Beam Losses During LCLS Injector Phase-1 1 Operation & Paul Emma September 28, 2006 Radiation Safety Committee Review Scope of Phase 1 Operation Request for Three 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 1
Scope of LCLS Phase-1 1 Operation RF Gun & Solenoid Commissioning of Injector thru BC1 ending at TD-11 will Begin in Early 2007 L0a&L0b S-Band Linacs Gun Energy Spectrometer Laser-Heater Transverse RF Cavity OTRs & Wire Scanners L1 S-Band Linacs Bunch Compressor 1 Wire Scanners Straight Ahead Spectrometer X-Band Linac Bunch Length Diagnostics TD-11 2
Requesting for Approval for LCLS Injector Phase-1 1 Operation We request approval for the following operating modes during Phase-1 of LCLS Injector commissioning: 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 unless the BCS proposal for LCLS downstream of the Dump TD11 is approved by RSC/RSO. 3. IF the BCS proposal is approved, and there are no new radiation sources from Dump TD11 to the LINAC/BSY/ESA, LCLS beam can operate beyond Dump TD11 to the LINAC/BSY/ESA. 3
LCLS Injector Commissioning Dates ( 06( - 07) July 24: Aug. 29: Dec. 18: Dec. 19: Dec. 20-Jan. 1: Jan. 2: Jan. 12: Jan. 12-Feb. 4: Sector-20 ready for laser installation Laser installation complete Virtual cathode fully characterized (ready to install gun) RF gun installation starts (10 days) + pre-beam checkout + laser rate switched to 30 Hz (5 days) Holidays VVS s switched on (RF power available) First laser UV-light on cathode! Electrons in GTL and gun-spect spect.. (RF processing L0a,b, L1, LX) Feb. 5: Beam into L0a, L0b and down to 135-MeV spect. Feb. 20: ~June: Beam into main linac (to TD11 dump) Take beam down full linac (to BSY SL2 stopper) 4
LCLS Installation and Commissioning Time-Line Drive-Laser Commissioning Drive-Laser Install undulator LTU/und. First FEL hall ready Install Light linac/bc2 Install First Spont. Light JJ A S O N D J F M A M J J A S O N D J F M A M J J 2006 2007 2008 Gun/Inj./BC1 Gun/Inj./BC1 Install Commissioning (8/21 1/5) 5 linac/bc2 Commissioning LTU/undulator Commissioning FEL Comm.
LCLS Phase 1 Operation 6
Nominal Beam: Losses in the Gun-to-Linac (GTL) Region RF Gun Nominal operation 120 Hz., 1 nc, 6.2 MeV 0.744 watts Stopped in Either FC01/YAG01, FCG1 or YAG02 Nominal beam loss locations in the gun-to-linac region, not including dark current Penetration to Drive Laser Rm. L0-a 7
Nominal Beam Power Along Injector Gun: 6 MeV, 0.7 W 135 MeV, 16 W 250 MeV, 30 W SDMP: 135 MeV, 16 W TD11: 250 MeV, 30 W 8
Dark current energy sources and power estimates for the LCLS injector at 120 Hz where dark current is generated where dark current is observed dark current energy (MeV) dark current charge/pulse (nc) current at 120 Hz (μa) average beam power (W) in gun after gun 6.2 3 0.36 2.2 in L0-a after L0-a 56 0.16 0.019 1.1 in L0-b after L0-b 130 0.32 0.019 2.5 3-nC initial gun dark current based on worst-case GTF operations 9
Nominal and Tune-up up Beam Losses from Gun through BC1 ending at TD11 Component Description Area Linac z [m] LCLS z [m] Energy [GeV] Power [W] FC01 Gun Faraday cup gun 2018.42-0.006 3 aa FCG1 Spec. Faraday cup gun 2018.47-0.006 1.15 aa GSDMP gun-spec. dump gun 2018.44-0.006 1.15 a SDMP inj.-spec. dump SAB 2036.08-0.135 16 b BX01 DL1 bend chamber DL1 2032.07-0.135 2 c L1X X-band struc. iris BC1 2044.76-0.260 0.5 c CE11 energy collimator BC1 2049.34-0.250 < 0.1 c TD11 tune-up dump BC1 2058.57-0.250 30 d note 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). 10
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 d energy. 11
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) = 2.5 microc, at 120 Hz, current is 0.30 microa. Studies show 85% lost in GTL, average loss is (4 MeV) (0.30 μa) (85%) 1.0 kw. The 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 μc) (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 MeV+56 MeV)/2 110 MeV, average power is (110 MeV) (0.38 μc) (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 μc) (150 MeV) (120 Hz) 0.9 kw. Acceleration to 25MeV, MCB ~ 6μA*250MeV=1.5kW after L1 MCB in TD11 ~ 1.5 kw DL1 bend off: 5.0 kw lost in and after the spectrometer dipole. 12
Location Summary of Maximum Credible Beam Power Along the Injector and into the Linac Average Energy (GeV) Charge per pulse (μc) Current at 120 Hz (μa) Beam Power (kw) Gun exit 0.004 2.5 300 1.2 Beam loss in gun region 0.004 2.1 260 1.0 Beam on FCG1 Faraday cup in gun spectrometer 0.004 0.38 45 0.18 L0-a exit 0.048 0.38 45 2.2 Max. beam loss in L0-b 0.048 0.38 45 2.2 L0-b exit 0.110 0.38 45 5.0 Beam loss at straight ahead spectrometer 0.110 0.38 45 5.0 Beam transported to main linac (nom. DL1 setting) 0.110 0.050 6.0 0.6 X-iris 0.250 0.050 6.0 1.5 Bunch Compressor BC1 0.250 0.050 6.0 1.5 Dump TD11 0.250 0.050 6.0 1.5 LCLS GRD 1.1-001 at: http://www-ssrl.slac.stanford.edu/lcls/prd/1.1-001.pdf. 13