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MCTF
Andreas Jansson MUTAC Meeting 8-10 April 2008 1
MCTF EXPERIMENTAL ACTIVITES
- towards demonstrating 6D cooling
MCTF
MCTF Experimental Goals
• Goal: Establish feasibility of strong muon cooling required for collider.
• Efficient muon cooling channels involve RF operating in a strong magnetic field.– Don’t know if this is a problem for vacuum cavities.– We know that cavities filled with pressurized gas work in
magnetic field, but not sure how they work with beam.• Initial goals: Determine viability of Helical Cooling Channel (HCC):
– Investigate HPRF behavior in beam.– Find a realistic way to incorporate RF into the HCC– Define a suitable section of HCC to build and test
Andreas Jansson MUTAC Meeting 8-10 April 2008 2
MCTF
Why is HCC interesting?
• Possibility of high average gradient yielding fast cooling and less decay losses.
• Early simulation results showed cooling factor 50000x in 160m (200MHz RF throughout)
Andreas Jansson MUTAC Meeting 8-10 April 2008 3
200MHz RF
MCTF
Helical Solenoid
• Smaller coils than in a snake design– Smaller peak field– Lower cost
• Field components determined by geometry– Over constrained– Coil radius is not free
parameter
Andreas Jansson MUTAC Meeting 8-10 April 2008 4
MCTF
MANX
• Muons Inc has proposed to test the helical cooling channel without RF first.
• The MCTF approach is that we would at least first need to understand if and how RF can be incorporated.
Andreas Jansson MUTAC Meeting 8-10 April 2008 5
MCTF
MTA beamline
• HCC uses HP hydrogen cavities
• Test with beam needed to understand if HPRF is a real possibility.
• Major activity and budget item for MCTF this year.
• Separate talk (Johnstone)
Andreas Jansson MUTAC Meeting 8-10 April 2008 6
MCTF
HPRF experiment
• First test will be done using the existing Muons Inc test cell
• Linac proton beam can generate level of ionization similar to muon beam.– About 50% make it into
cavity, at ~100MeV/c– Each proton ~5MIPs– 6e12 protons ~1.2e13
muonsAndreas Jansson MUTAC Meeting 8-10 April 2008 7
MCTF
What we expect to see?
• Possible build up of ionization electrons, distorting the field and loading down the cavity.– Effect growing linearly
during linac pulse
• Estimates depend on hydrogen purity and vary wildly.– Test e.g. SF6
• Are the ions a problem?• If appropriate: Follow up
with “real” cavity
Andreas Jansson MUTAC Meeting 8-10 April 2008 8
Vrf +
Vrf -
Cavity
Vrf = 0
Vrf = 0
Cavity
Neutral
positivedeltaZ
MCTF
How to implement a real HCC?
Andreas Jansson MUTAC Meeting 8-10 April 2008 9
“Type I” “Type 2” “Type 3”
•RF inside coil•Highest possible RF packing factor•Cavity must be smaller than the coil -> high frequency
•RF between coils•Lower RF packing factor•Difficult H2 cryostat design and assembly
•RF and coils separated•Lower RF packing factor•Requires good matching between sections•Likely easier to build and maintain.
MCTF
More HCC simulations
• More realistic, but still Rcavity > Rcoil. Need Rcavity < Rcoil
Andreas Jansson MUTAC Meeting 8-10 April 2008 10
LEMC07 (Rcavity =1.1*Rcoil), 4000x cooling factor
MCTF
Balbekov’s HCC “rules of thumb”
• Equilibrium emittance is proportional to helix period (and is higher for HCC compared to e.g. Guggenheim lattice). – 1-2mmrad at 1m helix and 250MeV/c
• There is an optimal RF frequency for each helix period. The cavity size roughly scales with the helix period.– 200MHz @ 1m, 400MHz @ 50cm, etc
• Obtainable cooling factor (ratio of acceptance and equilibrium emittance) is ~4.5 in each plane, 6D cooling ~90x. – Further cooling requires shorter helix (higher B field and RF
frequency).
