Post on 24-Feb-2016
description
Booster Synchrotron Cavities: An Overview in the Context of PIP
Mohamed Hassan, Timergali Khabiboulline , Vyacheslav Yakovlev
07/03/2013
Fermilab’s Booster Parameters
The Fermilab Booster is a synchrotron that accelerates protons from 400 MeV to 8 GeV The Booster circumference is 474.2 meters, the magnetic cycle is a biased 15 Hz and
the RF operates at harmonic 84 of the revolution frequency
Proton Improvement Plan• Objectives: Increase the Proton Source throughput while maintain good availability
and acceptable residual activation through 2025. S. Hederson, Dec 2010 • Goals:
– PIP should enable Linac/Booster to • deliver: 1.80E17 protons per hour (12 Hz) by May 1, 2013 • deliver 2.25E17 protons per hour (15 Hz) by January 1, 2016
– while maintaining Linac/Booster availabilty > 85% and residual activation at acceptable levels and ensuring a useful operation life of the proton source through 2025. S. Hederson, Dec 2010
S. Henderson, Accelerator Advisory Committee, Nov. 7-9, 2011
Specifications for Design of New Accelerating Cavities for the Fermilab Booster
Current Modified
Frequency Range 37.80-52.82 MHz Same
Vacc 55 KV 60 KV (possibly more)
R/Q ~50 ~50
Duty Cycle Effectively 25% 50%
Repetition Rate Effectively 7 Hz 15 Hz
Cavity Tuning Horizontal Bias Same
Beam Pipe Diameter
2.25” >3”
Higher Order Mode Impedance
<1000 Ohm <1000 Ohm
Cooling LCW at 95 F, Water flow up to 21 gpm
Same
Brainstorming
Frequency Tuning
Variable Volume
Variable Permeability
Variable Permittivity
Tuning Mechanis
mPiezoelectric
Magnetostrictive
Ferromagnetic
Ferroelectric
Tuning Range
<0.05%
~40%
~10%
Slow versus Fast Frequency Tuning
Slow
• Using motor driven mechanism
• Response time ~60 s
Fast
• Using piezoelectric/ magneto-strictive element
• Response time ~10 ms
Faster
• Using a ferromagnetic material
• Response time ~ ms
Fastest
• Using Ferroelectric material
• Response time ~ ns
Ferromagnetic Tuning
Classical way of tuning microwave components using bias current that will change the permittivity of the material
Parallel Biased Cavities Bias Field is Parallel to the RF
Field Ferrites with High Saturation
Magnetization (Ni-Zn) Larger values of Mu (Larger
Losses, Lower Q) Relatively limited by the
heating in the ferrites Gradient is limited also by
voltage breakdown in air
H h
𝐻 φ̂+h φ̂=(𝐻+h) φ̂
Perpendicular Biased Cavities Bias Field is Perpendicular to the RF
Field Ferrites with Relatively Low
Saturation Magnetization (Mn-Zn) Smaller values of Mu (Smaller
Losses, Larger Q) Cooling is difficult Some environmental hazards
because of Beryllium Oxide Only prototypes (up to our
knowledge)
Hh
rotating (on cone) magnetic vector – Gyromagnetic Resonance H=f/2.8
Comparison Between Booster CavitiesFNAL Booster TRIUMF SSCL LEB EHF-Booster
Energy Range [GeV] 0.4-8.0 0.45-3.0 0.6-11 1.2-9.0
Bias Parallel Perpendicular Perpendicular
Frequency [MHz] 37.7-53.3 46.1-60.8 47.5-59.8 50.5-56.0
Peak Gap Voltage [kV]
2*27 62.5 127.5 2*36
Cavity Length [m] ~2.4 ~1.23 ~1.25 ~3.25
Accelerating Time [ms]
35 10 50 20
Repetition Rate 7 50 10 25
Ferrite Material Ni-Zn Yttrium Garnet Yttrium Garnet
Ferrite Material Toshiba, Stackpole
TT-G810 TT-G810
Cavity Q 250-1200 2200-3600 2800-3420
Cavity R/Q 50 35 36
Status Operating Prototype Prototype
Tunable Booster Cavities
Parallel Biased Perpendicular Biased
Bias Field is Parallel to the RF Field Bias Field is Perpendicular to the RF Field
rotating (on cone) magnetic vector – Gyromagnetic Resonance H=f/2.8
Ferrites with High Saturation Magnetization (Ni-Zn)
Ferrites with Relatively Low Saturation Magnetization (Mn-Zn)
Larger values of Mu (Larger Losses, Lower Q)
Smaller values of Mu (Smaller Losses, Larger Q)
H h
Hh
Voltage Breakdown
• In Air ~ 3 MV/m (30 KV/cm)
• In Vacuum (according to Kilpatrick) is ~ 10 MV/m (theoretical) 18 MV/m (measured)
Theoretical KilpatrickTheoretical Peter et. Al.
Measured
W. Peter, R. J. Fael, A. Kadish, and L. E. Thode, “Criteria for Vacuum Breakdown in RF Cavities,” IEEE Transactions on Nuclear Science, Vol. Ns-30, No. 4, Aug 1983
Max Field in AirElectric Field for 55KV
1.7 MV/m
Assumed 0.25” Blend Radius upon John Reid’s recommendation
Max Electric FieldElectric Field for 55kV
1.7 MV/m
Electric Field for 60 kV
1.85 MV/m
3.3 MV/m3.6 MV/m
Why Perpendicular Biased Cavity Could Achieve Higher Voltage Gradient?
Vacuum fills most of the cavity volume (breakdown ~ 100 kV/cm)
Vacuum windows are right away on the tuner connection
Tuner is filled with dielectric
Air fills most of the cavity volume (breakdown ~30 kV/cm)
Vacuum windows are nearby the gap
Tuner is filled with air
Possible Changes to the Current Design
• How about rounding the stem corners with large radius >0.25”?
• How about enlarging the stem connection between the tuner and the cavity?
• How about moving the vacuum window position? • How about filling the tuner with dielectric medium (though it
might be a problem for cooling)?• How about designing a perpendicular biased tuner to be
used with the current cavity?• How about using TRIUMF cavity (we have one somewhere
here in FNAL)?
Conclusion
Possible design changes have been identified Major changes in the current tuner have been
suggested Perhaps TRIUMF cavity could be used as a test
prototype for perpendicular-biased option
Ferroelectric Booster Cavity?
High Q across the band ~1000 Fast Response ~ ns But 10% tunability Need high voltage to be applied 50 kV/cm Bias Circuit will be completely different
Conceptual, No Prototype Very early developement Would require quite involved
development
Newsham, D., N. Barov, and J. S. Kim. "RAPIDLY TUNABLE RF CAVITY FOR FFAG ACCELERATORS."
Uranium Compounds under Low Temperature& High Pressure
It might be a day that we see ferromagnetic superconducting cavities
Aoki, Dai, and Jacques Flouquet. "Ferromagnetism and superconductivity in uranium compounds." arXiv preprint arXiv:1108.4807 (2011).
Ferromagnetic Superconducting?