1. PADME project at DAFNE BTF (part 1)
Mauro Raggi & Paolo Valente
Seminario INFN Sezione di Perugia
Perugia, 9 Marzo 2015
BTF website:

2. Outline DAFNE complex in Frascati and the Beam-Test Facility
Single electrons vs. high intensity mode
BTF operation principle
BTF beam and diagnostics
LINAC primary beam
LINAC beam dump
BTF users, operations and duty-cycle
Planned and possible upgrades
New control room
Improved shielding (roof)
Additional beam lines
LINAC energy upgrade
M. Raggi & P. Valente
Perugia, 9/3/2015

3. DAFNE complex in Frascati
DAFNE, replacing ADONE (operational until 1993), has been running as e+e- collider at 1,02 GeV since 1999, for KLOE, DEAR, FINUDA, Siddharta, and now KLOE/2 …
Synchrotron light source operational with 3 lines (X, UV, IR)
High current electron/positron linac + damping ring + test facility
Power supplies
modulators
linac
Synchrotron light
DAFNE
KLOE hall
Pumps
BTF
Cryogenics
Power supplies
Damping ring
M. Raggi & P. Valente
Perugia, 9/3/2015

4. LINAC parameters
Design
Operational
Electron beam final energy
800 MeV
510 MeV
Positron beam final energy
550 MeV
RF frequency
2856 MHz
Positron conversion energy
250 MeV
220 MeV
Beam pulse rep. rate
1 to 50 Hz
Beam macropulse length
10 nsec
1 to 40 nsec
Gun current
8 A
Beam spot on positron converter
1 mm
norm. Emittance
(mm. mrad)
1 (electron)
10 (positron)
< 1.5
RMS energy spread
0.5% (electron)
1.0% (positron)
electron current on positron converter
5 A
5.2 A
Max output electron current
>150 mA
350 mA
Max output positron current
36 mA
100 mA max
Trasport efficiency from capture section to linac end
90%
Accelerating structure
SLAC-type, CG, 2π/3
RF source
4 x 45 MWp SLED-ed klystrons TH2128C
The “shotgun” of the system is of course the high-current linac
M. Raggi & P. Valente
Perugia, 9/3/2015

5. The beam test facility BTF LINAC Main rings BTF control room 10 m
Power supplies
BTF
BTF
control room
Damping
Ring
transfer line
LINAC
10 m
transfer line
Main rings
M. Raggi & P. Valente
Perugia, 9/3/2015

6. BTF line splitting
The idea was to use the LINAC beam only when not injecting, sharing the transfer line to damping ring
This resulted in a very low duty-cycle, especially in topping- up operation of the collider
An upgrade of the original scheme planned immediately after the BTF commissioning (2002):
2004: fast dipole + three-way thin vacuum chamber installed, BTF attenuating target and energy selector on an independent beam-line
2008: new pulsed power supply, possibility of choosing individual bunches
DC extraction magnet and energy selector
LINAC
spectrometer
Pulsed dipole:
0°/3°
Energy
selector 6° 3°
Pulsed dipole
0°/6°
M. Raggi & P. Valente
Perugia, 9/3/2015

7. BTF: beam attenuation
The original scheme was already to have two different operation modes:
Single particle mode
Extraction of the full LINAC beam
All electrons
< 10 mrad
Use a (variable depth) target to increase the energy dispersion of the incoming beam
Select a well defined energy by means of a dipole + a collimating slit system
Further attenuation by means of additional collimators (upstream and downstream)
< 4 mrad
Upstream slits in order to:
Flatten the energy distribution
Bound the entrance angle in the dipole magnet
M. Raggi & P. Valente
Perugia, 9/3/2015

8. BTF: beam attenuation 42° selector dipole Tungsten collimators
1.7, 2.0 or 2.3 x0 copper target
Energy resolution made up by two terms:
Upstream slit aperture d and thickness D determining the input divergence
Downstream slit aperture h and distance r
M. Raggi & P. Valente
Perugia, 9/3/2015

9. Intensity fine tuning Without changing the momentum resolution:
Adjustment of the number of particles can be achieved:
Without changing the momentum resolution:
Modulating the LINAC current [not possible in ‘parasitic mode’, rough] (transport optics or modulators power/phase, etc.)
Collimating the beam before the target, using the up-stream vertical slits [large range]
Choosing one of the three target depths [step change, very reproducible]
Collimating the beam after the dipole, using the down-stream vertical slits [fine, small range]
Also changing the momentum resolution:
Closing/Opening the horizontal collimators [both upstream and downstream]
M. Raggi & P. Valente
Perugia, 9/3/2015

