Operational experience with profile monitors for MeV and kev antiproton beams at CERN AD

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1 Operational experience with profile monitors for MeV and kev antiproton beams at CERN AD Anna Soter, Masaki Hori Max Planck Institute for Quantum Optics, Garching, Germany

2 Antimatter research at MPI for Quantum Optics The following people are involved in the detector, laser, and trap development work described here: A.Soter, D. Barna, A. Dax, R.S. Hayano, T. Kobayashi, K. Todoroki, W. Pirkl, M. Hori Munich-Centre for Advanced Photonics (MAP)

ASACUSA collaboration Atomic Spectroscopy And Collisions Using Slow Antiprotons 1997 at Antiproton Decelerator (AD) of CERN University of Tokyo, Max Planck Institute

3 ASACUSA collaboration Atomic Spectroscopy And Collisions Using Slow Antiprotons 1997 at Antiproton Decelerator (AD) of CERN University of Tokyo, Max Planck Institute for Quantum Optics, RIKEN, SMI Vienna, KFKI Budapest, INFN Brescia, Aarhus University, University of Swansea, Queens University of Belfast, ATOMKI, Debrecen Asakusa, Tokyo

4 ASACUSA - physics goals with antiproton beams We use antiproton beams of various energies for atomic and nuclear physics experiments: 5 MeV -- microwave spectroscopy of antiprotonic helium atoms 6-1 kev -- Doppler-free 2-photonspectroscopy of antiprotonic helium: antiproton to electron mass ratio, CPT test 1 ev -- atomic ionization experiments with antiprotons on hydrogen, helium and argon gases < 1 ev -- antihydrogen production in traps

5 Accelerators at CERN LEAR ( ) AD (1999-)

History: LEAR (Low Energy Antiproton Ring) All photos from

26-GeV beam of PS Captured by Antiproton Collector Stored by

6 History: LEAR (Low Energy Antiproton Ring) All photos from CERN archives construction:1983 Antiproton production with 26-GeV beam of PS Captured by Antiproton Collector Stored by Antiproton Accumulator Decelerated to 69 MeV/c by PS Injected to LEAR. Provided 1 1 antiprotons within 1 minutes pulsed and continuous beams energy range from 5 MeV above 1 GeV shutdown: 1996

7 The Antiproton Decelerator at CERN constructed in 1999 using US, European, Japanese user funding. low-cost antiproton facility, dedicated to atomic physics (antihydrogen) experiments, 188 m synchrotron All-in-one: capture, deceleration, cooling, ejection All photos from CERN archives

Cooling and decelerations at AD Injection at 3.

8 Cooling and decelerations at AD Injection at 3.5 GeV/c, transverse acceptance ~ 2 π mm mrad momentum spread Δp/p = 6 %, after pulse stretching 1.5 % After stochastic cooling and decelerations: deceleration by RF fields in 2 steps (2 GeV/c... 3 MeV/c ), between them stochastic cooling emittance ~ 3-4 π mm mrad momentum spread Δp/p ~.7% cern ad, the machine pictures, technical data After electron coolings and deceleration: emittance ~.3 π mm mrad momentum spread Δp/p ~.1% Ejection: 1-ns-long beam, 4x1 7 antiprotons of energy 5.3 MeV

Pulse rate 1 Hz 3 mm aperature, deceleration efficiency >25%.

9 The RFQD Energy variable 1-13 kev f=22.5 MHz 3.5 m long, 3 RF cells in ladder structure, 33 MV/m peak electric field buncher + energy corrector +RFQ Pulse rate 1 Hz 3 mm aperature, deceleration efficiency >25%. CERN and ASACUSA constructed the RFQD (Radiofequency Quadrupole Decelerator) to decelerate the antiprotons from 5.3 MeV to kev energies needed for atomic physics experiments. All photos from CERN archives

10 The RFQD and the low-energy beam transport Microwire secondary electron emission detectors Parallel Plate Ionization Chamber Phosphor screens 5.3 MeV ~6keV the low-energy beam is transported by an acromatic momentum selector: 2 dipoles, a matching quadrupole triplet point-to-point focus PRL 91, (23) M. Hori et al.

