Antiproton Stacking and Cooling by dfhdhdhdhjr

VIEWS: 4 PAGES: 33

									Beam-based vacuum observations and their
             consequences


            Sergei Nagaitsev
            August 18, 2003
                        Design goals

Stochastic cooling only
 Emittance growth rate (n, 95%): 2 μm/hr
 Lifetime of 10-μm emittance pbar beam with
  cooling: ≥ 200 hrs
Stochastic+electron cooling
 Emittance growth rate (n, 95%): 4 μm/hr
 Lifetime of 10-μm emittance pbar beam with
  cooling: ≥ 200 hrs

 The lifetime cannot be greater than:
                             Ax Ay                         A
           6Λ                             30 
                  
                  n , 95%
                             ( Ax  Ay )               
                                                        n , 95%



              Recycler vacuum shutdown work review - Nagaitsev     2
                                                     Design goals
Stochastic cooling only
 Emittance growth rate (n, 95%): 2 μm/hr
            1


 Lifetime of 10-μm emittance pbar beam with cooling: ≥ 200 hrs
Stochastic+electron cooling
       Relative beam lifetime




 Emittance growth rate (n, 95%): 4 μm/hr
            of
 Lifetime0.1 10-μm emittance pbar beam with cooling: ≥ 200 hrs




                                0.01
                                       0      10             20             30                40
                                             Normilized 95% emittance [mm mrad]



 Relative Coulomb scattering loss rate for the Recycler beam,
  assuming a 40-μm acceptance in both planes.
 The design emittance is 10 μm (n, 95%)

                                           Recycler vacuum shutdown work review - Nagaitsev        3
                       Today’s menu

 I will present the beam-based measurements and
  demonstrate that the results of these
  measurements are consistent with Coulomb
  scattering off residual gas.




              Recycler vacuum shutdown work review - Nagaitsev   4
                        Today’s menu

 I will present the beam-based measurements and
  demonstrate that the results of these
  measurements are consistent with Coulomb
  scattering off residual gas.
 Assuming that all scattering is elastic, I will derive
  the partials pressures. These are an order of
  magnitude higher than what we obtain from our
  vacuum model.




               Recycler vacuum shutdown work review - Nagaitsev   5
                        Today’s menu

 I will present the beam-based measurements and
  demonstrate that the results of these
  measurements are consistent with Coulomb
  scattering off residual gas.
 Assuming that all scattering is elastic, I will derive
  the partials pressures. These are an order of
  magnitude higher than what we obtain from our
  vacuum model.
 I will critique my own model and consider
  uncertainties.




               Recycler vacuum shutdown work review - Nagaitsev   6
                        Today’s menu
 I will present the beam-based measurements and
  demonstrate that the results of these
  measurements are consistent with Coulomb
  scattering off residual gas.
 Assuming that all scattering is elastic, I will derive
  the partials pressures. These are an order of
  magnitude higher than what we obtain from our
  vacuum model.
 I will critique my own model and consider
  uncertainties.
 Finally, I will demonstrate that the goal of 4 μm/hr
  could be achieved with a successful bakeout.
  The goal of 2 μm/hr is likely to be unattainable with
  the present vacuum system.


               Recycler vacuum shutdown work review - Nagaitsev   7
           Observations (coasting beam) Aug 2, 2003

   One hour of observations with 9E10 protons (no MI ramps)
   Initial emittance:     10 μm (95%, Schottky)
                          7 μm (100%, scraper)
   Final emttance:        20 μm (95%, Schottky)
                           17 μm (95%, scraper)
   Growth rate: 10 ± 1 μm/hr
   Zero-current, pencil beam lifetime: 90 hours
   Acceptances: Ax = 60 μm, Ax = 40 μm
   The emittance growth rate and the lifetime are
    selfconsistent!




