Linac Beam Physics Design and Special Requirements of

Linac Beam Physics Design and Special Requirements of H vs e P. N. Ostroumov Physics Division

Content n Project X parameters n HINS Proton Driver parameters n Basic concepts for the Linac design – General design philosophy: 2 -freqeuncy option – RFQ – MEBT – Front end, 325 MHz – High energy section, 1300 MHz n Choice of lattice parameters – High energy section – 325 MHz Front End linac – H-minus versus electrons n RF distribution system – H-minus versus electrons n Other physics design issues n Conclusion P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 2

Project X: Linac main parameters Parameter Project X Particle Species H-minus Output Beam Energy 8 Ge. V 8 -Ge. V Beam Power, Pulsed Average 72 MW 360 k. W Particles per Pulse 5. 625 1013 Pulse Repetition Rate 5 Hz Beam Pulse Length 1 msec Pulse Beam Current, Average Peak 9 m. A 14. 36 m. A Chopping at 2. 5 Me. V - 6% at 89 k. Hz for 700 ns RR/MI abort/extraction gap - 33% at 53 MHz for ‘prebunching’ for transfer to RR Particles per Linac bunch 2. 73 108 P. N. Ostroumov HINS PD 200 MW 2 MW 10 Hz 25 m. A 40 m. A 7. 58 108 Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 3

8 -Ge. V Linac conceptual design for the HINS Proton Driver n RF power fan-out from one klystron to multiple cavity – Same as in the ILC – Similar concept can be applied in the Front End • SC technology for the whole linac but an initial 10 Me. V section n Use two-frequency Linac option to produce multi-Ge. V proton or Hminus beams: – Apply 1300 MHz ILC cavities above ~1. 2 Ge. V – Develop and use S-ILC cavities (beta=0. 81) in the energy range ~400 Me. V-1. 2 Ge. V – Spoke loaded SC cavities operating at ILC sub-harmonic frequency in the front end n Select sub-harmonic frequency for the front end: 1/4. Motivation: spoke loaded SC cavities are developed at ~345 -350 MHz. Requires 30% less number of SC cavities compared to 433 MHz option. Klystrons are available from JHF developments. n Below 10 Me. V: use the RFQ and 16 RT-CH cavities. P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 4

Linac conceptual design (cont’d) n 325 MHz SSR-1, SSR-2 and TSR from 10 Me. V to ~418 Me. V n Apply SC solenoid focusing to obtain compact lattice in the front end including MEBT – Compact focusing period – Less sensitive to errors and beam mismatch than quads – Less beam halo formation n RFQ delivers axial-symmetric 2. 5 Me. V H-minus beam n MEBT consists of 2 re-bunchers and a chopper. Smooth axialsymmetric focusing mitigates beam halo formation n Beam matching between the cryostats: adjust parameters of outermost elements (solenoid fields, rf phase) n In the frequency transition at ~420 Me. V, matching in ( , W)-plane is provided by 90 “bunch rotation” n Avoid beam losses due to halo formation, machine errors and Hminus stripping P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 5

Linac Structure Major Linac Sections Front end Squeezed ILC-style 325 MHz 1300 MHz ILC-style 1300 MHz Will be installed in the Meson Lab (60 Me. V) SSR-2 0. 05 0. 0652. 5 10 10 P. N. Ostroumov 32 33 110 123 Linac Beam Physics Design, Project X Workshop 410 418 November 12 -13 , 2007 6

Radio Frequency Quadrupole n Well established accelerator (SNS, J-PARC, …. ) n Basic Proton Driver requirements: – Cost-effective – Produce axially-symmetric beam – Small longitudinal emittance P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 7

RFQ Beam Parameters (2. 5 Me. V, 43 m. A) Image of 100 million particles - W/W XX P. N. Ostroumov YY - W/W Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 8

MEBT RFQ MEBT P. N. Ostroumov Linac Beam Physics Design, Project X Workshop 1 st period November 12 -13 , 2007 9

Fast Chopper 11 sec 0. 7 sec 1/52. 8 sec Pulser voltage ± 1. 9 k. V Rep. rate 53 MHz Rise/fall time 2 nsec (at 10% of the voltage level) Beam target power: 37 k. W pulsed, 370 W average P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 10

