Rings Program Valeri Lebedev PIPII Collaboration Meeting Fall

Rings Program Valeri Lebedev PIP-II Collaboration Meeting - Fall 2015 9 -10 November 2015

Outline • PIP-II Performance Goals • Design Concept and Design Choices – Booster – Recycler and MI • Summary 2 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

PIP-II Performance Goals • Increase MI power from 700 k. W (NOv. A) to >1 MW (LBNF) in the energy range 60 – 120 Ge. V • Increase Booster power from 80 to 160 k. W – 8 Ge. V program: SBNE, … • Future upgrades – Mu 2 e at 0. 8 Ge. V and ~100 k. W – Beam power to LBNF to >2 MW – Provide a platform supporting a high duty factor/CW operation for future intensity frontier experiments 3 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

PIP-II Components • New 0. 8 Ge. V linac – L≈210 m • Includes 4 empty slots at the linac end, L≈40 m – Beam energy stabilization – Possible energy upgrade • New Linac-to-Booster transfer line – L≈280 m • Upgraded Booster – 20 Hz, 800 Me. V injection • New injection girder • More RF cavities • Upgraded Recycler & MI – RF and collimation 4 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

PIP/PIP-II Performance Goals Performance Parameter PIP-II Linac Beam Energy 400 800 Linac Beam Current 25 2 0. 03 0. 5 msec 15 20 Hz Linac Beam Power to Booster 4 18 k. W Linac Beam Power Capability (@>10% Duty Factor) 4 ~200 k. W NA >100 k. W 4. 2× 1012 6. 5× 1012 Booster Pulse Repetition Rate 15 20 Hz Booster Beam Power @ 8 Ge. V 80 160 k. W Beam Power to 8 Ge. V Program (max) 32 80 k. W 4. 9× 1013 7. 6× 1013 1. 33* 0. 7 -1. 2 sec 0. 7* 1. 0 -1. 2 MW NA >2 MW Linac Beam Pulse Length Linac Pulse Repetition Rate Mu 2 e Upgrade Potential (800 Me. V) Booster Protons per Pulse Main Injector Cycle Time @ 60 -120 Ge. V LBNF Beam Power @ 60 -120 Ge. V LBNF Upgrade Potential @ 60 -120 Ge. V *NOv. A operates exclusively at 120 Ge. V 5 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15 Me. V m. A

Approach to the PIP-II Accelerator Physics Design • New SC Linac – Design compatible with CW operation => Small beam current of 2 m. A (advantageous for painting) – MEBT bunch-by-bunch chopper chops out bunches at boundaries of RF buckets and from the extraction gap – Energy stability of ~10 -4 to support longitudinal painting – Emittance less than 0. 3 mm mrad (rms, norm) • to minimize injection loss, and to support tailless transverse painting • Booster upgrade – Rep. rate: 15 -> 20 Hz (leaves more power at 8 Ge. V) – Injection energy: 400 -> 800 Me. V => intensity 1. 5, reduction DQSC – Transverse and longitudinal painting: small Ibeam helps • Reduces tails and DQSC • Recycler – Rep. rate increase => larger momentum separation in slip-stacking => smaller loss 6 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Primary Challenges/Risks in the Ring Side of PIP-II • Booster operation at 1. 5 times larger intensity – Transition crossing with 1. 5 times larger beam current but with the same L & emittances • Slip stacking in Recycler – Slip stacking with 1. 5 times larger beam intensity • • Beam loss minimization efficiency of collimation ep instability Efficiency of instability damping for slipping bunches is unknown • Main injector – Lossless transition crossing – Beam stability with increased current 7 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Linac to Booster Transfer Line • H- Lorentz stripping (<10 -8 m-1) limits dipole field to 2. 77 k. G – for 1 Ge. V beam => the bending radius of dipoles to 20. 7 m • Simple optics: One family for dipoles; most quads are in two families Two arcs and a short straight between them • Sufficient place for collimators and possible debunching cavities • Crossing Tevatron tunnel: straight through or above. No final choice • Changed beam dump location • Swapped locations of linac tunnel and service building 8 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Booster Injection • H- strip injection occurs through vertical dogleg allowing simple suppression of vertical dispersion • Vertical painting is done by changing dogleg dipoles and fast correctors in the beam line or by the correctors only – linac beam stays at the same point of the foil • Booster correctors are used for horizontal painting • Foil – 600 mg/cm 2 9 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Transverse Painting • H- strip injection – Linac beam comes to the foil corner • Like in the SNS – Reduced beta-functions for linac beam to reduce secondary hits of stripping foil • Zero dispersion of linac beam • Non-zero Booster dispersion and non-zero momentum offset reduce secondary hits 10 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Transverse Painting (continue) X and Y coordinates of injected particles relative to the current orbit position for particles incoming to the Booster (left) and at the end of injection process (right). Left - the particle distribution over transverse CS invariant. Right– the integrals of particle distributions (normalized to unity) presented in the left pane; e 95%n=17 mm mrad 11 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Bunching in Booster • Linac and Booster RF frequencies are not harmonically related – Linac bunch frequency – 162. 5 MHz – RF frequency at injection 44. 7 MHz • Slip factor at 800 Me. V is ~2 times smaller (0. 258 versus 0. 458) – Together with ramp frequency increase (15 Hz->20 Hz) that makes adiabatic bunching ineffective (bunching time ~2. 4 times longer) => RF is on at injection & bunch structure is formed in the linac • Bunch structure for injection is determined by the bunch-bybunch chopper in MEBT – Bunches are removed from the RF bucket boundaries and extraction gap • About 50% of bunches are removed => RFQ current is ~4 m. A 12 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Longitudinal Painting in the Course of Booster Injection Linac current Duration of injection 2 m. A 0. 55 ms - || - 290 turns - || - 7 synchr. periods Linac rms mom. spread 2∙ 10 -4 Booster bucket height 2. 2∙ 10 -3 Momentum offset +7∙ 10 -4 • Small tails in L. distribution => 10 -4 energy stability 13 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Beam Based Energy Stabilization • Local cavity feedback is expected to stabilize its voltage and phase to better than 0. 1% and 0. 1 o rms – Energy stability of ~10 -4 is required • Beam based stabilization – Beam is sent to the beam dump for 10 - 30 ms – Energy measurement • To stabilize energy to 0. 01% rms – Time of flight can be used 4 empty slots are reserved at the linac end, ~40 m – Or energy measurements in the first arc with BPMs; dispersion ~ 4 m (10 -4 ↔ 0. 4 mm) – Fast dipole corrector and Septum to switch the beam from the beam dump to the Booster • Located in the straight line between arcs 14 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Foil Heating in the Course of Transverse Painting • Secondary foil heats make major contribution to the foil heating • Foil thickness - 600 mg/cm 2 => ~100% stripping efficiency – Negligible effect on emittance growth – 0. 1% single scattering loss – Total beam loss <2% (mostly particles missing the foil) • Foil temperature is below 650 Co => long lifetime 15 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Acceleration in Booster • Transition from 15 to 20 Hz rep. rate does not require additional RF voltage if beam current is small – Due to smaller slip factor at injection • Increase of beam current (planned for PIP-II) requires additional voltage – Deceleration due to RW impedance – Suppression of quadrupole oscillations after transition 15 Hz 16 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 20 Hz 11/9/15

