1. Proposed R&D topics Y. Derbenev
MEIC R&D meeting , August 06, 2015
R&D planning

2. Outline 2 I. R&D in frame of Base Line
<Magnetized source ERL cooler>
Study of gear change impacts
Choice of move magnets version
II. Optimizing Linac and Rings designs
1. Small emittance e-collider ring
MeV linac + two boosters ion injector
III. Advanced studies
1. <EC with CCR>
2. Scanning Synchronization
3. Circular Modes Optics for ion rings
4. MEIC advanced beam physics study with a prototype of a front-end ion accelerator complex 2 2

3. Synchronization Base line Synchronization
1. Move magnets is a baseline for today. Move electron magnets in arcs overall feels preferred (though doglegs and also matching CEBAF – ring spacing may be needed). Chicanes look disadvantageous because of the design and alignment complexity.
Gear vision 2. In my opinion, gear must be allowed - especially once N-physicists want to use it. In case, necessary stabilizing measures must be implemented.
After all, I am sure that gear does not present a dynamical problem. 3

4. Gear impacts an cure Gear + Gaps effect vision
Kink instability (which is an actual reduction of the gear dynamics, as to me) will be suppressed by Landau damping: collective dipole excitation of ion beam (as well as the electron one) happens in the non-linear field of the encountering beam with its fundamental non-linear tune spread. This tune spread exceeds the kink increment by one order of value for i-beam and two orders for e-beam. Similar picture should be actual in the longitudinal direction.
Gear + Gaps effect vision
Gear with gaps lead to stochastic incoherent dynamics in, again,
non-linear beam-beam field. Potential heat mechanism for ion
beam. However, my estimations show that it can be suppressed by
electron cooling. I think we are able to develop an analytical study based on dynamics
modeling with Vlasov + Liapunov + Landau stability equations.
We should invite for cooperation Alexei Burov and Davresh Khasanyan.
Of course, gear dynamics must be simulated in an adequate code way. 4

5. Need small emittance e- ring
Long PEP-II dipoles do not allow one to design the required electron emittance
Possible improvement to investigate;
- replace PEP II quads with SF quads (twice as strong)
- also replace PEPII dipoles with short ones (same field). Use SFQ or may be even SCQ. quads.
Are sextupoles absolutely needed in arcs?
Place them in CCB ?/ gaining reduction of the 2nd order chromatic tune?/ 5

6. 100 MeV linac + two boosters ion injector
100 MeV linac suggests about 100 M$ cost reduction (!)
Design a (reasonably) shortest 3 GeV racetrack booster. Advantages:
- reduction of Sp. Ch. by a factor about 2 (better emittance or higher current)
two times shorter SC solenoid for proton spin
Large Booster:
E-ring to serve as large ion booster
Design separate CF LB ring (400 M circumference) 6

7. Scanning Synchronization
Physical concept
The RF kicker is supposed to provide transverse variation of bunch traces in the Interaction Region (IR)
Electro-dynamic concept
Modeling of energy transfer into the buffer cavity
Conceptual scheme
Concept of energy recovery is a fast transfer of the energy stored in the deflecting cavity into buffer cavity and back by beats. 7
G. Kazakevich

8. Controlled Magnetron RF Source for Scanning Synchronization
Scan. Syn.:
Controlled Magnetron RF Source for Scanning Synchronization
A novel method of the scanning synchronization of colliding bunches for the MEIC project has been proposed. The method utilizes a controlled RF deflection of electron bunches, combined with the intrinsic magnetic optics of the Interaction Region, providing a periodically moving (in length) bypass controlled by the RF power.
The magnetron transmitter providing a wideband phase and power control
A novel method of energy recovery in the deflecting cavities, based on a fast transfer by beats of the stored energy in coupled high Q-factor cavities has been proposed and considered for use at the scanning synchronization.
The proposed RF energy recovery method using efficient transmitters based on magnetrons frequency-locked by phase-modulated wide-band signal will be cost-effective and will allow a significant decrease of the RF power required for the deflecting cavities at the scanning synchronization. 8
G. Kazakevich

9. Scan. Syn. : Superfast Switch
Photoconductive Semiconductor Switch (PCSS) for use
in “MEIC Scanning Synchronization”.
The PCSS switch was proposed as an advanced alternative to the PIN diode microwave switching circuit for control the energy transfer process in coupled resonators-cavities (see. G. Kazakevitch Conceptual scheme).
The PCSS switch is a very fast photo-electrical  switch-device with a lot of potential applications including sub-nanosecond fast microwave switching. However, for use in the MEIC Scanning Synchronization the microwave circuit with embedded one or more optically controlled PCSS devices has to be designed, simulated and tested. Some PCSS models and semiconductor raw material dedicated for application in PCSS are available from the market (Kyma Technologies).
V. Popov
V. Popov 9

10. Scan. Syn. : Superfast Switch
List of questions which need to be answered:
1.       What type of semiconductor is preferred
2.       On/Off timing and ratio.
3.       Insertion loss
4.       Long term stability
5.       Operation inside of high strength microwave field.
A possible microwave circuit and light pulse control system also must be designed and tested.
V. Popov 10

11. 11 An investment: Circular Modes Optics of ion rings Advantages:
Circular Modes Optics for ion rings
A conventional background controversy: low emittance from linac – but large emittance in the rings due to the Laslett limit
An investment: Circular Modes Optics of ion rings
Advantages:
1) Overcoming the Sp. Ch. Limit (stacking, cooling, collider operation)
2) Potential to raise the e-cooling rate
3) Potential to overcome the SC limitation of luminosity
Special tricks:
- Round to flat ion beam transformation in IR
- Matched Electron Cooling (matching i-beam with cooling solenoid) - 11

12. Circular Modes Optics for Low 4D Emittance
Design beam transport around a ring with strong coupling (inserting the skew quads “on regular basis”), creating two circular modes (CM) of two naturally opposite helicities.
Each of two individual CMs will look at a point of the orbit as a round (more generally, elliptical) turn by turn rotating pencil of particles with some phase advance.
Similar to magnetized beam phase space structure, beam space charge can be “settled” just to one of two CMs, leaving other “empty” i.e. having a very low emittance.
Such state can be achieved by initial filling one mode by injection from linac to the first, small booster (pre-booster) 12

13. Low energy ion front-end Test Facility
Polarized ion source, universal
RFQ and DTL 10 MeV
Small booster-synchrotron 200 MeV with DC EC
Coupled optics (circular modes)
Polarimetry
Study spin resonance, natural and RF (figure 8 ring)
Space charge with Circular Modes)
Matched El. Cool. for low 4D emittance 13

14. Backup slides 14

15. Circular Modes Optics for Low 4D Emittance15

16. RF-painting for stacking in one CM16

17. Potential to overcome the SC limitation of luminosity
While maintaining such cooled state around the ring, one can transform round to flat beam to the IP, in this way gaining luminosity over the SC limit. 17

18. Potential to raise the e-cooling rate
EC rate is fundamentally limited by the electron current (trivial!) and proton bunches 6D phase space size (less trivial…).
Once the 6D emittance decreased by having one transverse canonical emittance small, one can account on a significant increase of cooling rate when cooling the large (as usual) emittance of the “large” CM.
Naturally IBS will try to heat the low emittance CM. But EC would prevent the heating to some degree, anyway (see below in more detail). 18