1. Kaoru Yokoya CRWG Meeting, Feb.2, 2016
Issues to be Solved v3
Kaoru Yokoya
CRWG Meeting, Feb.2, 2016
CRWG Yokoya

2. Contents Tune-up dump Emergency dump Primary dump
Positron target region
Remote handling of positron target
10Hz operation
Auxiliary positron source
Muon wall
Special caverns
Commissioning process
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3. Tune-up dumps Location Consisting of Role Power capability
E+ side : after e+ linac
E- side : after dogleg downstream of undulator
Consisting of
Monitor
Fast kicker after skew correction, emittance diagnostics, and polarimeter
TDR says “fast kicker” but I don’t understand yet. Why fast kicker? Will come back in “emergency kicker” section.
Glen raises the question on “fail-safe stopper”
Beamline to the dump
Fast sweeper (to sweep the beam on the dump window)
dump
Role
Beam dump for linac commissioning when detector is not ready
Up to full intensity
Emergency beam dump, too ??
Power capability
Same as the primary (full) dump, i.e., 14MW
Energy band width 10%? (plus 1%, minus 10%?)
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4. From Benno Remarks: Two different chicanes: Fast kickers:
Energy measurement: before extraction to dump. This is a fixed angle chicane
Polarimeter chicane: after extraction to dump. Fixed field chicane (wide aperture vacuum system / magnets)
Fast kickers:
For e+ BDS, there is no other emergency extraction between ML and IP, therefore tune-up dump serves as emergency extraction dump as well. Requires large momentum acceptance.
On e- side, an additional emergency extraction line exists in front of helical undulator, so extraction to tune-up dump does not need fast kickers. But we assumed that both sides would be symmetrical.
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5. TDR v3 part2 p.135
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6. TDR v3 part2 p.91
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7. Emergency Dump Questions
Erroneous bunches go through undulator and dogleg? (worry of Benno)
How large is the energy band width of dogleg?
There used to be an emergency dump just before undulator (in my memory) for avoiding erroneous beam to hit the undulator. Has it been removed? No, TDR shows a dump EFAD.
When we moved the undulator to linac end, it was claimed another MPS would be needed if the undulator is in the middle of linac.
TDR shows a “fast kicker” just downstream of polarimeter. Should this be a DC magnet? “Fast kicker” should be upstream of undulator? Correct me if I am wrong!!
TDR shows a beamline EFADL. This should be below the undulator line (same side as the dogleg). Otherwise, it will block the pathway.
Emergency kicker
Response time ~300ns ?
Flat-top ~200ms ? (remaining pulse up to 1ms is stopped at DR exit)  Okugi, LCWS Whistler, but is this the kicker he considered?
Emergency extraction in front of undulator still exists (EFADL: E- Fast Abort Dump Line) (Benno)
Location
627m from kicker (TDR v3 part2 p.91)
275m (EUPM) + 379m (EUND) = 653m, so the dump ends before dogleg
What does EUPM stand for?
TDR mentions about “pilot bunch” as an option (v3 part2 p.173)
Single, weak bunch (1%)
10ms (long enough to excite protection system, short enough compared with linac fill time) ahead of the main pulse
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8. Primary Dump Is there an accepted design of the dump hall?
Registered in EDMS D ,B,1,1
done by B. smith from CCLRC ( Rutherford labs) (next page shows the drawing but download the original one for higher resolution.)
Not a job of CRWG except
The size of the dump hall
Emergency signal
Access to surface?? Or, to IR?
Access for personnel with shielding to pumps and filters etc? along with safety routes! (Ewan)
But whose job?
Somebody has to check the entire dump system
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9. CRWG Yokoya

10. Positron Target Region
Target must be shielded
1 meter think concrete (A.Ushakov) ?
Perhaps, heavy concrete is better for saving space
Space for maintenance included on one side in Ushakov’s drawing
Keep the corridor in the beam tunnel for installation of cryomodules for 5GeV SC linac
Air and water?
Access principle
When the main beam is on, no access allowed to beam tunnel and service tunnel
What about the case when only auxiliary source is on (only to DR, not to main linac)? Intensity is 1/100 or 1/(100*1312). (drive electron intensity is ~10x?)
See auxiliary source
When beam is off, access is allowed to the beam tunnel, too. (1 hour cooling after beam-off?)
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11. From Benno
Andrij Ushakov has shown studies how much radiation comes out of 1m concrete shielding during operation (beam on). This is largely irrelevant if access during beam on to tunnel is forbidden.
Ushakov’s study is a FLUKA model to get an idea of the order of magnitude of necessary concrete shielding. This is not an engineering design.
Second (more severe?) problem: dumps for spent photons beam and electrons. We have no design for that.
