SLS at the Paul Scherrer Institute (PSI), Villigen, Switzerland Michael Böge 1
SLS Team at PSI Michael Böge 2
Layout of the SLS Linac, Transferlines Booster Storage Ring (SR) Beamlines and Insertion Devices Contents Important Subsystems for Top-up Pulsed Magnets Digital Power Supplies Timing System Digital BPM System Top-up Operation Stability - Slow Orbit Feedback The Future Michael Böge 3
SLS Layout Linac 100 MeV Booster 100 MeV to 2.7 GeV @ 3 Hz ɛ x = 9 nm rad Storage Ring (SR) 2.4 (2.7) GeV, 400 ma ɛ x = 5 nm rad Initial Four Beamlines: MS 4S, PX 6S, SIS 9L, SIM 11M Michael Böge 4
Linac - Design 100 MeV, 3 GHz S-Band turn key System: 90 kv grid gun: 1 ns pulse or 500 MHz train Sub-Harmonic Pre-Buncher (500 MHz) 4-cell Travelling Wave (TW) Buncher (β = 0.6) 16-cell TW Buncher (β = 0.95 4 MeV) 2 50 MeV TW Accelerating Structures (5.2 m, β = 1) Michael Böge 5
Linac - Specifications, Diagnostics, Optics SLS 100 MeV Pre Injector Layout Diagnostic description Except the Integrating Current Transformers (standard ICT monitors from Bergoz) all the diagnostics have been developed at PSI and optimised to cover the large dynamic range of the SLS pre injector. FCUP 1 (Coaxial Faraday Cup) transient beam meas. behind the gun at 90 KeV. bandwidth: >6 GHz can be moved into a beam with pneumatic actuators Gun, bunching section and first accelerating structure WCM 1 and WCM 2 (Wall Current Monitors) transient beam meas. behind the gun and in the transfer line at 100 MeV cut off: <100 khz bandwidth: ~4 GHz ICT 1 and ICT 2 (Integrating Current Transformers) beam transmission efficiency trough Linac resolution: <5% BPM (strip line Beam Position Monitors) mismatch design for high sensitivity and max. aperture for low current Top up mode SMs OPTICAL diagnostics six optical Screen Monitors (SM) have been used during the commissioning. All SM have been intensively used for fine beam alignment and focus optimisation. SM 5 and SM E have been used for emittance and energy spread measurements. two different monitors are installed in each SM station for high resolution measurements of the transverse beam parameters: a high sensitivity YAG:Ce detector for low current operation (charge < 1nC). an Al foil producing Optical Transition Radiation (OTR). all SM monitors can be moved into the beam with 3 stage pneumatic actuators. Beam specifications Goal: Fast injection into the SLS storage ring (up to 200 ma/min). Constraints: Narrow apertures of the innovative SLS booster synchrotron. Radiation protection limitations. Modes of operation: A single bunch mode (max. 1.5nC, 1ns). A variable multi bunch mode (max. 1.5 nc). In addition an optional low current mode is planned to perform a top up injection, keeping the mean current in the storage ring nearly constant. Max single bunch width 1ns Bunch train length 0.2 0.9µs Max Charge 1.5nC (both modes) Energy >100 MeV Pulse pulse energy stability <0.25% Relative energy spread <0.5% (rms.) Normalized emittance (1σ) <50 πmm mrad Single bunch purity <0.01 Repetition rate 3.125 Hz, 10 Hz (max.) RF Frequency 2.997912 GHz Faults <1 fault/hour RF distribution Two 35MW pulsed klystrons, TH2100 from Thomson, are used to power the travelling wave bunchers and the accelerating structures. The power distribution between bunchers and section 1 is performed by means of two variable power splitters. The RF power needs for a 100 MeV operation are listed here below. 