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Tune spread control with Tevatron Electron Lens. Aleksandr Romanov Vladimir Shiltsev Alexander Valishev Gennady Kuznetsov Giulio Stancari. Some theory. - PowerPoint PPT Presentation
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Tune spread control with Tevatron Electron Lens
Aleksandr Romanov
Vladimir Shiltsev
Alexander Valishev
Gennady Kuznetsov
Giulio Stancari
Some theoryBeam-beam effects, space charge and nonlinear
elements causes betatron tunes of particles in a circulating beam to be different. All variety of this tunes forms a tune-spread (footprint).
To avoid loss of the particle due to chaotic drift, its tunes should be located away from harmful resonances.
Beams intensities are often limited by maximal size of footprint that can be fitted between resonances.
• Several things pushe particles to harmful resonances:– Tune spread in one bunch could be too big to fit between resonances– Circulating bunches could have different work points– And others…
Some theory
• Electron lenses could be used to fight mentioned problems:– Right beam shape and intensity allows footprint compression– Fast modulation allows bunch to bunch adjustments of work point
Electron Lenses vs. Regular Magnet
Wider variety of field configuration
Yes No
Bunch to bunch strength adjustment
Yes No
Overall strength of field
Small Any
Gaussian profile vs. SEFT profile . Ability to compensate tune spread
Good Moderate
Ability to shift work point
Moderate Good .
r Gx(x,0) Gx(0,y)
x, y, r x, y, r
Other ways to use electron lenses• Abort gap cleaning (in use)
– By pulsing gun every 6 turn during the abort gaps, unwanted particles are eliminated by excitation of high order resonance.
• Halo cleaning (proposal)– By forming tube electron beam and
aligning it with treated one, it is probably possible to decrease the lifetime of halo particles, without affecting the core.
Plans• Gaussian gun
– Test profile quality– Install the gun into TEL2 instead of the SEFT one– Study the tune spread control ability theoretically – Study the tune spread behavior of the treated
beam
• SEFT gun– Install the gun into the test bench– Test profile quality– Look if we can adjust gun’s parameters to make
“hollow” profile
Outline of a Gun design
Anode
Control Electrode
Magnetic Field
Cathode
Filament
Impregnated cathodes
Tungsten BaO, …During activation, chemicals
from porous react and form a monoatomic layer of Ba. This layer is very fragile, and in case of destruction requires time consu-ming reactivation procedures.
Testing the guns: test benchGun
Gun solenoid
Vacuum chamber
Pickups and other electrodes
Collector
Profile meterCorrector solenoids
Main solenoid Collector solenoid
Tube
Testing the guns: perveances
Cathode needs activation after exposure to the air or even a long standing without filament current. For the Gaussian gun it took about a week. The SEFT gun didn’t fully restore after two weeks.
Testing the guns: Gaussian gun profile
Date: 19 Feb 2009Magnetic fields: 1-1-1 kGsFilament current: 4ACathode & Control electrode: -5kV
Testing the guns: Gaussian gun profile
• Date: 24 Feb 2009• Magnetic fields: 1-1-1 kGs• Filament current: 4.15 A• Cathode & Control electrode: -6 kV
Testing the guns: Gaussian gun
• Date: 27 Feb 2009• Magnetic fields: 3-3-3 kGs• Filament current: 4 A• Cathode & Control electrode: -6 kV
Testing the guns: SEFT gun
• Date: 8 Jul 2009• Magnetic fields: 1.5-1.5-1.5 kGs• Filament current: 6.7 A• Cathode & Control electrode: -0.5 kV
Solenoidal field profile
Field profile in TEL-2 main solenoid, at 439.4A, corrected with dipole correctors.
