MAP vacuum RF cooling meeting July 23 2013 - PDF document

1 MAP vacuum RF cooling meeting, July 23
MAP vacuum RF cooling meeting, July 23 2013 Y. Alexahin (FNAL APC) Status of Low -  FOFO Snake for Final Stage of 6D Ionization Cooling  Some history from � 3 years ago  Unreported old simulations results which may help understand the recently encountered problems with the later stage 6D cooling  Plans FOFO snake for final 6D cooling Phase advance �180  /cell  small  - function at absorber  smaller emittance. With ~ half - integer tunes  PIC? Simplest structure – just two solenoids: 10*By Bz (T)  =0

2 .007  x,y [cm] z z Q1, Q2 ï
.007  x,y [cm] z z Q1, Q2 c” orbit lengthening p/100 - no 2 nd order chromaticity, - momentum compaction too small and of the wrong sign! HFOFO Status - Y. Alexahin 3 rd MCDW BNL December 2, 2009 15 p/100 Return to FOFO - 180 ° HFOFO Status - Y. Alexahin 3 rd MCDW BNL December 2, 2009 Bzmax=15.5 T for p0=100MeV/c - within the reach of Nb3Sn technology Since there is no clear g

3 ain in going to 270 ° (just problems),
ain in going to 270 ° (just problems), more effort was applied to find solution for 180 ° . A superposed dipole field generated by additional coils can do the job. Such a field can not be obtained by displacing solenoids: By / BLS Dy Bz / BLS x y Dx 19 FOFO - 180 ° Momentum Acceptance 20 HFOFO Status - Y. Alexahin 3 rd MCDW BNL December 2, 2009 p/p0 – 1 p/p0 Q2 - 1 p/p0  _min [cm] Q1 - 1  This design is not finished yet  Search for a helical configurat

4 ion is underway  Emittances well
ion is underway  Emittances well below 0.5mm can be expected Summary & Outlook 15 Low -  HFOFO Status - Y. Alexahin NFMCC Meeting Oxford, MS, January 14 2010  FOFO - 180  promises large momentum acceptance, DA and small emittances. However, no way to equalize the transverse mode cooling rates has been found yet. Still, there are some possibilities to explore.  H FOFO - 270  can provide emittances  T ~ 0.35mm,  L ~0.5mm with LH2 absorbers, but the transmission is poor. It can be (probably) improved with no

5 nlinear shape of the absorbers reducing
nlinear shape of the absorbers reducing ionization losses for low - momentum muons.  If both efforts fail, retreat below 180  : the allowed maximum field of 19T (on the coil) will be achieved with smaller cell length  the increase in  min and emittances will be moderate Problems with Final FOFO Snake 6 Low - beta FOFO snake – Y.Alexahin, MAP meeting 07/23/2013 Aftr NFMCC’10 mting I continu for a whi to work on th snak trying to sov th following problems:  Equalizing the transverse norma

6 l mode cooling rates  Momentum ac
l mode cooling rates  Momentum acceptance limited from above by sign change of the slippage factor.  Momentum acceptance limited from below by fast increase in the ionization loss rate The final configuration and results are presented on next slides. Modified Geometry* 7 Low - beta FOFO snake – Y.Alexahin, MAP meeting 07/23/2013 *) in order to reduce field on the coil and increase the reference momentum) Total length of 2 - cell period 2  38cm = 76cm Bz_axis=11.5T (Bz_coil=17.3T) for p0=100MeV/c, constant By=0.023T To achieve

7 longitudinal cooling it was necessary t
longitudinal cooling it was necessary to introduce LiH wedges with 10  angle. The transverse modes cooling rates can be equalized by adding periodic sextupole field with gradient  0.033T/cm 2 between the sols. and by rotation of LiH wedges. In particular case the wedge angle was vertical on one side of the LH2 absorber, but horizontal on the other (?!) normal mode tunes (including cooling rates) and normalized equilibrium emittances: tune 1.24577+0.00159615i 1.21721+0.00159538i 0.0949777+0.000572584i  (mm) 0.228302 0.202806 0.790427 2cm LH2 absorber

8 with 1mm LiH windows, possibly with we
with 1mm LiH windows, possibly with wedge angle Rout= 38cm 2  8cm open cell 600 MHz RF cavities, Emax=18MV/m 16cm 38cm Rin= 14.5cm G4BL simulations 8 Low - beta FOFO snake – Y.Alexahin, MAP meeting 07/23/2013 Periodic orbit with LiH wedges computed with MICCD (red) and with LH2 trapezoids in G4BL (blue) y z x LiH wedges were replaced with 45  angles of the LH2 absorber in the corresponding planes, no windows added. The absorber is represented by two trapezoids pz (MeV/c) z (cm) y (cm) z (cm) G4BL Tracking 9

9 Low - beta FOFO snake – Y.Alexah
Low - beta FOFO snake – Y.Alexahin, MAP meeting 07/23/2013 x (cm) y (cm) t (ns) px/p0 py/p0  p/p0 The major mechanism of losses is diffusion ovr th maimum of ong. kintic nrgy” – change of the slip factor sign at higher values of momentum. p0 = 120 MeV/c  p/p0 p0 = 100 MeV/c Evoution of th initia watrag” istriution (u ots) ovr 15 prios (r ots). Losses (no decay) over 15  0.76 m = 11.4 m ~1%. Longitudinal Dynamics at Higher Ref. Momentum

10 10 Low - beta FOFO snake – Y.A
10 Low - beta FOFO snake – Y.Alexahin, MAP meeting 07/23/2013 With both the lattice and reference momentum increased by 50% (p0=150 MeV/c), transverse dipole field reduced by a factor of 3 (and correspondingly increased the LiH wedge angle) the sippag” ffct coms isastrous Conclusions 11 Low - beta FOFO snake – Y.Alexahin, MAP meeting 07/23/2013  It does not seem possible to cool both signs in a Low - beta FOFO - snake – wedges of some kind are necessary  The major

11 performance limitation is imposed by sig
performance limitation is imposed by sign change of the slippage factor at higher values of momentum.  it seems possible to lower the reference momentum much below 100 MeV/c but wi proay rquir a mor comp RF (pus?) as in Bo’s fina cooing.  Possible solution is a large - angle wedge between RF cavities but it noticeably increases the emittance (beta/dispersion ratio  ).  Equalizing the transverse normal mode cooling rates requires a strong sextupolar field:  is it really necessary?  can the solenoi

12 ds tilt do the job? Plans 12 Low
ds tilt do the job? Plans 12 Low - beta FOFO snake – Y.Alexahin, MAP meeting 07/23/2013  Optimization of the final stage Low - beta FOFO - snake, a lot of parameters to scan:  reference momentum, transverse dipole field (solenoid pitch?), sextupole field, wedge angle and orientation, RF frequency (or pulse form?)  Tapered channel design for post - merge cooling .  what are the plausible initial conditions? .  Helical FOFO - snake for initial 6D cooling with 325MHz RF Total of ~6pm (or ~0.5 FTE) is requi