500 MHz prebuncher 500 W 4 cell buncher 2.7 MW 16 cell buncher 3.7 MW Accelerating section 1 11.5 MW Accelerating section 2 18 MW Optics Low energy region (up to 10 MeV): 31 solenoids. Drift section at 50MeV: Quadrupole triplet to matches the beam through the second accelerating structure. Linac main components The electron source: A 90 kv triode gun with Pierce geometry. In the single bunch mode the cathode is pulsed with respect to the grid. In the multi bunch mode the grid is modulated at 500 MHz with respect to the cathode. The bunching section: SPB: 500 MHz sub harmonic pre buncher. TWB1: 4 cells travelling wave buncher (b=0.6, 2p/3). TWB2: 16 cells trav. wave buncher (b =0.95, 8p/9). Two travelling wave accelerating structures: Structures based on SBTF design (b=1, 2p/3, 5.2 m long). The transfer lines: To the beam dump. To the booster. Michael Böge 6
Linac - Measurements Emittance @ 100 MeV Energy spread @ 100 MeV Acceptance tes t s ummary Beam energy = 99.99 MeV/c Rms energy spread = 0.089 % During the acceptance tests, the long term stability of the system has been demonstrated within the specified beam parameters Horizontal Beta: 9.871 m Alfa: 1.758 rad Emittance: 14.7 mc mm mrad [9%] Vertical Beta: 10.425 m Alfa: 1.995 rad Emittance: 15.8 mc mm mrad [6%] emittance x/y: ~ 15/16 mm mrad Dispersion = 0.831 m energy spread: 0.089% single bunch m ulti bunch Single bunch width 1 ns Multi bunch width 0.5 µs Charge in a 2 nc 2.1 2.3 nc bunch/ bunch train Energy 102 MeV 103 MeV Pulse to pulse energy stability < 0.1% < 0.1% Energy spread (rms) 0.2% 0.3% >0.089 % Normalized 50 mm mrad 40 mm mrad emittance (1σ) > 15 mm rad Single bunch purity < 0.01 Repetition rate 3.125 Hz 3.125 Hz RF reflected power interlock trips 1 trip/4hours 2 trips/4hours Michael Böge 7
Linac - Linac-Booster Transferline Linac Booster Transferline ε x =0.7m Booster Horizontal Scraper + 0.5 % 0 m 19 m 34 m Linac Bending ALIMA BY 15/45 deg Injection Kicker +-0.5 % energy filtering -> 60 % of the charge remains for injection into the booster booster energy acceptance 7 % restricted to 2 % by the acceptance of the vacuum chamber at 100 MeV and 0.5 % by the maximum RF voltage of 0.5 MeV @ 2.4 GeV Michael Böge 8
Booster - Design 3 FODO arcs with 48 BD (+SD) 6.4410 and 45 BF (+SF) 1.1296 3 6 Quadrupoles for Tuning, 54 BPMs, 2 54 Correctors ± 15 mm ± 10 mm Vacuum Chamber Energy: 100 MeV 2.7 GeV, Repetition Rate: 3 Hz, Circumference: 270 m Magnet Power: 205 kw, ɛ x @ 2.4 GeV: 9 nm rad Storage Ring Injection OTR Booster Injection 0 5 10 15 20 25m Linac Maximum Energy GeV 2.7 Circumference m 270 Lattice FODO with 3 strai ght s of 8.68 m Harmonic number (15x30=) 450 RF frequency MHz 500 Peak R F voltage MV 0.5 Maximum current ma 12 Maximum rep. Rate Hz 3 Tunes 12.39 / 8.35 Ch romaticities 1 / 1 Momentum compaction 0.005 Equilibrium v alues at 2.4 GeV Emittance nm rad 9 Radiation l oss kev/ turn 233 Energy spread, rms 0.075 % Partition numbers (x,y, ε ) (1.7, 1, 1.3) Damping times (x,y, ε) ms (11, 19, 14) Michael Böge 9
Booster - Ramp 2.8 2.4 2.4 GeV booster ramp 2.4 GeV 100 MeV 0.2 0.16 MPCT 2.4 GeV energy [GeV] 2 1.6 1.2 0.8 0.4 100 MeV -0.04 25 ms 0 0 40 80 120 160 200 240 280 320 50 MeV 25 ms time [ms] current [ma] 0.12 0.08 0.04 0 100 MeV 320ms 0 50 100 150 200 250 300 350 400 450 500 time [ms] Gas desorption by synchrotron light @ high energies (bad lifetime @ injection) Cosinusoidal fast Booster Ramp starts @ -50 MeV (injection @ 100 MeV after 25 ms) 0.16mA Tune/chromaticity correction through quadrupole/sextupole ramp tables ( wave forms ) (avoid 3Q x = 37, compensate eddy current induced sextupole components) Michael Böge 10