K. Buesser & N. Walker TF Studies: A very first look.
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Transcript of K. Buesser & N. Walker TF Studies: A very first look.
![Page 1: K. Buesser & N. Walker TF Studies: A very first look.](https://reader035.fdocuments.in/reader035/viewer/2022062519/56649cb55503460f94978c76/html5/thumbnails/1.jpg)
K. Buesser & N. Walker
TF Studies: A very first look
![Page 2: K. Buesser & N. Walker TF Studies: A very first look.](https://reader035.fdocuments.in/reader035/viewer/2022062519/56649cb55503460f94978c76/html5/thumbnails/2.jpg)
What is required for TF?
z
y
Shift the waist (focal point) of each z-slice by -z/2
Apply an additional (coherent) shift of -√3sz/2
Note: Guinea Pig applies to both planes
First idea: use strong sextupole in FD with fast orbit bump to generate additional focus over bunch length (crab cavity)
![Page 3: K. Buesser & N. Walker TF Studies: A very first look.](https://reader035.fdocuments.in/reader035/viewer/2022062519/56649cb55503460f94978c76/html5/thumbnails/3.jpg)
Generating The Crab Waist
IP
crab cavity location
FD
metre from IP
R12
(m
)
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Effectiveness of Orbit Bump
Waist shifts at IP as a function of horizontal kick at cavity location
dWx/dq ~ 7×105 m dWy/dq ~ 7×103 m
Very small kick required (<% s)Very linearFactor 100 stronger in x than y (not unexpected)
(Ideally we would like to have two independent knobs)
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Impact on beam size
Relative change in beam size at the shifted waist as a function of kick
Typically <1% effect for <1% s kick
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Required Cavity Kick for TF
• Can’t control both so just set vertical
• Waist shift of particles at z in bunch = z/2– i.e. dWy/dz = ½ [ dW⇒ x/dz = 50 !]
• At crab cavity:dq/dz = 0.5 / 7×103 = 7.14×10-5 m-1
– 300mm × dq/dz = 20 nrad (0.003s)
• For a 1.3 GHz cavity / 250 GeV: V = 650 kV
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Comments on Tracking Simulation
• Gaussian 6D bunch generated first at IP
• Initial coherent waist shifts (√3sz/2) applied numerically.– In real world assume this to be done with waist knobs.
• Back-tracked through FFS to location of cavity to provide initial tracking distribution– Generates the correct correlations in bunch
• Required horizontal crab-kick applied and particles tracked forward to the IP
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Initial Results
• Tracked particle files (electrons/positrons) used in Guinea Pig
• First result showed reduction of luminosity by ~30% (i.e. 1.4×1034)
horizontal beam size at IP shows increased width (due to large crab waist shift?)
Vertical looks superficially good.
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Guinea-Pig Simulations
• Simulated interactions for– RDR 500 GeV– SB2005 500 travelling focus– SB2005 500 no travelling focus
• Dependency of luminosity vs vertical beam offsets
• Depenency of luminosity on gaussian vertical beam jitters
• Dependency of vertical kicks vs beam offset
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Vertical Kick vs Beam Offsets
RDR-500 (left), TF-500 (right)
Kick angle (urad)
Kick angles RMSIn each bunch (urad)
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Lumi vs Vertical Offset
RDR-500 (top)
SB2009 500-nTF (middle)
SB2009 500-TF (lower)
Offset in Sigma_y:5.7 nm for RDR5.9 nm for 500-
nTF3.8 nm for 500-TF
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Lumi vs Vertical Beam Jitter
RDR-500 (top)
SB2009 500-nTF (middle)
SB2009 500-TF (lower)
Offset in Sigma_y:5.7 nm for RDR5.9 nm for 500-
nTF3.8 nm for 500-TF
Error bars show RMS of lumi distributions