10. Single particle regime
SiPM
saturation
Courtesy: TWICE-Insulab
BGO-OD
Journal of Physics: Conference Series 587 (2015)
Nota bene:
BTF energy spread fixed at 1%
M. Raggi & P. Valente
Perugia, 9/3/2015

11. BTF beam-line 45° line Equipped with detector testing gadgets:
Remote-control table
Beam spot and intensity diagnostics for medium and low intensity beam:
Calorimeters
GEM TPC
Fiber hodoscope
Silicon pixel (FITPIX)
Straight line
More background from target
Used mainly for high-intensity;
neutron photoproduction
equipped with fluorescence flag
M. Raggi & P. Valente
Perugia, 9/3/2015

12. Beam spot diagnostics E=385 MeV sx=1.25 mm sy=0.65 mm FITPIX detector
Nota Bene:
Limited by multiple scattering on 0.5 mm Beryllium exit window (+air)
M. Raggi & P. Valente
Perugia, 9/3/2015

13. BTF beam summary Energy spread Dp/p ~1% Beam spot: 1 – 2 mm RMS
Divergence: 1 – 1.5 mrad
Effect of multiple scattering and Bremsstrahlung on the Beryllium exit window and in air has to be considered
Both size and divergence depend on the optics
Beam position: 0.25 mm RMS
Pulse duration: 1.5 – 40 ns
10 ns during collider operations
Measurement of the beam E spread
Beam spot size
Beam spot center
Beam E spread
Nucl. Instrum. Meth. A718 (2013) 107–109
M. Raggi & P. Valente
Perugia, 9/3/2015

14. High intensity Radioprotection limit:
<n> = 3.125×1010 particles/s
Typical charge to damping ring:
>1 nC/pulse for e-
nC/pulse for e+
But…
Much higher charge on positron converter
8 A (12 A) from gun cathode
A few measurements on the maximum LINAC charge, driven by beam-dump experiments requirements
M. Raggi & P. Valente
Perugia, 9/3/2015

15. High intensity diagnostics
Difficult range >103 and <107 particles/pulse
Below 103, GEM or FITPIX are OK
Above 107 integrating current toroid (WCM) OK
Iwcm= ∫Vds- Iped
Qout= Iwcm/R
ICT
M. Raggi & P. Valente
Perugia, 9/3/2015

16. High intensity diagnostics
Difficult range >103 and <107 particles/pulse
Below 103, GEM or FITPIX are OK
Above 107 integrating current toroid (WCM) OK
Use diamond detectors in the intermediate regime
F. Burkart et al.
Cross-calibration of WCM with ionization counter
F. Burkart et al.
CIVIDEC diamond vs. ionization counter
M. Raggi & P. Valente
Perugia, 9/3/2015

17. High charge from LINAC +30% ×3 - ×5 DAFNE LINAC gun
Upgraded pulser electronics [change pulse height]
DAFNE LINAC gun
+30%
Decreasing grid stopping potential
×3 - ×5
Increasing gun pulse height
10 ns
10 ns
M. Raggi & P. Valente
Perugia, 9/3/2015

18. High charge from LINAC ×4
Increasing pulse length to 40 ns
Upgraded pulser electronics [change pulse lenght]
10 ns
20 ns
At 20 ns, 400 V pulse height, DAFNE beam monitors already saturated (>10 nC)
Expect 25 nC up to 50 nC/pulse
40 ns
M. Raggi & P. Valente
Perugia, 9/3/2015

19. Extending the LINAC pulse length
Can we increase the beam width above 40 ns?
Accelerating a ≈ ns long pulse should be possible with the present configuration
Even taking into account same saturation, we should go in the ≈100 nC regime…
10 ns, 100 mA
40 ns, 150 mA
M. Raggi & P. Valente
Perugia, 9/3/2015

20. Extending the LINAC pulse length
Adding two more 180° phase inversions, 240 ns with <0.5% energy spread achieved at SLAC for E-154 experiment
Another 2× factor, even though saturation effects can show up…
Investigation on a variable pulser up to the ms range started (KENTECH)
M. Raggi & P. Valente
Perugia, 9/3/2015

21. How many electrons on target?
Let’s compute how many eot/y* for 10 nC/pulse so we can scale easily with the charge available from the LINAC
10 nC = 10-8/1.6×10-19 = 6.25×1010
At 49 Hz (1 pulse to spectrometer line) = 3×1012 e/s
2 orders of magnitude more than present BTF authorization
Standard year = 1 y*= 120 days at 100% efficiency (107 s)
3.175×1019 eot/y*
25 nC translates in 0.8×1020 eot/y*
Considering measurements at 725 MeV, 40 ns, in the present LINAC configuration and quite conservative assumptions
Further extension of the pulse to 150 ns seems feasible with the present RF configuration, and should bring us to ≈100 nC, i.e. 3×1020 eot/y*
Where can we dump 3×1012 to 3×1013 e/s ?
M. Raggi & P. Valente
Perugia, 9/3/2015

