Beam Diagnostics Challenges WimBlokland – ORNL / SNS Dave Johnson, Peter Prieto, Gianni Tassotto, Randy Thurman-Keup, Vic Scarpine, Dan Schoo, Dave Slimmer, Duane Voy, Arden Warner, Manfred Wendt, Jim Zagel, and many others – Fermilab
Beam Instrumentation at Fermilab • AD-Instrumentation Department activities • ~30 techs, EEs and accelerator physicists • Operation, maintenance, improvements on RunII, NuMI, SY (M-Test) and many other beam diagnostics (>1000 units). • Support upcoming projects and facilities, NoVA, proton improvement plan, HINS (MDB), ILC-TA (NML), mu2e, g-2,… • R&D for future projects and facilities, e.g. Project X, still a little bit ILC, various collaboration activities. • Good foundation for standard beam instruments • Read-out systems applying digital signal processing techniques for beam intensity and orbit (BPM) monitoring • Integrated calibration techniques. • Many improvements on beam profile monitors, e.g. SEMs.
The High Beam Power Challenge • Fermilabs intensity frontier future requires • High beam power, today ~300 kW (NuMI), soon ~700 kW (NOvA), in the future > 2 MW (Project X). • Non or minimum invasive beam diagnostics detectors with low residual losses. • Possible solutions: • It is simple (solved) for electromagnetic beam detectors (toroids, WCM, BPM). • Not trivial for transverse beam profile (emittance) measurements! • Flying or scanning wires, SEM mulitwires: invasive. • Ionization profile monitor (IPM) based on residual gas. • Laser wire photo-detachment (requires H- beams) • Electron-beam scanner.
SEM Multiwire • UT/ Fermilabmultiwire SEMs • Used in NuMI, and other beam-lines • Ti strips (5x125μm), wires (25 μm dia.), 1.0 / 0.5 mm pitch. • Carbon monofilament SEM R&D (PM118) • Reduce residual losses (low Z material), greater wire heating capability. • 33 μm diameter carbon monofilament, density 1.8 g/cm3, 12 g tension, 1 mm pitch thermal simulation 5 µm strip, 260 kW
Ionization Profile Monitor (IPM) • Based on the ionization of the residual gas • p or pbar collisions • Gas molecule -> ion + e • Collect either • Ions • Subject to space charge • or Electrons • Needs magnetic a guidefield, such that the spin diameter < detector strip width • Used for turn-by-turn measurements • Booster: 2.25 – 1.5 μsec • MI: 11.1 μsec • TeV: 21 μsec (also single bunch)
MI IPM Installation Permanent magnet @ 1kG 10 kV clearing field MCP and field shaping assembly lifted to show copper pick-up strips.
IPM vs. Flying Wire • Left: Flying Wire • Right: H2IPM • Left peak: pbar RR -> TeV • Right peak: pbar ACC - > RR Sigma for H2IPM and FW
Laser Wire for H- Beams • H- neutralization by photo-detachment • Cross-section σmax ≈ 4.2x10-17cm2 • Electron binding E0 = 0.7543 eV • Typical HINS / PX MEBT parameters • Ebeam = 2.5 MeV, Nd:YAG laser 1064 nm,900 angle, -> σ≈ 3.66x10-17 cm2 • Requires laser energy ~ 10-30 mJ F-Cup Galvanometer e- E or B H- Beam H- H- +γ H- +H0 Laser Beam Laser beam
MI-8 Laser Wire • Laser Profile Monitor details • Q-switch laser • Laser energy: 50 mJoule • Wavelength: 1064 nm • Pulse length: 9 nsec • Fast rotating mirrors (±40 / 100 µsec) • e- detector: scintillator & PMT detector port BPM BPM H- beam double dipole laser beam optical box First horizontal profile scan!
Electron-Beam Scanner • Non-intrusive profile measurement of high intensity p-beams • SNS / Fermilab R&D collaboration for Project X, beams in MI • Evaluate measurement techniques for available electron gun • Setup simulation • Look at the deflected projection of a tilted sheet of electrons due to the proton beam charge [1,2,3] • Neglect magnetic field (small displacement of projection) • Assume path of electrons is straight (they are almost straight) • Assume net electron energy change is zero (if symmetric) • Proton bunch length >> electron scan i.e. take the derivative to get the profile
E-Beam Scanner (cont.) • Deflection options • Cavity or other fast deflector • Sheet beam 5-10 GHz X X protons protons Gate dθ dx dθ dx electrons electrons Gate X X Y Y Cathode Scrapers Deflectors S S Cathode X X Quadrupole(s) Scrapers
E-Beam Scanner Test Setup at NWA Gun Parameters Energy: 1 – 60 keV Current: 10 A – 6 mA Spot size: 50 m – 10 mm Gateable: 2 s – DC; 5 kHz max rate Actuators Electron Gun EGH-6210 Gun Solenoid Cave at NWA X1 X2 Firewire Cameras Faraday Cup / Dump
Low Beam Intensity Challenge • μ2e extinction measurement: • Beam: 3.7x107 p / bunch (3.5 μA, 25 kW) • No beam: single particle count in the search window (~0.2 pA), with 20 nsec time resolution. • Possible Solution: SQUID-basedCryogenic Current Comparator (CCC) • Successfully operation at GSI and elsewhere • SC shield & coil, plus high performance SQUID • Measurement in the flux quantum regime • Requires exceptional effective shielding beam current
SQUID FB Electronics • Example (~10 years old):UJ 111 DC-SQUID performance • Bandwidth: DC-70 kHz • Sensitivity: 167 nA / ϕ0 • Flux noise: 8x10-5ϕ0 /√Hz • Current noise: 13 pA/√Hz
Superconducting Quantum Interference Device • DC-SQUID • Detects the magnetic field of ibeam • Consists out of a SC ring with two weak links (“DC Josephson effect”) • Quantization of eh magnetics flux is observed by an interference phenomena. • DC-SQUID & Josephson junction • Solution of the affiliated wave-functions of Cooper-pairs tunneling the barrier: • Current in the SC loop () • If a magnetic flux threads the area of the loop, the phases differ by: • With the current writes:
SQUID Array Sensors • DC SQUIDs (i.e based on two Josephson junctions) • Important figure of merit for SQUID current sensors: • Coupled energy resolution : εc = SI Lin /2 ( where SI is input referred noise and Lin is input inductance) • According to the theory a well coupled dc-SQUID should have an energy resolution below 20 times Planck’s constant h. • However in practice : • A coupled dc-SQUID generally have a higher noise level than predicted by simple theory; A coupled energy resolution below 100 h at 4.2 K is difficult to achieve with high Lin SQUIDs. For the DESY CCC coupling = 543 h • We are exploring anew family of robust low noise SQUID devices that are optimized for operation with a high-speed direct coupled flux-locked loop (FLL). • Some main Features: • Series array of SQUIDS with < 3 nH input inductance. • A current noise level of 9 pA/(Hz)1/2 at 4.2 K • Ultra high speed operation was demonstrated using FLL electronics in close proximity to the SQUID array • FLL bandwidth of 350 MHz achieved, more than an order of magnitude better than others before • For Applications requiring larger input inductance (up to 2 µH) two stage sensors were developed consisting of a single front-end SQUID with double transformer coupling read-out by a SQUID array) • The voltage-flux characteristics of the arrays are reported to be single-SQUID-like with coupled energy resolution ~ 50 h (50 times Planck’s constant) • Reference: IEEE Trans. Appl. Supercond. 17 (2007) • also direct conversation with DietmarDrung of PTB, Germany.