Electron Cooling Commissioning Update

1
Electron Cooling Commissioning Update

• Run II meeting
• May 12, 2005
• L. Prost, Ecool Group

2
Outline

• Goal, design, plan, installation highlights
• Commissioning progress highlights
• Some specifics of what has been achieved
• Whats ahead, some important issues that remain
• Conclusion

3
People of Ecool

• Recycler department head
• Sergei Nagaitsev
• Recycler deputy department head
• Cons Gattuso
• Ecool Project engineer
• Jerry Leibfritz
• Ecool Safety officer
• Mike Gerardi
• Electron cooling group
• Alexey Burov
• Kermit Carlson
• Grigory Kazakevich
• Tom Kroc
• Lionel Prost
• Sasha Shemyakin (GL)
• Mary Sutherland
• Vitali Tupikov
• Arden Warner

• Recycler department personnel
• Valeri Balbekov
• Dan Broemmelsiek
• Jim Crisp
• Martin Hu
• Dave Johnson
• Dave Neuffer
• Bill Ng
• Stan Pruss
• Meiqin Xio
• Other AD departments
• Brian Chase
• Paul Joireman
• Ron Kellett
• Brian Kramper
• Valeri Lebedev
• Mike McGee
• Jerry Nelson
• Lucy Nobrega

4
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.

5
Performance goal for the long. equilibrium
emittance 54 eV-s
6
Electron beam design parameters

• Electron kinetic energy 4.34 MeV
• Absolute precision of energy ? 0.3
• Energy ripple 500 V rms
• 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

7
Commissioning challenge

• Technical issues not fully resolved with
  prototype system at Wide Band
• Poor reliability of operation at 4.3 MV
• Insufficient quality of the cooling section
  magnetic field
• High beam losses
• Low-frequency electron beam motion
• Inadequate protection system
• Concurrently attain stable operation at 4.3 MV,
  0.5 A with rms angular spread lt 0.2 mrad in
  cooling section

8
Commissioning guiding principles

• Establish some beam and verify optics (pulsed
  beam, first order)
• Choice of a pulsed beam over low-current DC beam
• Check polarities, calibration, of all lenses and
  correctors
• Increase beam intensity (pulsed ? DC)
• Low current loss to maintain recirculation
• Make the beam cold (i.e. good understanding of
  the optics and beam control)
• Only way to achieve cooling
• Maintain hardware integrity (i.e. avoid drilling
  a hole !)
• U-Bend mode to develop and test protection systems

9
The commissioning project plan summary

• On Feb 1, 2005 the Recycler starts to contribute
  to HEP luminosity (mixed-source 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
• 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
• 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

10
The commissioning project plan summary (cont)

• 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
• 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.

Plan assumed no major component failures and no
lab wide shutdown in 05
11
Major changes to the plan (so far)

• Commissioning began 1 month late
• Increased number of shifts/week to compensate
• Should not affect milestone for first observation
  of electron cooling of pbar
• U-bend and full line are being commissioned in
  parallel
• Partly because of late start of commissioning
• Partly because of delays in getting DC beam
  permit
• Higher number of shifts allows simultaneous
  progress

12
Electron Cooling Installation Schedule/Highlights

• 5/04 MI-31 Building Construction Complete
• 5/04 RD Operations at Wide Band Complete
• 6/04 Disassembly/Move of Pelletron Begins
• 8/04 13-week Lab Wide Shutdown
  Begins(Pelletron Assembly Suspended)
• In situ magnetic field measurements of the
  cooling section solenoids
• 11/04 Lab Wide Shutdown Complete(Pelletron
  Assembly Resumes)
• 2/05 Pelletron/E-Cool Installation Complete
• 3/05 Commissioning Begins

13
Electron cooling system setup at MI-30/31
Added section
(includes additional pumping)
Beam line accommodates both U-bend and vertical
bend magnets
Fast acting valves
Magnetically shielded to protect e beam from
fields imposed by the MI bus
14
Electron cooling system setup at MI-30/31
Pelletron (MI-31 building)
Cooling section solenoids (MI-30 straight section)
15
Mechanical oscillations of the Pelletron

• Mechanical vibrations in the Pelletron were
  greatly reduced between the Wide Band assembly
  and the current assembly at MI-31
• May help reduce beam motion in accel/deccel tubes
• May help HV stability (i.e. avoid full
  discharges)

MI-31 assembly Wide Band lab assembly Peak _at_
3 Hz Chain transverse oscillations Peak _at_ 30
Hz Rotating shaft
16
Commissioning Milestones Highlights

