Status of High Energy Electron Cooling at FNAL’s Recycler Ring XX th Russian Conference on Charged...

Status of High Energy Electron Cooling at FNALs Recycler Ring XXth Russian Conference on Charged Particle Accelerators

September 13th, 2006L. Prost, Recycler Dpt. personnelFermi National Accelerator Laboratory

XXth Russian Conference on Charged Particle Accelerators L. PROST, et al.

OutlineContext of electron cooling at FNALElectron beam propertiesElectron cooling in operationConclusion


Fermilab complexThe Fermilab Collider is an Antiproton-Proton Collider operating at 980 GeV


Antiprotons and LuminosityStrategy for increasing luminosity in the TevatronImprove the performance of the injector chainAlignment and lattice changes in the TevatronSee A. Valishev reportIncrease the number of antiprotonsImprove stacking rateProvide a third stage of antiproton cooling with the Recycler


Antiprotons production and storageThe Antiproton Source is made up of four parts. (1) Target: Fermilab creates antiprotons by striking a nickel target with protons. (2) Debuncher Ring: This triangular shaped ring captures the antiprotons coming off of the target. (3) Accumulator: This is the 1st storage ring for the antiprotons.(4) Recycler:This is the 2nd storage ring for the antiprotons. It provides the final cooling.


Antiprotons flow (Recycler only shot)AccumulatorRecyclerTevatronTransfer from Accumulator to RecyclerShot to TeV2600e9400 e10200 mA100 mA ~30 hours


Beam Cooling in the RecyclerThe missions for cooling systems in the Recycler are:The multiple Coulomb scattering (IBS and residual gas) needs to be neutralizedThe emittances of stacked antiprotons need to be reduced between transfers from the Accumulator to the RecyclerThe effects of heating because of the Main Injector ramping (stray magnetic fields) need to be neutralized


Fermilab cooler main featuresElectrostatic accelerator (Pelletron) working in the energy recovery modeDC electron beam100 G longitudinal magnetic field in the cooling sectionLumped focusing outside the cooling section


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

Electron cooling system setup at MI-30/31Pelletron(MI-31 building)Cooling section solenoids(MI-30 straight section)


Electron cooling status: From installation to operation Bringing electron cooling into operations consisted of three distinct parts Commissioning of the electron beam lineTroubleshoot beam line componentsCheck safety systemsEnsure the integrity of the Recycler beam line at all timesEstablish recirculation of an electron beam

Cooling demonstrationEnergy alignmentInteraction of the electron beam with anti protonsCooling demonstrationReduction of the longitudinal phase space

Cooling optimization (continued focus at this time)Optimization of the electron beam qualityStability over long period of timesMinimize electron beam transverse anglesDefine best procedure for cooling anti protonsMaximize anti protons lifetimeUnderstand and model the cooling force


Beam quality: Longitudinal temperatureThe cooling process is determined by an effective energy spread consisting primarily of two components, the electron energy spread at a fixed time and the Pelletron voltage rippleThe energy spread is determined by IBS (the main contributor) and by density fluctuations at the cathode. According to simulations, at currents 0.1 0.5 A the energy spread is 70 150 eV. The Pelletron voltage ripple is 200 - 300V r.m.s. (probably, fluctuates from day to day). The main frequency is 1.8 Hz, which is much shorter than a cooling time. Hence, the effective energy spread is equal to these two effects added in quadratures.


Beam quality: Electron angles in the cooling section *Angles are added in quadrature Recent measurements indicate that we might have underestimated this contribution


Component

Present estimation, (rad

Diagnostics

Comments

Temperature

70

OTR + pepper pot

Aberrations

50

30

Simulated

BPMs

@ 1 mm (rms)

Envelope scalloping

120

Movable orifices (scrapers)

For the 0.5 A beam boundary at 10-5 level of losses

Dipole motion caused by magnetic field imperfections

40

Magnetic measurements + BPMs

Beam motion

40

BPMs

With a slow feedback

Drift velocity

20

Calculated

For I =0.5 A

Total

160*

Recirculation Stability: High duty factor has been met (>95%)Running at high current (> 0.2 A) induces full discharges (~1-2 per week) until the Pelletron needs to be reconditioned.24 hoursNo full discharges5 recirculation interruptions2 nTorr2 nTorr0.4 MV0.2 ABeam currentDecel. side pressureAccel. side pressurePelletron voltage


