1. Diagnostics developments at CEA Saclay: Beam Loss and Profile Monitors
8th Open Collaboration Meeting on Superconducting Linacs for High Power Proton Beams (SLHiPP-8)
Uppsala, June 13th 2018
J. Marroncle – CEA Saclay

2. Preamble Doppler EMU nBLM NPM Talk about:
Schedule 1.8
AIK 7.1
Schedule 1.9
AIK 7.2
Schedule 1.11
AIK 7.9
Schedule 1.6
AIK 7.3
Talk about:
nBLM (neutron Beam Loss Monitors)
NPM (Non intrusive Profile Monitors
Doppler and EMU (Allison scanner)  already delivered!
2018/06/13
nBLM & NPM - SLHiPP8 - JM

3. nBLM DSM/Irfu, CEA Saclay
S. Aune, J. Beltramelli, Q. Bertrand, T. Bey, M. Combet,
D. Desforge, F. Gougnaud, C. Lahonde-Hamdoun,
P. Le Bourlout, P. Legou, O. Maillard, Y. Mariette,
J. Marroncle, V. Nadot, T. Papaevangelou, L. Segui,
G. Tsiledakis
ESS project manager, Lund
I. Dolenc Kittelmann

4. T. Shea, ESS BI forum, Bilbao, Oct. 4th 2016
Why new BLM?
Tom Shea’s, beam diagnostics leader at SNS in 80th and BI leader of ESS
MPS: not be fulfilled due to
software subtraction
during tuning and commissioning X-rays may vary and it is not sure that “waveform subtraction” works properly
T. Shea, ESS BI forum, Bilbao, Oct. 4th 2016
Waveform subtraction
Pulse frequency = 59.9 Hz
Every 10 s there is an empty RF pulse with no beam
The reference waveform is acquire at blank pulse and stored in software to be subtracted from real pulses
Software MPS accounts for that and reports real loss only
Hardware MPS is compromised
“…the x-ray component is quite significant and can be even greater than the loss itself. A detector that is sensitive to neutrons and not sensitive to x-rays could be a possible solution. Unfortunately it is hard to create such a detector that would work in analog mode.”
A. Zhukov, WEYA2, PAC2013
SNS IC signal
Proposition:
BLM sensitive to fast neutrons  nBLM
BLM insensitive to
X-rays and 
thermal neutrons
2018/06/13
nBLM & NPM - SLHiPP8 - JM

5. Micromegas in few words
-1000 V
-500 V
0 V
drift region
amplification
region
Y. Giomataris, P. Rebourgeard, J.P. Robert and G. Charpak,
Micromegas: A high-granularity position sensitive gaseous detector for high particle-flux environments”,
NIM A 376 (1996) 29.
Based on Micromegas detector
Multi-Pattern Gaseous Detector, invented in 1995 at CEA Saclay1
Parallel plate detector with a strengthened thin mesh dividing the gas volume in 2 parts:
drift region (1 to 10 mm)  E ≈ 0.1 kV/mm
amplification region (30 to 100 µm)  E ≈ 10 kV/mm
Grounded read-out: conductive strips connected to FEE
Pillars are used to reinforce the response uniformity
2018/06/13
nBLM & NPM - SLHiPP8 - JM

6. 2 nBLM types: Slow & Fast SLOW nBLM SLOW nBLM IPHI FAST nBLM
Time response of the slow nBLM detector
SLOW nBLM
SLOW nBLM
neutro-phagus envelop  absorbs the incident thermal neutrons
Polyethylene moderator:
thermalized the incident fast neutrons
absorbed the remaining thermal neutrons
Micromegas:
B4C layer (7 × 7 cm2)
Gas (1 atm): He or N2, Ne…
(He better for avoiding )
Simulations done with Geant4 and Fluka
B4C deposition on cathode done by ESS Detector Coatings Workshop, Linköping University, Sweden
Time response of the fast nBLM detector and beam current on target.
FAST nBLM
2018/06/13
nBLM & NPM - SLHiPP8 - JM

7. The proof of nBLM system working
First test in AMANDE (Cadarache, March 18) very positive. Proof of Gammas/neutron discrimination capability. With similar n and γ fluxes:
Neutron run 191 cts/s
Gammas cts/s
With shown threshold rejection of
No noise subtraction
Higher threshold would result in complete gamma suppression
More tests to follow (IPHI at CEA Saclay , LINAC4 and GIF++ at Cern)
Amande - Cadarache
Slow nBLM
2018/06/13
nBLM & NPM - SLHiPP8 - JM

8. nBLM summary
nBLM may work in 2 modes, since expected rates are difficult to estimate
neutron counting (< 106 cts/s)
current
gas  90% He + 10% CO2
Fast/Slow nBLM (to get almost all neutrons)
timing  <15 ns / µs
sensitivity  % / 0.5 %
Electronics
FEE pre-amplifiers (high BW, low noise, gain=34)
FPGA for data processing (waveform analysis for counting mode)
Project
Kick-off  7/2016
PDR1 & 2, CDR1  ok
CDR2  not yet scheduled
End of project  end 2019
2018/06/13
nBLM & NPM - SLHiPP8 - JM

9. nBLM for ESS To be produced for ESS: 42 × nBLM pairs
FAST
SLOW
moderator
Slow nBLM with its FEE
size ≈ 20 × 25 × 25 cm3
weight ≈ 10 kg
Note: neutro-phagus envelop is not represented
2018/06/13
nBLM & NPM - SLHiPP8 - JM