• Feb, 21st All vacuum work Complete
• Feb, 22nd First HV on terminal
• Feb, 25th Installation Complete
• Mar, 2nd Stable 500 kV in air
• Pulsed beam to first BPM
• Mar, 7th All systems ready for commissioning
• Charging system, gun, pulser work
• Mar, 8th Stable 2.5 MV (tank pressurized w/
  SF6) Begin tubes conditioning
• Mar, 10th First light on OTR (acceleration
  side)
• Mar, 12th End of tubes conditioning (5 MV
  stable)
• Mar, 17th 4.3 MeV, 0.5 A pulsed beam to
  collector (U-Bend mode, low losses)
• Regulation system works properly
• Mar, 21st Correctors to compensate dipole
  effects of Ecool on Recycler optics commissioned

17
Commissioning Milestones Highlights (cont)

• Mar, 27th 4.3 MeV, 50 mA pulsed beam through
  cooling section
• Correctors settings very different from
  calculations based on magnetic measurements
• Mar, 28th Apr, 5th Shutdown (Pelletron tank
  opened)
• Charging circuitry fixed
• Updated gun lens power supply
• Removed hard-wired -5 kV Ready for DC beam
• Apr, 7th 4.3 MeV, 35 mA DC beam to collector
  (U-Bend mode)
• Apr, 12th Low intensity, 4.3 MeV pulsed beam to
  collector (full line)
• Protection systems commissioned with pulsed beam
• Apr, 20th First DC beam (few mA) in Recycler
  beam line
• Apr, 27th 4.3 MeV, 350 mA pulsed beam to
  collector (full line)
• Correctors settings based on magnetic measurements

18
Commissioning Milestones Highlights (cont)

• May 3rd 4.5 MeV, 750 mA DC beam to collector
  (U-Bend)
• Low magnetic flux configuration
• Preparation for long run
• but full discharge occurrences increase
• May 4th First beam size measurements in cooling
  section (pulsed beam)
• Recycler empty

19
Tubes conditioning

• Pelletron is divided into 6 sections
• Each section was conditioned to 1.2 MV
• All sections together were conditioned to 5 MV
  (the operation voltage is 4.32 MV)
• Conditioning took 5 days (elapsed time)
• Detail for individual sections
• Other info
• First vacuum activity began at 0.55 0.75 MV for
  individual sections
• A Java Final State Machine was used for
  conditioning
• Conditioning was interrupted several times for
  some beam related studies at low energy

20
Tubes conditioning - Sections 1-3 (example)
21
High Voltage Stability

• Reliable operation at 4.3 MV
• Partly due to added section
• Wide Band vs MI-31

Pulsed beam
Intentional
Pulsed beam, 3 hoursMultiple discharges
Pulsed and DC beam, 6 hours No discharge
22
Protection system

• Fast acting valves between Pelletron and Recycler
  ring (on Supply and Return lines)
• Activated if pressure rises on the Pelletron side
  (as a result of a full discharge for instance)
• Monitor several dozen signals with the Pelleron
  Mode Controller (Java Application)
• Signals include
• - All BLMs
• - Capacitive pickups (CPOs) (e.g. for terminal
  voltage discharges)
• When one channel is out of tolerance
• - Gun is closed (i.e. beam extraction is
  interrupted)
• - Trip flag is up (need operator to reset
  before re-establishing beam)
• - All signal waveforms are saved in the buffer
  (512 ms long over a time window that includes the
  trip)
• Both the Fast acting valves logic and the
  Pelletron Mode Controller were tested
• Improvements were made (increase response speed,
  more devices recorded, adjusted limits,)

23
Protection system (cont)

• To avoid full discharges and/or damaging the
  tubes , it is important to shut off the gun as
  fast as possible
• Right now, it takes about 1 ms to close the gun
  after the beam permit has been taken off
• Faster circuit will be installed during next
  shutdown

Gun closes
YellowFast CPO CyanBeam permit WhiteCathode
current transformer
1 ms
Permit removed
24
Diagnostics

• YAG crystal, OTR monitors throughout the beam
  line
• Beam size (shape), distribution
• Used to compare to optics models
• 1 multi-wire scanner
• Beam size and shape after 180 bend
• Removable apertures in the cooling section
• Between each of the ten cooling section solenoid
• Beam size and angle
• BPMs
• Between each of the ten cooling section solenoid
  16 in other beam lines (accel, supply, return,
  transfer, decel)
• Can measure both pulsed and DC beam
• Capable of monitoring both electrons AND pbars

25
OTR Detectors for the Medium Energy Electron
Cooler

• Detector characteristics
• 5 µm foil
• Lower current limit 20mA
• Resolution 50 µm
• Applications
• Real-time charge density distribution and beam
  size measurements
• Measurement of beam initial conditions in the
  acceleration section
• Beam ellipticity measurements
• Beam temperature measurements with pepper-pot

