Dielectric-Filled

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• Dielectric-Filled
• RF Cavities

Milorad Popovic FNAL
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• A Tale of Two Cavities

Best of Times-Worst of Times
For HCC
Vacuum Cavity
Cu/Steel
ceramics
Vacuum/H/He
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Motivation

• To fit pressurized cavities in HCC, size of
  cavity has to be reduced
• 800 MHz (from Katsuya) Maximum RF cavity radius
  0.08 m, (pillbox cavity 0.143)Radius of
  effective electric field (95 from peak) 0.03
  m
• 400 MHzMaximum RF radius 0.16 m (pillbox
  cavity 0.286) Radius of effective electric field
  0.06 mOptimum electric field gradient 16 MV/m

For Pill Box Cavity, resonant frequency is
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• HCC Canal has High Magnetic Fields
• No Magnetic Materials
• Acceleration should be Continues
• Dielectric Loaded RF Cavities

Cu/Steel
ceramics
Vaccum/H/He
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HCC Concept
Central Orbit and Beam Envelope
Set of Coils
Basic Building Block can be Cavity Coil
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MANX RF ?
MICE will have ?MV _at_200MHz
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• Ceramics can play additional role, making
  volume of Hydrogen smaller and making cavity
  stronger so the walls do not have to be as thick
  as without ceramics.
• RF power can be fed using loop between two
  rings.
• Cavities can be put next each other so the
  side wall can be made thin
• We should do experiments in the MTA
• 201MHz (with solenoid?)
• 805MHz with solenoid!

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400MHz-16MV/m, Q, Power
Power dissipation 3240.4953 kW Q
10438.9 Re_eps9.5, Im_eps0.00029
Power dissipation 2252.4457 kW Q 15018.0
Re_eps9.5, Im_eps0.0
Lossless Dielectric
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PAC09 Paper
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Did Not Get
FIRM NAME Muons, Inc. RESEARCH INSTITUTION Fermi National Accelerator Laboratory Milorad Popovic, subgrant PI
ADDRESS 552 N. Batavia Ave. Batavia, IL 60510 ADDRESS
But Main Issues did not go away
Loss tangent tan d 1/Qdielectric-1/Qair Loss
tangents of specially formulated alumina with
TiO2 have been reported to be close to sapphire
at 1e-5 . So it is easy to see that todays
ceramics may be used in this novel idea without
suffering a great deal in cavity Q at low
frequencies.  The other problem with ceramics in
vacuum with beams is that of surface charging of
the ceramic. And again, much work has been done
in coatings, from Chromium Oxide to TiN to, more
recently, ion implantation Air gap between the
dielectric and metal plates will be one of the
issues that must be tested experimentally
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Main Issues

• Ceramics, Loss Tangent
• Surface coating
• Dielectric Cooling/Tuning Liquid
• Geometric/Power Optimization
• RF and Mechanical Engineering

50k 1FTE to Start
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Other Applications (Vacuum Cavities)
May be we can use this type of cavity for
Neuffers Phase Rotation Canal. This was Cary
Yoshikawa suggestion. The canal needs many
cavities in range from 300 to 200MHz. We can
use, let say two sizes of Pill Box Cavity (same
size different dielectric!) and adjust frequency
in between using different iner radius,
re-entrant nose cones!
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Cavities for Neutrino Factory
Schematic of the Neutrino Factory front-end
transport system. Initial drift (56.4 m), the
varying frequency buncher (31.5m), The
phase-energy (?-?E) rotator (36m) , a cooling
section. (A 75m cooling length may be optimal.)
Parameter Drift Buncher Rotator Cooler
Length (m) 56.4 31.5 36 75
Focusing (T) 2 2 2 2.5 (ASOL)
Rf frequency (MHz) 360 to 240 240 to 202 201.25
Rf gradient (MV/m) 0 to 15 15 16
Total rf voltage (MV) 126 360 800
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Open Pill Box in Strong Magnetic field, Vacuum
Cavity
Vacuum
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t(ns) E(MV/m) ConvInsu
1 104.27 23.366
501 30.01801 4.6643
1001 26.13199 3.898269
1501 24.09519 3.509672
2001 22.74676 3.257625
2501 21.7529 3.074633
3001 20.97312 2.932763
3501 20.33563 2.817927
4001 19.79908 2.722089
4501 19.33756 2.64026
5001 18.93382 2.569146
5501 18.57586 2.506466
6001 18.25497 2.45058
6501 17.96468 2.400269
7001 17.70002 2.354609
7501 17.45714 2.312882
8001 17.23295 2.274518
8501 17.02498 2.23906
9001 16.83119 2.206136
9501 16.64992 2.175437
10001 16.47975 2.146709
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Try to Establish Modeling Capability Locally
(E-Cool people, Lionel Prost)
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Geometry for electrostatic calculations
Length 12 cm I/M 2 Upstream electrode -100
kV Downstream electrode 100 kV er
7 EquipotentialsDU 4 kV
M
I
Based on Leopold et al.Optimizing the
Performance of Flat-surface, High-gradient Vacuum
Insulators
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Electron trajectories calculations
Initial conditions- 10-6 keV (program does not
accept 0)- No transverse velocity- Rini 0.99
cm (bore radius is 1 cm)
I
M
Trajectory for an electron generated at the metal
surface
Trajectory for an electron generated at the
insulator surface
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SuperFish
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Main Issues

• Ceramics, Loss Tangent
• Vacuum Surface Coating
• Dielectric Cooling/Tuning Liquid
• Geometric/Power Optimization
• Design, I/M Ratio
• RF and Mechanical Engineering

50k 1FTE to Start
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What is Next, 5-Years Plan
The projected funding for the 5-year program
proposed here..
We will also accomplish sufficient hardware RD
(RF, magnets, and cooling section prototyping) to
guide, and give confidence in, our simulation
studies.
In order to produce a practical helical cooling
channel, several technical issues need to be
addressed, including magnetic matching
sections for downstream and upstream of the HCC
a complete set of functional and interface
specifications covering field quality and
tunability, the interface with rf structures, and
heat load limits (requiring knowledge of the
power lead requirements) To prepare the way
for an HCC test section we would Develop,
with accelerator designers, functional
specifications for the magnet systems of a
helical cooling channel, including magnet
apertures to accommodate the required rf systems,
section lengths, helical periods, field
components, field quality, alignment tolerances,
and cryogenic and power requirements. The
specification will also consider the needs of any
required matching sections. Perform
conceptual design studies of helical solenoids
that meet our specifications, including a joint
rf and magnet study to decide how to incorporate
rf into the helical solenoid bore, corrector
coils, matching sections, etc.
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(near)FUTURE
(Vacuum Cavity)

• In week or two
• I hope, DC results with existing dielectric
• NuFact09-This Summer
• I hope, RF(low power) results with low loss
  dielectric

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Test Cavity
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