Download - The State of the Art in Hadron Beam Cooling
The State of the Art inThe State of the Art inHadron Beam CoolingHadron Beam Cooling
HB2008 42nd ICFA Advanced Beam Dynamics Workshop on
High-Intensity, High-Brightness Hadron Beams
August 25th, 2008
L.R. Prost, P. Derwent
Fermi National Accelerator LaboratoryFermi National Accelerator Laboratory
ICFA-HB2008 L. PROST 2
Acknowledgement and disclaimerAcknowledgement and disclaimer
Work and results presented in this talk come from many sources and represent the efforts (and successes) of many groups and individuals around the world FNAL, BNL, CERN, BINP, GSI, Kyoto University, IMP
Lanzhou,… Special thanks to:
• Vasily Parkhomchuk, Mike Blaskiewicz, Alexey Fedotov, Gerard Tranquille
Best effort to include and cover the most I could in ~30 minutes, but: I will focus on what is being done today at various facilities I have an inevitable bias
• Recycler Electron Cooler and electron cooling in general There is a non-negligible possibility that I overlooked some
important results/achievements• I apologize in advance for those who feel they belong to this
category
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OutlineOutline
What is cooling, cooling techniques Stochastic cooling
Bunched beam
Electron cooling Low energy coolers
• Beam shaping High energy coolers
• FNAL
Other (less advanced) work/projects Beam ordering Optical stochastic cooling Coherent Electron Cooling (CEC) Proton ionization cooling
Conclusion
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Beam cooling techniquesBeam cooling techniques
Definitions of ‘beam cooling’ Beam cooling corresponds to an increase of the 6D phase-
space density Equivalently, cooling is a reduction in the random motion
of the beam particles
Cooling techniques currently widely used Stochastic cooling Electron cooling Synchrotron radiation cooling
• Negligible for hadrons– Small effects (good and bad) start with LHC energies
Laser cooling• For certain type of ions only
Resistive cooling• At very low energy in electromagnetic traps
– Not really a hadron beam anymore
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Stochastic cooling at FNALStochastic cooling at FNAL
Used for antiproton production in 3 different rings From production to extraction (from the Recycler), 6D
phase-space density increases by ~200 million• Electron cooling directly contributes to only a factor of ~5-10
DebuncherInjection
DebuncherExtraction
AccumulatorInjection
AccumulatorExtraction
RecyclerInjection
RecyclerExtraction
1.E+00
1.E+01
1.E+02
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Stochastic cooling at FNAL – Main features highlight Stochastic cooling at FNAL – Main features highlight (I)(I)
Debuncher: Optical notch filter
• >30 dB depth, ~ ±1 ppm dispersion (i.e. notch position jitter)• 1 and 2 turn delays (switches during a cycle)
Accumulator: Implemented equalizers – made of passive electronics - on
almost all systems (the last one will be done shortly)• Brings gain and phase closer to ideal (i.e. zero phase and
linear gain as a function of the frequency in the band considered)
Without equalizer With equalizer
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Stochastic cooling at FNAL – Main features highlight (II)Stochastic cooling at FNAL – Main features highlight (II)
Recycler: Optical transmission across the ring
• Cable is too slow ! Gated cooling possible
• Cooling over different sections of the ring with different systems and/or gains
Along with electron cooling (later slides), cooling in the Recycler allowed the accumulation of ~1015 antiprotons since the beginning of this year
Evacuated pipe installation for laser-light link
Laser alignment
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Bunched beam stochastic coolingBunched beam stochastic cooling
Stochastic cooling is an effective and well-established technique, however problems arise for bunched beam High density of the bunches
• Stochastic cooling efficiency scales as 1/N Synchrotron motion affects mixing Creates coherent spikes in the Schottky spectra that needs
to be eliminated• Coherent power dominates the spectra which limits the gain
and power that can be applied– Example: Schottky spectrum from BNL (5 ns bunches)
Coherent bunched signal ~30 dB larger than the Schottky signal
M. Brennan et al. COOL’07 Proceedings
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M. Brennan et al. COOL’07 Proceedings
Bunched beam stochastic cooling at RHICBunched beam stochastic cooling at RHIC Motivation
Counteract IBS during stores to increase integrated luminosity
Prevent de-bunching (halo cooling) Challenges
A cooling time of about 1 hour is required Beam energy is 100 GeV/nucleon
• Produce HV kicker (3 kV amplitude) in the 5-8 GHz band The beam is bunched to 5 ns in 200 MHz rf buckets