22. LINAC beam dump 50 cm 30 cm 25 cm 20 cm
[Remove some lead brick and explore dump hole during a long shutdown]
M. Raggi & P. Valente
Perugia, 9/3/2015

23. LINAC beam dump
DHPTT01
A new thin vacuum chamber for DHPTT01 with a double exit
Exactly the same design of DHPTT02
A straight vacuum pipe to the inside of the cavity
Possibly, use DR pumps hall for dump experiments
DHPTT02
DR pumps hall
M. Raggi & P. Valente
Perugia, 9/3/2015

24. Compatibility with DAFNE running
Clearly a beam dump experiment is not compatible with running the collider, due to:
We need the LINAC in electron mode only
We need the maximum electron energy (725 MeV today)
We want to extract the maximum charge from the LINAC gun
However, a sharing of the solar year can be conceived
Experiments with a intermediate intensity positron beam on a thin target can be compatible with the collider running, in a similar way as BTF standard running
How much is the BTF duty-cycle?
Another relevant point is about using the BTF for a significant fraction of the year for dark photon experiments
Not only from the point of view of the beam delivery, but also of the occupation of the area with a permanent installation
This is one of the main reasons for considering a second BTF beam- line
M. Raggi & P. Valente
Perugia, 9/3/2015

25. BTF duty-cycle with collider operations
Very dependent on DAFNE running conditions: lifetime, injection problems, etc.
98% out of injection
20%-50% during injection
Switching time cannot be used
Accumulator
Generally beam delivered to BTF only during e- phase (not the e+ one) due to different primary LINAC beam charge (2 nC/pulse vs 1 nc/pulse)
LINAC operating at 25 Hz during the last years
BTF duty-cycle good enough for most use-cases of HEP detector testing
After a major maintenance, running at 50 Hz since 2014
BTF line
Main rings
Spectrometer
DHPTB101
DAFNE phases:
LINAC = 1 LINAC shot to the spectrometer line for energy measurement
LINAC+BTF = LINAC shots delivered with selectable duty cycle to BTF from 1 to 24(49) pulses/s. Remaining pulses are dumped at the end of the transfer line
GLOBAL = LINAC shots delivered with a variable duty cycle to BTF depending on the injection parameter in ACCUMULATOR:
NO INJECTION: selectable from 1 to 24(49) pulses/s to BTF. Remaining pulses dumped.
INJECTION: the injection needs are DAFNE CR controlled. Typically an injection sequence pulses at 2Hz, taking from 1 up to 10(19) LINAC bunches per sequence. In this configuration 22(46) down to 10 bunches/s are delivered to BTF
M. Raggi & P. Valente
Perugia, 9/3/2015

26. BTF duty-cycle with collider operations
A 2014 typical day (Nov. 9th, 2014)
Almost injections
BTF live-time ≈ 40%
Very frequent topping up (Mar. 4th 2015)
More than injections
BTF not yet running
M. Raggi & P. Valente
Perugia, 9/3/2015

27. BTF Users community
Mainly detector testing from the HEP and astro-particle community with low intensity electron/positrons and gamma
But also high intensity tests and experiments: channeling experiments, beam diagnostics (pepper-pot, diamonds), neutron and charged particles production, etc.
11 years of steady running
Average beam-time: 220 days/year
Average shift : 8 days
70% of the beam time during collider operations (parasitic mode)
30% of foreign users
M. Raggi & P. Valente
Perugia, 9/3/2015

28. First Users Workshop and upgrades
About 40 participants
More than 20 talks
Essentially results from users in the last 3 years
Thorough discussion on possible upgrades
M. Raggi & P. Valente
Perugia, 9/3/2015

29. More on ideas for BTF future
BTF upgrades reviewed in light of the proposed dark photon experiments:
Both high intensity LINAC beam for dump experiments…
…and intermediate intensity BTF beam for thin target experiments
M. Raggi & P. Valente
Perugia, 9/3/2015

30. BTF upgrades/1 1. Move the control room upstairs Useful area
M. Raggi & P. Valente
Perugia, 9/3/2015

31. Control room Present control room Future control room Almost ready!
M. Raggi & P. Valente
Perugia, 9/3/2015

32. BTF upgrades/2 2. Improve shielding: add concrete roof
M. Raggi & P. Valente
Perugia, 9/3/2015

33. Add concrete roof Project ready
Dismantling and installation of new shielding configuration planned in July
M. Raggi & P. Valente
Perugia, 9/3/2015

