Injection schemes for intense beams Dr. Sabrina Appel, Accelerator - PowerPoint PPT Presentation

GSI Helmholtzzentrum für Schwerionenforschung GmbH Injection schemes for intense beams Dr. Sabrina Appel, Accelerator Physics Department, GSI, Darmstadt GSI Helmholtz Centre for Heavy Ion Research Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 1

Outline § Multi-Turn Injection § SIS18 § Intensity limitation Septum Y § Optimization § Algorithms § Genetic Algorithms § Particle swarm algorithms X § Technical solution § EMTEX § Skew quadrupoles Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 2

Overview injection into SIS18 TK f TK = 36 MHz f TK =36 MHz E kin =11.4 MeV/u Alvarez SIS18 We assume that the longitudinal and transverse planes are decoupled f 0 =214 kHz During MTI injection the RF in the SIS18 is turned off N B ≈ 170 The micro-bunches debunch, filament and form a coasting beam T rev =5 μs within a few turns Final full momentum spread after injection should be within the rf bucket area Δ p / p ≤ 10 − 3 (equivalent parabolic distribution) Transverse beam size (4 rms physical emittance) should be within the machine acceptance ε x = 150 mm mrad ε y = 50 mm mrad (equivalent K-V distribution) Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 3

Intensity limit: Space charge 1 . 0 The (incoherent) transverse space charge force is the 0 . 9 main intensity limiting effect in the FAIR synchrotrons 0 . 8 Q y 0 . 7 Beam loss 0 . 6 0 . 5 0 . 5 0 . 6 0 . 7 0 . 8 0 . 9 1 . 0 Q x 2 q fast beam loss if N 4 Tune shift: sc D Q - ? y m B fb c 2 3 one crosses low f 0 0 order resonances Δ Q sc ! 0.1 − 0.5 Intensity limit: G. Franchetti, GSI Report (2005) Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 4

Intensity limit: Dynamic vacuum For intermediate charge state ions, the loss-induced vacuum degradation is another important key intensity-limiting factor. Results of STRAHLSIM simulations for the desired SIS18 booster operation with different (uncontrolled) initial beam loss. P. Spiller {SIS18} upgrade: Status, Present and Expected Performance Low Charge State Heavy Ion Beams. MAC, (2013) Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 5

Momentum spread of SIS18 coasting beam Debunching in the SIS18 § SC and UNILAC momentum spread are the main sources of the SIS18 momentum spread TK f TK =36 MHz Alvarez Minimum momentum 2 + 2 K L Δ f = Δ i SIS18 spread given by SC η 2 z m , i f 0 =214 kHz 2.5 Measurement Ar 18+ Model 2.0 SC energy § SC energy of the micro-bunches is transformed 1.5 ∆ / 10 -3 into incoherent thermal momentum spread 1.0 § Since the SC effect depends on bunch length, 10 -3 the micro-bunches are stretched in TK 0.5 § Further optimization might be possible 0.0 0 1 2 3 4 5 I / mA S. Appel, O. Boine-Frankenheim, Phys. Rev. ST Accel. Beams 15, 054201 (2012) Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 6

Multi-turn injection (MTI) into SIS18 SIS18 electrostatic injection septum Injected Septum Beam Cathode Orbit bumps Orbit bumps Circulating beam 300 kV Reduction of Anode orbit amplitude SIS18 flexibility in providing a broad range of ions Measured MTI performance in SIS18 allow only Liouvilian injection schemes 30 Modell m= I MTI has to respect Liouville’s theorem: U 28+ current in mA I 0 Injected beams only in free space 20 The beam from linac is injected until machine 10 ≈20 turns acceptance is reached and maximize intensity T rev ≈5 μs 0 Loss at septum and acceptance should be as low as 0 50 100 150 possible due to loss induced dynamic vacuum time in µ s Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 7

MTI into SIS18: Model § Multi-objectives: I max( m ) I = mI 0 - stacked current (maximize) output 1-2 m min( η ) η = I loss - beam loss (minimize) m = (1 − η ) n nI 0 - emittance f x § Constraints: n x s - Position of septum - A Machine acceptance Model in φ i ( Q x ) - Closed orbit (bumper kick) simulation code x' Septum § Parameters: Acceptance x c , ′ - Position of incoming beam at septum x c , M x 0 , ′ x 0 , τ - Initial bump amplitude and its decreasing x t - Injected turns n - Horizontal tune Q x - Horizontal emittance x f x - Coupling strengths k Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 8