High-precision spectroscopy of antiprotonic helium metastable 3-body system ~ 4 μs lifetime exciting the antiproton transitions with laser beams high-precision methods to investigate the antiproton

11 High-precision spectroscopy of antiprotonic helium metastable 3-body system ~ 4 μs lifetime exciting the antiproton transitions with laser beams high-precision methods to investigate the antiproton mass and fundamental symmetries. highlighted results: mantiproton/melectron = (5) (M. Hori et al, PRL 96, (26)) assuming CPT symmetry, result was used as one of the data sets in CODATA26 to determine the mproton/melectron mass ratio

12 Laser and trap developments At MPQ and CERN: high-precision laser systems (stabilization by frequency comb, chirpcompensated pulse-amplification) radiofrequency traps (M. Hori et al, PRL 96, (26))

13 Future: ELENA, the possible extension of AD Our group is participating in a proposed project to build a new storage ring inside the AD, which can provide: 1 kev electron-cooled antiprotons intensity up to ~ 2*1 7 Δp/p ~.2% emittance: 5 π mm mrad (M. -E. Angoletta et. al., CERN-AB-27-79, 27)

14 Measuring antiproton beams Beam profile and intensity measurements of MeV - GeV antiproton beams were studied in the 197 s to 9 s at FNAL and CERN MWPC s, flying wires, residual gas ionization detectors, Schottky pickups, scintillation and phosphor screens, intensified cameras, parallel plate ionization and avalanche detectors. kev to ev beams were studied at AD in the 9 s and 2 s. Secondary electron emission detectors, microchannel plates, delay line anodes, pixel detectors.

15 Design constraints of detectors for AD and beyond Strong magnetic field and low temperature and UHV: some detectors work in B>1 Tesla, T<5-77 K and P<1-1 mbar. Low maintenance: few adjustment parameters, don t need specialists to maintain it, if possible avoid detector gases and components that wear out. Common use: detection of ev to MeV-energy antiproton beams, continuous and pulsed antiproton beams. Continuity: Parts available after 1-15 years of use in the facility. Low cost: AD, ELENA, etc. are constructed relying on user funding. 2 keuro per detector including vacuum chamber, software, manpower costs, etc.

16 Behavior of antiprotons in detectors When antiprotons annihilate, following particles are produced: 1): Around 3 charged, minimum-ionizing pions 2): Recoiling nuclear fragments 3): Gamma rays (pi decays) Charged pions are useful for reconstructing annihilation vertex. Can become a backgound in scintillators. Heavy ions can become background in MCP s (tracks) Antiprotons produce.1-3 secondary electrons depending on incident energy 1 kev - 5 MeV and target material. Pions do not produce very much secondary electrons.

17 Strategy we adopted at ASACUSA For 5-5 MeV antiproton beams: Parallel plate ionization/secondary electron emission chamber Scintillation screens Cherenkov detectors For 1 ev - 1 kev antiproton beams: Microwire secondary electron emission detectors Microchannel plate Scintillation / phosphor screens Annihilation vertex reconstruction detectors

18 Transducer gauge Parallel plate ionization chamber Test charge inputs Wide band preamplifier 1 cm Gas Bias voltage Control valve µ t d= 2 m polyimide beam windows Beam Gas 2 mm Y profile signal PTFE signal cables Y projection cathode foil 2 ch charge preamplifier X profile signal Anode foil X projection cathode foil NIM-A 522, 42 (24) M. Hori Constant flow of P1 (Argon + 1% methane) gas at pressure 65 mbar. Parallel electrodes + reduced gas pressure to minimize space-charge effects.

19 1 M +7 V 1 k Detector electronics 2.2 µ F Wide band voltage amplifier 1 µ F 1 nf X projection cathode 25 Digital oscilloscope Peak hold ADC +12V Active filter amplifier Y projection cathode Anode 6.8 nf 12V 1 M Gain control amplifier Pulse generator 1 1 pf 1 pf 47 pf Charge sensitive preamplifier (1 of 2 channels) NIM-A 522, 42 (24) M. Hori Timing information from common anode read out by voltage amplifier. Spatial information from X-Y cathodes read out by charge-sensitive preamplifiers.