Booster Longitudinal Impedance • Beam aperture in the Booster is formed by poles of laminated combined function dipoles – That greatly amplifies Booster impedance • Theoretical model yields results close to the wire measurements (J. Crisp, 2001) – But there is a discrepancy between measurements of F and D dipoles 17 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Beam Based Calibration of Booster Longitudinal Impedance • Measurements are based on dependence of the accelerating phase with beam intensity – That resulted in minor correction of parameters used in the model • Deceleration achieves its maximum at the transition (shortest bunch) ~150 k. V/turn in the bunch center for PIP-II parameters 18 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Initial Naïve Idea for Booster Transition Crossing • RF voltage jump technique looks as a promising method for transition crossing • Requires additional RF voltage ~300 k. V – 150 k. V due to impedance deceleration – And 150 k. V for voltage jump • Total required RF voltage – 1. 1 MV • Only odd part of the voltage dependence on coordinate contributes to excitation of quadrupole oscillations – Major contribution comes from the space charge impedance 19 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Present Transition Crossing in Booster • Phase swing starts ~200 turns before transition • For short time the RF phase is moved close to -90 o (maximum deceleration) • Numerical simulations aimed to understand the process were recently initiated – New trustable software (Ostiguy) • Simulation for PIP-II parameters will follow when good understanding of the present crossing is achieved 20 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Slip Stacking in Recycler • Twelve Booster batches are slip-stacked in Recycler • An increase of Booster rep. rate from 15 to 20 Hz requires faster slipping => larger momentum separation => larger RF bucket size => smaller loss at slip stacking 21 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Beam Acceleration in MI • The accelerating rate in MI is determined by maximum slue rate of magnetic field and RF voltage – That determines the dependences of (1) cycle time duration and (2) beam power on the final beam energy • MI RF power upgrade is required to support the beam intensity increase 22 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

MI Transition Crossing • Increased beam intensity and larger longitudinal emittance complicate transition crossing • gt jump is preferred method for transition crossing in MI • ESME simulations do not show significant increase of L. emittance and longitudinal tails • Additional hardware for fast tune change is required 23 V. Lebedev, Rings Program, PIP-II Collaboration Meeting Phase space distribution after transition in MI. The hole in the center is a result of slip stacking 11/9/15

Beam Stability in Recycler and MI • A study shows that instabilities related to beam interaction with vacuum chamber do not present outstanding problem • However, presently, a strong transverse instability is observed in Recycler – The only credible explanation is related with electron multipacting which results in the ep instability • Studies are going on • An instability threshold is increasing with time – Vacuum chamber conditioning is the most probable reason – A number of actions is planned to mitigate the problem for NOv. A • Better understanding of instability is required to make reliable prediction of beam stability for PIP-II parameters 24 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Summary • The PIP-II proposal is described in detail in PIP-II Reference Design Report • The concept is solid and did not get significant changes during last year • Better understanding of transition crossing in Booster and beam stability in Recycler are required – Study of present Booster transition crossing are underway – Simulation of the PIP-II transition crossing will follow shortly 25 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Backup Slides 26 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Coulomb Tune Shifts • Increased injection energy and KV-like transverse distribution reduce tune shifts due to beam space charge by more than factor of 2 relative to the present operation Betatron tune shifts due to beam space for horizontal and vertical planes within accelerating cycle. The reduction of tune shifts due to non-Gaussian shape of the particle distribution is taken into account 27 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15

Booster Beam Stability Studies • A study of transverse instabilities in Booster is going on – A. Burov, T. Zolkin and A. Macridin • Good coincidence between analytical model and computer simulations is obtained for: – shape and frequencies of head-tail modes in the presence of strong space charge, – Landau damping rates. • Reliable simulations of stability boundaries for Booster will follow Curtesy of A. Macridin 28 V. Lebedev, Rings Program, PIP-II Collaboration Meeting 11/9/15