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~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
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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 2010
1Ben Constance IoP HEPP/APP annual meeting 2010
~31 km
The International Linear Collider and its beam structure
2Ben Constance IoP 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 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
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
3Ben Constance IoP 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 Constance IoP HEPP/APP annual meeting 2010
Beam-beam kick simulation
5Ben Constance IoP 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 Constance IoP 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 Constance IoP HEPP/APP annual meeting 2010
FONT5 at the ATF2 extraction line
8Ben Constance IoP 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 Constance IoP 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 Constance IoP HEPP/APP annual meeting 2010
QD10X QF11X QD12X QD14XQF13X QF15XK1 K2
P2 P3P1
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 Constance IoP 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 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
12Ben Constance IoP 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 Constance IoP HEPP/APP annual meeting 2010
Beam test results (2)
• Upstream corrector dipole magnet used to introduce a variety of beam offsets
14Ben Constance IoP 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 Constance IoP HEPP/APP annual meeting 2010
Latest beam test results (4) – jitter reduction
• Repeated this experiment 18/02/10 for 25 minutes
16Ben Constance IoP 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 determinedby calibration
17Ben Constance IoP HEPP/APP annual meeting 2010
2 2 12 1 22 2 3 3 13 1 23 2
2 3
,0
y y g g y y g gy y
22 3 23 2 13 2 12 3
1 212 23 22 13 12 23 22 13
,g y g y g y g yg g g g g g g g
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 Constance IoP HEPP/APP annual meeting 2010