Experimental Beam Physics Program at Fermilab s IOTA Ring

Transcription

1 Experimental Beam Physics Program at Fermilab s IOTA Ring Sergei Nagaitsev Fermilab 2014 Advanced Accelerator Concepts Workshop July , San Jose, CA

2 Acknowledgements A.Burov, K.Carlson, A.Didenko, N.Eddy, V.Kashikhin, V.Lebedev, J.Leibfritz, S.Nagaitsev, L.Nobrega, G.Romanov, A.Valishev, S.Wesseln, D.Wolff (FNAL), D.Shatilov, A.Romanov (BINP), G. Kafka (IIT) S. Danilov (ORNL), S. Antipov (U of Chicago) J. Cary (Tech-X) D. Bruhwiler, S. Webb (RadiaSoft) F.O Shea, A.Murokh (RadiaBeam) JINR (Dubna) MIT 2

3 ASTA at Fermilab : Schematically 3

4 ASTA Parameters Parameter Value Range Unit Comments MeV/m maximum is subject of R&D Cavity gradient Energy MeV Bunch charge nc Bunch spacing ns Bunch train T ms Train rep rate Hz 1500 MeV with 6 cryomodules maximum determined by cathode QE and laser power maximum limited by modulator and klystron power minimum may be determined by egun T-regulation and stability considerations Depends on bunch charges and Emittance rms norm 5 <1 >100 m laser configuration Function of charges & compressor Bunch length rms ps design (two stages needed for Peak current 3 >9 ka 3 ka with low energy bunch compressor; 9 ka possible with 3.9 GHz linearizing cavity 4

5 Super-conductive RF Research and Development CC2 installed at ASTA 1 cavity ILC Milestone 31.5 MV/m Collaboration: DESY, INFN, SLAC, ANL, JLab Status: system tests without beam Operations start: late 2015 (with beam) 5 CC1 1 cavity

6 Electron photo-injector commissioning Beam line installed up to the dump in front of the Cryo Module Electron gun: 5 MeV, 3-nC achieved 6 Toroid: 3-nC bunches Faraday cup 150 s pulse

7 IOTA (Integrable Optics Test Accelerator) Component production and procurement 2014 and 2015 Installation in 2015 and 2016 e- beam to IOTA in 2016 HINS move in 2016 with commissioning in

8 ASTA : Downstream part (now) beam dump IOTA 8

9 IOTA Parameters Nominal e - beam energy 150 MeV(γ=295) or lower Nominal e - beam intensity Circumference 40 m Bending field 0.7 T Beam pipe aperture 50 mm dia. Maximum b-function (x,y) 12, 5 m Momentum compaction Betatron tune 3 5 Natural chromaticity Transverse emittance r.m.s. 0.1 m SR damping time 0.6s ( turns) RF V,f,q 10 kv, 30 MHz, 4 Synchrotron tune Bunch length, momentum spread 2 cm,

10 IOTA Ring elements in hand Dipole magnets (ordered) 32 quads from JINR (Dubna) received Vacuum chambers for dipoles (received) 10 Magnet support stands from MIT (received)

11 IOTA ring research program Experimental demonstration of integrable optics lattice at IOTA FNAL, SNS, JINR, Budker INP, U. of Chicago, UMD Tech-X, RadiaBeam, RadiaSoft Optical Stochastic Cooling Demonstration at IOTA FNAL, LBNL, ANL Space Charge Compensation in High Intensity Circular Accelerators FNAL, CERN, SNS, UMD Experiments require the IOTA Ring Difficult to implement needed linear optics in existing facilities Lack of ring facilities in the US Our approach: use electrons first then protons 11

12 Integrable Optics Experiments 12

13 Motivation The main feature of all present accelerators linear focusing lattice: particles have nearly identical betatron frequencies (tunes) by design. Such machines are built using dipoles and quadrupoles. All nonlinearities (both magnet imperfections and specially introduced) are perturbations and make single particle motion unstable due to resonant conditions S.Nag aitsev, IOTA Progra 13 m x