                    Recycler vacuum shutdown work review - Nagaitsev   8
                Emittance growth rate

 Our measurements demonstrate that:
   The transverse emittance growth is linear with time
   The rate is insensitive to beam intensity and bunching
    structure
   The rate does not depend on beam emittance
   The rate does not depend on tunes (within limits)




                Recycler vacuum shutdown work review - Nagaitsev   9
                         Emittance growth rate

 Our measurements demonstrate that:
    The transverse emittance growth is linear with time
    The rate is insensitive to beam intensity and bunching
     structure
    The rate does not depend on beam emittance
    The rate does not depend on tunes (within limits)
 This all points to Coulomb scattering
 I will be using the following growth rate
  expression for my analysis:
                        crp2                           e (Z i ) 
   
                 12     ave  ni Z   n ( Z i ) 
                                       
                                                 2
                                                                  
                                                        Zi 
       n , 95%                                  i
                                i                                



                        Recycler vacuum shutdown work review - Nagaitsev   10
           Observations (coasting beam) Aug 2, 2003




       -12 MeV/c                  12 MeV/c        -12 MeV/c             12 MeV/c


 1 hour, 9E10 p’s, long. Schottky at 1.75 GHz (no MI ramps)
 The average revolution frequency has decreased by 32 mHz
    This corresponds to a 0.37-MeV energy shift
 The rms momentum spread has increased (1.0 to 1.3 MeV/c)
 The low energy tail has developed
                     Recycler vacuum shutdown work review - Nagaitsev              11
           Observations (coasting beam) Aug 13, 2003
                   dB




                                             Frequency

   30 min, 1E10 p’s, long. Schottky at 79 GHz (no MI ramps)
   Energy loss: 0.42 MeV/hr
   The rms momentum spread has increased.
   The low energy tail has developed.
                     Recycler vacuum shutdown work review - Nagaitsev   12
                      The low-energy tail

 We’ve proved that the low-energy tail comes from
  ionization losses.




-12 MeV/c                     12 MeV/c

 1.9E11 protons before scrape                      0.9E11 protons after scrape

                   Recycler vacuum shutdown work review - Nagaitsev              13
                 The low-energy tail

 The scrape was done with a horizontal scraper at a
  location with a horizontal beta-function of 52 m,
  zero dispersion (~20 cm) and with equal tunes.
 The scraper was stopped 6.2 mm away from the
  beam center, which corresponds to a 7-μm
  acceptance, and then withdrawn.
 How can one scrape the low energy tail at zero-
  dispersion location?




              Recycler vacuum shutdown work review - Nagaitsev   14
                 The low-energy tail

 The scrape was done with a horizontal scraper at a
  location with a horizontal beta-function of 52 m,
  zero dispersion (~20 cm) and with equal tunes.
 The scraper was stopped 6.2 mm away from the
  beam center, which corresponds to a 7-μm
  acceptance, and then withdrawn.
 How can one scrape the low energy tail at zero-
  dispersion location?
 The answer is: proton-electron collisions.




              Recycler vacuum shutdown work review - Nagaitsev   15
                                        Proton collision with a stationary electron

 Max. energy transfer Tmax= 91 MeV
                                            5



                                            4
Transverse momentum, MeV/c




                                                            Outside of ±0.3%
                                            3

                             p perp (  )

                                            2
                                                           momentum acceptance

                                            1




                                            0
                                                0    20             40             60           80     100
                                                                           t( )
                                                           Energy transfer per collision, MeV


                                                    Recycler vacuum shutdown work review - Nagaitsev         16
                                 Proton collision with a stationary electron
          2
     1 p
Jn             ave
     2 M p c
           2 2


                                      40




                                      30
  Betatron action, mm-mrad




                                               Scraped to 7 mm-mrad
                             J(  )   20




                                      10




                                      0
                                           0        5                10                 15        20
                                                                     t( )
                                                        Energy transfer per collision, MeV


                                               Recycler vacuum shutdown work review - Nagaitsev        17
           Observations (coasting beam) Aug 2, 2003




