# Presentation: 587641

## Electron Cooling in the Recycler Ring

- Alexander Shemyakin (Fermilab/AD)
- May 31, 2005

## Tevatron luminosity and antiprotons

- The Tevatron luminosity is linear with the total number of antiprotons available for the Tevatron store.

- The antiproton beam quality is characterized by the phase-space density.  To achieve higher luminosity this density needs to be increased.

## Fermilab’s antiproton production chain

- Inconel target

**Debuncher **(stochastic cooling)

**Accumulator **(stochastic cooling)

- 8 GeV

- 8 GeV

- Until 2005

- Electron cooling in the Recycler Ring eliminates one of the bottlenecks in the long chain of the antiproton production.

-   is the relative phase-space density

## Idea of Electron cooling

- The idea of electron cooling is a heat exchange through Coulomb scattering between hot heavy particles (antiprotons) and cold electrons while the beams are mixed in a cooling section.

- Was invented in 1967 by G.I. Budker (INP, Novosibirsk) as a way to increase luminosity of p-p and p-pbar colliders.

- First tested in 1974 with 68 MeV protons at NAP-M storage ring at INP (Novosibirsk).
- CERN- ICE 1977 – 1979
- Fermilab 1979 - 1982

## Low energy coolers

- Well – established techniques for electron energies below 300 keV.
- A strong, continuous longitudinal magnetic field from the gun to the collector
- An electrostatic accelerator working in the energy- recovery mode

- Example of a 300 keV, 3 A cooler produced by Budker INP for IMP, Lanzhou (China).
- The voltage difference between the gun and collector ~ 3 kV.

## Difficulties of implementing at relativistic energies

- High electron beam power:
- 4 MeV * 0.5 A = 2 MW DC!
- Beam quality:
- The electron beam temperature (in the rest frame) should be comparable with the cathode temperature of 1200K (only a factor of ~10 increase is allowed for the transverse degree of freedom)

- Design parameters of the RR ECool beam
- Energy		4.34 MeV
- Beam current	0.5 Amps DC
- Angular spread	0.2 mrad
- Effective energy
- spread		 300 eV

## History of relativistic electron cooling

- Fermilab, 1983: D. Cline et al., “Intermediate energy electron cooling for antiproton sources using a Pelletron accelerator”
- For a pulsed electron beam in a Pelletron the beam quality is adequate for electron cooling
- Novosibirsk, 1987: successfully tested a prototype 1-MV,
- 	1-A electron beam system.
- Continuous magnetic field
- Acceleration tubes are not sensitive to vacuum UV
- Fermilab, UCLA, NEC, 1989: tested a 2-MV, 0.1-A DC recirculation system with a Pelletron.
- Poor stability
- Fermilab, IUCF, NEC, 1995: started to work on a 2-MV Pelletron again- beginning of the RR ECool project

## Premise

- Solution for a high-power beam generator: use of a “standard” electrostatic accelerator (Pelletron) and non-standard focusing scheme
- Recirculation (energy/charge recovery) scheme
- No continuous magnetic field
- A low-magnitude longitudinal magnetic field in the cooling section and at the cathode, but a lumped focusing in the remaining part of the beam line
- Failure of the previous attempt was recognized to be caused by high losses in the acceleration tubes
- Current losses needs to be decreased below 0.01%
- New solutions for the gun and collector were found.
- A gun with a negatively biased control electrode to suppress the beam halo and provide the beam transport at all currents
- Effective suppressing of secondary electrons in the collector can be done by applying a transverse field in the collector cavity

## GOAL
To demonstrate a stable (~1 hour)  generation of  a 0.2 A relativistic beam using an existing 2 MV Pelletron at NEC

Nov. 95:	project started
Jan. 97:	first recirculated current (10 μA)
Dec. 97:	Max. recirculated current of 0.2 A
May. 98:0.2 A for 1 hours at 1.3 MeV
Dec. 98:	Max. current of 0.7 A
Jan. 99:	Gun solenoid (200 G) installed	
Feb. 99:	 5 MeV Pelletron ordered
May.99:	0.9 A with 200 G at the cathode

- To demonstrate a stable (~1 hour)  generation of  a 0.2 A relativistic beam using an existing 2 MV Pelletron at NEC
- Nov. 95:	project started
- Jan. 97:	first recirculated current (10 μA)
- Dec. 97:	Max. recirculated current of 0.2 A
- May. 98:0.2 A for 1 hours at 1.3 MeV
- Dec. 98:	Max. current of 0.7 A
- Jan. 99:	Gun solenoid (200 G) installed
- Feb. 99:	 5 MeV Pelletron ordered
- May.99:	0.9 A with 200 G at the cathode

- Stage I -  Test at NEC (Middleton, WI)

- How to scale the result for 1.3 MeV beam in a 2-MV tubes to a 4.3 MeV beam in a 5-MV accelerator ?

## Stage II – short line at WideBand Building (Fermilab)

- New means to improve stability: ion stoppers, crash scraper, closing the gun in 1 ms
- Diagnostics: BPMs, scrapers, flying wire
- Operation was stable only at 3.5 MV. The tubes clearly needed to be extended.
- Now the main question was the beam quality.

