Beams Stability at Fermilab Complex Alexey Burov Fermilab Many thanks to R. Ainsworth, Y. Alexahin, C. Bhat, V. Lebedev, A. Macridin, E. Metral, K. Seiya, C.Y. Tan, T. Zolkin MW Rings, Fermilab, May 2018 1 AB �
Accelerator complex • H - linac Beams Stability at Fermilab Complex • Booster - h = 84 - 15 Hz Alexey Burov - 400 MeV -> 8 GeV Fermilab • Recycler - h = 588 - Slip-stack 12 batches (double bunch intensity) Many thanks to R. Ainsworth, Y. Alexahin, C. Bhat, V. Lebedev, A. Macridin, E. Metral, K. Seiya, • Main Injector C.Y. Tan, T. Zolkin - 8 GeV -> 120 GeV MW Rings, Fermilab, May 2018 2 14/03/18 3 Rob Ainsworth I US-Japan Meeting AB �
Power evolution • PIP Beams Stability at Fermilab Complex • 700 kW (~0.5 x 10 11 ppb) • 15 Hz Booster • 80 kV RF for recycler • 1260 Hz separation for slip-stacking Alexey Burov • PIPII Fermilab • 1.2 MW (~0.8 x 10 11 ppb) • 20 Hz booster • 140 kV RF for recycler Many thanks to • 1680 Hz separation for slip-stacking R. Ainsworth, Y. Alexahin, C. Bhat, V. Lebedev, A. Macridin, E. Metral, K. Seiya, • PIPIII C.Y. Tan, T. Zolkin • 2.4 MW • No more slip-stacking, most likely replace booster with new RCS MW Rings, Fermilab, May 2018 3 14/03/18 5 Rob Ainsworth I US-Japan Meeting AB �
Transverse Impedances Transverse Impedances C. Bhat & C.Y. Tan, HB2016 4 AB �
Transverse Impedances Transverse Impedances 1000 3.8MHz Turn 1085 800 600 Amplitude (Counts) 400 200 0 -200 -400 -600 -800 -1000 0 10 20 30 40 50 60 70 80 Bunch # after cc before cc Horizontal Instability, damper off. growth rate ≈ 2 ⋅ 10 − 3 ω s 5 AB �
Transverse Wakes Transverse Wakes X and Y wakes are dominated by the laminated magnets (Alex Macridin et al) 6 AB �
Synergia Simulations (A. Macridin et al) Synergia Simulations (A. Macridin et al) With these wakes, A. Macridin et al. got very good agreement between the Synergia tracking and observations and the most unstable CB ′ Q x th ≈ − 19 modes 1-10 (all very close): ′ Q x = − 5 7 AB �
Some qualitative explanations Some qualitative explanations Q x σ s ′ 1. At the threshold chroma, the head-tail phase is: χ x ≡ ≈ 0.25 η R 0 It’s value is determined by relative values of the destabilizing long-range wake and χ th ~ CBwake the stabilizing short-range one, . SBwake ′ 2. The coupling helps, allowing smaller . Why? | Q x | th At the threshold, the vertical chroma is too small, so the chroma sharing (E. Metral) cannot be the answer. However, there is also the wake sharing , β x W x → β xn W x + β yn W y which increases more than , qualitatively explaining the SBwake CBwake stabilization by coupling (Y. Alexahin et al, 2012). 8 AB �
Booster: Emittance (2017 results) Transverse emittance at MI-8 line 95% Longitudinal emittance at Recycler Injection 16 0.14 Horizontal emittance Vertical emittance PIP-II Goal 14 0.12 Longitudinal emittance [eV-sec] 12 Emittance [pi mm-mrad] 0.1 10 0.08 8 0.06 6 0.04 4 2 0.02 0 0 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Intensity[protons per pulse] Intensity[protons per pulse] Intensity @4.4E12 ppp Kiyomi Seiya H_emittance: 12pi mm-mrad PIP-II Machine Advisory Committee V_emittance: 13pi mm-mrad 10-12 April, 2017 L_emittance: 0.1 eV-sec 9 K. Seiya (Fermilab Booster) 4/10-12/2017
SC Tune Shift SC Tune Shift 10 AB �
Beam loss occurs in first 2-3 ms after injection Small fast loss There is beam loss at the 4-6 ms in the from notching cycle. Time scale for loss is about 2-3 ms after injection. We see this loss even at low intensity < 0.6e12, ~8%. Similar to high intensity! Therefore, it is *not* space charge. This unexplained loss now dominates the losses in Booster. 2 turns at low intensity 20 turns at high intensity 11 C.Y. Tan, K. Seiya & C. Bhat | Finding the cause of beam loss 25 Apr 2017
Could the head-tail modes get unstable ? Could the head-tail modes get unstable ? In principle, it can happen at higher intensity. If so, we may run the Booster with the Damper ON and slightly positive chromas. In this case, the rigid-bunch mode would be stabilized by the damper; thus, CB modes would be stable, while the HT modes would be stabilized by the SBwakes. E-cloud has never been seeing in the Booster; we do not know why. 12 AB �
Slip-stacking at RR • Slip-stacking allows us Beams Stability at Fermilab Complex to double the intensity of the bunches in the Recycler Alexey Burov Fermilab Many thanks to R. Ainsworth, Y. Alexahin, C. Bhat, V. Lebedev, A. Macridin, E. Metral, K. Seiya, C.Y. Tan, T. Zolkin MW Rings, Fermilab, May 2018 13 14/03/18 4 Rob Ainsworth I US-Japan Meeting AB �
at RR 14 AB �
Transverse Instabilities Transverse Instabilities CB instabilities, f < 2.5MHz are suppressed by the LF damper CB instabilities, f > 2.5 MHz are suppressed by SB impedance at Q’<0; this requires |Q’| > something. SB instabilities for HT modes do not have enough time to manifest; this may require |Q’| < something 15 AB �
TMCI with SC: only 2 types are possible TMCI with SC: only 2 types are possible https://arxiv.org/abs/1711.11110 16 AB �
TMCI with SC: vanishing TMCI TMCI with SC: vanishing TMCI Coherent tune shift ~ SC tune shift BB impedance model f=1.3GHz sigma_s = 30cm (Quatraro & Rumolo, IPAC’10) 17 AB �
TMCI with SC: SSC case TMCI with SC: SSC case ABS, cos wake ABS, sin wake Coherent tune shift ~ 1/SC tune shift In the parabolic potential and sin wake, there is no TMCI at SSC (contrary to ABS) Thus, for the smooth potential and realistic wakes, all TMCI are of the vanishing type. 18 AB �
Many thanks! � 19 AB �
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