       -12 MeV/c                  12 MeV/c        -12 MeV/c             12 MeV/c


 1 hour, 9E10 p’s, long. Schottky at 1.75 GHz (no MI ramps)
 The average revolution frequency has decreased by 32 mHz
    This corresponds to a 0.37-MeV energy shift
 The rms momentum spread has increased (1.0 to 1.3 MeV/c)
 The low energy tail has developed
                     Recycler vacuum shutdown work review - Nagaitsev              18
           The rms momentum spread increase

 IBS

                    p2                        ||
     d 2
     dt
         
         ||   
                 d  || 
                 dt  p 2 
                            
                                 rp2 cNLC
                              2   C 
                                 3 3      2
                                            1
                                                2
                         
   Lc - is the Coulomb logarithm,
   C – is the ring circumference,
   σ – is the rms beam size and
   θ – is the rms angular spread.




                  Recycler vacuum shutdown work review - Nagaitsev   19
                                  IBS (coasting beam)
 The rms momentum growth                                         1 10
                                                                      6

  rate (MeV/c per hour) as a
  function of the rms                                                             εn =5 μm

  momentum spread (MeV/c)
  for various transverse                                   1( p )
                                                                                      10 μm

  (n,95%) emittances.                                      2( p )                   15 μm

 N = 9x1010 protons                                       3( p )

                                                           4( p )                   20 μm
 Measured:
       Initial 1.0 MeV/c
       Final 1.3 MeV/c
 Need to add rms spreads in                                      1 10
                                                                      5

                                                                          1 10
                                                                              5
                                                                                                1 10
                                                                                                       6
                                                                                                                  1 10
                                                                                                                      7

  quadrature!                                                                                 p    M p
                                                                                                                  d

 The ibs can explain a      Without any cooling the momentum spread diffusion rate is (for a 10 pi emittance):


  portion (0.1-0.2 MeV/c) of
  the measured momentum
  spread.


                               Recycler vacuum shutdown work review - Nagaitsev                                       20
            The rms momentum spread increase

 IBS

 Energy-loss straggling
            1.2 10
                       5




              1 10
                       5                         Landau probability
                                                 density
              8 10
                       6

                                                                       Mean energy loss: 0.42 MeV
        g( p ) 6 10
                       6
                                                                       Most probable loss: 0.3 MeV

              4 10
                       6




              2 10
                       6




                           0
                                      2 10    4 10       6 10   8 10   1 10
                                          5        5           5       5       6
                               0
                                                       p
                                              Energy loss, MeV


                                   Recycler vacuum shutdown work review - Nagaitsev                  21
               Momentum distribution
 A Gaussian(σ=1 MeV/c) distr. is folded with the
  Landau probability density.
                                                    8




                                                 18.4




                                                 28.8

                                         FD jj

                                         GD jj


                                                 39.2




                                                 49.6




                                                  60
                                                  2.4 10     1.92 10       1.44 10          9.6 10   4.8 10
                                                          7          7              7                6         6
                                                                                                                   0
                                                                                         jj
                                                                         Momentum spread: +/- 12 MeV/c




 The result is that by fitting the energy loss alone,
  I am able to reproduce both the low-energy tail
  and the rms spread increase
 Energy loss due to resistive impedance is negligible

               Recycler vacuum shutdown work review - Nagaitsev                                                        22
              Summary of beam-based measurements

Emittance growth rate:
                     crp2                         e (Zi ) 
  
             12     ave  ni Z   n ( Z i ) 
                                   
                                          2
                                                              10  1 m/hr
                                                   Zi 
   n , 95%                               i
                            i                              

Beam average energy loss: 0.40±0.04 MeV/hr
      This corresponds to a mean energy loss of 0.42±0.04 MeV/hr

                                       Tmax        
MeV 
               0.307     Zi
                2
                        A xi [g/cm ]  I  
                                   2
                                      ln       2   0.42  0.04 MeV
                       i  i            i           




                            Recycler vacuum shutdown work review - Nagaitsev   23
                Partial pressures model

