Electron Cooling Commissioning Plans

1
Electron Cooling Commissioning Plans

• Sergei Nagaitsev
• September 16, 2004
• Contributions from C. Gattuso,
• A. Shemyakin and D. Broemmelsiek

2
Recycler stack evolution with rapid transfers
Cold antiprotons 50 eV-s, 10 ? mm-mrad Ready for
a transfer to the Tevatron
0
8
15
At present, the max. number of stored pbars is
15e11
3
Prepare 9 (6 eV-s each) bunches for extraction
4
Recycler transfers with gated cooling

• Every 30 min, a new batch of 22E10 pbars (15-p
  mm-mrad, 15 eV-s) arrive from the Accumulator and
  is kept separately for 25 minutes.
• During 25 min, the batch is pre-cooled by gated ?
  SC. The ? emittances are cooled from 15 to below
  10 p mm-mrad. The longitudinal emittance is kept
  unchanged.
• After that, the stack of 50 eV-s, 7-p mm mrad is
  merged with a 15-eVs, 10-p mm mrad batch. Now the
  electron cooling is applied. After 30 min, the
  phase space is cooled from 65 to 50 eVs, making
  it ready for the next merge.

5
Recycler transfers with gated cooling
Gated cooling ON OFF
Cold Stack
New batch
6
Gated Cooling
Two segments of beam (25e10 pbars each) one
cooled/gated and one not. The uncooled bunch
shows natural emittance growth due to IBS and
coulomb scattering.
7
Electron Cooling Long. Rate Design Goal

• Cooling needed 30 eV-s per hour
• To minimize the IBS rate, a 65-eV-s stack will be
  kept in a 4-µs long bunch 95 of particles will
  have its energy offset 8 MeV.
• For particles with ?E 8 MeV the drag rate needs
  to be about 4 MeV/hr to cool 15 eV-s in 30
  minutes.

8
Calculated long. drag rates
Design goal
9
Equilibrium long. emittance

• For a nearly constant drag rate F0 4 MeV/hr the
  equilibrium energy distribution is not gaussian
  but exponential f(E) exp(-E/s), where s
  D/(2F0) and D is the diffusion rate.
• The diffusion rate is mostly determined by the
  intra-beam scattering
• All our experience with the stochastic cooling
  system in Recycler to date is consistent with the
  IBS being the second (after new batch injection)
  largest longitudinal heating mechanism.

10
Calculated IBS diffusion rates for various
emittances 6,7,8 and 10 µm
11
Performance goal for the long. equilibrium
emittance 54 eV-s
12
The commissioning project plan summary

• Will begin on Dec. 1, 2004 an approximate date
  for the end of the shutdown.
• The Recycler will be brought to its pre-shutdown
  state. Same team, which commissioned the Recycler
  in 2004.
• The Electron cooling group will continue the
  installation until Feb 1, 2005.
• On Feb 1, 2005 the Recycler starts to contribute
  to HEP luminosity (mixed-source operations).
• The Recycler operations group and systems group
  becomes responsible for operations.
• This continues uninterrupted until about Apr 1,
  2005.
• On Feb 1, 2005 the effort switches over to the
  electron beam commissioning.
• Pelletron and U-bend start-up
• All of the electron cooling group the Recycler
  team.

13
The project plan summary

• On Mar 15, 2005 start commissioning of the
  complete electron beamline.
• Run electron beam in a pulsed mode
• Pbar operations are uninterrupted
• On Apr 4, 2005 start establishing a DC beam.
• The Recycler beam may be interrupted
• 2-weeks cycle 5-days ecool work (two shifts per
  day), 9-days pbar operations
• Investigate and correct MI ramp effects on the
  electron beam
• Minimize the effects of the electron beam on the
  Recycler beam, start running pbar and electron
  beams concurrently
• Establish a 500-mA dc electron beam by July 08,
  2005
• On July 11, 2005 start adjusting the electron
  beam parameters
• 500 mA dc beam is stable
• Establish and adjust the beam trajectory in the
  cooling section
• Measure the electron beam properties
• The pbar beam is interrupted when electron
  envelope is measured.
• By Sep 08, 2005 demonstrate the electron cooling

14
The project plan summary

• In Sep-Dec 2005 the Recycler continues to operate
  and contribute to the HEP luminosity.
• The cooling rates are measured electron cooling
  is optimized
• Dec 31, 2005 project ends.

