Tune spread control with Tevatron Electron Lens Aleksandr Romanov Vladimir Shiltsev Alexander Valishev Gennady Kuznetsov Giulio Stancari

Some theory Beam-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 SmallAny

Gaussian profile vs. SEFT profile. Ability to compensate tune spread Good Moderate Ability to shift work point Moderate Good. rr G x (x,0) G x (0,y) 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 TungstenBaO, … 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 bench Gun Gun solenoid Vacuum chamber Pickups and other electrodes Collector Profile meterCorrector solenoids Main solenoidCollector 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 2009 Magnetic fields: kGs Filament current: 4A Cathode & Control electrode: -5kV

Testing the guns: Gaussian gun profile Date: 24 Feb 2009 Magnetic fields: kGs Filament current: 4.15 A Cathode & Control electrode: -6 kV

Testing the guns: Gaussian gun Date: 27 Feb 2009 Magnetic fields: kGs Filament current: 4 A Cathode & Control electrode: -6 kV

Testing the guns: SEFT gun Date: 8 Jul 2009 Magnetic fields: 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

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 beamSlices

 (0,y)  (x,0) y x y x  0,y)  0,x) Sanity check for slices To check the quality of the sliced fit it is useful to look at difference between this fit and numerical integral: 1 slice2 slices4 slices3 slices5 slices +-1  pitch Gaussian profileSEFT profile

10 4 particles with gaussian distribution Theoretical tune spread GaussSEFT  y  x  y  x

Tune spread compensation GaussSEFT  y  x  y  x Perfect alignment Amount of compensation: from 0% to 150%

Tune spread compensation: symmetrical tilt in X-Z plane scan GaussSEFT Full compensation. x i varied from 0 to -3  x f varied from 0 to 3  y i = 0, y f = 0  y  x  y  x

Tune spread compensation: symmetrical tilt in XY-Z plane scan GaussSEFT  y  x  y  x Full compensation. x i, y i varied from 0 to -2  x f, y f varied from 0 to 2 

Tune spread compensation: shift in X-Z plane scan GaussSEFT  y  x  y  x Full compensation. x i, x f varied from 0 to 2  y i = 0, y f = 0

Tune spread compensation: symmetrical tilt in X-Z plane scan GaussSEFT  y  x  y  x Half compensation. x i varied from 0 to -3  x f varied from 0 to 3  y i = 0, y f = 0

Tune spread compensation: symmetrical tilt in XY-Z plane scan GaussSEFT  y  x  y  x Half compensation. x i, y i varied from 0 to -2  x f, y f varied from 0 to 2 

Tune spread compensation: shift in X-Z plane scan GaussSEFT  y  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 AB PC 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 BPMs Initialization 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.