IoP HEPP/APP annual meeting 2010

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


• 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


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


Beam-beam kick simulation


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


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


FONT5 at the ATF2 extraction line


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


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


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!


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


Results from winter 2009/10 beam tests

P2 – to – K1 feedback loop closed and analysed

• Position feedback performed

(see simulations to the right)


Beam test results (2)

• Upstream corrector dipole magnet used to introduce a variety of beam offsets


Latest beam test results (3) – jitter reduction

• We allowed the feedback to operate on a nice beam 17/02/10


Latest beam test results (4) – jitter reduction

• Repeated this experiment 18/02/10 for 25 minutes


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


2 2 12 1 22 2 3 3 13 1 23 2

2 3

,

0

y y g g y y g g

y 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 y

g 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


IoP HEPP/APP annual meeting 2010

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