Beam Losses During LCLS Injector Phase1 Operation

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Beam Losses DuringLCLS Injector Phase-1 Operation

• Scope of phase 1 operation
• Operating modes
• Operating plan for phase 1
• Beam power and losses during nominal operation
• Maximum credible beam
• Summary of maximum credible beam in injector and
  linac

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Scope of LCLS Phase-1 Operation
Commissioning of Injector thru BC1 ending at
TD-11 will Begin in March 2007
RF Gun Solenoid
L0aL0b S-Band Linacs
Laser-Heater
Transverse RF Cavity
OTRs Wire Scanners
Bunch Compressor 1
Gun Energy Spectrometer
L1 S-Band Linacs
Wire Scanners
TD-11
X-Band Linac
Straight Ahead Spectrometer
Bunch Length Diagnostics
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Modes for LCLS Injector Phase-1 Operation
The following modes of operation for phase-1 of
LCLS injector commissioning have been approved
1. Beam operation from the LCLS injector gun to
dump SDMP during LINAC operation, which is
located in Sector 21-1. Magnets BX01/BX02 will be
locked off. 2. Beam operation from the LCLS
injector gun to dump TD11, which is located in
sector 21-3. Dump TD11 will be disabled in.
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LCLS Injector Commissioning Dates (2006 - 2007)
Dec 22 PPS Certified Dec 20-Jan 1 Holidays Jan
2 VVSs switched on for PEP-II (RF power
available) Jan 15 L0a, L0b, L1 RF processing
begins Feb. 1 X-band RF processing begins Feb
20 GTL beamline installation complete Mar
6 Virtual cathode fully characterized (ready to
install gun) Mar 7 RF gun installation begins
laser rate to 30 Hz Mar 16 First laser UV-light
on cathode! Mar 17 Electrons in GTL and
gun-spectrometer Apr 9 Beam through L0a, L0b
and down to 135-MeV spectrometer Apr 24 Beam
into main linac (to TD11 dump) July Take beam
down full linac (to BSY SL2 stopper)
http//www-ssrl.slac.stanford.edu/lcls/internals/c
ommissioning/documents/commissioning-dates-2006-20
07.ppt
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LCLS Phase 1 Operation
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Nominal Beam Losses in the Gun-to-Linac (GTL)
Region
RF Gun
Nominal beam loss locations in the gun-to-linac
region, not including dark current
Penetration to Drive Laser Rm.
L0-a
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Nominal Beam Power Along Injector
Gun 6 MeV, 0.7 W
135 MeV, 16 W
250 MeV, 30 W
TD11 250 MeV, 30 W
SDMP 135 MeV, 16 W
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Dark current energy sources and powerestimates
for the LCLS injector at 120 Hz
3-nC initial gun dark current based on worst-case
GTF operations
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Nominal and Tune-up Beam Losses from Gun through
BC1 ending at TD11
Estimated average beam power loss and location
along the LCLS in nominal and special tune-up
conditions. Power levels set in bold type occur
in normal operating conditions. Non-bold entries
are special configurations as described in the
note column.
Table Notes aa. This loss occurs only when
this Faraday cup is inserted (6 MeV, 120 Hz). a.
This loss occurs only with beam on the gun
spectrometer (6 MeV, 120 Hz). b. This loss
occurs only with beam on the injector
spectrometer (135 MeV, 120 Hz). c. This is a
normal loss due primarily to dark current from
gun and injector. d. This loss occurs only
with beam on this tune-up dump (120 Hz).
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Maximum Credible Beam
Source in a RF Photocathode Gun is Explosive
Electron Emission
Explosive electron emission occurs from the
photocathode if the drive laser intensity exceeds
the threshold for plasma production. This
emission persists until it has depleted the gun
of all its stored energy.
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Estimate for Maximum Credible Beam
The maximum stored energy in the gun is 10 J at
140 MV/m. Beam loading gives 4 MeV energy,
therefore the max charge/pulse is (10 J)/(4 MeV)
2.5microC, at 120 Hz, current is 0.30mA.
Studies show 85 lost in GTL, average loss is (4
MeV)?(0.30mA) ?(85) ? 1.0 kW.
The macro pulse 1.2 A is accelerated by L0-a,
with beam loading it will have energies between
21 to 76 MeV, with 48 MeV average energy.
Average beam power at L0-a exit (48 MeV)?(0.38
mC)?(120 Hz) ? 2.2 kW.
The quads between L0-a and L0-b transport 64 MeV
electrons so will over-focus MCB electrons
causing lost in the L0-b structure. Max power
deposited in L0-b is assumed to be the full beam
power of 2.2 kW.
Quads OFF this beam could be accelerated by
L0-b, with range of 56 to 160 MeV, for the max 62
MW RF power and beam loading. The average energy
is (160 MeV56 MeV)/2 ? 110 MeV, average power is
(110 MeV)?(0.38 mC)?(120 Hz) ? 5.0 kW after L0-b.
Max energy is 160 MeV and DL1 energy acceptance
is ?5, the highest energy with max transmission
is (1 - 5)?(160 MeV) ? 150 MeV. Worst case MCB
to main linac is 150 MeV with average power of
(13)?(0.38 mC)?(150 MeV)?(120 Hz) ? 0.9 kW.
Acceleration to 250MeV, MCB 6mA250MeV1.5kW
after L1
MCB in TD11 1.5 kW
DL1 bend off 5.0 kW lost in and after the
spectrometer dipole.
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Summary of Maximum Credible Beam PowerAlong the
Injector and into the Linac
LCLS GRD 1.1-001 at http//www-ssrl.slac.stanford
.edu/lcls/prd/1.1-001-r0.pdf.