14 System: linear FOFO; 100 A; linear KV w/ mismatch Result: quickly drives test-particles into the halo Space Charge Effects in Linear Optics Lattice dq_sc ~ -0.7 Tech-X, RadiaSoft simulations passes; beam core (red ) is mismatched; halo (black dots) has 100x lower density

15 Halo formation from beam mismatch Particle-core halo model [Wangler, Gluckstern, Fedotov, others] D.L. Bruhwiler, Lowest-order phase space structure of a simplified beam halo Hamiltonian, AIP Conf. Proc. 377, p. 219 (1996). LEDA and UMER (NA PAC 13, H.D. Zhang et al.) have confirmed the theoretical basis for halo formation in spacecharge dominated beams Linear optics + breathing mode => parametric resonance is the engine driving particles into halo IOTA goal is to suppress beam halo 15

16 Motivation: Landau damping Report at HEAC 1971 CBX layout (1962) 16 S.Nag aitsev, IOTA Progra m 1965 Priceton-Stanford CBX: First mention of an 8-pole magnet Observed vertical resistive wall instability With octupoles, increased beam current from ~5 to 500 ma CERN PS: In 1959 had 10 octupoles; not used until 1968 At protons/pulse observed (1 st time) head-tail instability. Octupoles helped. Once understood, chromaticity jump at transition was developed using sextupoles. More instabilities were discovered; helped by octupoles, fb

17 Let s add non-linearity Betatron oscillations are no longer isochronous: The frequency depends on particle amplitude Stability depends on initial conditions Regular trajectories for small amplitudes Resonant islands (for larger amplitudes) Chaos and loss of stability (for large amplitudes) octupole S.Nag aitsev, IOTA Progra 17 m

18 Motivation - summary The Strong Focusing principle, invented in 1952, allowed for a new class of accelerators to be built and for many discoveries to be made, e.g.: Synchrotron light sources: structure of proteins Proton synchrotrons: structure of nuclei Colliders: new elementary particles However, chaotic and unstable particle motion appears even in simplest examples of strong focusing systems with perturbations A nonlinearity shifts the particle betatron frequency to a resonance (nω = k) The same nonlinearity introduces a time-dependent resonant kick to a resonant particle, making it unstable. It is the driving term and the source of resonances simultaneously S.Nag aitsev, IOTA Progra 18 m

19 Focusing: linear vs. nonlinear Accelerators are linear systems by design (freq. is independent of amplitude). In accelerators, nonlinearities are unavoidable (SC, beam-beam) and some are useful (Landau damping). All nonlinearities (in present rings) lead to resonances and dynamic aperture limits. y Are there magic nonlinearities with zero resonance strength? k x l y x m The answer is yes (we call them integrable ) 3D: S.Nag aitsev, IOTA Progra 19 m H F( J1, J2, J3)

20 Nonlinear focusing systems Search for solutions that are strongly nonlinear yet stable Orlov (1963) not successful McMillan (1967) first 1D solution Perevedentsev, Danilov (1990) generalization of McMillan case to 2D, round colliding beams. Require non-laplacian potentials to realize Round colliding beams possess VEPP-2000 at BINP (Novosibirsk, Russia) commissioned in Record-high beam-beam tune shift ~0.25 attained in 2013 Chow, Cary (1994) Nonlinear Integrable Optics: Danilov and Nagaitsev solution for nonlinear lattice with 2 invariants of motion that can be implemented with Laplacian potential, i.e. with special magnets Phys. Rev. ST Accel. Beams 13, (2010) S.Nag aitsev, IOTA Progra 20 m

21 2D Generalization of McMillan Mapping 1D thin lens kick p 2D a thin lens solution can be carried over to 2D case in axially symmetric system S.Nag aitsev, IOTA Progra 21 m i x i x i 1 p i 1 f ( x ) ci si si ci i f ( x) Ax 1. The ring with transfer matrix 2 p 2 Bx Dx Ax Bx C 2 2 c cos( ) s sin( ) 1 0 I p xp C x p Dxp const B x 2. Axially-symmetric thin kick () r kr 2 ar 1 Can be created with electron lens