Dealing with the coherent components: Filter the pick-up signal Use filter built from coaxial cables adjusted to precise
5.000 ns intervals with small 100 ps coaxial trombones
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Results with Gold ionsResults with Gold ions
The beam loss rate has been reduced to the “burn off” level (beam is lost to collisions only)
Cooling prevented de-bunching Gated off during abort gap
First store with cooling running in the Yellow ring
M. Brennan et al. COOL’07 Proceedings
Gold ion lifetime in both rings (yellow and blue) for 5 stores
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Stochastic
cooling
Main challenge remaining Beam in the satellite buckets
• Currently addressed by trying to reduce the emittance growth during acceleration
Plans Yellow ring longitudinal system is operational
• Blue ring longitudinal system operational this coming run• Yellow vertical system will also be commissioned
New transverse pickups are being designed• Hope to have one installed for the next run
To address the formation of satellite bunches:• Working on quadrupole damper to damp transition mismatch• A 2nd harmonic cavity is being designed (to be completed
~2011)– This device should eliminate satellite bunches
Status and plansStatus and plans
Satellites
M. Blaskiewicz et al.PRL 100 174802 (2008)
Blue: simulationRed: data
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Low energy electron coolingLow energy electron cooling Relatively modest design evolution since the early 70’s
Some new features on the two latest coolers (LEIR at CERN and CSRm at IMP, Lanzhou) built by BINP Very precise magnetic field obtained through a large
number of trim coils ‘Hollow’ electron beam (or more generally speaking, beam
shaping capability)• Avoids “overcooling of the core”, which leads to instabilities• Reduces ion-electron recombination
Electrostatic bends• Reduces trapping of secondary particles Improves electron
beam stability
Other more subtle innovations Magnetic expansions
• Allows adjustments of the electron beam size High magnetization High perveance
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Innovative features High perveance gun Beam expansion Electrostatic bend Pancake structure
of magnets Variable electron beam
profile
Similar electron coolers for LEIR and CSRmSimilar electron coolers for LEIR and CSRm
G. Tranquille et al. COOL’07 Proceedings
V. Parkhomchuk et al. COOL’07 Proceedings
CSRm cooler
LEIR cooler
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Produce the Pb ion beam with the characteristics required for the first LHC ion run (Nions = 2.2x108, εh,v < 0.7 μm)
Standard 3.6s LEIR cycle 2 LINAC pulses are cooled-stacked in 800ms at an energy
of 4.2 MeV/n After bunching the Pb ions are accelerated to 72 MeV/n for
extraction and transfer to the PS.
Goals of the commissioning runs at LEIRGoals of the commissioning runs at LEIR
Successful Successful !!
G. Tranquille et al. COOL’07 Proceedings
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Acceleration
BunchingCooling OFF
2nd injection
1st injection
Profile at 2nd injection
Profile at the end of cooling
Horizontal beam profile measured on the IPM.
Cooling performance at LEIRCooling performance at LEIR
The cooling time is about 0.2 s After switching off the
electron beam, the emittance blows up from 0.1 to 0.3 π mm mrad by the action of IBS
Courtesy ofG. Tranquille
V. Parkhomchuk et al. COOL’07 Proceedings
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Increase the intensity of heavy ions accumulated for extraction to the experimental ring (CSRe) Transverse cooling of the ion beam after horizontal multi-turn
injection allows beam accumulation at the injection energy Cooling times of 100 to 2500 ms depending on the ion
species• Horizontal emittance from decreased from 150 to < 20 p mm
mrad• Momentum spread reduced by a factor of 10 (from ~10-3 to ~10-
4)
Intensity increase in a synchrotron pulse by more than one order of magnitude has been achieved In a given accumulation time interval of 10 seconds, 108
particles have been accumulated and accelerated to the final energy
The momentum spread after accumulation and acceleration in the 10-4 range has been demonstrated in five species of ion beam
Goals and results for CSRmGoals and results for CSRm
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Stability issues have been observed for ion beam cooled with electrons Beam-beam effects leading to
• (slow) Ion loss or diffusion• Injection ‘fast loss’ • Development of instability in a well cooled ion beam due to its
interaction with the electron beam (known as ‘electron heating’)
Instability when secondary ions are trapped in the electron beam• Also addressed by electrostatic bends
Proposed mechanism is ‘overcooling’ of the core of the ion beam Sets a limit of the densities that one can achieve (V.