 Assume that the residual gas consists only of Z=1
  and Z=8 atoms (H2 and H2O)
 Solving equations for 10±1 μm/hr and 0.42±0.04 MeV
  results in:
    pH = 3.3±1.7x10-9 Torr
    pW = 1.0±0.2x10-9 Torr




                Recycler vacuum shutdown work review - Nagaitsev   24
                Partial pressures model

 Assume that the residual gas consists only of Z=1
  and Z=8 atoms (H2 and H2O)
 Solving equations for 10±1 μm/hr and 0.42±0.04 MeV
  results in:
    pH = 3.3±1.7x10-9 Torr
    pW = 1.0±0.2x10-9 Torr
 If I assume that one of the gases is hydrogen with
  a know concentration nH, and then try looking for
  another gas with a new Z (A = 2Z), nZ ≤ nH, I am
  unable to find any solution unless pH > 1.5x10-9 Torr
  and Z ~ 5.




                Recycler vacuum shutdown work review - Nagaitsev   25
                Partial pressures model

 Assume that the residual gas consists only of Z=1
  and Z=8 atoms (H2 and H2O)
 Solving equations for 10±1 μm/hr and 0.42±0.04 MeV
  results in:
    pH = 3.3±1.7x10-9 Torr
    pW = 1.0±0.2x10-9 Torr
 “Water” alone contributes 8.3 μm/hr to the
  emittance growth




                Recycler vacuum shutdown work review - Nagaitsev   26
                Partial pressures model

 Assume that the residual gas consists only of Z=1
  and Z=8 atoms (H2 and H2O)
 Solving equations for 10±1 μm/hr and 0.42±0.04 MeV
  results in:
    pH = 3.3±1.7x10-9 Torr
    pW = 1.0±0.2x10-9 Torr
 “Water” alone contributes 8.3 μm/hr to the
  emittance growth
 Before Jan 2003 shutdown the measured emittance
  growth rate was 5 μm/hr. There were no beam
  energy loss measurements.
 Present measurements are consistent with the
  water content doubled after the shutdown.


                Recycler vacuum shutdown work review - Nagaitsev   27
   What could have increased the water content?

 Work done during Jan 2003 shutdown:
 Installed new ion pumps, capable of pumping Ar at
  a higher rate. Installed some diagnostics (RGAs,
  ion gauges).
 Out of 27 vacuum sectors, 20 were vented with
  “dry” nitrogen and then only 5 sectors baked to
  120C. Of these five, three have been vented since
  then without a bake.
 Many new ion pumps were not baked in situ.

 Unrelated to the Jan 2003 shutdown:
    BPMs and bellows (total equiv. length of about 500m)
     were never baked at all.


                Recycler vacuum shutdown work review - Nagaitsev   28
                                  So, what’s the problem with this model??

                        There are two problems with my pressure model.
                       1. Terry’s vacuum model predicts an order of
                          magnitude low pressures.
                                      Recycler Pressure Profile Using Average RGA Data from Pump Locations

                                                                                                                    Total
                  1.0E-09
                                                                                                                    IG Readings
                                                                                                                    Hydrogen
                                                                                                                    Water
                  1.0E-10                                                                                           Carbon Dioxide
                                                                                                                    Carbon Monoxide
Pressure (Torr)




                                                                                                                    Methane/Ethane

                  1.0E-11                                                                                           Argon
                                                                                                                    Unknown



                  1.0E-12




                  1.0E-13
                            0   500   1000   1500     2000       2500        3000   3500   4000    4500      5000
                                                             Distance (cm)




                                                Recycler vacuum shutdown work review - Nagaitsev                                  29
      So, what’s the problem with this model??