Ag+C paste Gold strip Copper strips Ag+C paste Gold strips Laser beam Cutting of 8-um wide strips in metal layer

20 <2 micron thick electrodes made by laser trimming (a): 2 mm (c): Laser trimmed strip 5 µ m Aluminized or gold-sputtered polyester or Mylar foils. Ag+C paste Gold strip Copper strips Ag+C paste Gold strips Laser beam Cutting of 8-um wide strips in metal layer using Nd:YAG or excimer nanosecond laser trimmer. (b): (d): scan Transparent Mylar or polyester foils are left intact. Signal wires Glass epoxy Polyester t = 1.5 µ m d NIM-A 522, 42 (24) M. Hori

21 Response of PPIC at high beam intensities Anode signal (mv) Various P1 gas pressures used. 5 (a): 65 mbar,.75 V/mm electronic signal 25 ionic signal 5 (b): 65 mbar, 7.5 V/mm 25 (c): 65 mbar, 75 V/mm 4 2 Anode response (antiprotons / pulse) x (d): 75 V/mm 4 V/mm 7.5 V/mm.75 V/mm Time (µs) Beam intensity (antiprotons / pulse) x1 9 Relatively linear up to 2x1 9 antiprotons/pulse. NIM-A 522, 42 (24) M. Hori

22 Beam position and intensity measurements at LEAR Intensity (a.u.) XY beam profiles (a): Position (mm) 1 (c): Beam position centroid X Y Position (mm) Position (mm) 1 5 (b): Intensity (a.u.) Antiprotons / pulse -1 x (d): Beam intensity Extracted pulses NIM-A 522, 42 (24) M. Hori

Parallel plate secondary electron emission chamber (a): Cherenkov counters Charge sensitive preamplifiers Ceramic isolator 1 cm Avoid using detector gases and beam windows, put 9 Vacuum 1 x 1 mb

23 Parallel plate secondary electron emission chamber (a): Cherenkov counters Charge sensitive preamplifiers Ceramic isolator 1 cm Avoid using detector gases and beam windows, put 9 Vacuum 1 x 1 mb detector directly in beamline. Laser pulse Cryogenic helium target Antiproton pulse Rely on secondary electron Y projection cathode foil 4 mm X projection cathode foil Anode foil 25 liter/s turbo molecular pump emission. UHV-compatible materials (b): (ceramic, fluxless solder). Copper beryllium readout contacts Gold readout pads µ 1.5 m thick aluminized polyester foil Silver paste thick film printed Signal intensity reduced by two orders of magnitude Position sensitive aluminum electrodes Guard electrodes compared to ion chamber. Ceramic substrate 3 cm NIM-A 522, 42 (24) M. Hori

24 Beam profile and intensity measurements at AD Intensity (a.u.) 2 1 (a): Position (mm) 2 (c): X Y Y-position (mm) X-position (mm) x1 7 4 (b): (d): Intensity (a.u.) Extracted pulses Antiprotons / pulse NIM-A 522, 42 (24) M. Hori Clear profiles can be observed using the detection of secondary electron emission 2x1 7 antiprotons/pulse.

Microwire secondary electron emission chamber (a) X-projection preamplifiers Beam Y-projection preamplifiers 5 cm X-projection cathode grid

Ceramic frame Readout pins and sockets RSI 76, 11333 (25), M. Hori Gold-sputtered tungsten wires or carbon filaments diameter 5-3 um placed in UHV.

25 Microwire secondary electron emission chamber (a) X-projection preamplifiers Beam Y-projection preamplifiers 5 cm X-projection cathode grid Y-projection cathode grid UV, X-ray, or particle beam Vacuum chamber Readout pins X-projection grid Readout sockets Y-projection grid anode grids (b) Ceramic frame Readout pins and sockets RSI 76, (25), M. Hori Gold-sputtered tungsten wires or carbon filaments diameter 5-3 um placed in UHV. Wires intercept 1-3% of the beam % travel through without being affected. Gold-coated tungsten wires Gold microstrips Secondary electrons detected by preamplifiers.

26 J-FET based charge sensitive preamplifier system Shielded copper case on detector (1 of 64 channels) 5 V 1 G +12V Transconductance amplifier 64 discrete junction FET hybrid amplifiers Cf =.5 pf, Rf = 5 GOhm, 2 V/pc. Input Q i 2.7 nf 12V 5 G.5 pf 15 k 1 µ F 6.8 nf Differentiator =5 µs 7.5 k Transmission via 2-Ohm differential transconductance amplifier (minimizes RF interference and ground-loops) Active filter amplifier ADC Front end computer Waveform digitizer CAMAC to SCSI interface Personal computer RSI 76, (25) M. Hori Active filter amplifier t = 2 us. 1 differentiator, 4 integrators Equivalent noise charge RMS=2. (calibrated with Si detector + 241Am source)

27 Time/space-resolved measurement 5 x=6 mm Signal (V) x=4 mm x=2 mm x= mm x=-2 mm x=-4 mm x=-6 mm Time elapsed (µs) RSI 76, (25), M.Hori

28 Response against pulsed Nd:YAG laser beams Attenuators Telescope nm BBO crystals CCD Nd:YAG pulsed laser Evacuated beamline Monitor 1 Monitor 2 Single-shot measurement of beam Nd:YAG pulsed laser profile at several point along beamline. Enables rapid determination of beam emittance, beam tuning. Intensity Intensity 2 (a) X-position (mm) 2 (c) X-position (mm) Y-position (mm) Y-position (mm) 16 (b) Intensity 16 (d) Intensity RSI 76, (25), M. Hori

29 Photoelectron emission yield measurement x1 4 Photoelectrons 1 (a) 213 nm.1.2 Laser energy (nj) x1 4 Photoelectrons 1 (b) 266 nm 1 Laser energy (nj) W-value of gold = 4.6 ev 213 nm (5.8 ev) g= nm (4.6 ev) g=1-5 proceeds via single-photon. relatively linear. x1 4 Photoelectrons 1 (c) 355 nm 5 Laser energy (µj) x1 4 Photoelectrons 1 (d) 532 nm 5 Laser energy (µj) 355 nm (3.5 ev) g= nm (2.3 ev) g=1-9 proceeds via two-photon, non-linear. Needed field =5-2 kw/cm2 RSI 76, (25), M. Hori

30 Response against <1 kev antiprotons Beam profile monitor Isolation vacuum Detection of 6-1 kev beam of 2e6 antiprotons, and 289-nm laser beam Antiproton beam Laser beam Intensity (arb. u.) 2 (a) X-position (mm) Y-position (mm) (b).8-µm-thick PEN window 1 2 Intensity (arb. u.) Cryogenic helium gas Fused silica window RSI 76, (25), M. Hori

31 Time-resolved measurement of Linac4 chopper 3-MeV chopped beam 45 kev 3 M ev 5 MeV 1 M ev 16 M ev H - RFQ DTL source LEBT chopper line CCDTL PIMS 5x18 particles 86 m Chopped beam <5 particles f=35 MHz

32 Nanosecond foil detector Vacuum chamber Carbon target foil 1 cm Acceleration grid A - 3-MeV H ion beam Retraction mechanism Permanent ring magnet Permanent ring magnet Phosphor screen Fiber optic conduit F Fiber optic conduit G Secondary electrons Acceleration grids B-E RF coaxial line 5 V RF coaxial line 5 kv Type-HN coaxial feedthroughs Thermoelectrically cooled CCD NIM 588, 359 (28), M. Hori, K. Hanke

33 Time-resolved gating system V A V C Phosphor screen 1 MΩ 1 MΩ Grid D Grid E CCD Target foil 1 µ F 1 µ F Grid B Grid C Grid A V off V off V off V off 5 kv, 1-ns FET switch F V off -1 kv, 1-ns FET switch G -5 V avalanche diode switch I V off V off Timing signal Gate and delay generator H 3.5 kv avalanche diode switch J NIM 588, 359 (28), M. Hori, K. Hanke

34 Side view of detector Up/down mechanism Electron emission target foil H- beam Acceleration grid 1 Fiber conduit Acceleration grid 2 Phosphor screen 5 kv / 1 ns RF feed

35 High-speed shutter electrodes RF striplines Phosphor screen Acceleration grid 1 Fiber conduit Acceleration grid 2 5 V / 1 ns RF feed 5 kv / 1 ns RF feed

36 High-speed shutter electrodes Four parallel 5-Ohm lines for effective impedance 12.5 Ohm allows fast switching of voltage potential 1-µm-diam gold-coated tungsten wires Ceramic substrate Phosphor screen 5-Ω gold striplines (a) (b) 3 mm Chrome frame 5-Ω gold striplines SMA connector RF connectors NIM 588, 359 (28), M. Hori, K. Hanke

37 Grid biasing and pulsing scheme 1.5 Electrode voltage (kv) (a): (b): (c): Target foil Grid B Grid D Two FET switches Two avalanche diode switches Open circuit at end of coaxial lines (d): Phosphor NIM 588, 359 (28), M. Hori, K. Hanke Time elapsed (ns)

