Overview of long pulse experiments at NML Nikolay Solyak PXIE Program Review January 16-17, PXIE Review, N.Solyak E.Harms, S. Nagaitsev, B. Chase, G. Cancelo, W. Shappert, Y. Pischalnikov, J. Reid, D. Johnson, C. Ginsburg, V. Yakovlev, A. Vivoli, …

Outline 3-8 GeV Pulsed Linac: Parameters and Requirements Results of Long pulse studies at NML Summary Future plans PXIE Review, N.Solyak2

Project X Pulsed Linac PXIE Review, N.Solyak 3 One-sigma Transverse (above) and Longitudinal (below) beam envelope Gradient 23.5 MV/m; Sync.phase = - 8° HWRSSR1SSR2  =0.6  = MeV 1.3 GHz ILC 8 GeV 3 GeV MEBTRFQ LEBT Pulsed CW RT

Basic Parameters of the Pulsed Linac Pulsed Linac is based on ILC/XFEL technology: Cryomodule: ILC type with SC quad in center of CM (8 cav+Quad /CM) Focusing : FODO Lattice, each Quad has X/Y correctors and BPM Cavity: Average Gradient 25 MV/m; gradient spread ± 10% (ACC7/FLASH) Q 0 =1∙10 10 ; Q L =1 ∙ 10 7 (Matched Q L =2.5∙10 7 => BW 1/2 =26Hz - too small ) Filling time = 3 (4) ms, flat-top = 4.4 ms RF source: 50 kW per cavity ; ~50% overhead (LLRF, detuning, losses) One RF source per one (two) cryomodules: Total: 28 (14) RF stations Power 0.4 (0.8) MW klystron per 1(2) CM Pulse length = 8.4 ms; Rep. rate = 10 Hz H - input beam parameters: Current = 1 mA; ( max 5 mA MHz) Input Energy 3GeV; ε T = 0.3 mm·mrad;  E = 0.5 MeV (init); Δt=2ps (rms) PXIE Review, N.Solyak4

Power requirements for ~70 Hz detuning are similar for Q L in range: 6∙10 6 1∙10 7 ) Cavity RF power vs. detuning PXIE Review, N.Solyak5 requirements Cavity detuning RF power Specs for RF power/cavity

LLRF issues Lorentz Force Detuning (LFD) compensation for long pulses: o Detuning at 25 MV/m is > 600Hz, if not compensated o Adaptive LFD compensation should provide <30 Hz freq. stability o Studies at NML and HTS LLRF: Only VS is regulated (flat), individual cavity gradients tilt (A & φ) o Non constant beam energy gain along bunch train. o Potential emittance growth, final energy spread and beam loss due to tilts in A & φ Acceptable Gradient spread (± 10%)? o Reduce gradient spread or minimize impact. o Use optimum Q L and power distribution for a given gradient spread. Bringing up the LINAC o How much gradient overhead is needed to go from I beam =0 to 1 mA? PXIE Review, N.Solyak6 Simulations & experimental studies at FLASH and NML S tudies at NML, HTS

Adaptive LFD compensation studies for long pulses at NML PXIE Review, N.Solyak7 Goal : Demonstration of the cavity compensation at the level < 30 Hz in long pulses (9 ms) for the nominal parameters: E acc =25MV/m, Q L =1.e7. Configuration: Two DESY-type cavities (#5 & #6) with quench limit: 26 & 27 MV/m. Powered by one 120 kW klystron ( 50 kW/cavity + losses) Studies with set of variables in matrix: RF power: 80 kW; 100 kW, 120 kW (per two cavities). External Q: ; ; ; Gradient: 15MV/m; 20 MV/m; 25 MV/m; DESY type CM1 at NML Saclay type Tuner with fast piezo

Adaptive LFD compensation in Long pulse operation PXIE Review, N.Solyak8 DESY type CM1 at NML Published in IPAC12, Linac 12 proceedings filling time Flat-top Cav#5 detuning: STD=3.65 Hz Cav#6 detuning: STD=2.27 Hz 0.5 hrs of operation Cavity RF Freq detuning Piezo-waveform LFDC panel (W.Shappert) Cavity detuning results (~2000 pulses )

LLRF control at NML PXIE Review, N.Solyak9 One RF pulse is shown B.Chase, G.Cancelo,

LLRF: A&Φ Stability of the VectorSum at 25 MV/m PXIE Review, N.Solyak10 cavity: std ~ 0.92° cavity: std ~ 1.05° Each cavity has ~1% x3  pk-to-pk (anti-correlated), while VS is more stable < 0.1% x 0.3  Q=1·10 7 Q=6·10 6

Closed loop: stability of the VS and cavities PXIE Review, N.Solyak11 Detuning in individual cavity are not correlated, but VS is stabilized by LLRF.  Amplitude & Phase variations of the two cavities are strongly anti-correlated VS is one order of magnitude more stable (~0.1% & 0.1°) than individual cavity (pulse-to-pulse amplitude and phase variations of up to 1% & 1°) Phase Phase correlation Amplitude

Residual detuning and microphonics PXIE Review, N.Solyak12 Microphonics 2-3 Hz rms Level of microphonics was measured after RF pulse (signal decay), when LFD compensation was OFF Piezo excites additional jitter in detuning (~20Hz pk-to-pk) with ~1kHz modulation. Can be improve in future studies Q=3.e6 E acc =18 MV/m ~1 kHz LFDC ON LFDC OFF 20 Hz 5 Hz

SUMMARY of Studies PXIE Review, N.Solyak13 Active LFD compensation is able to limit cavity detuning in long pulses operation to the level < 30 Hz pk-to-pk (Q L =10 7, E acc =25 MV/m). This is comparable to the pulse-to-pulse detuning variations due to non-deterministic sources. The residual detuning is dominated by a single deterministic sinusoidal component with a frequency near 1kHz. Compensation might be improved further if this component can be suppressed. Microphonics level of 2-3 Hz rms were observed during long pulses. This is similar to the levels measured during 1 ms pulses. The detuning responses of the two cavities tested were different prior to compensation, but similar after compensation. The compensation algorithm is able to adapt the piezo waveform to the detuning response of each individual cavity. While further improvements may be possible these studies clearly demonstrate that a pulsed linac employing active compensation of Lorentz force detuning could already meet the phase and amplitude stability requirements for Project X

Future Plans PXIE Review, N.Solyak14 Repeat these studies for ILC-type cavities with Blade-tuner, installed in CM2 at NML. Improve LFD compensation algorithm and hardware to reduce residual detuning and suppress 1kHz component. Update LLRF control software to provide flexible operation in long pulse. Collect and analyze LFD compensation data from HTS. Each ILC cavity tested at HTS should be routinely tested in long pulses as well. All required hardware (long-pulse klystron) and software are available. Saclay Tuner Blade Tuner