1. Terry’s vacuum model predicts an order of
   magnitude low pressures.
   None of the ion gauges show pressures above 5x10-10 Torr




                Recycler vacuum shutdown work review - Nagaitsev   30
                                                                              Pressure (Torr)




                                                                     1.E-10
                                                                              1.E-09
                                                                                          1.E-08
                                                                                                               1.E-07
                                                               R:IP220
                                                               R:IP221
                                                               R:IP222
                                                               R:IP224
                                                               R:IP225
                                                               R:IP226
                                                               R:IP227
                                                               R:IP228
                                                               R:IP229
                                                               R:IP230
                                                               R:IP231




                                                                                                                                                                              Torr.
                                                               R:IP232
                                                              R:IP301A
                                                              R:IP301B
                                                              R:IP302A
                                                              R:IP302B
                                                              R:IP303A
                                                              R:IP303B
                                                              R:IP304A
                                                              R:IP304B
                                                              R:IP305A
                                                              R:IP305B
                                                              R:IP306A
                                                              R:IP306B
                                                              R:IP306C
                                                               R:IP307
                                                               R:IP308
                                                               R:IP309
                                                               R:IP310
                                                               R:IP311
                                                               R:IP312
                                                               R:IP313
                                                               R:IP314
                                                               R:IP315
                                                               R:IP316
                                                               R:IP317
                                                               R:IP318
                                                               R:IP320
                                                               R:IP321
                                                               R:IP323
                                                               R:IP324
                                                               R:IP325
                                                                                                                                                                                                                                            magnitude low pressures.




                                                               R:IP326
                                                              R:IP327A
                                                              R:IP327B
                                                               R:IP328
                                                   Location
                                                               R:IP329
                                                               R:IP330
                                                               R:IP331
                                                               R:IP332
                                                               R:IP333
                                                               R:IP334
                                                               R:IP335
                                                               R:IP336
                                                                                                                        Recycler 30 - 40 House Ion Pump Pressure Profile




                                                               R:IP337
                                                               R:IP338
                                                               R:IP339
                                                               R:IP340
                                                               R:IP341
                                                               R:IP400
                                                               R:IP401
                                                              R:IP402A

Recycler vacuum shutdown work review - Nagaitsev              R:IP402B
                                                              R:IP402C
                                                               R:IP403
                                                               R:IP404
                                                              R:IP4051
                                                              R:IP4052
                                                                                                                                                                                                                                         1. Terry’s vacuum model predicts an order of




                                                               R:IP406
                                                               R:IP407
                                                                                                                                                                                                                                                                                        So, what’s the problem with this model??




                                                               R:IP408
                                                               R:IP409
                                                               R:IP410
                                                               R:IP411
                                                                                                   1/10/2003




                                                               R:IP412
                                                                                                                                                                           There is only one ion pump that show pressures above 1x10-9




                                                               R:IP413
                                                               R:IP414
                                                               R:IP415
                                                               R:IP416
                                                               R:IP417
                                                               R:IP418
                                                               R:IP419
                                                               R:IP420
                                                                                                   7/11/2003




                                                               R:IP421
                                                               R:IP422
                                                               R:IP423
                                                               R:IP424
                  31




                                                               R:IP425
      So, what’s the problem with this model??

2. We know that the total gas capacity of our TSPs
   is 0.2-0.4 Torr-L. Assuming we understand the
   TSP’s pumping speed at the beam pipe, pressures
   of 3x10-9 Torr would saturate the TSPs in 10-20
   days, yet the TSPs last on the average 100 days.




              Recycler vacuum shutdown work review - Nagaitsev   32
                           Conclusions

 The evidence for the residual gas scattering from
  beam-based measurements is overwhelming.
 I can not reconcile the beam-based measurements with
  the instrument measurements.
 All beam-based measurements point to the fact that
  amount of heavy molecules (most likely water) in the
  system has doubled after the Jan 2003 shutdown.
 The model can not answer how much CH4, CO or CO2 is
  in the system. If I assume that all heavy molecules
  are water, eliminating them completely reduces the
  emittance growth rate to 2 μm/hr. It is likely that we
  will never reach this value with a present system. I
  estimate that reaching a 4-μm/hr rate is possible with
  a successful bakeout.

                 Recycler vacuum shutdown work review - Nagaitsev   33

								
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