MCTF Andreas Jansson MUTAC Meeting 8-10 April 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

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 MHz 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

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

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

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 muons Andreas Jansson MUTAC Meeting 8-10 April

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 Vrf + Vrf - Cavity Vrf = 0 Cavity Neutral positive deltaZ

MCTF How to implement a real HCC? Andreas Jansson MUTAC Meeting 8-10 April “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 R cavity > R coil. Need R cavity < R coil Andreas Jansson MUTAC Meeting 8-10 April LEMC07 (R cavity =1.1*R coil ), 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. 1m, 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

MCTF Recent simulations - varying cavity size Initial and final emittances for different frequency cavities (fixed coil diameter). Green arrow indicates where R cavity = R coil It appears that decreasing the cavity size (increasing the frequency) more than ~10% from R coil is not possible. Andreas Jansson MUTAC Meeting 8-10 April

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 H 2 cavity radius at various frequencies –Only 200MHz version appear to be possible. Andreas Jansson MUTAC Meeting 8-10 April FrequencyCavity Radius 200 MHz55cm (22”) 400 MHz28cm (11”) 800 MHz14cm (5.6”) 1600 MHz7cm (2.8”) (assuming 200atm H 2 ) 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 At 1500PSI (100atm) SS316: 1.25” wall required Inconel 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 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

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

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

MCTF Cooling channel exclusion plot Andreas Jansson MUTAC Meeting 8-10 April Average gradient 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 RF cavity Primary helix 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 * M&S+SWF fully loaded (estimate)