NLC Intra-PulseFast Feedback

Simon Jolly

Oxford University

NLC Beam Delivery Meeting

July 2001

Simon JollyOxford University 2

Before we begin...QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

I have stolen parts of this talk from: Glen White, Steve Smith, PT and then some…..

Simon JollyOxford University 3

Plan of Action

• Requirements of a feedback system.• Current design:

– Physical specs.

– Signal filtering electronics.

– Simulated performance.

• Current status and planned tests.• Track reconstruction.• A brief word on beam jitter.• Short term and long term plans.

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Simon JollyOxford University 4

Fast Feedback - Who needs it…?

• Jitter inherent in beams and accelerating structures - leads to relative position offset of beams.

• Position offset leads to

large luminosity loss:

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Y position offset (y)

Percentage Luminosity Loss

0 10 20 30

40

20

40

60

80

100

Simon JollyOxford University 5

Fast Feedback - System Constraints

• Recover significant amount of lost Luminosity.• Correct offset within a single bunch train (266ns -

hence ‘fast’...).• Dominant time factor should be distance to IP,

NOT speed of feedback - too fast for ‘analytical’ electronics.

• Be unaffected by intra-train jitter…..

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

A corrective feedback system needs to:

Simon JollyOxford University 6

NLC Fast Feedback SystemQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

System consists of 3 components:

•BPM (+ BPM processor).

•bunch charge gain adjuster. •Kicker (and kicker driver).

Bunch Charge

Use beam-beam interaction to enhance offset measurement

4m

Simon JollyOxford University 7

Design of Feedback System

• Initial system design and “proof of principle” in Simulink simulation by Steve Smith.

• Glen White (Oxford) simulation makes a number of improvements:– Includes “gain” effects.

– Accurate beam-beam interaction model - original flat beyond 12 (GUINEA-PIG).

– Effects of intra-train (bunch-to-bunch) jitter considered.

• System currently only corrects position offset (no angle jitter).

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Simon JollyOxford University 8

Simulink Block DiagramQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Beam parameters (posn. and charge) Beam-beam

interaction

BPM processor

Beam kicker

Delay cable

Effect of kicked beam

Flight of bunches from/to IP

BPM to kicker transport delay

Simon JollyOxford University 9

BPM Processor

Most signal conditioning executed by BPM processor

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Bunch Charge

But what does it do…?

Simon JollyOxford University 10

BPM ElectronicsQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Band pass filter Mixer Low pass filter

Simulink diagram for BPM processor

Local oscillator for mixer

2nd stripline

1st stripline

Sum and difference

Simon JollyOxford University 11

BPM Signal FilteringQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Time (ns)5 10 2515 20 30

Signal on BPM

Mixer output

Band pass filter output

Low pass filter output

Simon JollyOxford University 12

BPM Electronics OutputQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Time (ns)0 100 200 266

BPM processor output

Position of bunch at BPM

Signal from delay cable (Kicker)

Kicker input (BPM + delay signal)

Simon JollyOxford University 13

Beam Correction at IP (Simulink)QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Time (ns)0 100 200 266

Vertical offset (nm)

0

-8

-6

-4

-2 Uncorrected beam position at IP

Corrected beam position at IP

Simon JollyOxford University 14

Effect of Feedback SystemQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Effect of the feedback system on the luminosity loss (Glen White).

0 5 10 15 20 25 30 35 400

10

20

30

40

50

60

70

80

90

100

Vertical Beam Offset ( y )

% Luminosity Loss

Feedback Off = 4.0 Gain × 10-6

= 5.0 Gain × 10-6

= 6.4 Gain × 10-6

Y position offset (y)

Simon JollyOxford University 15

What Happens Next?QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

• Bench test BPM electronics.• Beam test of stripline BPM and electronics.• Confirm design of kicker dimensions and power

requirements - dependant upon location, train structure.

• Beam test of complete system (location on a need to know basis….).

• Reconstruction of tracks in beam test use PT’s Collimator Wakefield Matlab routines.

Simon JollyOxford University 16

Collimator Wakefields (PT)

• 4 collimation slots used.• Determination of bunch kick due to

wakefield effects.• To reconstruct kicks:

– Measure positions of bunches (25 per step) along sector 2.

– Subtract ‘reference’ track (100 bunches).

– Use transport matrices to reconstruct bunch position and angle at slot. Collimator slot

dimensions

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Simon JollyOxford University 17

Reconstructed wakefield kickQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Collimator slot height vs. angle deviation

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Simon JollyOxford University 18

Reconstructed kicks (slot 1)

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Simon JollyOxford University 19

Angular Jitter on Kick ReconstructionQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Wakefield box slot y posn. (mm)

RMS angular jitter (r)

0-0.5-1 0.5 10

0.5

1.0

1.5

2.0

2.5

Collimator slot height vs. angular jitter for reconstructed wakefield kicks (slot 1)

1.4-1.4

3.5

3.0

4.0

Simon JollyOxford University 20

2D Histogram of beam jitter

A Quick Look at Position JitterQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Data taken from 160 data samples over 12 days

XY

500 x 500 m

Simon JollyOxford University 21

X and Y jitter on SLC e- beamQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

x distance from mean orbit posn. (m)

Histogram of jitter in x Histogram of jitter in y

y distance from mean orbit posn. (m)

0 50 100-100 -500 50 100-100 -50

x = 17.65 m y = 14.34 m

Simon JollyOxford University 22

Time Dependence of JitterQuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Run number

Beam jitter in y for 3 BPM’s

y (m)

Chart shows beam jitter (rms deviation from mean) for 3 BPM’s during 160 runs. Each point is rms of y position for 100 bunches (1 reference scan).

Includes 12 days worth of data.

Simon JollyOxford University 23

Time Dependence of Jitter (2)QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

Run number

0 40 80 120 160

Beam jitter in y for 7 BPM’s BPM #

114

146

301

411

511

631

801

Simon JollyOxford University 24

And Finally...

• Next step is to bench test BPM electronics.• Start looking at possible solutions for kicker

design.• Longer term: beam tests of BPM systems, kicker

design and complete system.• Very very long term: install system in the NLC….

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.