Electron cooling in operationIn the present scheme, electron cooling is typically not used for stacks < 200e10Allows for periods of electron beam/cooling force studiesOver 200e10 storedElectron cooling used to help stochastic cooling maintain a certain longitudinal emittance (i.e. low cooling from electron beam) between transfers or shot to the TeV~1 hour before setup for incoming transfer or shot to the TeV, electron beam adjusted to provide strong cooling (progressively)This procedure is intended to maximize lifetimeIn addition, electron beam intensity is kept at 100 mAImprove beam stabilityNo full discharges in monthsHigher currents do not cool faster/deeperMay help lifetime too


Adjusting the cooling rateTwo knobsElectron beam currentBeam stays on axisDynamics of the gun varies between low and high currentsHence, changing the beam current also changes the beam size and envelope in the cooling section Electron beam positionAdjustments are obtained by bringing the pbar bunch in an area of the beam where the angles are low

5 mm offset2 mm offsetArea of good coolingpbarselectronselectronspbars


Typical minimum cooling time (100 mA, on-axis)e-folding cooling time: 20 minutes


Electron cooling between transfers/extractionElectron beam is moved inStochastic coolingafter injectionElectron beam out (5 mm offset)Electron beam current 0.1 A/divTransverse emittance 1.5 p mm mrad/divElectron beam position 1 mm/divLongitudinal emittance (circle) 25 eVs/divPbar intensity (circle) 16e10/div~1 hour100 mA195e10~60 eVs


Issues related to electron cooling and large stacksSince started to use the electron beam for cooling, we have dealt with two main problemsTransverse emittance growthDuring mining Lifetime degradationWhen the beam is turned on and/or moved towards the axis (i.e. strong cooling)MINING


Emittance growth during miningEmittance growth likely due to a quadrupole instability (see A. Burov, for instance: ICFA-HB2006 in Tsukuba, Japan)Growth rate kxy Ie Ip , (kxy coupling parameter)Increase tune split to reduce kxy0.414/0.418 (H/V) 0.451/0.468 (H/V)(A)(B)Initial growth rate: (A) 36 p mm mrad per hour(B) 3 p mm mrad per hour/ ~10


Lifetime degradation throughout a storePbar intensityLifetime (1 hour running average)500 hours60 1010400 hours


Changing the operating point also helped the lifetimeLifetime (1 hour running average)Pbars intensity500 hoursLifetime at injection/extraction?


Evolution of the number of antiprotons available from the Recycler (~1 year period)Mixed mode operationEcool implementationRecycler only shots


Chart1

42

47

85

90

91

54

56

78

67

74

89

37

37

45

45

49

49

91

91

72

71

71

69

70

71

71

86

86

81

81

68

16

57

48

78

64

85

92

98

91

43

76

65

70

63

56

124.1

113

166

51

74

58

39

108

60

116

90

138

124

121

143

144

44

66

138

94

56

69

58

14

16

59

7

33

32

42

45

49

47

65

52

128

85

51

59

74

43

71

95

30

90

32

62

106

83

53

100

81

58

61

60

94

109

51

46

92

137

116

111

Ecooling

59.5

90.7

30.6

85

48

100

60

100

143

126

59

59

89

85

92

81

97

116

112

137

111

182

46

41

98

110.5

143

60

109

64

70

136

70

113

165

129

134

141

142

216

241

90

55

69

77

225

280

235

257

183

153

209

117

197

228

111

168

191

219.57

223

285

247

266

320

220

256

89

171

248

204

200

300

248

252

174

99

132

77

181

72

55

163

219

288

236

137

270

255

273

260

354

326

323

289.7

284

198

154

115

127

182

30

107

176

201

139

209

181

334

258

258

418

197

131

150

283

166

243

Number of antiprotons (x 1010)

Sheet1

data

DateIntensityLong emittance 90%Long emittance 95%RMS mom spread90% mom spreadBucket lengthTrans emittanceNotes

