Magnet Motion Produces Luminosity Loss

NLC Feedback Operation

Kicker Gain

Bunch Charge

•Measure deflected bunches with BPM and kick other beam to eliminate vertical offsets at IP

•Feedback loop assesses intra-bunch performance and maintains correction signal to the kicker

•Minimise distance of components from IP to reduce latency

Feedback Performance vs. Gain

[[0 SIGMA_Y]; [267e-9 0]]

Y Posi tionBeam 2

[[0 Y_OFFSET ]; [267e-9 0]]

Y Posi tionBeam 1

Terminator

In1

In2

Store Beam Info

Round-tripDelay

In1

Kicker Angle

Kicker Monitor

Kicker

IP angle Def lection at BPM

IP-to-BPMDynamics

IP scope

Beam 1

Beam 2Out1

IPDynamics

1

Gain1

1Gain

[[0 bunch_charge]; [250e-9 0]]

Bunch ChargeBeam 2

[[0 bunch_charge]; [ 250e-9 0]]

Bunch ChargeBeam 1

Q

Y Out1

Beam2

Q

Y Out1

Beam1In1 Out1

Beam Ji tter

BeamQ

Y

BeamParameters

BPMCableDelay

Kick angleKick at IP

BPM-to-IPDynamics

BPMScope

Beam In Position Out

BPM

Latency ~ 37 nsLatency ~ 37 ns

Luminosity Performance w. Feedback

•Lower gains gives better performance at smaller offsets, higher gains give better performance at higher offsets

•Vary gain dependent on observed beam conditions

0 5 10 15 20 25 30 35 400

10

20

30

40

50

60

70

80

90

100

Vertical Beam Offset ( sy )

% L

um

ino

sity

Lo

ss

Feedback OffGain = 4.0 ́10 -6

Gain = 5.0 ́10 -6

Gain = 6.4 ́10 -6

Feedback Performance w./ 2-stage Gain

•Gains chosen automatically based on linearisation of beam-beam kick curve.

•Gives good luminosity performance over whole offset region.

FONT Beam Test on the NLCTAQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Colliding beams Single beam

BPM

Kicker

BPMProcessor

KickerAmplifier

Round-tripDelay

(short cable delays, long trip time)

(shorten trip time, lengthen cable delays)

NLC NLCTA

4.5m

NLCTA LayoutQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Gun Chicane Structures BeamDump

FONT region

NLCTA FONT InstallationQuickTime™ and aPhoto - JPEG decompressor

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Magnet assembly and X-band BPM installed onto NLCTA downstream of RF structures.

Feedback loop

Beam direction

Magnet AssemblyQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Kicker

Dipole

X-band button BPMQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Pickups

BPM installed in NLCTAPickups tuned to 11.424 GHz

Results: 27 Sept 2002~x10 Improvement in Position

BPM for 5 Dipole Settings

After 1 Latency Period Position

corrected independent of gain, then loop

“turns off”

As above but loop ON:

Beam stays corrected

until end of pulse