22 Research goals Our goal is to create practical nonlinear accelerator focusing systems with a large frequency spread and stable particle motion. Benefits: Increased Landau damping Improved stability to perturbations Resonance detuning S.Nag aitsev, IOTA Progra 22 m

23 Example: Nonlinear systems can be more stable! 1D systems: non-linear (unharmonic) oscillations can remain stable under the influence of periodic external force perturbation. Example: 2 z 0 sin( z) asin( 0t) 2D: The resonant conditions k ( J, J ) l ( J, J ) m are valid only for certain amplitudes. Nekhoroshev s condition guaranties detuning from resonance and, thus, stability. S.Nag aitsev, IOTA Progra 23 m

24 System: Integrable; 100 A; generalized KV w/ mismatch Result: nonlinear decoherence suppresses halo Integrable Optics Lattice with Space Charge dq_sc ~ -0.7 Tech-X, RadiaSoft simulations passes; beam core (red contours) is mismatched; halo (blue dots) has 100x lower density

25 Nonlinear Lenses Integrable Optics solutions: Make motion regular, limited and longterm stable (usually involves additional integrals of motion ) Can be Laplacian (with special magnets, no extra charge density involved) Or non-laplacian (with externally created charge e.g. special e-lens or beam-beam E(r) ~r/(1+r^2) Both types will be tested in IOTA 25

26 Integrable Optics at IOTA Main goals for studies with a pencil electron beam: Demonstrate a large tune spread of ~1 (with 4 lenses) without degradation of dynamic aperture ( minimum 0.25 ) Quantify effects of a non-ideal lens and develop a practical lens (m- or e-lens) 1.0 FMA, fractional tunes Large amplitudes ν y 0.5 Small amplitudes (0.91, 0.59) FNAL Concept: 2-m long nonlinear magnet SBIR Phase I and II: Radiabeam Technologies NA-PAC13: F. Shea et al., Measurement of Nonlinear Insert Magnets A single 2-m long nonlinear lens creates a tune spread of ~0.25 ν x 26

27 IOTA Layout In the ultimate integrable optics scenario: 4 elements of periodicity (cells) with four 2m-long drifts for nonlinear magnets 5m-long straight section for the Optical Stochastic Cooling experiment. OSC 27

28 Prior Research IUCF Cooler Ring: experiments CE-22 and CE-48 (DOEfunded, ) Nonlinear beam dynamics, study of 1D and 2D resonances and chaos 45 MeV protons (pc = 300 MeV) pencil beam (electron cooled) using kickers and BPMs studied phase-space trajectories 28

29 IOTA: What s new? IUCF Cooler experiments studied natural ring nonlinearities. Mostly linear system and a single isolated resonance No attempt was made to make the system highly nonlinear and integrable IOTA is the first step in controlling strong nonlinearities We are proposing 4 different studies with nonlinear lenses: 2 with an electron lens 2 with special electromagnets In all experiments the electron bunch is kicked transversely to sample nonlinearities. We intend to measure the turn-by-turn BPM positions as well as synch light to obtain information about phase space trajectories. 29

30 Two kickers create an arbitrary transverse kick Horizontal + vertical stripline kickers Rectangular pulses up to 25 kv ~ 100 ns duration. Repetition rate < 1 Hz Adjustable voltage 0 V max 07/17/14

31 Beam position can be measured precisely 20 horizontal and vertical BPMs Button type 1 μm closed orbit resolution 100 μm turn-by turn resolution 8 SR ports to measure beam size 31 07/17/14

32 Experimental procedure Two kickers, horizontal and vertical, place particles at arbitrary points in phase space Measure beam position on every turn to create a Poincare map As electrons lose energy due to synchrotron radiation, they will cover all available phase space Can control the strength on the nonlinearity Final goal measure dependence of betatron frequency on amplitude 07/17/14