2/14/041.88E+0114.018.215linear ramp, two bunches

4/7/041.60E+017.09.13.36linear ramp,single bunch

2/20/041.20E+0263.081.95.37Barrier bucket

3/12/043.50E+0121.027.32.37Barrier bucket

3/14/047.80E+0151.061.23.110.54.87Barrier bucket

3/25/043.57E+0131.938.32.89.23.33Barrier bucket

4/7/041.60E+017.09.23.511.70.36Barrier bucket

4/8/043.10E+0111.314.33.70.67Barrier bucket

4/12/045.20E+0120.625.6413.21.26Barrier bucket

4/23/049.70E+0149.058.83.110.34.64Barrier bucket

4/21/047.50E+0140.752.9

4/24/048.70E+0151.066.35.4

4/26/041.26E+0264.083.26

4/27/041.23E+0254.164.93105.33Before instability

4/30/041.17E+0250.060.03.110.34.74.2Barrier bucket

4/30/041.30E+0258.169.6310.25.73.6

5/3/041.45E+0263.876.53.210.65.854.3

5/28/044.33E+0116.319.72.58.41.855

6/9/046.70E+0130.837.23.311.12.65before mining for mixed mode

6/29/047.78E+0123.428.43.210.925Barrier bucket, before mining, after linear rf

7/6/047.50E+0123.028.03.411.61.85Barrier bucket, before mining, after linear rf


7/20/046.04E+0122.327.23.310.81.825.4Barrier bucket, before mining, after linear rf