34. BTF upgrades/3 3. Additional beam lines M. Raggi & P. Valente
Perugia, 9/3/2015

35. More beam lines High Intensity Just one possible configuration with:
15°
Just one possible configuration with:
3 different lines
2 not fully independent halls
45°
3.5×4.5 m2
45°
M. Raggi & P. Valente
Perugia, 9/3/2015

36. More beam lines High Intensity Another possible configuration with:
15°
Another possible configuration with:
2 different lines
2 fully independent halls
45°
45°
M. Raggi & P. Valente
Perugia, 9/3/2015

37. BTF upgrades/4 4. Re-design the tagged photon source
The present system, based on active Bremsstrahulung target and tagging detectors inside the magnet yoke, has some limitations:
Highly non linear relation between g energy and reconstructed position of the hit in tagging modules
Requires single track in active target and cut on track reconstruction
Diverging electrons+ multiple scattering in target material
Requirement of single cluster in the tagging modules
Spurious tagged g’s due to background electrons (or photons), hitting tagging modules from outside
Limited active (vertical) area of the tagging modules inside the magnet gap;
Loss of good g events due to the showering of the electron after the radiation
Non-linear resolution ≈1/E(g), ranging from 40% at E(g)=40 MeV and 2% at E(g)=420 MeV;
Overall complexity of DAQ and reconstruction system (5736 channels Si micro-strip detectors)
New design based on open-yoke magnet (C-shaped in place of H-shaped) and tagging detectors in the focal plane and in vacuum
2% resolution down to 50 MeV with 5 mm granularity and channels
M. Raggi & P. Valente
Perugia, 9/3/2015

38. BTF in AIDA-2020
Task 15.4 Improvements of the test beam infrastructure at INFN Frascati
15.4.1: Additional beam line equipment
In order to perform detector studies, it is necessary to add to the existing GEM time-projection trackers, that will equip one of the two beam-lines, a new tracking system, capable of proving a real-time feed-back on the beam spot size and position, and also a fast and accurate (<1 mrad) measurement of the direction of the particles. This pixel detector, including the mechanical system, has to be designed, built and installed, and the DAQ system should be integrated in the BTF acquisition. A calorimeter, made of a matrix of crystals, for the precise measurement of the energy of the beam, is needed for the monitoring of the beam parameters also on the second beam-line.
15.4.2: Photon tagging upgrade
A re-design of the existing tagged photon source will allow to greatly increase the efficiency and to improve the energy resolution by replacing the H-shaped magnet with a open-yoke one, allowing to place tagging detectors in vacuum and in the focal plane of the dipole. This allows to relax the requirements on the tagging detector: a 5 mm spatial resolution should ensure a tagging resolution at the level of 2% in the range between 10% and 70% of the incoming beam energy.
M. Raggi & P. Valente
Perugia, 9/3/2015

39. LINAC energy upgrade(s)
Current DAFNE LINAC RF power layout
45 MW
45 MW
45 MW
45 MW
550 MeV e+
750 MeV e-
250 MeV e-
M. Raggi & P. Valente
Perugia, 9/3/2015

40. Proposal following the footprints of R. Boni, http://arxiv
Make use of 15 m drift space before splitting to spectrometer and BTF lines
M. Raggi & P. Valente
Perugia, 9/3/2015

41. Add 4 sections + 2 SLED-ed klystrons
+320 MeV:
Reach:
1070 MeV electrons
870 MeV positrons
M. Raggi & P. Valente
Perugia, 9/3/2015

42. Add 4 sections + 4 SLED-ed klystrons
+180 MeV:
+320 MeV:
Reach:
1250 MeV electrons
1050 MeV positrons
Add two more SLED-ed klystrons and split power only in two sections instead of four
M. Raggi & P. Valente
Perugia, 9/3/2015

43. Outlook
The DAFNE LINAC is a important asset of the Frascati laboratory, and can provide high intensity electron and positron beams, in addition of being the injector of the 1 GeV e+ e- collider
The BTF can further tune the LINAC beam in a very flexible and controlled way and provide well characterized electrons and positrons in a wide range of energy, intensity, beam size, etc.
The beam pulse charge and width can be increased, in a interesting range for dark photon search experiments
An alternative area of the accelerator for dumping the high intensity beam is needed
A staged program for further pushing the LINAC and BTF beam parameters has been proposed:
First stages already funded and started
The more ambitious program of energy upgrade of the LINAC is probably also the most interesting for dark photon experiments
M. Raggi & P. Valente
Perugia, 9/3/2015

44. PADME project at DAFNE BTF (part 2)
Mauro Raggi & Paolo Valente
Seminario INFN Sezione di Perugia
Perugia, 9 Marzo 2015
PADME website: