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

OUTLINE Scientific motivation and setup Experiment and DAQ Experimental results Summary

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

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

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

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

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

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 2734.5 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

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

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

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

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

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

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) 219-227

Experimental results Coasting ion beam cooling process by the electron beam pulse Nuclear Inst. And Methods in Phys. Research, A 902 (2018) 219-227

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

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

Experimental results Bi-Gaussian fitting 𝑦= Γ 𝑐 2𝜋 1 σ 𝑐 exp 𝑡− 𝑡 0 2 2 𝜎 𝑐 2 + Γ 𝑡 2𝜋 1 σ 𝑡 exp 𝑡− 𝑡 0 2 2 𝜎 𝑡 2 +δ

Experimental results Bi-Gaussian fitting Weighted bunch length 𝑦= Γ 𝑐 2𝜋 1 σ 𝑐 exp 𝑡− 𝑡 0 2 2 𝜎 𝑐 2 + Γ 𝑡 2𝜋 1 σ 𝑡 exp 𝑡− 𝑡 0 2 2 𝜎 𝑡 2 +δ Weighted bunch length 𝜎= 𝑆 𝑐 𝜎 𝑐 + 𝑆 𝑡 𝜎 𝑡 𝑆 𝑐 + 𝑆 𝑡

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

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

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

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

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

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