mctf andreas jansson mutac meeting 8-10 april 2008 1 mctf experimental activites - towards...

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


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)


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


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.


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)


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


Vrf +

Vrf -

Cavity

Vrf = 0

Vrf = 0

Cavity

Neutral

positivedeltaZ

MCTF

How to implement a real HCC?


“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


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).


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.


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.


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


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.


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.


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


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”.


MCTF

Cooling channel exclusion plot


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


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.


* M&S+SWF fully loaded (estimate)

mctf andreas jansson mutac meeting 8-10 april 2008 1 mctf experimental activites - towards...

Documents

fast cooling

cooling factor

muon beam

real hcc

test celllinac proton

hcc interesting

hprf experimentfirst

hcc simulationsmore