High intensity beam physics n Phase advances of transverse oscillations for zero current beams must be below 90º n Wave numbers of oscillations must change adiabatically along the linac despite of many lattice transitions with different types of focusing and intercryostat spaces, cavity TTF. n Avoid strong space charge resonances (Hoffman’s Chart) n Consider equipartitioning of betatron and synchrotron oscillation temperatures along the linac, primarily in the front end n Beam matching in the lattice transitions is very important to avoid emittance growth and beam halo formation n Short focusing periods in the Front End n Analyze HOM and avoid excessive power losses on cavity walls P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 11

Properties of an ion SC linac and lattice design n The acceleration is provided with several types of cavities designed for fixed beam velocity. For the same SC cavity voltage performance there is a significant variation of real-estate accelerating gradient as a function of the beam velocity. n The length of the focusing period for a given type of cavity is fixed. n There is a sharp change in the focusing period length in the transitions between the linac sections with different types of cavities n The cavities and focusing elements are combined into relatively long cryostats with an inevitable drift space between them. There are several focusing periods within a cryostat. n Apply an iterative procedure of the lattice design – Choice of parameters – Tune for “zero” beam current – Tune for design beam current – Multiparticle simulations – Iterate to improve beam quality and satisfy engineering requirements P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 12

Accelerating cavities ( not to scale) NC spoke ILC, 9 -cell P. N. Ostroumov SC single spoke ANL 345 MHz TSR FNAL 325 MHz TSR Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 13

Cavity parameters and focusing lattice (Proton driver, 40 m. A peak current) CH S-ILC SSR-1 ILC-1 SSR-2 TSR ILC-2 P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 14

Project X Linac lattice n ILC Reference Design Report-2007: 15 RF units (45 cryomodules) will be available as a result of industrialization of the ILC project n Provide the largest fraction of the total Linac voltage using ILC cryomodules and RF system without extra development n ILC cavities can be operated at -mode and accelerate H-minus beam from 600 Me. V n Front End up to 600 Me. V – Can be normal conducting, will require substantial engineering effort • Requires CCL in the energy range of 100 to 600 Me. V • Requires 975 MHz klystrons – Superconducting as HINS PD • Can be single frequency – 325 MHz • Invest into the development of SC cavities instead of RF system • Well advanced, still the concept must be demonstrated • Flexible for upgrades – Increase beam pulse length or pulsed current with installation of additional klystrons – Potentially can produce much higher beam power P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 15

Project X Linac structure Only two frequencies: ILC (use primary and 8 /9 mode) and ¼ harmonic for spoke cavities. Major Linac Sections Front end ILC, 8 /9 325 MHz Standard ILC 1300 MHz Will be installed in the Meson Lab (60 Me. V) SSR-2 0. 0652. 5 0. 05 2. 5 10 10 P. N. Ostroumov 32 33 110 123 Linac Beam Physics Design, Project X Workshop 600 410 November 12 -13 , 2007 16

Analytical description of the fields in the ILC cavities P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 17

ILC cavities, mode n Frequency spectrum of the passband modes in the ILC cavity (TESLA report, 1998 -20) n Outstanding feature: 8 /9 -mode is just 0. 8 MHz off from -mode P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 18

ILC cavity 3 D-simulations n Field distribution P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 19

How to tune cavity to 8 /9 -mode? n Tuning of cavity cells and a cavity as whole to -mode’s frequency of 1300. 8 MHz. Such a tuning may be required for each cell before the cavity assembly because the standard cavity tuner’s frequency range is limited to 300 k. Hz. n For the frequency control of each cell and tuning of the cavity field “flatness” on 8 /9 -mode, standard procedures can be applied. n Tuning the frequency of the 8 /9 -mode to be 1300 MHz in the fully loaded cavity at cryogenic temperature. n In addition, some tuning of a coupler and fast tuner may be required for cavities operating on 8 /9 -mode. Specifications to the cavity coupler and fast tuner should be investigated during cavity prototyping. Stretch to increase frequency by 0. 8 MHz P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 20

Project X: Linac lattice 680 P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 21