10. NPM DSM/Irfu, CEA Saclay
P. Abbon, F. Belloni, F. Benedetti, G. Coulloux, F. Gougnaud,
C. Lahonde-Hamdoun, P. Le Bourlout, Y. Mariette,
J. Marroncle, J.P. Mols, V. Nadot, L. Scola
Iphi
N. Chauvin, D. Chirpaz-Cerbat, M. Desmond, Y. Gauthier,
M. Oublaid, G. Perreu, B. Pottin, J. Schwindling, F. Senée, O. Tuske
ESS project manager, Lund
C. Thomas

11. NPM for ESS IPM FPM (Ionization Profile Monitor)
(Fluorescence Profile Monitor)
2018/06/13
nBLM & NPM - SLHiPP8 - JM

12. Why IPM as NPM?
On ESS beam line, there is 2 kinds of NPM (Non intrusive Profile Monitor)
FPM (Fluorescence Profile Monitor)
IPM (Ionization Profile Monitor)
Comparison FPM / IPM
Cross section: FPM < IPM
Particle emission: photon (4π) / pair e-ion (4π, but electric field to catch “all of them”)
Space charge effect  profile distortion: negligible FPM / may important IPM
Design: FPM << IPM
Cold part of ESS (between cryomodules)  Presidual gas ≈ 10-9 mbar
Counting rate estimation
σ · Presidual gas · Ibeam
For IPM (1 cm – Ibeam=62.5 mA mbar – Δt=2.86ms
79% H2+10% CO+10% CO2+1% N2)
90 MeV  17 fC/pulse beam
500 MeV  6 fC/p
2 GeV  4.4 fC/p
FPM  140 (90 MeV) et 46 (570 MeV) photons! ( C. Thomas)
 / 1500 at 90 MeV!
2018/06/13
nBLM & NPM - SLHiPP8 - JM

13. Few IPM challenges Feasibility  too low signal?
uniform Bkgd
non-uniform Bkgd
Feasibility  too low signal?
Bethe-Bloch formulae
 at ESS nominal value and for 1 cm RO length, charge varies between 4.4 fC and 17 fC
Background due to uncorrelated particles with beam
uniform background  ok
non-uniform background  ?
beam dynamics group to make calculation, not yet
Electric field uniformity ( Florian Benedetti)
Profile distortion  mirage effect
Electric field simulation (Comsol…)
Sided degraders + grounded disks to reinforce homogeneity
without any correction
with grounded disk + degraders
“mirage” effect
Sym. IPM
Sym. IPM E
strips
2018/06/13
nBLM & NPM - SLHiPP8 - JM

14. SC effects on profile Space Charge effect ( Francesca Belloni)
beam profile distortion induced by the interaction between the ionization by-products (e- and ions) and the beam.
Developed an algorithm (F. Belloni & C. Thomas) to evaluate effects and to correct profiles offline.
How to minimize SC
increase: E , B , beam size
decrease: beam intensity, energy
ion detection instead of electrons
SC  Ep=90 MeV - σX=σY & σZ=2mm - 𝐄 =300kV/m
X (mm)
electrons
ions
2018/06/13
nBLM & NPM - SLHiPP8 - JM

15. IPM Read-0uts Electric field cage 10× 10× 10 cm3
IPM1 read-out  MCP + strips (1mm) + RO (charge)
IPM2 read-out  pMCP + optical system + CCD camera
IPM3 read-out  strips (Gaussian) + RO (charge)
With:
MCP: MultiChannel Plate ( electrons)
pMCP: MCP with a phosphorescent screen ( photons)
pMCP + optics + CCD
(MCP) + Strips + RO
2018/06/13
nBLM & NPM - SLHiPP8 - JM

16. Test bench in our lab installation at IPHI 2018/06/13
nBLM & NPM - SLHiPP8 - JM

17. preliminary results: (MCP)+strips
All tests done at IPHI (Saclay): proton beam, 3 MeV, Imax≈70mA, Δtpulse≈120µs, 1Hz
MCP + constant strips
Comparison MCP+strips/CCD
Read-Out: D. Etasse et al., Faster system
LPC Caen, France.
Ibeam = 32mA mbar - Δt=100µs (1Hz)
σcore=2.63 mm
σcore=2.48 mm
Profile
σcore
position
Ibeam = 32mA mbar - Δt=100µs (1Hz) - σ≈3.3mm
Profile positions: CCD/Strips/BPM
2018/06/13
nBLM & NPM - SLHiPP8 - JM

18. preliminary results: pMCP + CCD
Electric field study with Comsol
 Resistors for sided degraders. Note that calculation was done on Symmetric IPM mode
pMCP+CCD
Asymmetric polarization
σ = 1.81
σ = 2.00
Symmetric polarization
σ = 2.30
Comsol prediction
Focusing effect when used in Asymmetric mode  ok
Size ratios: ( )/2=1.21 – Calculated: 1.27
Double Gaussian fit:
More accurate: halo + beam core
2018/06/13
nBLM & NPM - SLHiPP8 - JM

19. NPM summary Two IPM types tested at IPHI
pMCP + optical system + CCD camera
(MCP +) + Strips
 Promising results
New data taking at IPHI on September 2018
MCP  better understanding
Strip  RO improvement
Accurate extrapolation to ESS conditions
Space Charge bench-marking code
Project
Kick-off  5/2016
PDR  ok on 02/2017
CDR1  July 2018
End of project  mid 2020
2018/06/13
nBLM & NPM - SLHiPP8 - JM