Linac Front end design

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Linac Front end design

• Gennady Romanov
• March 15 , 2005

with the help from Peter Ostroumov, Bill Foster,
Doug Moehs, Ivan Gonin
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Outline

• Ion Source
• Radio Frequency Quadrupole RFQ
• Medium Energy Beam Transport MEBT.
• Room Temperature Triple Spoke Resonators section.
  
• Superconducting spoke resonators sections
• Single Spoke, Double Spoke and Triple Spoke
  resonators
• Conclusions.

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Front end general layout

• Ion source H-, LEBT , 0.065 MeV
• Radio Frequency Quadrupole, 4-5 m, 3 MeV
• MEBT, 2 bunchers, 4 SC solenoids, chopper, 4 m
• RT TSR section, 21 resonators, 21 SC solenoid, 10
  m, 15.2 Mev
• SSR section, 16 resonators, 16 SC solenoids,
  12.5 m, 33.5 MeV
• DSR section, 28 resonators, 14 SC solenoids,
  17 m, 108 MeV
• TSR section, 42 resonators, 42 quads, 64 m,
  408 MeV

Frequency 325 MHz Total length 112 m
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Ion source

• The ion source is a multicusp, rf-driven,
  cesium-enhanced source of H-.
• Output energy 65 keV, output peak current 12.7
  (38) mA, pulse length 3.0 (1.0) ms, pulse rate
  2.5(10) Hz

• Design concept - SNS
• Design issues in general these
• sources are well understood.
• SNS ion source can be used
• for PD. Longer RF antenna
• lifetime is desirable.

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Toward Selecting an H- Ion Source

• Beam tests on the SNS RF H- ion source (Doug
  Moehs)
• 3.1 ms long pulse, 11.5 mA average, at 5 Hz
• The SNS routinely runs 1 ms long pulses, 30 mA at
  60 Hz

• The SNS Ion Source Test Bench and LEBT

• Plan to test the DESY H- source at 3 msec pulse
  length
• in next few months

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RFQ

• RFQ accelerates H- from 0.065 to 3 MeV , Ip up
  to 28 mA

• Now RFQs are standard devices for proton
  machines. There are good designs (J-PARC, SNS)
  and we can copy appropriate

technical solutions.

• Our additional requirement
• for RFQ beam dynamics design
• is axisymmetric output beam
• to reduce halo formation in
• MEBT and RT TSR section. (P.Ostroumovs proposal).

J-PARC 30 mA RFQ
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RFQ

• For mechanical design the main issues will be 1)
  Machining of big parts with high accuracy ( 25
  microns for vane tips) and 2) The way to assemble
  the RFQ body. We consider brazing (SNS
  approach), though the clamping with ring contacts
  works well too (J-PARC).
• Currently basic RFQ parameters are found. RF
  design and mechanical design are planned to be
  done by ANL-FNAL collaboration.

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MEBT

• MEBT has three main functions, i.e., matching the
  
• beam from the RFQ exit plane into the MEBT
  chopper
• plane, cleanup chopping, and matching the
  remaining
• particles into the RT TSR section. Plus beam
  diagnostic.

Rebuncher
Chopper
Target
Quadrupole lens
SNS MEBT
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MEBT

• In our MEBT we have an axisymmetric beam after
  RFQ.
• 4 SC solenoids are used for focusing and matching
• 2 RT TSR are used as the rebunchers
• One chopper
• This is conceptual design. The detailed design is
  still ahead.

SC solenoid
MEBT
RT TSR
TRACK simulation
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MEBT

• The MEBT installed at KEK.

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RT TSR section

• Why this room temperature section?
• Beam dynamics at low beta demands adiabatic
  acceleration, smooth transition from RFQ to SC
  sections which have high accelerating rate.
• That means
• - variable beta accelerating lattice - gaps
  and dis-tances between them change with particle
  velocity
• - focusing period should be as short as
  possible
• - smooth increasing of accelerating rate
• It is expensive and difficult to design and
  produce beta variable SC cavities. This is not a
  problem for RT cavities

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RT TSR section

• Our solution is Room Temperature Triple Spoke
  Resonator (aka Cross-bar H-type resonators)
  section from 3 MeV to 15 MeV .

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RT TSR section

• The main advantage of RT TSR is its high shunt
  impedance.

For 3-15 MeV losses in copper DTL 1.06 MW RT
TSR 0.4 MW Diameter of resonator DTL, SDTL
70 cm RT TSR 40 cm RT TSR should be cheaper
RT TSR
SDTL (J-PARC)
DTL (J-PARC)
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RT TSR section

• SC solenoids in individual cryostats are to be
  used to maintain axisymmetric focusing
• Common vacuum tank with integrated RT TSR and SC
  solenoids seems to be effective mechanical design.

Helps to keep period short. End walls of
cavity are unstressed.
SC solenoid in individual cryostat
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RT TSR section
There no prototypes of RT TSR and SC solenoids
that meet our requirements , but we can find
similar efforts elsewhere
Cold model of CH resonator (Frankfurt).
SC quadrupole lens in individual cryostat
(Berkley)
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RT TSR section

• Past results
• RF parameters are defined for all RT TSR. The
  fields are simulated and used in 3D beam dynamic
  study
• Preliminary design of SC solenoids has been
  done and feasibility confirmed (Y.Terechkine)
• Plans
• RT TSR optimization, couplers and mechanical
  design
• SC solenoid design
• Vacuum tank design

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SC Spoke Resonator sections

• SC Spoke Resonator sections provide acceleration
• from 15 MeV up to 400 MeV.
• We study and optimize all three types of
  resonators

Successful power tests are done for all SR (ANL,
LANL, ORSAY). So, we are optimistic about
performance of these resonators.
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SC Spoke Resonator section

• What is done
• RF simulations are done for all cavities and
  fields are used in 3D beam dynamic study
• Optimization of cavity shapes is in progress
• HOM study has been started for TSR
• Plans
• Further RF optimization of SR designs
• Development of universal power coupler design
• Mechanical design
• Design of SC solenoid and quadrupole lens for
  this section

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CONCLUSIONS

• PD Front End is technically feasible
• - SNS and J-PARC machines are built
• - HIPPI project works in the same direction
  and has made a good progress
• No reasons to expect high cost of Front End
• Based on existing machines, we estimate risk of
  building PD Front End to be from low to moderate.
• We developed short and long term plans of work,
  they contain RD issues mentioned above.