC-like beam. The building can
be extended to fit 3 cryomodules.
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ILC-like beam?

• 3.2 nC/bunch _at_3 MHz, up to 3000 bunches _at_ 5Hz
• Bunch length 300-µm rms
• Transverse emittance not important (5 µm)
• Energy 30-40 MeV (to avoid overfocusing in the
  CM operating at 31 MV/m)
• Need known and frozen beam parameters at the
  cryomodule entrance

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Existing Fermilab Photoinjector
The existing photoinjector and the laser will be
moved to NML in 2008.
13m
(CC-1)
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Fermilab Photo Injector

• The PhotoInjector has been in operation since
  late 90s and has been a training ground for SCRF
  technology
• Provides 17MeV bunches (up to few hundred) at 1
  MHz rate at 1 pulse/sec
• Two 1.3-GHz klystron-based RF systems power the
  RF Gun and Capture Cavity
• RF systems will be moved to NML in 2008

Capture Cavity and beamline
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Existing rf gun

• Very high dark current
• rf break down for pulses longer than 300us
• We will not use this gun cavity at NML

RF Gun prior to solenoid installation
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Proposed NML Injector Layout
22m
(CC-1, CC-2)
(intended initially for ILC crab cavity tests)
P. Piot
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NML injector layout
6
4
8
1
2
5
3
7

• 1 Gun cavity, 2 Coaxial rf coupler, 3 dark
  current kicker, 4 laser mirror cross, 5
  current monitor BPM, 6 - collimator, 7 Tesla
  cavity (CC1), 8 Tesla cavity (CC2)

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NML cathode system
Gun Transfer
Transport System
GUN
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Fermilab plans for the rf gun

• We are planning to copy (and improve) a DEZY-PITZ
  gun
• RF gun sub-systems needed at NML
• Cathode system -- need new, will be supplied by
  INFN Milano
• UV laser system -- exists, needs upgrades
• Gun cavity need new, will be supplied by DESY
• Focusing solenoids need new
• Coaxial coupler need new
• Dark current kicker need new
• Laser mirror cross need new
• RF system (5-MW or more, 1.5-ms modulator)
  exists (needs updrades)
• Water, temperature control system -- exists

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Cathode system

• The cathode system is being provided to us by
  INFN-Milano.
• Two sub-systems
• A stand-alone vacuum chamber for cathode
  preparation with Cs and Te sources
• A cathode loading chamber connected to the gun
  cavity.
• Discussions underway on how to redesign the
  cathode socket (and spring) in the gun cavity.
  Goal reduce the dark current
• Would like to hide the rf contact spring
• See next slides

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RF spring contact (from D. Sertore, INFN)

• Two different spring types have been used, in
  the same insert!
• The insert was designed for a WELDED Watch-band
  type spring.

• Cantend coil spring
• CuBe uncoated.
• Available coated with Ag, Au etc
• Welded by the manufacturer

• Watch-band type
• CuBe hard, silver coated spring
• Difficult to weld (becomes hard)
• Critical number of convolutions

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Our latest proposal to INFN and DESY

• Two springs one for centering and one locking

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UV laser system

• Already have at photoinjector
• Needs some upgrading
• Will be moved to NML in Jan 2008
• Can run a single gaussian pulse or stacked (4)
  pulses at 3MHz

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Gun cavity

• Have all DESY drawings at Fermilab. Do not yet
  have a complete set of procedures (brazing,
  tuning etc)
• Would like to make some modifications to design
  cathode socket, rf probe, reduce max. fields
• Will take time to develop expertise.
• DESY has agreed to make a gun cavity for us at
  DESY.
• Currently negotiating small changes to their
  design (cathode)
• We will start making our own gun cavity and the
  coupler shortly after DESY will start the
  manufacturing.
• KEK STF has asked us to supply a gun cavity for
  them. No official agreement yet.

22
RF probe - possible location
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Focusing solenoids

• Will make two identical solenoids (like main
  solenoid above) instead of two different ones
• Present bucking coil design interferes with a
  possible rf probe installation at the gun cavity
  cathode wall.
• Solenoids can be ordered from Danfysik (they have
  drawings, fixtures) 30k each
• PS needed 500A, 50V, 10 ppm 27k Eur

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Laser mirror

• Have drawings from DESY
• Laser mirror alignment will be difficult because
  coaxial coupler inner diameter is small

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RF system

• Already have a 5MW Klystron at the photoinjector
• TH 2104C
• Need a new 1.5-ms modulator and a pulse
  transformer
• Planning to build at Fermilab
• Plan to run the gun at 40 MV/m at the cathode
• From DESY simulations gradient 23
  MV/m(PMW)1/2
• For 40 MV/m need about 3 MW. For conditioning
  need more power.

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Water system

• Temperature stability is crucial
• Average power at 1ms flattop, 5 Hz 15 kW
• Simulations freq. shift -23 kHz per one-degree C
• Plan temperature control to 1F (0.5 degree C)

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Overall summary

• Would like to have beam at NML in Apr 2008
• The rf gun will be capable of providing ILC-like
  beams. For 4-stacked laser pulses at 40 MV/m _at_
  cathode
• 3.2 nC per bunch
• 4.2 MeV kinetic energy at gun exit
• 4-µm rms norm emittance
• 2.4 mm rms bunch length
• 1.2 rms momentum spread