Parkhomchuk)
Stability of cooled beamsStability of cooled beams
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Both cooler at LEIR and CSRm have the capability to provide beam current density distributions of various ‘hollowness’
Variable profile electron gunVariable profile electron gun
X. Yang et al. COOL’07 Proceedings
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At both LEIR and CSRm, number of accumulated ions increased with a partially hollow beam By ~2× at LEIR mostly because of a better lifetime
Cooling with a hollow electron beamCooling with a hollow electron beam
0.7 × 109 Pb ions 1.3 × 109 Pb ions
More systematic measurements at CSRm show better accumulation results for Ucontr/Uanode ~ 0.2-0.4
V. Parkhomchuk et al. COOL’07 Proceedings
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High energy electron coolingHigh energy electron cooling
One unique facility at FNAL’s Recycler ring First demonstration of relativistic electron cooling in July
2005 Operational since mid-October 2005
• Used in parallel with stochastic cooling Other facilities are being considered/designed (RHIC at
BNL, FAIR’s HESR at GSI)
All proposals (including at FNAL) Long interaction region (15-20 m instead of 1-3 m for low
energy coolers)• Cooling times much longer than for low energy coolers
Energy recuperation scheme• Energy recovery Linac for bunched electron beam• Electrostatic accelerator for DC electron beam
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FNAL’s Recycler Electron Cooler (REC)FNAL’s Recycler Electron Cooler (REC)
Goal of cooling in the Recycler Increase longitudinal (and transverse) phase space density
of the antiproton beam in preparation for• Additional transfers from the Accumulator• Extraction to the Tevatron
Electron energy MeV 4.338
Beam current used for cooling
A 0.05 - 0.5
Magnetic field in CS G 105 Beam radius in the cooling section
mm 2.5 - 5
Pressure nTorr 0.2 - 1 Length of the cooling section
m 20
Main features Electrostatic accelerator (Pelletron)
working in the energy recovery mode DC electron
beam Lumped
focusing outside the coolingsection
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Accumulation performance Accumulation performance
Use of electron cooling allowed the storage and extraction of more than 450 × 1010 antiprotons > ~3 times what would be possible with stochastic cooling
alone• Much faster too
Delivers very consistent bunches (i.e. same emittances shot to shot)
Plays a major role in increasing the initial and integrated luminosities in the Tevatron
• Record initial luminosity > 300 × 1030 cm-2 s-1
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Momentum offset [MeV/c]
Am
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Longitudinal Schottky distribution
Before extraction to the TeV:
N = 375 × 1010
L (95%) = 68 eV s
t (95%, n) = 3.1 p mm mrad (Schottky)
08/22/08
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Electron cooling in operationElectron cooling in operation
Electron beam adjusted to provide stronger cooling as needed (progressively) Adjustments to the cooling rate are obtained by bringing
the pbar bunch in an area of the beam where the angles are low and electron beam current density the highest
This procedure is intended to maximize This procedure is intended to maximize lifetimelifetime
Similarly to low energy coolers, cooling seem to induce secondary beam-beam effects. In our case, it affects the lifetime of the cooled beam.
5 mm offset 2 mm offset
pbars
electrons
Area of good cooling This procedure can
be regarded as ‘painting’ and, in fact, is almost equivalent to the ‘hollow beam’ concept for low energy coolers.
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Cooling performanceCooling performance
Cooling rates show a fairly strong dependence on the antiproton beam emittance Importance of stochastic cooling to reduce transverse ‘tails’
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Bunched Unbunched Model based on cooling force measurements
All measurements made with electron beam on axis(i.e. maximum cooling)
Rates ‘corrected’ to take into account differences of the initial momentum spread
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Beam orderingBeam ordering
Refers to experiments aimed at achieving conditions such that ions in the beam re-arrange themselves in a crystal-like structure 1D ordering was demonstrated at GSI (1996) with heavy-ions 3D ordering much tougher to achieve
• Succeeded at very low energy with PALLAS (2001)• High energy ordering limited by ‘shear heating’
– One solution: dispersion free lattice
Beam ordering experiments are being carried out at Kyoto University A new ring (S-LSR) has been commissioned
• Dispersion suppressed lattice• Both laser and electron cooling can be used (but not
simultaneously) 1D ordering of protons was achieved with electron cooling
• T. Shirai et al., “One dimensional beam ordering of protons in a storage ring”, Phys. Rev. Lett., 98 (2007) 204801
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First laser cooling results at S-LSRFirst laser cooling results at S-LSR
Fixed laser frequency and induction voltage deceleration (not in the dispersion free mode) High momentum spread after cooling believed to be due to
transverse-to-longitudinal redistribution through IBS• Need to reduce the number of particles to achieve ordering (1D)
– Need better diagnostics before proceeding
~108 Mg+
A. Noda et al. COOL’07 Proceedings
• At EPAC’08,reportedp/p 6.2 × 10-5 (1)with ~106 Mg+
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Optical stochastic cooling (I)Optical stochastic cooling (I)
Idea proposed by Mikhalichenko and Zolotorev (PRL 71 4146 (1993)) Ultra-broadband system
• Traditional (microwave) stochastic cooling is bandwidth limited Transit-time method (M. Zolotorev & A. Zholents, Phys.