7/20/04626234.5

7/21/04505023.1

8/5/04424220.9

8/11/04303018.8

8/12/04404020.3

From This Time on we started

12/29/046.62E+0118.928.02.9101.85Barrier bucket, before mining, after linear rf




1/15/05331414




1/27/054016.0





2/1/056.72E+0121.626.231024.2Barrier bucket, before mining, after linear rf




2/8/058.93E+0134.241.63.7612.42.464.5

TDR2.60E+0254.070.25538.547.75

6.50E+0254.070.25538.5125

1.80E+0254.070.25538.536.855

2.00E+016.07.85.854.0954.095

2.00E+010.00.0000

0.00E+000.0

1.80E+0296.0

6/30/047932

7/6/047728

7/16/049235.3

12/23/044120.9

12/29/046628

1/10/054220

1/12/054722

1/17/058536

1/18/059040

1/20/059143

1/24/055422.1

1/28/055627

1/30/057829

2/1/056726

2/3/057428

2/8/058941

2/13/053719

2/13/053718

2/17/0545

2/17/054522

2/22/054932

2/22/054932

2/23/059148

2/23/059144

2/24/057236

2/26/057130

2/26/057129

2/27/056939

2/27/057038

3/4/057135

3/4/057135

3/5/058640

3/5/058640

3/7/058140

3/7/058140

3/8/056837

3/9/05168.5

3/10/055728

3/12/0548

3/14/0578

3/15/056430

3/17/058543

3/18/059248

3/20/059847

3/21/059148

3/25/054323

3/26/057641

3/27/056530

3/29/057033

3/30/056328Started using ibs to help cool

4/2/055628

4/4/05124.147

4/7/05113.046.0

4/8/05166.059.3

4/10/0551.025.0

4/14/0574.031.0

4/17/0558.027.0

18-Apr39.019.0

4/20/05108.040.0

4/23/0560.028.0

4/24/05116.054.0

4/25/0590.035.0

4/27/05138.052.0

4/29/05124.045.0

4/30/05121.045.0

5/2/05143.052.0

5/4/05144.051.0

5/7/0544.020.0

5/9/0566.028.0

5/12/05138.051.0

5/13/0594.037.0

5/17/0556.022.0

5/18/0569.026.0

5/19/0558.024.0

5/19/0514.09.0

5/21/0516.010.0

5/23/0559.025.0

5/23/057.06.3

5/24/0533.014.0

5/26/0532.013.0

5/27/0542.018.0

5/28/0545.020.0

5/29/0549.024.0

5/31/0547.021.0

6/2/0565.028.0

6/4/0552.025.0

6/6/05128.051.0

6/7/0585.032.0

6/8/0551.035

6/10/0559.031.0

6/11/0574.030.0

6/17/0543.020.0

6/18/0571.030.0

6/19/0595.042.0

6/20/0530.014.0

6/22/0590.041.0

6/23/0532.014.0

6/24/0562.024.0

6/26/05106.045.0

6/28/0583.033.0

7/1/0553.023.0

7/5/05100.040.0

7/23/0581.026.0

7/26/0558.041.0

7/30/0561.025.0

7/31/0560.026.0

8/2/0594.041.0

8/7/05109.040.0

8/16/0551.025.0

8/18/0546.022.0

8/22/0592.044.0

8/26/05137.078.0

8/27/05116.078.5

8/29/05111.076.0

Ecooling

7/16/0559.515.9

7/18/0590.727.0

7/19/0530.68.5

7/21/0585.028.0

7/22/0548.019.0

7/25/05100.028.0

7/28/0560.020.0

8/1/05100.034.0

8/4/05143.051.0

8/6/05126.040.0

8/8/0559.018.0

8/10/0559.018.0

8/12/0589.024.0

8/13/0585.024.0

8/14/0592.028.0

8/18/0581.025.0

8/19/0597.035.0

8/23/05116.035.0

8/24/05112.031.0

8/26/05137.054.0

8/30/05111.037.0

9/1/05182.062.0

9/2/0546.018.0

9/3/0541.016.0

9/5/0598.030.0

9/6/05110.522.9

9/8/05143.036.0

9/9/0560.016.0

9/12/05109.028.0

9/13/0564.021.0

9/14/0570.021.0

9/16/05136.051.0

9/17/0570.027.0

9/18/05113.027.0

9/20/05165.067.0

9/22/05129.050.0

9/22/05134.047.5

9/24/05141.055.0

9/25/05142.049.0

9/26/05216.064.0

9/28/05241.065.0

9/28/0590.035.0

9/30/0555.020.0

10/1/0569.023.0

10/2/0577.028.0

10/4/05225.062.0

10/5/05280.060.0

10/8/05235.065.0

10/10/05257.066.0

10/12/05183.078.0

10/13/05153.051.0

10/15/05209.065.0

10/15/05117.032.0

10/16/05197.066.0

10/17/05228.066.0

10/19/05111.035.0

10/21/05168.057.0

10/22/05191.068.0

10/23/05219.657.0

10/25/05223.067.0

10/27/05285.067.0

10/29/05247.078.0

10/28/05266.066.0

10/31/05320.072.0

11/2/05220.071.0

11/3/05256.080.0

11/4/0589.045.0

11/5/05171.051.0

11/6/05248.065.0

11/7/05204.070.0

11/9/05200.070.0

11/10/05300.068.0

11/12/05248.065.0

11/13/05252.067.0

11/15/05174.055.0

12/12/0599.040.0

12/13/05132.060.0

12/14/0577.035.0

12/16/05181.058.0

12/17/0572.037.0

12/18/0555.028.0

12/19/05163.065.0

12/21/05219.063.0

12/22/05288.066.0

12/23/05236.064.0

12/25/05137.040.0

12/27/05270.065.0

12/28/05255.059.0

12/30/05273.065.0

1/2/06260.067.0

1/6/06354.072.0

1/7/06326.076.0

1/8/06323.070.0

1/10/06289.766.0

1/11/06284.068.0

1/14/06198.055.0

1/19/06154.061.0

1/23/06115.069.0

1/27/06127.074.0

1/28/06182.069.0

1/30/0630.049.0

2/2/06107.041.0

2/3/06176.041.0

2/4/06201.061.0

2/5/06139.040.0

2/6/06209.059.0

2/7/06181.090.0

2/9/06334.075.0

2/10/06258.055.0

2/12/06258.067.0

2/14/06418.066.0

2/17/06197.066.0

2/18/06131.054.0

2/19/06150.055.0

2/20/06283.058.0

2/21/06166.054.0

2/22/06243.059.0

2/1/06274.062.0

2/1/06240.043.0

Damper Test

8/23/0558.09.8

8/24/05112.024.0

now110.522.9

2.2222222222

7.5

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Cons data

Pbar intensity, xE10

Long emittance (95%), eV-s

Recycler's best long. emittance as of 04/10/05

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Pink Line

Post IBS Cooling (3/05 - 8/05)

blue Line

Ecool (7/05 - present)

'Feb/04 - Dec/04'

Last 5 to Tev



Recycler's Long. Emittance with Electron Cooling

Sheet3

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blue Line

Pink Line

'Feb/04 - Dec/04'



