1. Pulsed electron beam cooling experiments: data & preliminary results
Lijun Mao
on behalf of Jlab-IMP collaboration team
Institute of Modern Physics, CAS

2. OUTLINE Scientific motivation and setup Experiment and DAQ
Experimental results
Summary

3. electrostatic accelerators are NOT available
Motivation
all electron coolers are operated base on the DC electrostatic accelerators
energy up to 4.3 MeV electron beam (Recycler, FNL)
G.I.Budker
Powerful (electron) beam cooling is required R&D advances for EICs.
electrostatic accelerators are NOT available
RF acceleration bunched electron beam

4. A bunched (pulsed) electron beam cooling investigation was done at IMP
Motivation
A bunched (pulsed) electron beam cooling investigation was done at IMP
Basic idea: Switch on/off electron beam by the grid electrode

5. Pulsed electron beam is obtained with:
Motivation
Pulsed electron beam is obtained with:
The pulse width from 70 ns to DC
The peak current up to 70 mA
The repetition frequency up to 450 kHz
5us electron pulse
70ns electron pulse

6. Heavy Ion Research Facility at Lanzhou (HIRFL)
Experiment & DAQ
Heavy Ion Research Facility at Lanzhou (HIRFL)

7. Heavy Ion Research Facility at Lanzhou (HIRFL)
Experiment & DAQ
Heavy Ion Research Facility at Lanzhou (HIRFL)

8. The main parameters of the experiments
Experiment & DAQ
The main parameters of the experiments
Item
value
Ion
86Kr25+
Energy
4.98 MeV/u
Revolution frequency
191.4 kHz
Harmonic number 2
RF voltage
600 V
Stored particle number
~108
Electron energy V
Electron current (DC)
~30 mA or even less
Anode voltage
400 V, 600 V, 800 V (different e current)
Pulse width
300 ns to 1200 ns for bunched ion beam
500 ns to 4000 ns for coasting ion beam

9. Total measurement cycle is 50 seconds
Experiment & DAQ
Total measurement cycle is 50 seconds
Beam stacking with DC cooling, around 10 seconds
Continuously DC cooling, to improve the beam quality, around 2 seconds
Switch off the DC electron beam (without cooling), beam blows up, around 4 seconds
Switch on the detectors, including BPM, Schottky and IPM
Switch on RF system, after 500 ms, switch on the pulsed electron beam.
Beam stacking with DC cooling
Switch of DC cooling, heating
Switch on measurement device
Switch on RF
Switch on pulsed e-beam

10. Total measurement cycle is 50 seconds The DCCT data in operation
Experiment & DAQ
Total measurement cycle is 50 seconds
The DCCT data in operation
Accumulation, 10sec
Beam heating, 4 sec
Pulsed e-beam, 9.5 sec
Additional cooling, 2 sec

11. Experimental results Synchronization
The repetition frequency of electron pulse must be matched to the ion beam revolution frequency

12. Experimental results Group effects
The coasting ion beam (without RF in the ring) can be cooled and captured in the electron pulse.
Finally the ion pulse length is equal to the electron pulse length
0.6 us
BPM signals
time
pulse width

13. Experimental results
At the edge of the pulse electron beam, a “barrier bucket” is produced by the space charge field:

14. Experimental results
At the edge of the pulse electron beam, a “barrier bucket” is produced by the space charge field
The ions (with the energy spread smaller than the bucket height) will be captured in the bucket
Nuclear Inst. And Methods in Phys. Research, A 902 (2018)

15. Experimental results
Coasting ion beam cooling process by the electron beam pulse
Nuclear Inst. And Methods in Phys. Research, A 902 (2018)

16. Bunched ion beam cooling by pulsed electron beam
Experimental results
Bunched ion beam cooling by pulsed electron beam
The ion bunches can be cooled by pulsed electron beam
Even the electron pulse width is smaller than the initial ion beam bunch length

17. The cooling process with different electron pulse length
Experimental results
The cooling process with different electron pulse length
300 ns
1200 ns
1000 ns
800 ns
700 ns
600 ns
500 ns
400 ns
time
bunch length
courtesy by Shaoheng

18. Experimental results Bi-Gaussian fitting
𝑦= Γ 𝑐 2𝜋 1 σ 𝑐 exp 𝑡− 𝑡 𝜎 𝑐 Γ 𝑡 2𝜋 1 σ 𝑡 exp 𝑡− 𝑡 𝜎 𝑡 δ

19. Experimental results Bi-Gaussian fitting Weighted bunch length
𝑦= Γ 𝑐 2𝜋 1 σ 𝑐 exp 𝑡− 𝑡 𝜎 𝑐 Γ 𝑡 2𝜋 1 σ 𝑡 exp 𝑡− 𝑡 𝜎 𝑡 δ
Weighted bunch length
𝜎= 𝑆 𝑐 𝜎 𝑐 + 𝑆 𝑡 𝜎 𝑡 𝑆 𝑐 + 𝑆 𝑡

20. Longer electron pulses, faster cooling equilibrium bunch length
Experimental results
Longer electron pulses, faster cooling
too slow…
equilibrium bunch length

21. Experimental results
It is also observed that the cooling is faster with higher peak current (the electron pulse length is the same)
300 ns
400 ns
Ie=13.4mA
Ie=13.4mA
Ie=21.1mA
Ie=21.1mA
Ie=29.6mA
Ie=29.6mA
courtesy by Shaoheng

22. Experimental results
The cooling rate increases with increasing of the electron pulse length
It also increases with increasing the peak current? (too difficult to say that…)
𝜆 𝑐𝑜𝑜𝑙𝑖𝑛𝑔 = 1 𝜏 𝑐𝑜𝑜𝑙𝑖𝑛𝑔 = 1 𝜎 𝑏 𝑑 𝑑𝑡 𝜎 𝑏

23. Ionization profile monitor data
Experimental results
Ionization profile monitor data
The transverse cooling process is clearly observed
courtesy by Haipeng

24. Summary
Both coasting and bunched ion beam can be cooled by pulsed electron beam in transverse and longitudinal phase space;
The electron pulse and ions should be synchronized
A group effect is observed while the coasting ion beam cooled by pulsed electron beam.
A dependence of cooling rate on different pulse electron beam parameters is summarized preliminary.
Saturated core width is not strongly related to the electron pulse width

25. thanks for your attention!