I assume: the whole target region, including photon dumps, will be extremely dirty, and should be sealed off towards the main tunnel with thick concrete shielding. I would assume that the main tunnel needs a transport path (tunnel enlargement) around this dirty region. But this is not a big cost driver.
The more important question: Do we need surface access from the target region? Possible reasons:
Extraction of radioactive targets, to avoid transport of radioactive material through main tunnels.
Surface access for ventilation, to prevent radioactive gases from entering the main tunnel. Gases may come from dumps, from spent target area, and maybe from accidents (rupture of a dump window).
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12. CRWG Yokoya

13. Photon and electron dumps are missing here.
electron beam to IP
Photon beam
Photon and electron dumps are missing here.
Radioactive region is much larger. (Benno)
Model used by Andriy Ushakov, LCWS2015
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14. Does not scale at all ~ 10m ~ 300m ~ 400m This has to be shielded
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15. Remote Handling of Positron Target
TDR shows a conceptual design
Is the concept compatible with Ushakov shield?
Missing detailed design  to be done by positron team
How big a space in the tunnel needed?
How often is the replacement?
How many used targets can be stored?
Eventually, the used targets should be moved to the surface (perhaps), after cooling of radiation to some level. Agree?
Transport path must be decided and prepared
Presumably to PM+8. ~2.5km.
How big is one target with container?
Container for long transportation can be thin lead-covered (only gamma ray is the issue)
The design for TDR vol.3-I says the part to be replaced is 1400×1140×1650mm, 5 tons
The container for replacement is 2680(w) x 3530(L) x 1900(h)
But it’s not clear which parts to be replaced
Target itself, flux concentrator,
NC cavity (cavities) (TDR says included), solenoid ???
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16. 1. General Layout Used Target & Container Target Handling Container
Base
Target Station
New Target
Utilities:
Water pump
Vacuum Pump
etc.
Target Handling Container
1. General Layout
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17. 10Hz Operation Should it be included at the project start?
Top-level decision needed, but, perhaps, the answer is NO
Presumably, the possibility of 10Hz operation should not be completely excluded  then, in the followings, only the space to be reserved is the issue
The spent electron beam (after creating positron)
Beam dump must be specified
6.3MW (5Hz, 150GeV, 3.2nC, 2625 bunches)
 use the tune-up dump, though it is a bit far.
The beam energy is well-defined
The beamline EPUNDDL, leading the spent electron (150GeV) to a beam dump, must be designed
BDS or sources  BDS group (judging from the expertise)
Need not care about emittance increase
 can be much shorter than the dogleg for colliding beam, can be lifted up to ceiling (need not care about vertical bend)
Even when 10Hz operation is not included at the project start, the tunnel space for the beamline must be reserved
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18. From Benno There are two kinds of 10Hz operation:
Alternating e- beams for e+ production (at 150GeV) and collisions ( GeV, maybe even 45GeV for Z0 running)
Standard operation of accelerator, but at higher than 5Hz repetition rate (“10Hz for physics”)
The 10Hz for e+ production is the baseline solution for centre of mass energies below 250GeV. TDR baseline says ILC must be operable between 200 and 500GeV CME. So, we have to provide 10Hz running, or submit a change request to restrict operating range with undulator source to more than 125GeV electron energy.
Physics community assumes that 10Hz scheme will also be used for Z0 calibration running. Z0 running for physics (“Giga-Z”) is not baseline, but many people think 10Hz running would make this easily possible. But that would require beams alternating between 45GeV and 150GeV, which may not work. Nick Walker has a different solution (bypass line to split the Main Linac into a 150GeV and a GeV part).
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19. TDR v3 part2 p.91
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20. 10Hz Operation (2)
Pulsed magnet (5Hz, vertical bend) must be inserted just upstream of the undulator in order to lead both 150GeV and ECM/2 beams to the center of undulator.
Is the space (longitudinal length) reserved? No, I think.
Orbit difference (vertical) for 150GeV and 45GeV beams ~ 4mm?
Assume the minimum ECM is 90GeV
150GeV can be 125GeV?
5Hz pulsed magnet (vertical kick, flat-top 1ms) to kick 150(125) GeV beam (not the beam for collision) and compensate ~4mm
Also another pulsed magnet (and septum) needed after undulator to separate EDOGL and EPUNDDL
Or, DC bend in dogleg can be used for separation ? if 150 GeV and ECM/2 are not too close.  No? 10Hz at ECM=250GeV.
Must be designed by BDS team
Only the space is needed for now.
What else for CRWG on 10Hz?
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21. From Benno
The big question is: Where is the “physics beam” in the 10Hz scheme separated from the e+ production beam?