Recycler's Long. Emittance Pre IBS Cooling

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Pink Line

blue Line

Ecool (7/05 - present)

last 5

dec '05

Jan '06

Feb '06



Recycler's Long. Emittance as of 2/28/06

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Pink Line

Post IBS Cooling (3/05 - 8/05)

blue Line

'Feb/04 - Dec/04'



Recycler's Long. Emittance Post IBS Cooling

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Mixed Mode Operations

EcoolImplementation

Recycler OnlyShots

Number of antiprotons (x 1010)

Long emittance

14

63

21

50.9913654065

31.908509866

7.0404649281

11.2891480685

48.9543515619

40.7

51

64

54.1471258502

50

49.9728362532

58.0912629581

63.8191827374

16.3045085162

30.7541904285

20.6061774981

7

Luminosity density by source


ConclusionFermilab has a unique operational electron cooling system for cooling of 8.9 GeV/c antiprotonsSince the end of August 2005, electron cooling is being used on (almost) every Tevatron shotIncreases of stash sizes are a direct consequence of the ability to cool the beam efficientlyElectron cooling allowed for the latest advances in the TeV peak luminosityChanged our operating point (tune space)Emittance growth during the mining process has been almost completely eliminatedLifetime of large number of particles has improved significantlyLongitudinal cooling force (drag rate) agrees to within a factor of 2 with a non-magnetized modelNot shown in this report (see ICFA-HB2006, EPAC06)


People of EcoolRecycler department head:Paul DerwentRecycler deputy department head:Cons Gattuso*Ecool Safety officer:Mike GerardiRecycler department personnel:Valeri BalbekovDan Broemmelsiek*Alexey BurovKermit CarlsonJim CrispMartin Hu*Dave NeufferBill Ng Lionel Prost*Stan Pruss*Recycler department personnel (cont):Sasha Shemyakin*Mary Sutherland*Arden Warner*Meiqin XioOther AD departments:Brian ChasePaul JoiremanRon KellettBrian KramperValeri LebedevMike McGeeSergei NagaitsevJerry NelsonGreg SaewertChuck SchmidtAlexei SemenovSergey SeletskiyJeff SimmonsKarl Williams* Main experimentalists (experimental studies, data analyses,); Primary ecool theorist (theoretical analyses); Primary technical support (tech support coordination,)


EXTRAS


Setup of Fermilabs Electron Cooler


Electron beam parameters (for cooling)Electron kinetic energy 4.34 MeV Uncertainty in electron beam energy 0.3 %Energy ripple250 V rmsBeam current 0.1 A DCDuty 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


Simplified electrical schematic of the electron beam recirculation systemBeam power 2.15 MWCurrent loss power 21.5 WPower dissipated in collector 1.6 kWFor I= 0.5 A, I= 5 A:The beam power of 2 MW requires the energy recovery (recirculation) scheme


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Electrostatic generator: the Pelletron (developed by NEC)Improved Van de Graaff generatorCharge carried by a chain (metal cylinders joined by nylon links) instead of a rubber beltInduction system to charge the chain (instead of rubbing contacts or corona discharges)


Preview of whats inside the pressure vesselHigh-voltage column with grading hoops partially removed to show the accelerating tube (right) and the charging chains (far center).


DiagnosticsYAG crystal, OTR monitors throughout the beam lineBeam size (shape), distributionUsed to compare to optics models

1 multi-wire scannerBeam size and shape after 180 bend

Removable apertures in the cooling sectionBetween each of the ten cooling section solenoidBeam size and angle

BPMsBetween 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


OTR Detectors for the Medium Energy Electron Cooler Detector characteristics5 m foilLower current limit 20mAResolution 50 m

ApplicationsReal-time charge density distribution and beam size measurementsMeasurement of beam initial conditions in the acceleration sectionBeam ellipticity measurementsBeam temperature measurements with pepper-pot

Beam Image from OTR at full current (acceleration tube exit)Beam profile versus Lens current on acceleration side


Neighborhood with the Main Injector

Magnetic fields of busses and MI magnets in the time of ramping causes an extensive motion of the electron beam (up to 0.2 mm in the cooling section and up to 2 mm in the return line)

MI radiation losses sometimes result in false trips of the ECool protection systemElectron beam motion and MI losses at R04 location in the time of MI ramping. 0.55 Hz oscillation is due to 250 V (rms) energy ripple.2 secMI bus currentMI lossXY1mm


Low magnetic field in the cooling sectionCooling is not magnetized

The role of the magnetic field in the cooling section is to preserve low electron angles,

A typical length of B perturbation, ~20 cm, is much shorter than the electron Larmor length, 10 m. Electron angles are sensitive to , not to B .Transverse magnetic field map after compensation (Bz = 105 G).Simulated angle of an 4.34 MeV electron in this field. RMS angle is < 40 rad.