15
Electron cooling system setup at MI-30/31
16
Electron cooling system setup at MI-30/31
17
Electron cooling system setup at MI-30/31
18
Electron beam design parameters

• Electron kinetic energy 4.34 MeV
• Absolute precision of energy ? 0.3
• Energy ripple ? 10-4
• Beam current 0.5 A DC
• Duty factor (averaged over 8 h) 95
• Electron angles in the cooling section
• (averaged over time, beam cross section, and
  cooling section length), rms ? 0.2 mrad

19
The Wide Band run - History

• 20-Mar-01- Fist time HV on both tubes
• 28-Dec-01 - 0.6 A in the short beam line
• 18-Nov-02 - beginning of a shutdown to switch to
  the full-scale line
• 17-Jul- 03 - DC beam recirculated through the
  full-scale line
• 30-Dec-03- 0.5 A DC beam
• 29-May-04- 0.1 A beam with no scalloping in the
  cooling section

20
The WideBand run History summary

• Short beam line
• 20 months of operation, including 8 months of
  shutdowns
• Operation learning unknowns (ions, crash
  dynamics, reliable acceleration rate)
  diagnostics
• Shutdowns 70 to repair, 30 to install new
  equipment
• Corresponding stage at MI-31 is supposed to take
  1.5 months
• 8-months shutdown to install the full-scale line
• Corresponding stage at MI-31 is supposed to take
  3 months
• Full-scale beam line (recirculation)
• 6 months of operation, including 2.5 months of
  shutdowns
• Operation diagnostics learning optics
  unknowns (wall charges, high losses)
• Shutdowns primarily for repairs
• Corresponding stage at MI-31 is supposed to take
  4 months
• Full-scale beam line (cold beam)
• 5 months of operation, including 1.5 months of
  shutdowns
• Operation diagnostics optics
• Shutdowns 10 to repair, 90 to install new
  equipment

21
The WideBand run Recirculation results
22
The WideBand Tests Electron Angles in the
cooling section
23
The Plan- stage 1

• Pelletron and U-bend commissioning 1.5 month
• Tubes conditioning
• Each section is conditioned to 1.1 MV. The total
  voltage of 5 MV is stable with all lenses on.
• Optics measurements in U-bend
• A pulsed beam is transported through the U-bend
  with low losses (lt 2).
• The OTR monitor under the acceleration tube and
  the pepper pot are commissioned. Data to restore
  the beam parameters at the acceleration tube exit
  are taken.
• DC beam in U-bend
• BPMs in the U-bend are commissioned.
• Crash diagnostics and the protection system are
  tested.
• 0.2 A beam stays at 4.34 MeV in a shift-long run
  with 95 duty factor.

24
The Plan- stage 2

• Full beam line commissioning 3 weeks
• A pulsed beam is transported through the entire
  beam line with low losses (lt 2 ).
• All BPMs (in the pulse mode) and the YAG/OTR at
  the end of the cooling section are commissioned.
• Trajectory responses are measured in the entire
  line, are analyzed, and major discrepancies are
  resolved.

25
The Plan stage 3

• DC beam commissioning 3 months
• Establish 5 mA DC beam.
• Beam line optics
• A program for measuring transfer matrixes is
  commissioned.
• All elements are measured with a DC beam. A
  simulated differential trajectory in the cooling
  section fits measurements within 0.05 mm.
• The absolute value of the electron energy is
  measured with precision of 0.3 by using the
  results of the longitudinal field measurements
  and the wave length of the electron trajectory in
  the cooling section.
• Energy stability
• Energy fluctuation in the bandwidth up to 100 Hz
  is estimated by analysis of a BPM signal from a
  high- dispersion region.
• Day-to- day energy variations are analyzed from
  measurements of the electron wave length in the
  cooling section. The relative value of both
  effects should not exceed 0.01 .