_**GOAL : **_To demonstrate a stable generation of  a 0.5 A, 4.34 MeV beam in a short beam line
- Feb 99:	  5 MV Pelletron ordered.
- May 01:	  First beam of 30 A in the collector.
- Dec 01:	  0.5 A at 3.5 MV
- Apr 02:	  NEC replaced acceleration tubes
- Oct 02:	 0.5 A at 4.34 MeV
- Nov 02:   Imax = 1.7 A at 3.5 MV
- 	  Shut down to install the full beamline

## Stage III – full- length line at WideBand

- The beam line was very similar to the final one at MI-31
- A novel type of the beam optics, angular momentum –dominated
- Developed a technique of precise measurements of the solenoid field quality
- Beam envelope measurements with movable orifices
- Final version of BPM electronics
- Jul- 03 - 	first DC beam in the 		full- scale line
- Dec-03- 	0.5 A DC beam
- May-04- 	 0.1 A beam with 			required properties 		in the  cooling section

## Final stage- Cooler in the Recycler

- Jun. 2004 – Jan. 2005- assembling the cooler in MI-31/30
- Oct 2004- magnetic measurements in cooling section
- Apr 2005- first DC beam in the collector passed through the cooling section

## Difficulties (some of them) and solutions

- Full discharges
- Improvements in the protection system (closing the gun in 1 s)
- Minimizing current losses to acceleration tubes (dI/I <10-5)
- Magnetic fields from the Main Injector
- Compensation of bus currents, additional shielding
- Changes in optics that made the system more tolerable to the beam motion
- Field angles
- Magnetic field measurements were  supplemented by a special tuning procedure employed Beam Position Monitors (BMPs)
- Energy matching
- Absolute energy calibration of the electron beam by measuring the wave length of the electron rotation in the magnetic field of the cooling section
- A special wide energy distribution of antiprotons to observe the first interaction between beams

## Cooling

- One of the first indications of interaction between antiprotons and electrons.
- The plot shows evolution of antiproton energy distribution (log scale) after turning on an electron beam. Initially antiprotons occupy the entire momentum aperture of the Recycler.

- First interaction - July 9, 2005
- First cooling-      July 11, 2005
- First electron cooling-assisted shot to Tevatron- July 12, 2005

## Drag Force as a function of the antiproton momentum deviation100 mA, nominal cooling settings

## First cooling rate measurements published

## Electron cooling between transfers/extraction

- Electron beam is moved ‘in’

- Stochastic cooling
- after injection

- 	Electron beam ‘out’ (5 mm offset)

**Electron beam current****0.1 A/div**
**Transverse emittance****1.5 ******** mm mrad/div**
**Electron beam position****2 mm/div**
**Longitudinal emittance (circle)****25 eVs/div**
**Pbar intensity****(circle)****16e10/div**

**~1 hour**

**100 mA**

**195e10**

**~60 eVs**

**254e10**

## Evolution of the number of antiprotons available from the Recycler

**Mixed mode operation**

**Ecool implementation**

**Recycler only shots**

- 01/10/05 – 02/18/06

## Remaining questions

- Life time
- The antiproton life time suffers at strong electron cooling
- Effect is not dramatic, but its removal will add additional percents to the number of antiprotons in Tevatron
- Ultimate strength of cooling
- ECool works at 3001010 , but additional work may be needed to cool effectively 6001010.

## Summary

- The relativistic, non- magnetized electron cooling has been demonstrated
- Allows other laboratories to proceed with further developments:
- BNL- electron cooling at RHIC, Ee= 54 MeV
- GSI & TSL- fast cooling of antiprotons, Ee= 4 - 8 MeV
- Fermilab has a world – record electron cooling system that has allowed recent advances in luminosity
- A hard limit  on the maximum number of antiprotons in the Recycler has been removed. The road to higher luminosities is open.

## The team (at the final stages)

- Beam studies
- A.Burov
- K.Carlson
- D.Broemmelsiek
- C.Gattuso
- M.Hu
- G.Kazakevich (BINP,  guest scientist)
- T.Kroc
- S.Nagaitsev
- L.Prost
- S.Pruss
- S.Seletskiy (U.of Rochester)
- A.Shemyakin
- C.Schmidt
- M.Sutherland
- V.Tupikov
- A.Warner

- Engineering support
- B. Kramper
- J. Leibfritz
- L. Nobrega
- G. Saewert
- K. Williams

- Technical support
- M. Frett
- R. Kellett
- J. Nelson
- J. Simmons

- 	International collaboration
- BINP (Novosibirsk, Russia)
- V. Parkhomchuk
- V. Reva
- COSY (Juelich, Germany)
- D. Prashun
- BNL
- A. Fedotov

- Physics discussions and modeling
- 	V. Lebedev

- JINR(Dubna, Russia)
- I.N. Meshkov
- A. Sidorin
- ANL
- W. Gai