Beam size measurements in the Cooling Section11 movable orifices (not in phase) in the cooling sectionThe scrapers are diaphragms of 15 mm diameter, located every 2 m. While only one of them is in place, the beam is shifted in some direction until it touches the scraper. The bpm data for the beam center is taken at this point. The beam is shifted in other direction, and the center coordinates at touch are detected again; usually 8 directions are used. Then, the entire procedure is repeated for other scrapers. From these data, the beam ellipse and the scraper offsets are found for every scraper involved.Initial conditions for the beam envelope are fitted for these ellipses. A cylindrical boundary might not guarantee low angles in the middle of the beam because of aberrations radial angletangential angledensity


Scraper Measurements Dec 1 (nominal settings, 500 mA)SCC00SCC70SCC60SCC50SCC40SCC30SCC20SCC10SCQ01SCC90SCC80Beam radius ~ 4.5 mmAveraged rms angle

Comparison of two focusing settings Envelope (fit) along the scrapers 0-5One lens changed by 2 AAverage rms envelope angle is 0.5 mradNominalAverage rms envelope angle is 0.2 mrad


Why sudden new interest in high energy cooling?The existing stochastic cooling technology is band-width limited (10 GHz or so).The lack of progress in bunched-beam stochastic coolingThe advance in electron gun and collector technology (experience of low energy e-cooling), and in recirculation of DC beams.The advance in recirculating linac technologies.The advance in linear optics on beams with a large angular momentum.


Commissioning Milestones HighlightsFeb, 25th Installation CompleteMar, 7th All systems ready for commissioningCharging system, gun, pulser workMar, 17th 4.3 MeV, 0.5 A pulsed beam to collector (U-Bend mode, low losses)Regulation system works properlyApr, 20th First DC beam (few mA) in Recycler beam lineJun, 3rd 4.3 MeV, 0.2 A DC recirculating in the full line. Jul, 9th First observation of electron beam interacting with antiproton beamJul, 15th Electron Cooling of 8 GeV antiprotons has been demonstrated Jul, 16th Electron cooling is used for a collider shotJul, 26th 0.5 A DC in the full line. All commissioning milestones are met.


Simulation of cooling demonstrationWithout cooling -- the momentum distribution remains flat over 0.3% span for 30 minutesCoasting beam, IBS+ECOOL simulation, n = 2 mm mrad, Ie=0.1 A, rms angular spread = 0.5 mrad


Recycler measured momentum distribution using Schottky1.5e11 pbars, n = 2 mm mradMomentum acceptance (flat central part): about 0.5% (+/- 22 MeV/c)


Cooling force Experimental measurement methodsTwo experimental techniques, both requiring small amount of pbars (1-5 1010), coasting (i.e. no RF) with narrow momentum distribution (< 0.2 MeV/c) and small transverse emittances (< 3 p mm mrad, 95%, normalized)Diffusion measurementFor small deviation cooling force (linear part)Reach equilibrium with ecoolTurn off ecool and measure diffusion rateVoltage jump measurementFor momentum deviation > 2 MeV/cReach equilibrium with ecoolInstantaneously change electron beam energyFollow pbar momentum distribution evolution

Both methods characterize the effectiveness of electron cooling (hence, the electron beam quality) quite locally and not necessarily the cooling efficiency/rate for large stashes


Example: 500 mA, nominal settings, +2 kV jump (i.e. 3.67 MeV/c momentum offset), on axis Traces (from left to right) are taken 0, 2, 5, 18, 96 and 202 minutes after the energy jump.~3.7 MeV/c2.8 1010 pbar3-6 p mm mrad


Extracting the cooling (drag) force15 MeV/c per hourEvolution of the weighted average and RMS momentum spread of the pbar momentum distribution function