Rev. E 50, 3087 (1994))
W. Franklin et al. COOL’07 Proceedings
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Optical stochastic cooling (II)Optical stochastic cooling (II)
Experiment to demonstrate the principle of OSC designed at the MIT-Bates south hall ring Realization plan for OSC demonstration with electrons over
3 years• Y1: Beam studies for OSC Lattice, amplifier bench tests• Y2: Install and commission OSC chicane, wigglers, amp• Y3: Experimental program to study OSC of damped electron
beam Awaits for funding
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New (or renewed) interestsNew (or renewed) interests
Lattice optimization for stochastic cooling Lattices that circumvent the ‘mixing dilemma’
• Often considered but never implemented• ‘Asymmetric’ lattice
– Low dispersion at the pickup– High dispersion at the kicker
Possible modular approach to construct cooling ring lattices consisting of small momentum compaction modules from pick-up to kicker and negative momentum compaction modules from the kicker to the pick-up
Use of an electron beam for stochastic cooling Relies on the idea of coherent electron cooling (CEC) (Y.
Derbenev)• General idea: Amplify response of e-beam to an ion by a micro-
wave instability of the beam– Combines advantages of both electron and stochastic
cooling Make it more realistic with the latest successes of FEL, ERL,
… technologies
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Ionization cooling of protonsIonization cooling of protons
Ionization cooling is not a new scheme* but not efficient/attractive with protons (and heavier ions) Nuclear reaction rate energy-loss cooling rate
Can work when/if the absorber is also the target FFAG-ERIT neutron source (Mori, KURRI)
• 10 MeV protons (β = v/c =0.145)• 10Be target for neutrons• 5µ Be absorber
K. Okabe et al. EPAC’08 Proceedings
Momentum spread induced by the target(analytical)
Momentum spread with energy recovery(assumes large transverse acceptance)
* Skinskii & Parkhomchuk, Sov. J. Part. Nucl. 12, 223, 1981
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R&D projects on future facilities (I)R&D projects on future facilities (I)
RHIC electron cooling projects Electron cooling for Low-Energy RHIC operation at of
2.6-12 (“critRHIC” project) is being pursued• See A. Fedotov’s poster presentation
Coherent Electron Cooling (CEC) emerged as the most powerful technique for cooling of hadrons for the future eRHIC (electron-ion collider) project. This technique is now the main focus of R&D at BNL
• Proof-of-Principle of CEC by cooling Au ions at about 40 GeV/n using an ERL (20MeV electrons) which is presently under construction at BNL
– Commissioning of the ERL is planned for 2009-2010
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R&D projects on future facilities (II)R&D projects on future facilities (II)
ELIC (polarized ring-ring electron-ion collider) electron cooler Conceptual design of the cooler based on:
• 30 mA, 125 MeV energy recovery linac (ERL) operating at 15 MHz
• 3 A circulator-cooler ring (CCR) operating at 1500 MHz bunch repetition rate
Ya. Derbenev et al. COOL’07 Proceedings
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R&D projects on future facilities (III)R&D projects on future facilities (III)
FAIR First phase of the project is approved and funded Stochastic cooling to be used in various rings
• Careful design of the lattices to optimize cooling Electron cooler on the HESR (at a later phase of the
project)• Current design based on an electrostatic accelerator similar to
the one use at Fermilab• One big difference: Expect to have continuous magnetic field
from the gun to the collector (FNAL used an interrupted-focusing transport line)