26
The Plan stage 3 (cont.)

• Beam position
• Drifts and oscillations of the electron beam
  position in the cooling section and in the entire
  line are measured and contributions of major
  sources of the motion, including MI ramp effects,
  are determined.
• A feedback loop stabilizing the beam position in
  the cooling section is commissioned.
• Effects of e-beam aborts on pbars
• Effects of e-beam aborts on pbars are measured,
  including recording pressure in MI-30 region and
  pbar positions.
• Establish 0.5 A DC beam

27
The Plan- stage 4

• Pbar cooling 2 months
• Low electron beam temperature in the cooling
  section

28
The Plan- stage 4 (cont.)

• Observe electron cooling
• The energies are aligned within 0.3 using
  absolute calibrations for both beams.
• Effect of electron cooling is observed by
  longitudinal Schottky monitor.

29
Pbar Beam Preparation for Cooling Demo

• 1010 antiprotons
• Coasting beam, No MI Ramps
• Ion trapping
• possible emittance growth
• Transverse Stochastic Cooling, wait until
  emittances are controlled
• Initial momentum cooling

30
Beam Preparation, II

• Use an RF level to smear momentum spectrum and
  fill the momentum aperture to 0.3
• 100Hz resolution bandwidth
• 3sec sweep, 20 averages
• After 4 minutes, spectrum has relaxed
• Tr. emittance remains small (3-pi). Loss of
  reliable emittance data

31
Cooling Model

• Electron beam
• Beam current 0.5 A
• rms angle spread 0.1 mrad (Teff 0.46 eV)
• rms energy spread (lab frame) - 200 eV
• Cooling section length 1.8 m (10 of total
  cooling section)
• Pbar beam
• Emittance (n, 95) 3-pi mm mrad
• full energy spread 28 MeV
• Relevant properties
• Coulomb log 7.2
• ve?gt vp?gtgt ve?? -- rest frame e-beam distribution
  is flat
• Cooling force for small vp?? is constant it
  is a drag rate, R0

32
Take Actual Spectra and Apply Model
33
15 Minutes 5dB signal
34
The Plan- stage 5

• Cooling optimization 2.5 months
• Adjustment of e-beam parameters
• Settings files for several beam currents and
  solenoid fields are composed.
• 0.5 A beam stays at 4.34 MeV in a shift-long run
  with 95 duty factor.
• Measurements of drag rate
• Gated stochastic cooling
• Recycler transfer commissioning
• Accumulation of 3?1012 pbars

35
Assumptions

• The commissioning team is identical to WBs as of
  May 04 (including B. Chase ( Co.), T.
  Bolshakov, B. Kramper, G. Saewert ( Co.), C.
  Schmidt) and/or expanded by the Recycler dpt.
• Two 6-hour shifts are run 5 days a week.
• By the beginning of commissioning (Feb. 1, 05),
  all equipment is installed and is ready to go.
• Interference with the Recyclers HEP operations
  is negligible.
• We are very lucky, and no major repairs are
  necessary during commissioning.
• No interruptions caused by a lab-wide shutdown
  are included.

36
Interference with the Recyclers work for
luminosity

• Effects of ECool bends and cooling section field
  on the pbar dynamics in RR- should be corrected
  anyway
• Effects of the ebeam space charge on pbar
  dynamics in RR- supposed to be negligible
• Changes in the pbar lifetime caused by a pressure
  rise in the cooling section- is negligible
  according to measurements in WB
• Drag force- e- beam measurements can be done
  either at low electron currents or at the
  electron energy shifted by 1
• Measurements of DC beam dimensions in CS and
  measurements with the YAG/OTR downstream of the
  cooling section- no pbars in RR

37
The summary

• The Recycler is brought up to its present level
  through a known and well-documented process
• The Recycler never stops contributing to the HEP
  luminosity, it just becomes more efficient over
  about 12 months period.
• The electron cooling beam is commissioned through
  a series of well-defined incremental steps.
• We have no schedule contingency in our plan
  everything has to work just right.