Theoretical tune spread
))/(1()(
40
eSEFT r
r
0
22
22
2
222
222
22
22 )(
/)(
)/)arctan((2),(
yx
yx
x
yx
yx
yx
xyyxv
e
exSEFTx
0
22
22
2
222
2222
22
22 )(
/)(
)2)(exp(12),(
yx
yx
x
yx
yx
yx
xyyxv
e
exGaussx
)2exp()( 220 eGauss rr
0,
2
1
cp
eLTELyxex
Since the length of the interaction region in the TELs is much smaller than beta-functions in its locations, then we can consider TELs as “short” elements. In this case, to model the imperfect aligning, one can split the simulated beam into several slices and summ the effects to model the influence.
Theoretical tune spread
Antiproton orbitElectron beam Slices
(0,y)
(x,0)
y
x
y
x
0,y)
0,x)
Sanity check for slicesTo check the quality of the sliced fit it is useful to look at
difference between this fit and numerical integral:
1 slice 2 slices 4 slices3 slices 5 slices+-1pitch
Gaussian profile
)0,0(
d))(),((1
),(1
),( 0
,,
G
ssyysxxGL
yyxxGN
yx i
L
eeTEL
isliceisliceslices
TEL
SEFT profile
104 particles with gaussian distribution
Theoretical tune spread
Gauss SEFT
y
x
y
x
Tune spread compensationGauss SEFT
y
x
y
x
• Perfect alignment• Amount of compensation: from 0% to 150%
Tune spread compensation: symmetrical tilt in X-Z plane scan
Gauss SEFT
• Full compensation.• xi varied from 0 to -3• xf varied from 0 to 3• yi = 0, yf = 0
y
x
y
x
Tune spread compensation: symmetrical tilt in XY-Z plane scanGauss SEFT
y
x
y
x
• Full compensation.• xi, yi varied from 0 to -2• xf, yf varied from 0 to 2
Tune spread compensation: shift in X-Z plane scan
Gauss SEFTy
x
y
x
• Full compensation.• xi, xf varied from 0 to 2• yi = 0, yf = 0
Tune spread compensation: symmetrical tilt in X-Z plane scan
Gauss SEFTy
x
y
x
• Half compensation.• xi varied from 0 to -3• xf varied from 0 to 3• yi = 0, yf = 0
Tune spread compensation: symmetrical tilt in XY-Z plane scanGauss SEFT
y
x
y
x
• Half compensation.• xi, yi varied from 0 to -2• xf, yf varied from 0 to 2
Tune spread compensation: shift in X-Z plane scan
Gauss SEFTy
x
y
x
• Full compensation.
• xi, xf varied from 0 to 2s
• yi = 0, yf = 0
Final choice: 1/3 of strength
Perfect alignment
X shift 0.5
X Pitch +-2 X&Y Pitch +-2
X shift 1 XY shift 0.5
BPMs of the TEL2
• One bad channel with strong reflections• Frequency dependence
– Different calibrations and different offsets for (anti)protons and electrons
Switch
Scope
A BPC
GPIB
ACNET
Algorithm for new program• Determine and subtract offset, using first N points
or whole sample.• Find minimum and maximum in signals from both
plates– Find moving average extremums– Fit MA extremum region with parabola and find it’s
precise position• Shift signals to match the extremums• Determine the regions of high signal to noise ratio
– Points where absolute values of fitting parabolas grater then half of the corresponding extremum
• Take average of (A-B)/(A+B) from points in the selected region
New Java based soft for BPMsInitialization of oscilloscope
and switch
Select appropriate channel with the switch
Set up timing for desired channel and particles’ type
Collect binary data from the oscilloscope
Treat the data in any way
Display result
Send data to the ACNET
Infinite loop
Conclusion
• Sensitivity of tune spread compensation to alignment of proton and electron beams was studied with analytical model.– Maintaining shift of less than 0.3 is critical.
• It is possible to partially compensate “gaussian” tune spread with SEFT electron beam.
• Gaussian gun was tested and installed in the TEL2• New java-based software for the BPMs on TEL2
was developed, but not fully tested because of shutdown.