Project X: Linac lattice Energy range Me. V Number of the ILC RF units 6001040 2 10402400 3 24005150 4 51508400 4 Total n More frequent focusing quads compared to the ILC lattice 13 P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 22

Project X: Linac lattice n Front End: 600 Me. V SC linac, 325 MHz n 13 ILC RF units, 1300 MHz P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 23

Cavity voltage (HINS PD and Project X) S-ILC 8 /9 -ILC NC SSR-1 SSR-2 TSR P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 24

Variation of lattice parameters along the linac (preliminary design) n Calculated with the TRACK code in realistic 3 D fields Phase advance P. N. Ostroumov Wave numbers of transverse and longitudinal oscillations Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 25

Synchronous phase (preliminary design) 4 ILC RF units, S =-5º P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 26

Peak RF power per cavity Due to high shunt impedance, the RT-CH cavities dissipate twice less rf power than a DTL cavity P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 27

Beam envelopes, 15 m. A peak current P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 28

RMS emittance growth (15 m. A) n These results are from the first iteration P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 29

H-minus vs electrons n Above 5 Ge. V – no changes are necessary for the ILC RF units – Frequency of synchrotron oscillations becomes very low and proton beam can be accelerated near the wave crest n Below 5 Ge. V: – Longitudinal focusing is essential – non-zero synchronous phase – Stronger transverse focusing is necessary - shorter focusing period, more quadrupoles • Defocusing due to accelerating field n Non-relativistic beam velocity – Static phase shifters with wide range (~180 deg) are necessary for each cavity P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 30

Relative energy spread along the linac Energy spread vs energy Beam is slightly mismatched Longitudinal focusing is required P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 31

RF distribution system in the TESLA Test Facility n Cavities are operated at different field level P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 32

SNS data P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 33

RF distribution in the H-minus Linac: one klystron feeds multiple cavities n Considerable variation of beam loading in the cavities belonging to the same RF unit – Beam Transit Time Factor n Variation of accelerating fields from cavity-to-cavity in realistic accelerator – Operating different field levels may be necessary to achieve design beam energy – Provide “flat” accelerating fields (amplitude and phase) within the beam pulse n Dynamic phase shifters may be necessary P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 34

Error studies n The most comprehensive error studies have been performed for the HINS proton driver – Higher beam current – Stronger transverse focusing in the beginning of the 1. 3 GHz linac P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 35

Errors and beam losses in the HINS PD n Total number of simulated particles is 100 million (100 seeds, 1 million) Note, the real losses are lower by the value of duty factor P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 36

Energy Jitter Correction (RF errors are 1. 0%, 1. 0 ) n Debuncher is located after 970 m drift space and requires ~35 MV voltage n RF RMS errors up to 1. 0%, 1. 0 are acceptable Before the debuncher After the debuncher , deg P. N. Ostroumov 3 Me. V 33 Me. V After the linac Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 37

Other aspects of the physics design n HOM – Preliminary studies show no impact on beam quality and cryogenic losses in the Front End linac n Validation of beam dynamics simulations with three different codes – TRACK (main workhorse) – ASTRA (DESY code) – IMPACT (LANL & LBNL code) n Monte-Carlo simulations of H-minus stripping in the BD tracking code – Implemented into the TRACK code n Acceleration of electrons in the last 11 ILC RF units (263 cavities) – Total available voltage is 8 Ge. V n Implement RF distribution scheme into the parallel TRACK code – Work in progress P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 38

Conclusion n Project X Linac consists of – 10 Me. V Normal Conducting linac – 10 -600 Me. V Super Conducting linac operating at 325 MHz – 13 ILC RF units n R&D is well advanced – Start prototyping of triple-spoke cavities for energy range of 100 -600 Me. V n Linac design status: it is ready for CD-0 P. N. Ostroumov Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 39

Acknowledgments n I thank my colleagues from ANL and FNAL for significant contributions to this presentation ANL Brahim Mustapha Jin Xu P. N. Ostroumov FNAL Vladislav Aseev Jan-Paul Carneiro Ivan Gonin Linac Beam Physics Design, Project X Workshop November 12 -13 , 2007 40