1. Auxiliary Positron Source
K. Yokoya
MiniWS, KEK
2016/4/19 CRWG MiniWS Yokoya

2. APS in TDR
Its specification in TDR is very brief (10 lines in vol.3 part.2 p.91)
500MeV S-band NC linac
Single bunch (intensity ~1%)
This presumably means 0.01/1312 = 10-5 of the nominal intensity
8 SLAC-type 3m-structures, 4 RF stations, each with a 100MW modulator, 50kW klystron and SLED
Location: side-by-side with the photon line from undulator. Share the target with the undulator source.
Length ~40m
2016/4/19 CRWG MiniWS Yokoya

3. Roles of the APS
Commissioning of positron DR, RTML, ML, BDS when undulator source is not available
KAS (Keep Alive Source)
Keep DR etc tuned while the electron ML is in (long) shutdown (due to any reason)
Really needed?
Positron beam for detector calibration at Z-pole
Does not require 10Hz operation
Parameter Group (led by Jim Brau) is making an inquiry to the detector groups on the calibration demand
Time scale: Santander WS
Presumably, the APS is too weak even for calibration.
APS is not needed when we start with e-driven positron source, so this question is not necessary. But CRWG will concentrate on undulator scheme.
2016/4/19 CRWG MiniWS Yokoya

4. Questions to ADI Group on APS
Question A
How high an intensity of the APS required for commissioning (and KAS)?
Bunch charge, number of bunches
Question B
Can the APS be replaced with an electron source? (in particular for the DR)
2016/4/19 CRWG MiniWS Yokoya

5. Answer from DR (David)
The problem is that it will be nearly impossible to detect such a low intensity bunch with the beam position monitors in the transfer lines and damping ring. A bunch intensity of 1E9 is probably the minimum required to measure orbits, coupling, beta-functions, etc.
One could imagine developing special BPM electronics that would be capable of precision position measurements of the very low intensity bunches. But this would be expensive, and obsolete as soon as the positrons from the undulator source are available.
2016/4/19 CRWG MiniWS Yokoya

6. Answer from DR (continued)
Another possibility would be to include hardware in the damping ring for accumulation of charge in a single bunch - pulsed bump magnets in the injection straight. Again, this hardware would not be useful for normal operation, but it could allow accumulation of sufficient charge in a single bunch to perform basic tuning of orbit, coupling, emittance etc.
Later added I imagine that we could accumulate charge in a single bunch without bump magnets by adjusting the injection kickers. In fact, there might be some combination of injection and extraction kickers that would be the equivalent of a bump. And if we could accumulate 1E9 particles in a bunch we could measure and correct orbit and perform emittance tuning which would be useful.
2016/4/19 CRWG MiniWS Yokoya

7. Answer from BDS (Glen)
Requirements are to enable commissioning of beam as much as possible on positron side and to maintain “tuned” beam as much as possible during long shutdown periods.
Commissioning means:
Commissioning and operating main beam diagnostic systems:
Cavity BPMs, Profile monitors in emittance measurement section and at image IP, current monitors etc
IP diagnostics with beam-beam scans (probably not)
Tuning “keep-alive” means:
Possibility to keep checking BBA
Maintain alignment at some level to combat continuous ground motion.
Degraded accuracy compared with full Q, but at least keep in range of feedback dynamic ranges etc
Single bunch, 1% nominal bunch charge (30 pC), low rep-rate (1 Hz min for sensible tuning timescales) seems reasonable.
No strong reason to have positrons, electrons OK.
Cost impact for having easily switchable polarities on all magnets?
2016/4/19 CRWG MiniWS Yokoya

8. Answer from BDS (continued)
BPMs:
1% nominal single-bunch charge will be OK
will want large AFE dynamic range and high bit-count digitizers etc.
Profile monitors:
Laser-wire system designed for full charge likely not useable for APS parameters.
IP diagnostics (beam-beam scans)
With 1% bunch charge, beam-beam deflection and beamstrahlung pairs only visible for very small beams (~100nm or less)
2016/4/19 CRWG MiniWS Yokoya

9. Conclusion
APS of TDR specification can be used for DR tuning (most important is the low emittance tuning) if APS bunches can be accumulated in a single DR bucket to reach ~1E9, though the rep rate would be reduced to Hz
High intensity phenomena (beam loading, electron cloud, etc) cannot be seen
This will also help BDS tuning
Replacement by electron source not realistic
Prepare to change polarity
Additional beam line
2016/4/19 CRWG MiniWS Yokoya