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

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 Ben ConstanceIoP HEPP/APP annual meeting 2010

~31 km The International Linear Collider and its beam structure 2Ben ConstanceIoP HEPP/APP annual meeting 2010 The ILC beam design is as follows: Pulsed operation at 5Hz, each pulse contains 2625 bunches Bunches separated by 370ns and contain 2x10 10 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

The ILC luminosity goal Luminosity target of cm -2 s -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 3Ben ConstanceIoP HEPP/APP annual meeting 2010

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 4Ben ConstanceIoP HEPP/APP annual meeting 2010

Beam-beam kick simulation 5Ben ConstanceIoP HEPP/APP annual meeting 2010

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 6Ben ConstanceIoP HEPP/APP annual meeting 2010

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 7Ben ConstanceIoP HEPP/APP annual meeting 2010

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

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 9Ben ConstanceIoP HEPP/APP annual meeting 2010

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 10Ben ConstanceIoP HEPP/APP annual meeting 2010 QD10XQF11XQD12XQD14XQF13XQF15XK1K2 P2P3P1 To dump FB board DAQ

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! 11Ben ConstanceIoP HEPP/APP annual meeting 2010

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 1x10 9 up to 5x10 9 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 2 nd bunch The corrected 2 nd bunch is then measured to produce a feedback for the 3 rd bunch, and so on 12Ben ConstanceIoP HEPP/APP annual meeting 2010

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

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

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

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

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 17Ben ConstanceIoP HEPP/APP annual meeting 2010

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 18Ben ConstanceIoP HEPP/APP annual meeting 2010