– 2 MeV cooler at COSYas an intermediate step
– Prototype of aHV section has beensuccessfullytested
V. V. Parkhomchuk, Electron Cooling for COSY,Internal Report (2005).
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ConclusionConclusion
Need/request for more intense and brighter beam requires sophisticated cooling systems Traditional cooling schemes (stochastic, electron) continue to
evolve• High energy, beam density profile for electron cooling• Better/optimum lattice designs, optical stochastic cooling,
stochastic cooling of bunched beam Development of FEL, ERL makes Coherent Electron Cooling
an attractive new cooling method for high energy, high intensity hadron beam
While I focused on experimental results, simulation of the various processes are being carried out along the way and allow for robust designs… … however, more needs to be understood and possibly
modeled
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Cooling techniques (not only for hadron beams) are discussed at a biennial “Workshop on Beam Cooling and Related Topics” Obviously, much more in depth presentations on all
topics touched on here… and others Next workshop: COOL’09 at IMP, Lanzhou, China
• Announcement in the coming months
The last word…The last word…
THANK YOU FOR YOUR ATTENTIONTHANK YOU FOR YOUR ATTENTION
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EXTRASEXTRAS
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Bunched beam stochastic cooling at RHIC (IV)Bunched beam stochastic cooling at RHIC (IV)
Data agree very well with simulationsM. Blaskiewicz et al. PRL 100 174802 (2008)
Blue: simulationRed: data
Bunch profile evolution from a wall current monitor –
top: without stochastic cooling;
bottom: with stochastic cooling
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With only the B field in the toroids, the relative current losses are as much as an order of magnitude higher than with a crossed electrostatic and magnetic field Currents of up to 530 mA can be obtained with both fields
on and the electrostatic field optimized
Electrostatic bend to improve electron beam Electrostatic bend to improve electron beam stabilitystability
G. Tranquille et al. COOL’07 Proceedings
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Setup of Fermilab’s Electron CoolerSetup of Fermilab’s Electron Cooler
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Cooling performance stabilityCooling performance stability
We have 3 major performance-limiting stability issues Degradation of the cooling section magnetic field
• Likely due to ground motion in the tunnel• Beam based alignment procedure was developed and
tested– Large uncertainties but it worked
Drift of the antiproton trajectories• May be due to ground motion too• Needs to be re-align (3-bump) every 1-2 months
High voltage stability (and calibration)• Next slides
± 0.5 mm
± 0.5 mm
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High voltage/Electron beam energy stabilityHigh voltage/Electron beam energy stability
Average energy drifts by up to 1-2 keV (over several weeks) Cooling efficiency is greatly reduced
Temperature dependent• ~ -300 V/C
– Mostly an issue at turn on (~6-10 hours to reach equilibrium)
– Equilibrium temperature stable to within 1C But not only…
Longitudinal Schottky profiles after cooling with the electron beam on axis for ~2h at 100 mA
Np = 200 × 1010 Np = 280 × 1010
Flatness of the distribution attributed to the electron beam energy to be offset
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rElectron cooling drag rate - TheoryElectron cooling drag rate - Theory
For an antiproton with zero transverse velocity, electron beam: 500 mA, 3.5-mm radius, 200 eV rms energy spread and 200 μrad rms angular spread
Non-magnetized cooling force model
e
pe
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ce
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e-folding cooling time: 20 minutes
111×1010 pbars
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Strong transverse cooling is routinely observedStrong transverse cooling is routinely observed
e-folding cooling time (FW): 25 minutes
100 mA, on axisStochastic cooling off
135×1010 pbars
6.5 s bunch
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Comparison with cooling force measured at low-energy Comparison with cooling force measured at low-energy coolerscoolers
Vp, cm/s
eV/m
Comparison with data for normalized longitudinal cooling force measured at low energy coolers adapted from I.N. Meshkov, Phys. Part. Nucl., 25 (6), p. 631 (1994).
)10/( 138||
* encmFF
Red triangles represent Fermilab’s data measured at 0.1 A. The current density is estimated in the model with secondary electrons.
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Coherent Electron Cooling (CEC) at BNL Coherent Electron Cooling (CEC) at BNL
1. Idea was suggested by Ya. Derbenev, Proc. of 7th Nat. Acc. Conf., V. 1, p. 269 (Dubna, Russia, 1980).
2. The high-energy scheme based on FEL amplification was developed by V. Litvinenko and Ya. Derbenev, Proc. of FEL07 (Novosibirsk, Russia, 2007).
3. Summary of R&D progress of CEC at BNL will be presented at FEL08 by V. Litvinenko et al.
(V.N. Litvinenko et al.)(V.N. Litvinenko et al.)