Cooling force measurements carried outThree types of measurements: Various electron energy jumpsDescription of the drag rate as a function of the antiproton momentum deviationFor various electron beam positionsVarious electron beam positions (w.r.t. antiproton beam)Mostly at 100 mAVarious electron beam currentOn axis (mostly) i.e. electron beam and antiproton beam are centeredBy-productDrag rate as a function of the transverse emittanceKeeping the transverse emittance low throughout the measurement has been sometimes challengingDifficulties measuring the real emittance at very low Dp/p and low number of particles


Drag Force as a function of the antiproton momentum deviation100 mA, nominal cooling settingsError bars statistical error from the slope determination


Drag rate as a function of the electron beam current3.67 MeV/c momentum deviation, on axis, nominal cooling settingsThe drag force is nearly constant at 0.1 0.5 A, while in simulations the current density at the axis is twice higher at 0.5 A than at 0.1 A. Not a real fitDrag force on axis appears to be independent of the electron beam current Quite consistent with equilibrium longitudinal emittance measurements


Electron cooling drag rate - TheoryFor an antiproton with zero transverse velocity, electron beam: 500 mA, 3.5-mm radius, 200 eV rms energy spread and 200 rad rms angular spreadNon-magnetized cooling force modelLab frame quantities


Comparison to a non-magnetized modelConstant:Coulomb log, L = 10Fitting parameters:Electron beam current density, JcsLab frame RMS energy spread, dELab frame RMS angular spread, qe100 mA, nominal cooling settings (both data sets)


Comparison to a non-magnetized model (cont)Results from the fitsRMS energy ripple, RMS angular spreadBest estimations (250 eV, 160 mrad) from measurementsBeam current densityFactor of ~5 higher than best estimate (assuming uniform current density)

Electron beam vertical offset, mm01.52JCS, A cm-21.20.70.3qe, mrad0.190.250.25dE, eV370370370


Better model for determining the current density in the cooling section ?For 100 mA, the beam current density distribution is NOT uniformUse SuperSAM gun simulations to estimate on-axis current densityElectron beam is quite uniform and linear (in phase space) over a limited emitter surfaceThis model reduces the discrepancy between measured and expected current density in CS by a factor of ~2


Drag rate as a function of the transverse emittance1.84 and 3.67 MeV/c momentum offsets, 100 - 500 mA e-beam, on axisScattered in the data likely dominated by the difficulties in getting similar machine conditions


Emittance growth during mininge-beam: 500 mA, +3.5 mm offsetpbars: 180e10e-beam: 500 mA, +3 mm offsetpbars: 180e10 Stochastic cooling system was turned off when mining, e-beam (when used) remained onDampers are on for all measurementspbars: 114e10 Initial rate: 17 p mm mrad/hourInstrumentation problem


Emittance growth during mining reduced by ~10Changed working point for the tunes (in order to split them more), from 0.414/0.418 (H/V) to 0.453/0.473 (H/V)Electron beam currentHorizontal emittanceElectron beam positionLongitudinal emittance (circle)Vertical emittance (circle)Pbar intensity (circle)Stochastic cooling system is turned off before mining~2 p mm mrad/hourPhase density when mining = 0.9Mining227e10100 mA


Correlation with presence of electron beam & cooling ?40 minutes of electron cooling on axis at 300 mALifetime drops and recovers ~1 hour laterBut phase density has increased by ~2 !Pbar intensity (1 1010/div)Longitudinal emittance (20 eV s/div)Vertical emittance (2 p mm mrad/div)Electron beam current (0.1 A/div)

Lifetime (1 hour running average) [circle](500 h/div)3.8 p mm mrad68 eV s158 10100 h2000 h


Comparison with cooling force measured at low-energy coolersComparison 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).

Red triangles represent Fermilabs data measured at 0.1 A. The current density is estimated in the model with secondary electrons.


Conclusion (II)Cooling force has been measured and compared to a non-magnetized modelReasonable agreement with expectationsUncertainties in the electron beam properties make this agreement no better than within a factor of 2-3Some questions are left openCooling force as a function of the electron beam currentSecondary electrons in the CS reducing the current density ?Optical Transition Radiation detector measurements may help resolve some of the discrepanciesData analysis underway


Status of High Energy Electron Cooling at FNAL’s Recycler Ring XX th Russian Conference on Charged...

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Transcript of Status of High Energy Electron Cooling at FNAL’s Recycler Ring XX th Russian Conference on Charged...