Beam Image from OTR at full current (acceleration
tube exit)
Beam profile versus Lens current on acceleration
side
26
Recirculation in U-Bend mode Short run

• 700 mA DC beam re-circulating with low losses
  (5-10 minutes without discharges)

GreenBias current CyanCollector
pressure BlueAcceleration tube
current RedNeedle current
Relative current loss at 0.5 A 6e-6
27
Beam in cooling section (i.e. in Recycler ring)

• Pulsed beam transported through the full line
  with low loss and low spatial oscillations in
  cooling section
• Correctors settings in cooling section based on
  magnetic measurements made in-situ during
  installation

Cooling section
Horizontal displacement
Vertical displacement
BPM intensities(correspond to 50 mA)
28
Optics measurements

• Understanding the beam lines optics (supply line
  in particular) is primordial in order to gain the
  beam envelope control necessary to achieve
  cooling
• Principle Differential trajectories measurements
  (good for linear optics only)
• Method
• - Take reference orbit
• - Apply kick and measure betatron motion of the
  beam
• - Repeat 4 times ( energy kick for
  dispersion)
• - Check reference orbit
• Preliminary measurements
• Determine that all lenses and correctors are
  hooked up correctly and/or identify problems
• Exercise/commission differential orbit
  measurement programs
• Calibration of power supplies
• Help achieving clean transport of the beam

29
Supply line optics Data vs OptiM

• After various problems were found and fixed, and
  several iterations for calibration purposes,
  measurements (with pulsed beam) are mostly
  consistent with OptiM calculations

Supply line
30
Preliminary energy measurements

• For cooling, the electron beam and pbar bunches
  energies need to be aligned, thus measuring the
  electron beam absolute energy is critical (lt0.3
  )
• Principle Measure the Larmor frequency of the
  beam oscillations in the cooling section solenoid
  (via differential trajectories measurements)

• So far, measurements indicate that the energy is
  lower than expected by 3
• Correlated by optimum bends settings found
• Awaits more precise measurements with DC beam

31
Preliminary total angles

• Except for dipole offsets, no attempts were made
  to minimize the angles (at this stage)

32
Whats next ?

• DC beam commissioning in the full line
• Beam line optics
• Needs to be analyzed and adjusted to establish
  design beam size and rms angular spread
• Energy stability
• Energy fluctuation is estimated by analysis of a
  BPM signal from a high- dispersion region
• Establish 0.5 A DC beam
• Observe electron cooling
• The energies are aligned within 0.3
• Effect of electron coolingis observed by
  longitudinal Schottky monitor

33
Interference with the Recyclers work for
luminosity

• Effects of ECool bends and cooling section field
  on the pbar dynamics in RR- Corrected and tested
• 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. Also, fast
  isolation valves installed and tested
• Drag force- many 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
• If above is correct, the electron cooling tune-up
  may be done with Recycler being emptied between
  the TeV shots and pbar shots from the Accumulator

34
Some Remaining Outstanding Issues

• Recirculation for long runs (i.e. hours) is not
  established
• Full discharges cannot be prevented (so far)
• Main injector beam loss trips our loss monitors
• Temporary fix increase protection system limits
  but
• beat the purpose
• Need MI people to work on reducing losses and/or
  additional shielding
• OTR cameras in MI-30 tunnel damaged by radiation
• Beam motion with MI ramps
• Prevents recirculation high intensity beam
• Additional magnetic shielding will be installed

35
MI losses (mostly detected on the return line)

• Losses appear to be related to slip stacking
• First attempts to reduce them were not successful

GreenC90 loss monitor RedR06 loss
monitor BlueR04 loss monitor CyanMI beam
current
Original trip level for DC beam operation
36
MI ramp induced beam motion

• Stray fields from the MI bus and/or QCL alter
  the beam orbit in the return line (mostly)
• Induces losses downstream

Beam loss spikes on the QCL negative slope
1 Hz repetition rate (random w.r.t. MI ramp)
37
Summary

• Achieved stable high voltage regulation (with
  beam) at designed Pelletron energy (4.3 MV)
• Achieved DC electron beam in the Recycler beam
  line (35 mA)
• Achieved stable (i.e. minutes) high intensity
  (i.e. 750 mA) DC beam in U-Bend mode
• Implemented and tested (in U-Bend mode) all
  protection systems
• Interference with Recycler operation was minimal
• Will increase now
• Although the commissioning started later than
  originally planned, we still expect to observe
  cooling of pbar by September 8, 2005.