Transcript Physics Division Future Plans

Summary of LHC-CC08 Workshop
Derun Li
Center for Beam Physics
Lawrence Berkeley National Laboratory
ICFA Mini-Workshop on Deflecting/Crabbing RF Cavity
Applications in Accelerators
Shanghai Synchrotron Radiation Facility
April 23 ~ 25, 2008
LHC-CC08
• First workshop on crabbing/deflecting cavity for luminosity
upgrade for LHC (Large Hadron Collider), jointly organized by
BNL, US LARP and CARE-HHH
• The workshop was held from Feb. 25 ~ 26, 2008 at Brookhaven
National Laboratory, New York
• 35 participants from 15 institutions and three continents around
the world
— Collider (LHC, ILC and KEK) and Light Source Communities
•
Beam dynamics (optics and beam instabilities)
•
RF physicists (NC and SC cavity and LLRF control)
•
Advanced computations
• Eight sessions
• A web site dedicated for LHC-CC activities & updates on future
progress
https://twiki.cern.ch/twiki/bin/view/Main/LHCCrabCavities
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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LHC-CC08 Web Page
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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LHC-CC08 Objectives
•
•
•
Define a road-map for a prototype crab cavity to be
installed for LHC luminosity upgrade
Discuss the associated R&D and beam dynamics
challenges
Eight sessions to discuss subtopics:
1.
2.
3.
4.
5.
6.
7.
8.
D. Li, LBNL
Introduction and Overview
Optics and LHC Integration
Crab Cavity Noise Effects
Design, Fabrication & Processing Challenges
Other Crab Cavity R&D in the World
Impedance Issues
RF Control
Discussion & Work Packages
LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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LHC-CC08 Program
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Key Conclusions (1)
• Frequency choice
— 800-MHz is the maximum, RF curvature may be critical, more
beam dynamics simulations are needed
— 400-MHz is preferred, but limited by available space
• 10-m at IP4 and 20-m at IP5, plus transverse space constrains (40cm at IP4)
— Choice of cavity structure
• Exotic geometries
• Conventional: cylindrical and squashed cavity geometry with LOM
and HOM damping
— Global and local schemes
• Global might be feasible
• Collimation has to evaluate the exact loss maps and additional heat
deposition from bunch oscillating
• Configuration must allow for an additional 0.5 orbit
D. Li, LBNL
LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Key Conclusions (2)
• Noise effect
— Need more strong-strong simulations to understand
remaining issues but current estimates and RF jitter
suggest that LLRF can keep the jitter within required
tolerances
— RF Control:
• Qext : 105 ~ 106
• Power handling - beam pipe coax + ferrites robust for high
currents
• Phase jitter can be controlled easily 1×10−2 degrees
• Need <1×10−3 degrees, the limit of the existing technology at
800-MHz
• Power Amplifiers
– IOT: 50 ~ 100 kW
D. Li, LBNL
LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Key Conclusions (3)
• Design, Fabrication and Processing
— Crabbing voltage of 2.5-3-MV for 2-cell 800-MHz cavity
• Epeak < 40 MV/m, Bpeak < 120 mT
— 1-2 crabbing cavity structures per beam
— Additional degrees of freedom from optics
— Squashed geometry is favored with a reasonable ratio of ~0.75 squash
ratio to fabricate and will fit for new optics with VV crossing
— Cavity iris aperture > 10-cm diameter
— Various designs of couplers available, beam pipe coax and
waveguides, WGs may be most effective and robust
• Cavity Impedance
— Both broad and narrow bands need to be simulated carefully to avoid
single and coupled bunch instabilities
D. Li, LBNL
LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Key Conclusions (4)
R&D Objectives
— Adapt from previous R&D achievements and experience
• KEK-B collider, ILC, light sources, etc.. on
– LLRF control
– Power couplers
– LOM and HOM couplers and damping
– Cryostat (LHC)
– Tuners
— Priorities
• Collimation studies
• Impedance
• Final cavity design and couplers, common cryostat
— Simulations
— Measurement on models (prototypes) and testing with beam.
— Investigate the potential and feasibility of compact cavity shapes and
associated multipacting problems
• Exotic cavities, open damping slots on cavity equator, spoke cavity, …
D. Li, LBNL
LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Current Status
• Existing cavities
— KEK-B collider
— ANL-Tsinghua Emittance Exchange Experiment (NC)
— LOLA (LCLS at SLAC)
— Diagnostics
• Prototypes
— FNAL (Kaon separation and ILC) 3.9-GHz multi-cell
— Cockcroft Institute/DL
—Tsinghua-LBNL cylindrical symmetric multi-cell
— ANL-JLAB-LBNL-Tsinghua for APS
• Proposed Cavities and Simulations
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Proposed Crab Cavity for LHC
Conceptual Design by Rama
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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KEKB Crab Cavity & Damping Scheme
Courtesy of K. Hosoyama
KEKB crab cavity utilizes a choked coaxial-coupler damping scheme
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Deflecting Cavity for Emittance Exchange
Experiment at ANL
3-cell normal conducting cavity at 1.3 GHz: design and fabrication at
Tsinghua University
Power coupler
Tuner
Water cooling
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Vacuum port
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Prototypes
SC Prototype for
APS ~ 2.815-GHz
3.9-GHz 9-cell crab cavity for ILC (FNAL)
Multi-Cell at DL
D. Li, LBNL
Multi-Cell with damping
at Tsinghua
LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Simulation Highlights
x-y dipole mode coupling
Region of high
surface fields
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Cylindrical versus Squashed
R/Q
Bmax
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Structures Under Study (1)
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Structures Under Study (2)
4mm
27mm
12mm
ILC Crab cavity Single
cell Qe LOM=150
72mm
7mm
25mm
A LOM coupler can be coaxial
hook type LOM coupler can
get very low external Q’s.
Waveguide LOM couplers are
also effective.
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Different options for the HOM damping and
the input coupler (FNAL)
a)
b)
c)
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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Next LHC CC Meeting
• Many cavity design alternatives
• Productive discussions
• Formed international collaborations
— Monthly meetings to update R&D progress
— Prototypes to benchmark simulation studies
• Next LHCC meeting
~ October 2008
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LHC-CC08 Workshop Summary, SSRF, Shanghai, China (April 23 ~ 25, 2008)
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