IoP HEPP/APP annual meeting 2010

1. Feedback on Nanosecond Timescales: maintaining luminosity at future linear colliders Ben Constance John Adams Institute, University of Oxford IoP HEPP/APP annual meeting 2010

2. Introduction • The problems associated with achieving high luminosity at linear colliders • Focus on ‘cold’ colliders – International Linear Collider bias… • Feedback system requirements • Description of the FONT interaction-point feedback system • FONT5 installation at the ATF, KEK Japan • Winter 2009/10 beam test results • Plans for spring 2010 Ben Constance IoP HEPP/APP annual meeting 2010 1

3. The International Linear Collider and its beam structure ~31 km • The ILC beam design is as follows: • Pulsed operation at 5Hz, each pulse contains 2625 bunches • Bunches separated by 370ns and contain 2x1010 particles • Structure driven by factors such as: • Klystron RF power sources and damping rings • Superconducting accelerating cavities • The long bunch spacing can be exploited for digital feedback Ben Constance IoP HEPP/APP annual meeting 2010 2

4. The ILC luminosity goal • Luminosity target of 1034 cm-2s-1 (same as the LHC target) • Single collision opportunity, therefore very small beams at IP • Just 5.7nm by 639nm at the interaction point • Need synchrotron cooling with damping rings • We can use very strong focussing not possible in a ring • Focus the beam so tightly at the IP that it is unstable afterwards • The positions of the beams must be very stable • Careful machine and beam alignment plus feedback systems Ben Constance IoP HEPP/APP annual meeting 2010 3

5. Fast IP feedback systems • Many effects can misalign the few nm beams, e.g. • Ground motion • Temperature fluctuations (cooling water, electronics) • Mechanical vibration • Bunch-by-bunch feedback • Determine the offset error of the first bunch after the IP • Calculate a correction to the next bunch’s position • Apply nm level correction before the next bunch reaches IP (< 370ns) • Repeat for entire train • IPFB makes use of beam-beam deflection after the IP • As the beams pass each other, they each receive a large kick • This kick is determined by the beams’ relative offset • Trivial to measure >100μm deflection after IP Ben Constance IoP HEPP/APP annual meeting 2010 4

6. Beam-beam kick simulation Ben Constance IoP HEPP/APP annual meeting 2010 5

7. The FONT project at the JAI • Feedback on Nanosecond Timescales • At JAI we are working on a digital bunch-by-bunch IPFB system for ILC • Measure deflection of one beam and correct the other • Delay loop ensures we retain and improve previous correction Ben Constance IoP HEPP/APP annual meeting 2010 6

8. ATF2 • FONT is currently being tested at ATF2 • The Accelerator Test facility in KEK, Japan • Designed to demonstrate ILC-like beam sizes • Single 1.3GeV electron beam, 150ns bunch spacing • Single linac, damping ring, extraction line • New final focus system Ben Constance IoP HEPP/APP annual meeting 2010 7

9. FONT5 at the ATF2 extraction line FONT5 installation region Final doublet and beam dump Ben Constance IoP HEPP/APP annual meeting 2010 8

10. ATF2 design goals • Demonstrate a 35nm beam size • New final focus installed • Beam characterisation and tuning very much in progress • Demonstrate nanometre–level stability • This needs micron stability at the entrance to final focus • FONT5 system has been commissioned to provide this • We have micron-resolution processors • Our kickers can provide micron-level corrections at ~1GeV • Resolution of FB system defined by smallest correction possible • A kick that provides 1μm correction at 1GeV provides 1nm correction at 1TeV • FONT goals at ATF and ILC are compatible Ben Constance IoP HEPP/APP annual meeting 2010 9

11. P1 P2 P3 To dump K1 QD10X QF11X K2 QD12X QF13X QD14X QF15X FB board DAQ FONT5 ATF2 beamline installation • Three stripline BPMs made to existing ATF ext. line specification • Two fast fixed-gap stripline kickers recovered from NLCTA (vertical orientation) • Next-generation FONT5 digital feedback board installed and operational • Flexible configuration allows a variety of feedback algorithms Control / feedback loops Ben Constance IoP HEPP/APP annual meeting 2010 10

12. FONT5 digital feedback board • Single feedback board controls multiple loops and all DAQ • Based around a powerful Xilinx Virtex5 FPGA • 9 ADC input channels at 357 MSPS (TI ADS5474) • 4 DAC output channels (AD9744) • Basic algorithm includes: • Removal of beam intensity fluctuations • Correction of extracted train shape • Compensation for kicker pulse droop • All signal mixing, DSP, amplification • plus rise of kicker takes place in < 130ns! Ben Constance IoP HEPP/APP annual meeting 2010 11

13. ATF pulse structure and feedback algorithm • We extract a three-bunch train • Repetition rate 2/3 Hz • Spacing variable from 140 – 154ns • Bunch charge from 1x109 up to 5x109 e- • FONT5 intra-train feedback • Aim is to reduce pulse-to-pulse jitter, i.e. correct jitter that is correlated between bunches • First bunch is a pilot bunch and is not corrected • 3 FONT BPM signals used to calculate intensity-independent position readings • Position values used to calculate 1 or 2 feedback signals and apply to kickers • Feedback signal applied to the 2nd bunch • The corrected 2nd bunch is then measured to produce a feedback for the 3rd bunch, and so on Ben Constance IoP HEPP/APP annual meeting 2010 12

14. Results from winter 2009/10 beam tests • P2 – to – K1 feedback loop closed and analysed • Position feedback performed • (see simulations to the right) Ben Constance IoP HEPP/APP annual meeting 2010 13

15. Beam test results (2) • Upstream corrector dipole magnet used to introduce a variety of beam offsets Ben Constance IoP HEPP/APP annual meeting 2010 14

16. Latest beam test results (3) – jitter reduction • We allowed the feedback to operate on a nice beam 17/02/10 Ben Constance IoP HEPP/APP annual meeting 2010 15

17. Latest beam test results (4) – jitter reduction • Repeated this experiment 18/02/10 for 25 minutes Ben Constance IoP HEPP/APP annual meeting 2010 16

18. Plans for spring 2010 • Two-loop angle feedback • Intend to close K1 and K2 FB loops simultaneously • Interaction between the two kickers means we must couple the loops • Coupling parameters easily determined • by calibration Ben Constance IoP HEPP/APP annual meeting 2010 17

19. Summary • Any future linear collider will require nm level stability at the IP • IPFB will be required • The FONT5 feedback system is installed and operational at ATF2 • Single-loop position feedback demonstrated • We will move on to two-loop angle feedback demonstration in the spring Ben Constance IoP HEPP/APP annual meeting 2010 18