Solution 1: Both beams go through undulator and the target bypass chicane, e- production beam is dumped in tuneup dump line
-> needs many, many pulsed magnets: magnets to line up beam in front of undulator, bends in target bypass chicane. Physics beam goes through many pulsed magnets, may have impact on emittance. E+ production beam goes through many optics sections that are tuned for a different beam energy.
Solution 2: Beams are separated directly after undulator. E+ production beam goes to dump via separate dump line, maybe even to a separate dump. Eases situation for BDS, but still has physics beam in undulator. Extraction would kick out the e+ production beam, i.e., no emittance issue for physics beam, extraction could be short.
Solution 3: Beams are separated in front of undulator. Needs a low- emittance extraction section for the physics beam, which will be longer than for 2, but this is only beam with less than 125 GeV, so dogleg can be much shorter than standard target bypass dogleg that is designed for 500GeV.
Solution 4: Beams are separated in Main Linac (Nick Walker’s solution). Requires long transport lines and maybe additional turnaround. Probably most expensive, but would work best, even for 45GeV.
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22. Auxiliary Positron Source
TDR
S-band normal-conducting, 500MeV linac
Share the target (and its downstream) with the undulator source
Positron intensity ~1% (single bunch)
Does this mean the pulse charge is 1/(1312*100) of the nominal beam?
Length < 40m
Role
Commissioning of positron DR (electron linac not ready yet)
Or keep alive of e+ DR during shut down of electron linac
Study of e-cloud issue is anyway impossible
Can an electron beam (additional e-gun before 5GeV booster) do this job? (Polarity of all the magnets in DR must be inverted)
Commissioning of positron linac before the electron beam reaches 150GeV
Detector calibration at Z0?
This makes sense only when 10Hz mode is not available
But luminosity may be too low even for calibration?
Ewan:
We do not know the minimum that is worthwhile.
Reconsider utility?
Further complicates region shielding and design.
Might be used only once i.e. to gain a few months in commissioning?
What do we need now?
Some more parameters on beam intensity
Ask DR group on minimum intensity for DR commissioning
Ask detector group (via Parameter Group) on minimum intensity for detector calibration
Leave the space in parallel with the photon line (width, length)
Laser is not needed
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23. From Benno
The fundamental question is: What is the purpose of the AUX source? And what requirements come from that purpose?
Purpose is clearly commissioning, of:
Positron source beamline (including 5GeV booster) to DR
Damping Rings
E+ RTML
E+ Main Linac
E+ BDS
My question: which of these things requires positrons? And is so: at what intensity per bunch and per pulse?
One idea: Can one do the commissioning with electrons and later reverse polarities? Would permit a full-intensity electron beam instead of a low-intensity positron trickle, could be used for vacuum system scrubbing.
This may work for commissioning but not as KAS (KY)
Cannot anyway test e-cloud problem (KY)
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24. CR11
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25. Muon Wall Don’t want to think of as CRWG issue
Basically a BDS issue
Can be a CRWG issue, if (as Okugi san suggested) a larger tunnel with fixed muon-wall size causes more muon background to the detector
Let’s wait for now for the conclusion of BDS team
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26. Special Caverns Is there any caverns that requires special access
Laser hut
Polarization monitor
Photo-cathode gun
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27. Commissioning Process (just to make sure)
According to TDR (v3 part2 p.244)
Excavation of access tunnel starts at year 1.0
DR commissioning can start at year 7.5
ML commissioning can start at year 9.0
DR commissioning
Use electron source (full intensity)
Use auxiliary positron source (very weak)
RTML and bunch compressor
ML commissioning
Up to full intensity
Use tune-up dump. This means the beam goes through undulator, dogleg, skew correction, emittance diagnostics, polarimeter.
Undulator field off.
Must guarantee detector works.
Positron source commissioning
First, undulator field on, target off (maybe, a hole on the target wheel). The photon beam is stopped at photon dump
Then, target on. Tune NC and SC linacs. Positron beam can be dumped at the end of PTRANH, if needed.
Followed by full commissioning of positron DR
BDS commissioning
One detector (SiD) sitting at IP
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28. Glen’s Message (Jan.28)
Concrete shielding wall in front of FD to reduce neutron flux into the detector region
PPS issues. Is this part of our mandate?
For example, in the past when considering the tune-up dump, fail-safe beam stoppers were required in case of failure of the bend magnets taking the beam to the tune-up dump line (and not aborting quickly enough). There, the muon wall also was required with at least a given thickness as a PPS device to limit the muon radiation coming from a bunch hitting that fail-safe stopper …
Do we need to identify resource to fully define PPS and MPS systems for CR beamlines so such issues can be properly thought through?
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