NLC - The Next Linear Collider Project

Intra-PulseBeam-Beam Scans

at theNLC IP

Steve SmithSnowmass 2001

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Beam-Beam Scans• Ultimate collider diagnostic

– Spots sizes– Alignment– Waists– Etc. etc. etc…

• Some Limitations:– Takes lots of time at one measurement per pulse train– Sensitive to drifts over length of scan

• Machine drifts• low frequency noise

• Can we do a scan in one bunch train?– Increase utility of diagnostic by increasing speed– Reduce sensitivity to drift and low frequency noise

• Yes– Leverage hardware from intra-pulse IP feedback.

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Intra-pulse Feedback

• Fix IP jitter within the crossing time of a bunch train (250 ns)

• BPM measures beam-beam deflection on outgoing beam– Fast (few ns rise time)

– Precise (~micron resolution)

– Close (~4 meters from IP?)

• Kicker steers incoming beam– Close to IP (~4 meters)

– Close to BPM (minimal cable delay)

– Fast rise-time amplifier

• Feedback algorithm to converge within bunch train.

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Intra-Pulse Feedback

Amp

BPMProcessor

IP Round Trip Delay

+

Amp

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Intra-Pulse Feedback(with Beam-Beam Scan & Diagnostics)

Amp

BPMProcessor

IP Round Trip Delay

Digitizer

Beam-Beam Scan& Diagnostics

Ramp

+

Amp

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Single-Pulse Beam-Beam Scan

• Fast BPM and kicker needed for interaction point stabilization

• Open the loop and program kicker to sweep beam

• Digitize fast BPM analog output

• Acquire beam-beam deflection curve in a single machine pulse

• Eliminates inter-pulse jitter from the beam-beam scan.

• Use to

• Establish collisions

• Measure IP spot size

• Waist scans.

• What else?

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Beam-Beam Scan

Beam bunches at IP: blue points

BPM analog response: green line

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Conclusions

• Given Intra-Pulse Interaction Point Feedback, we have tools to perform beam-beam scans within the bunch train.

• Speeds up beam-beam scans by an order of magnitude, maybe more.

• Increases the number of parameters which can be optimized by beam-beam scans, or the optimization update frequency.

• Reduces low frequency noise in beam-beam scans– Machine drifts

– 1/f noise

• Valuable

• Cheap!

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Limits to Beam-Beam Feedback

• Must close loop fast– Propagation delays are painful

• Beam-Beam deflection slope flattens within 1 • Feedback converges too slowly beyond ~ 20 to make a

difference in luminosity

• May be able to fix misalignments of 100 nm with moderate kicker amplifiers

• Amplifier power goes like square of misalignment

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Beam-Beam Deflection

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Simulated BPM Processor Signals

BPM Pickup (blue) Bandpass filter (green)and BPM analog output (red)

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Beam Position Monitor

• Stripline BPM– 50 Ohm

– 6 mm radius

– 10 cm long

– 7% angular coverage

– 4 m from IP

– Process at 714 MHz

• Downconvert to baseband

• (need to phase BPM)

• Wideband: 200 MHz at baseband

• Analog response with <3ns propagation delay (plus cable lengths)

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Fast BPM Processor

TopStripline

BottomStipline

RFHybrid

Bandpassfilter

Lowpassfilter

TimingSystem

ProgramableAttenuator

MPSNetwork

MIXER

Bessel4-pole

714 MHz360 MHz BW

Bessel3-pole

200 MHz

(Bunch Charge)

NormalizeBPM to

Bunch Charge

714 MHzPhase Reference

Kic

ke

rD

rive

Fast BPM Processor Block Diagram

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Stripline Kicker

• Baseband Kicker– Parallel plate approximation = 2eVL/pwc

• (half the kick comes from electric field, half from magnetic)

– 2 strips

– 75 cm long

– 50 Ohm / strip

– 6 mm half-gap

– 4 m from IP

– Deflection angle = eVL/pwc = 1 nr/volt

– Displacement at IP d = 4 nm/volt

– Voltage required to move beam 1 (5 nm) 1.25 volts (30 mW)

– 100 nm correction requires 12.5 Watts drive per strip

– Drive amp needs bandwidth from 100 kHz to 100 MHz

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Capture Transient

Capture transient from 2 initial offset

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Next Linear ColliderNext Linear Collider

Steve Smith Snowmass 2001

Capture Transient

Capture transient from 10 initial offset

(gain increased to improve large offset capture)