Andreas Jansson MUTAC Meeting 8-10 April 2008 11
MCTF
Recent simulations - varying cavity size
• Initial and final emittances for different frequency cavities (fixed coil diameter).
• Green arrow indicates where Rcavity = Rcoil
• It appears that decreasing the cavity size (increasing the frequency) more than ~10% from Rcoil is not possible.
Andreas Jansson MUTAC Meeting 8-10 April 2008 12
MCTF
Required clearance
• Coil and cavity at different temperatures require insulating vacuum gap.
• Estimated required clearance ~3”– This does not include
any RF feed
• Compare to HP H2 cavity radius at various frequencies– Only 200MHz version
appear to be possible.
Andreas Jansson MUTAC Meeting 8-10 April 2008 13
Frequency Cavity Radius
200 MHz 55cm (22”)
400 MHz 28cm (11”)
800 MHz 14cm (5.6”)
1600 MHz 7cm (2.8”)
(assuming 200atm H2 )
0.4” – 1”
coil support
HP cavity
coil
insulating vacuum
~1.25”
~0.8”
pressurized H2
~3”
MCTF
Ansys stress simulation
Andreas Jansson MUTAC Meeting 8-10 April 2008 14
At 1500PSI (100atm)
SS316: 1.25” wall requiredInconel 625: 0.75” wall required
ASME pressure vessel code used
MCTF
RF between coils
• Roughly same (~3”) clearance would apply longitudinally.
• Excludes very short helix periods.
• Likely to have poor equilibrium emittance.
• Has not been studied seriously.
Andreas Jansson MUTAC Meeting 8-10 April 2008 15
Δ
MCTF
Separate RF and helical solenoid
• To be efficient, would need a short(er) matching section.
• Problem: time-of-flight spread in helical section too large to recapture.
• Solution may exist, but not found yet.
Andreas Jansson MUTAC Meeting 8-10 April 2008 16
MCTF
Other HCC challenges
• Need to include beam diagnostics (beam position at minimum).– Experience show we can not operate
machines like this without beam position readback
• RF power dissipation in LH2– Cavity (window) design– Cooling requirements
Andreas Jansson MUTAC Meeting 8-10 April 2008 17
MCTF
HCC Summary
• We have a relatively good idea of the engineering clearances required in a HCC.
• So far, simulations of HCC structures obeying these constraints do not show cooling.
• However, an exclusion result is also a result (albeit not quite as exciting as a discovery).
• There are plenty of phase space left, but of course “a bird in hand is better than 10 in the woods”.
Andreas Jansson MUTAC Meeting 8-10 April 2008 18
MCTF
Cooling channel exclusion plot
Andreas Jansson MUTAC Meeting 8-10 April 2008 19
Ave
rage
gra
dien
t
Cooling factor (acceptance/equilibrium emittance)
HCC type I
HCC type II
HCC type III
Super Fernow
Guggenheim
RFOFO snake
Holy Graal
Excluded
?
Here be dragons
?
?
MCTF
Example of Modified Helical Solenoid HCC
• Adding more coils to the Helical solenoid could relax the geometrical constraints and allow to widen the primary coil– Overall solenoid could
allow independent tuning of Bz component
– Additional helical correction coil could give further tuning range.
• Needs further study
Andreas Jansson MUTAC Meeting 8-10 April 2008 20
RF cavity
Primary helix coil
Correction coil
Correction coil
MCTF
Plans and budget estimates
• HPRF test cell with beam ($1M*)
• “Real” HP cavity with beam ($500k*)
• Build and test either:– Section of HCC with RF ($3-5M*)– Section of Guggenheim ($3-5M*)– Section of RFOFO “snake” ($3-5M*)– MANX ($15-20M*)
depending on which appear most attractive in simulations.
Andreas Jansson MUTAC Meeting 8-10 April 2008 21
* M&S+SWF fully loaded (estimate)