1. HE-JLEIC: Boosting Luminosity at High Energy
Yuhong Zhang
June 28, 2018

2. JLEIC and eRHIC Ring-Ring Luminosity
Y. Zhang, 06/19/2018

3. Boosting Luminosity at Highest Energy
Higher proton beam current
needs stronger high energy cooling
Stronger collective effects
Improving high energy cooling efficiency
Higher cooling electron beam current
Dispersive cooling
Higher electron beam
KEKB LER current 3.6 A
Higher SR power, 15 even 20 kW/m  higher RF power
More SR at IR
Smaller beta-star
Short detector space
Unmatched beam spot size at IPs
Beam-beam very weak (~10% of nominal design value) at these energies

4. JLEIC and eRHIC Ring-Ring Luminosity: Optimized

5. HL-JLEIC Optimized Parameters
CM energy
GeV
63.3
(high)
89.4 98 p e E
Beam energy
200 5 10 12
Collision freq.
MHz
476
Particles/bunch
1010
0.49
3.9
5.2
0.66
0.93
1.4
0.72
0.54
0.81
Beam current A
0.375 3 4
0.5
0.71
1.07
0.55
0.41
0.62
Polarization % 80 75
RMS bunch cm 1
Norm. emitt., h. μm 54
2.5
432
1.5
2.7
746
Norm. emitt., v.
0.1
10.8 86
0.3
149
Horizontial β*
6.5
1.3
Vertical β*
0.8
7.5 2
Spot size, h µm
14.9
29.6
29.7
21.3
35.5
Spot size, v.
3.0
5.9
4.3
7.1
p vs. e
72%
60%
Vertical B-B
0.011
0.03
0.015
0.001
0.006
.0004
0.004
vs. BB limit
7.3%
3.6%
Laslett tuneshift
0.005
0.002
0.003
Hourglass (HG)
0.85
0.83
0.86
0.87
Lumi,w/HG,1033
/cm2s
14.0
18.7
1.1
2.2
1.0

6. Impact on Electron Injector
Fanglei Lin, Jiquan Guo
The electron injection from the CEBAF to the collider ring should have no problem. The injection time for the energy above 7 GeV is within a few minutes in the current design. At 12 GeV, it is only ~40 s as we estimated. The injection time is approximately proportional to the stored electron current in the colllider ring. So the injection time is still acceptable if we increase the beam current, say by 30%. Note that, the polarization lifetime is very short at high energies, ~6 minutes at 12 GeV. We better have the injection time short at this energy. The equilibrium polarization with a top-off injection can be maintained if we keep the same ration of I_ring/I_inj. That means we have to increase the averaged injection current while we increase the stored electron beam current in order to keep the equilibrium polarization unchanged. Otherwise, the equilibrium polarization is reduced. But we think we have enough room to do this. Overall, initial injection and top-off injection should be ok while increase the stored beam current at high energies.

7. Impact on Electron Collective Effects
Rui Li
I looked at the behavior of collective effects assuming the electron current increases by factor of 2 for E>= 10GeV, it looks like we are safe for the instabilities (here I assume the higher average electron current is achieved by increasing the single bunch charge). (1) The longitudinal microwave instability For I=3A, this instability causes most concerns for the electron energy E=3GeV, for which we still need to explore mitigation scheme. Yet it’s not a worry for E=10GeV. Even when the bunch current increases by a factor of 2 at E>=10 GeV, there is still a large safety margin for this instability. (2) The transverse mode coupling instability For I=3A, this instability is not a concern for the whole electron energy range. When the bunch current increases by a factor of 2 at E=10 GeV, there is still a large safety margin for this instability. (3) Longitudinal and transverse coupled bunch instability For I=3A, the growth time of these instabilities at E=10 GeV are many times longer than that for E=3 GeV. So with the increase of beam current by 2, and with the increase of the number of cavities (as Bob mentioned), the growth time is about the same (for the longitudinal case) or longer (for the transverse case) as that at E=3 GeV. This should be suppressed by the much stronger synchrotron radiation damping at 10GeV (and if necessary, bunch-by-bunch feedback system can help). (4) Fast Ion Instability The growth rate of this instability at 10 GeV is more than 2 orders of magnitude smaller than that at 3 GeV. With the increase of current by a factor of 2, the growth rate of this instability is about the same as that in the PEPII HER, and should be manageable. So in general, we should be fine with the higher current at the higher energy regime.

8. Impact on RF System
Bob Rimmer
if I understand it the simplest thing is to say that the bunched beam cooling will work at full ion current at top energy so the luminosity will be higher. if we have to raise the electron current we can add more power. Worst case this is about $10M/MW so an additional $50M plus about 10 more cavities. Hopefully we can get this number down to more like $1M/MW so it’s not such a big deal. More cavities gives more impedance but at high energy the damping is strong so probably this is OK. Using an ante-chamber design should allow higher current and higher kW/m Injection should be OK, I think. I guess polarization lifetime will be a bit shorter at 12 GeV. SR at IP will be harder if no changes are made to the layout, especially mask heating. All other resistive and resonant heating effects go up as I^2, but get easier if we relax the bunch length a bit. if we have extra power we can run full current to higher energy as well, fattening the luminosity in the mid range. We can run higher than 3A at low energy if other limits allow. All this gets easier if we can make the ring bigger.

9. Revisiting Detector Space
7 m
Focus length f equals detector space for thin lens approximation
f2=β*βmax σ*=(εβ*)1/ σmax=(εβmax)1/2
Reducing detector space  lowering beta-star (keeping same beam size/aperture)  decreasing beam spot size at IP  increasing luminosity

10. Luminosity Performance vs. Detector Space
βy=5mm
100 GeV p x 5 GeV e
βy=6mm
βy=10mm
βy=1.2mm

11. eRHIC Ring-Ring Luminosity
V. Ptitsym, 1st EIC Joint Accelerator Collaboration Meeting, 10/12/2017
Baseline curve relies on hadron cooling just strong enough to reach 1034 cm-2s-1 (IBS growth times > 2h)
Very low pt run curves are for collecting data with very forward proton scattering (pt ~200 MeV)