In-pulse-average: Search for multiples of t rf and t DAQ which “coincide”: 1891 t DAQ = ns ~ =41 t rf Calculate sample mean over blocks of 1891 data points improving quality of data within single macro pulse. Interleaving: Rearrange points and fold data into 1 t rf t n = fmod(n·t DAQ, t rf ) t(47) = (47 × 0.2)%t rf = = ns t(0) = 0 ps t(47) = 376 pst(93) = 152 ps t(1) = 200 ps t(48) = 576 ps : t(2) = 400 ps t(49) = 776 pst(369) = 4.7 ps The plots below show data of two pickups behind the buncher. Capacitive pickupsTime-Domain Data Analysis Procedure For the 7 MeV/u IH-DTL, the analysis procedure achieved an energy resolution σ(E)/E of 6x10 -5 for short-term measurements. Energy loss in 10 carbon stripping foils was measured with C 4 + and protons (2 foils): ΔE(C 4+ ) = (16.2±0.9) keV/u & ΔE(p) = (6±0.4) keV/u Relative thickness uniformity ~6 %. From model calculations „reasonable“ parameter estimates were possible: Effective bunch length at IH-DTL exit ~ (0.2±0.1) Momentum spread Δp/p ~ (0.2±0.1) %. These estimates agree with the design parameters. Electric field of moving charges induces displacement current: Pickup detects field variation, hence the signal is bipolar. Radiofrequency quadrupole Energy = 400 keV/u (β = 0.03) Frequency f RF =216.8 MHz or t = 4.61 ns Separation between bunches D = c β t ~ 41 mm Based on calculated current one expects a signal overlap. FHWM of single-particle response ~8 ns. Improved Signal Treatment for Capacitive Linac Pickups A. Reiter, C.-M. Kleffner, B. Schlitt GSI Helmholtz Centre for Heavy Ion Research GmbH, Darmstadt, Germany 1. In-pulse average to improve signal quality: Mean of up to 6 blocks of 41 RF periods (~378 ns). Every 41 periods, RF signal and sampling frequency are in phase; length of block is determined by RF period of 9.2 ns and sampling interval of 200 ps. 2. Interleaving to improve time resolution: Map 41 consecutive RF periods into a single RF period. If the signal shape is assumed to be the constant, the data for each of the 41 periods may be regarded as a single measurement of the same quantity. 3. Smoothing of signal shape: Apply moving average or FFT filter, background subtraction, etc. 4. Cyclic cross correlation to determine phase/time offset: Principle: Take advantage of periodic nature of pickup signals and sampling process The 108 MHz decelerator slows down a fraction of the 4 MeV/u input beam from a double drift buncher (operated at and MHz), thereby producing a complicated mixture of energies between 4.0 and 0.5 MeV/u, the input energy of the following RFQ decelerator. Obtain mean velocity v from flight time t spent to travel known distance L between two well defined positions: v = c = L / t Note: L unknown, but fix, causes a constant offset in T exp Lcauses systematic error & affects accuracy t scope causes random error & affects precision Basic formula for uncertainty: TOF measurement with bunched beam time PHP 1 PHP 2 Tag ID: distance L bunches TOF = N·T rf +T scope Measure time difference between bunches on fast oscilloscope Resolve problem of bunch number N: T scope = T(bunch 1) – T(bunch N+1) ≥ 0 Tag ID (wrt. P1) Bunch separation D = cT rf with T rf = rf period Example: T rf = 4.61 ns IH-DTL (7 MeV/u) =0.12: D~16 cm D Standard IH-DTL setup High RF power Use L to calculate energy as function of T scope : Optimise geometry 3 probes determine N N=1  T~45 keV/u Avoid T scope = 0. ns (N jumps!) Avoid N = 1 slope -1 ~ 41 ps/(keV/u) L/L ~ 2% Avoid large N (momentum spread p/p) Practical application: Double drift buncher Single-particle image charge Comparison of calculated and measured signals Signals of pickups, time offset applied to Ch1. Injector Linac: 400 keV/u RFQ (shown on the left incl. test bench) 7 MeV/u drift tube linac Practical considerations: Identical phase probes Low-noise amplifiers with identical behaviour in all ranges Identical cables length Deskew ADC time offset DAQ synchronisation Maximum drift distance Results of Linac Commissioning Test bench for time-of-flight measurements 1-2: 0.5 mm = 2.5 keV/u 1-3: 0.5 mm = 0.5 keV/u Dependence of RFQ energy on RF power Due to the internal re-buncher, the beam energy was measured over a wide range of RF power to find the working point. RFQ: Measurement of longitudinal focus position The RFQ is equipped with an internal double-gap rebuncher which provides a longitudinal focus for the IH-DTL injection. Buncher voltage is mechanically adjusted during commissioning. The working point is found when the energy curves measured with and without rebuncher intersect at 400 keV/u, the design injection energy of the IH-DTL (see energy diagramm). The longitudinal focus position was determined from the „phase space“ plot below by back-tracking of the distributions until the correlations vanished. From the centre of the rebuncher the position was 287 mm, close to the 1st gap of the IH-DTL at 293 mm. The 2D plot confirms the precise timing pickup of the method. Energy vs. time at pickup IH-DTL: Energy and parameter estimatesHITRAP: Observation of deceleration process Phase probe signals recorded during phase variation The sequence of pickup signal shows the beginning of the deceleration process and the following creation of different energies when the amplifier phase of the IH-DTL decelerator was changed. The sensitivity of the signal reconstruction is very good. The problems: How to interpret this signal? Identification of 500 keV component possible? PHP signals of data sample Good agreement between model calculation and data. For RFQ, bunch structure has little influence on pickup signal shape. Example HITRAP decelerator RF frequency: MHz DAQ: 5 GSa/s Comparison of calculated and measured signals The two oscilloscope screenshots show signals of all pickups (Ch1-3) and tank probe (Ch 4) at 4.5 and 5.1 Volt. Note the different signal amplitudes in both cases. 4 MeV/u Pickups are commonly used for phase and energy measurements. In the picture the protective plate has been removed to show the signal ring. Main pickup parameters 50 Ohm geometry (f Max. = 2 GHz) 10 mm long ring with 30 mm radius total length of pickup 50 mm ns Time / ns 0 10 ns 4 Sample No. Sample No. Beam pulse RF pulse