Multi-turn injection into SIS: Movie horizontal Gain factor ----- Acceptance Septum Normalized coordinates 15 turns injection with 15% loss vertical Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 9

Multi-turn injection into SIS: Optimization problem The analytically description characterize: Loss minimization at septum: tune Incoming beam position and this mismatch Linear orbit bump reduction: tune + size Unfortunately the MTI model is underrepresented: A few variables can be choose freely from a value range GA optimized MTI Discover by trial and error optimum settings or perform parameter scans Acceptance Septum Scan New approach is the use of genetic algorithms (GA) and particle swarm (PA) Darwin Finches J. Gould, Voyage of the Beagle Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 10

Multi-turn injection into SIS18 Optimization of loss Genetic algorithms can improve MTI Especially for longer injection GA discovers a much better solution Optimization of loss and gain factor 40 no sc 35 sc Dependence of gain factor on loss 30 previous studies 25 η [%] 20 Loss-free injection could be found 15 10 Space charge results in a similar PA front, but 5 with different injection settings 0 6 8 10 12 14 16 18 m Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 11

Multi-turn injection into SIS18 Optimization of loss, gain factor and beam emittance (injector) Dependence of interface parameter B= I m( η )= N I qf 0 ε 12.2 mA 13.2 mA 14.2 mA allows to define a frame, in which the required beam parameter can be matched at best for a high performance This crucial information gives more flexibility for the injector upgrade layout. New Alvarez DTL provide requirement beam brilliance (including errors) A. Rubin, Beam dynamics design of the new FAIR post-stripper linac, S. Appel et al: Nucl. Instrum. Methods A 852 (2017), pp. 73-79 GSI Accelerator Seminar, 14.05.17 Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 12

Multi-turn injection Smaller beam emittance increase MTI performance Titled septum Available acceptance limited MTI performance Y Besides the horizontal phase space, the vertical one can also be exploited, which can lead to higher gain factors Ø Titled septum or skew quadrupoles X m = A ε x = ε y d ≈ 1.5 − 2 Two Single plane: d ε Gain factor A x = 3 A y m = A x A y d ≈ 8 − 10 Two plane: d ε x ε y Single Emittance G.H. Rees in Handbook of accelerator physics and engineering Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 13

Multi-turn injection (Two plane) BRing of Titled septum HIARF project Need new technical development Titled septum and magnets in transfer line Coordinate rotation system Four additional bumpers (vertical) Emittance Skew quadrupoles ε x Using installed skew quadrupoles Linear coupling of hor. and ver. phase space Skew strength should be swift off after injection ε y Turns Which gain factors can be reached for a given beam emittance and loss for SIS18? For conventional, skew and titled septum injection? Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 14

Injector brilliance depending EMittance Transfer EXperiment (EMTEX) One consequence of single-plane MTI is that the required horizontal Gain factor m = A injection emittance is very demanding; to the other plane not. d ε Re-partitioning of the injected beam emittances: round-to-flat transformation would increase the injection efficiency Emittance EMTEX Beam line Repartition with constant emittance product: Effective solenoid exit fringe field + skewed quadrupole triplet Twiss-parameters are preserved Beam flatness amount is controlled by solenoid field The effective solenoid exit fringe field is created by changing the ion charge state L. Groening: Phys. Rev. ST Accel. Beams 14 064201 (2011) L. Groening et al: Phys. Rev. Lett. 113 264802 (2014) C. Xiao et al: Phys. Rev. ST Accel. Beams 16 044201 (2013) S. Appel et al: Nucl. Instrum. Methods A 866 (2017), pp. 36-39 Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 15

Injector brilliance depending EMittance Transfer EXperiment (EMTEX) MTI performance has been measured as a function of the amount of beam flatness flat beam y x round beam y x Excellent agreement between simulation and measured injection performance was achieved thanks to fast adjustment of the beam flatness without changing other beam parameters. Sabrina Appel | Accelerator Physics 10/10/2017 GSI Helmholtzzentrum für Schwerionenforschung GmbH 16