38 Response against 3 MeV proton beam at Orsay Y position (mm) (a) (c) (b) (d) Y position (mm) (a) CCD intensity (arb. u.) 5x1 7 photoelectrons 2 mm spatial resolution Y position (mm) CCD intensity (arb. u.) X position (mm) 4 2 (b) (c) -1 1 X position -1 1 (mm) X position (mm) Beam profile for various focusing settings of the Orsay beamline Beam profile for pinpoint laser beam NIM 588, 359 (28), M. Hori, K. Hanke

Linearity measurement x1 4 electrons Secondary 3 2 1 2 4 6 Protons per

Linearity measurements Beam diam 1 cm, f=1 MHz Integrated 1 pulses Linear

39 Linearity measurement x1 4 electrons Secondary Protons per microbunch x1 4 Secondary electrons Protons per microbunch Linearity measurements Beam diam 1 cm, f=1 MHz Integrated 1 pulses Linear response between Np=1 and 6x1 4 protons/pulse NIM 588, 359 (28), M. Hori, K. Hanke

cell Iris Telescope BBO crystal B 266 nm, 7 ps laser pulse To experiment Ultraviolet laser pulse generator to simulate

40 Stimulated Brillion backscattering laser Relay imaging telescope 532 nm, 4 ns laser pulse Nd:YAG laser 164 nm, 6 mj BBO crystal A Harmonic seperator Polarizing beamsplitter Telescope f=13 mm lens Fresnel Rhomb SBS amplifier cell SBS generator cell Iris Telescope BBO crystal B 266 nm, 7 ps laser pulse To experiment Ultraviolet laser pulse generator to simulate Linac-4 beam SBS process to compress Nd:YAG laser pulses to < 7 ps, 266 nm UV laser 1 Megawatt peak power NIM 588, 359 (28), M. Hori, K. Hanke

41 Time/space resolved measurement with B-field Magnetic field 1 Gauss, acceleration voltage 1 kv Stop motion pictures of the beam Y position (mm) (a) t = -5 ns (b) t = -4 ns (c) t = ns (d) t = 2 ns (e) t = 2.5 ns (f) t = 3 ns (g) t = 3.5 ns (h) t = 4 ns (i) t = 8 ns (j) t = 18 ns (k) t = 23 ns (l) t = 5 ns X position (mm) 5x1 8 photoelectrons, similar to Linac4 intensites. Swirling effect due to cyclotron motion. NIM 588, 359 (28), M. Hori, K. Hanke

42 Normalized CCD signal intensity (arb. u.) Time resolved measurement with B-field B=1 Gauss acceleration voltage 1 kv 5x1 8 photoelectrons, similar to Linac4 intensites. Many prepulses and afterpulses appear at regular intervals!? Time elapsed (ns) NIM 588, 359 (28), M. Hori, K. Hanke

43 Spatial distortion due to space-charge effects No magnetic field, lower acceleration voltage (some distortion due to space-charge seen) Y position (mm) Y position (mm) N e N e = 4 (a) t = -2 ns -1 1 = (g) t = -2 ns (b) t = -1 ns -1 1 (h) t = -1 ns (c) t = ns (d) t = 1 ns X position (mm) (i) t = ns (j) t = 1 ns (e) t = 2 ns (k) t = 2 ns (f) t = 3 ns -1 1 (l) t = 3 ns X position (mm) NIM 588, 359 (28), M. Hori, K. Hanke

44 Timing deterioration due to space-charge effects Normalized CCD signal intensity (arb. u.) 8 (a): No magnetic field, lower acceleration voltage N e = 4 x 1 8 (b): N e = 2 x 1 7 Better time res. less afterpulses Time elapsed (ns) NIM 588, 359 (28), M. Hori, K. Hanke

45 Future prospects We are developing several new types of detectors for AD and ELENA: Extremely low-cost and compact secondary electron emission detectors based on CMOS VLSI readout technologies. Extruded scintillation bar modules read out by wavelength shifting fibers and Geiger-mode silicon multipixel detectors. Optical fiber plate detectors. Laser-ionization based detectors.

46 Conclusions We developed scintillation screens, parallel plate ionization chambers, secondary electron emission detectors and used them at LEAR and AD since 1995 to measure both continuous and pulsed antiproton beams of energies 1 ev to 2 MeV. Some of the detectors are semi-non-destructive and work at cryogenic temperatures and high magnetic fields. Challenges lie ahead for high intensity, high speed beam facilities. A new series of detectors are being developed for future experiments, and ELENA at AD.

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