33 Example: betatron frequency for various particle amplitudes (method: Frequency Map Analysis) Tune spread: /17/14

34 Optical Stochastic Cooling Experiment 34

35 Goal: Optical Stochastic Cooling Experiment Experimental demonstration of the optical stochastic cooling technique (1 st no optical amplifier, then with OPA) Why IOTA: Need IOTA low energy (~100 MeV minimal synchrotron radiation damping) flexible lattice e- storage ring Motivation: Beam cooling for high energy accelerators 35

36 Optical Stochastic Cooling Suggested by Zolotorev, Zholents, and Mikhailichenko (1994) OSC obeys the same principles as the microwave stochastic cooling, but exploits the superior band-width of optical amplifiers, ~10 14 Hz Pick-up and kicker must work in the optical range and support the same band-width as the amplifier Microwave pickups can not be scaled to µm Undulators were suggested Initial experiments can be done without an amplifier but eventually we will need state-of-art optical amplifier High power Low delay 36

37 Principles of OSC 37

38 OSC experimental set-up (λ = 2 µm) Beam by-pass delay: ~4 mm IOTA 38

39 Main Parameters of IOTA OSC experiment Natural SR damping rate: ~1 s -1 39

40 Space-Charge Compensation Experiment 40

41 Space Charge Compensation (Bringing Protons to IOTA) After the IOTA commissioning, we will move the High Intensity Neutrino Source (HINS) 2.5 MeV RFQ into the ASTA hall to inject protons into the IOTA ring. 2.5 MeV RFQ HINS Allows tests of Integrable Optics with protons and realistic Space-Charge beam dynamics studies Allows Space-charge compensation experiments Unique capability DQ SC ~1 per one-turn injection 41

42 Goal: Space-Charge Compensation in Circular Accelerators Experimental demonstration of the space-charge compensation technique with electron columns/electron lenses at dq_sc >1 Why IOTA: Need 2.5 MeV high-current protons and IOTA flexible lattice storage ring Relevant accelerators: All current and future high intensity proton rings (Booster, MI, all LHC injectors, MC rings, etc) 42

43 Space Charge Forces & Compensation SC B f r p 4 n N tot 2 Z, beam direction B= E r, across the beam 43

44 E-column concept E-lens concept 1. The impact of electrons is equal to the total impact of space-charge over the ring 2. The transverse profile of the electron is made the same as that of the proton beam use of solenoid N ˆ b, totrcb I Nercb sc 2 3 e I b b b ( Iˆ / I ) 3. The system of electrons and protons is dynamically stable two-stream instability suppression (nonlinear magnet) N N b, tot e 1 2 b NecL 0 C ec 44

45 International Collaboration for Space Charge Experiment at the IOTA Ring at Fermilab Collaborating institutions (at present): Fermilab, ORNL, CERN, RadiaSoft, UMD Work on the scientific case, hardware development, simulations, planning and execution of space charge compensation experiments with protons in IOTA Major topics Operation of IOTA with protons, injection, and space charge measurements Space charge compensation in nonlinear integrable lattice special magnets electron lens Space charge compensation with electron columns Space charge suppression with circular modes 45

46 A roadmap to high-intensity rings (low-losses, stable beams) 1. Develop the theoretical basis for nonlinear halo suppression (reduce beam losses) 2. Develop the theoretical basis of beam instabilities with strong space charge (stable beams) 3. Develop highly-nonlinear focusing lattices with reduced chaos (increased dynamic aperture) 4. Reduce chaos in beam-beam effects (increased dynamic aperture in circular colliders) 5. Ultimately, develop rings for super-high beam intensity Self-consistent or compensated space-charge Strong non-linearity (for Landau damping) to suppress instabilities Stable particle motion at large amplitudes 46

47 Summary IOTA (ASTA) scientific goals are well aligned with P5 priorities and DOE investments in Intensity and Energy Frontiers; IOTA: Great opportunity to try something new with circular accelerators; ASTA Cryomodule Testing: Our bread and butter R&D effort benefiting our the short- and mid-term projects. Modest contribution to the ILC R&D. 47