Status of the TRASCO Project

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Status of the TRASCO Project
Oak Ridge National Lab June 25-26, 2001
SNS-Miniworkshop
Carlo Pagani INFN Milano-LASA University of
Milano
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The TRASCO linac INFN-TC-00-23
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TRASCO_AC Activities and Partners

• Source
• LNS
• Hitec
• Sistec
• Low and Intermediate Energy Section
• LNL
• Cinel
• Uni/INFN Bo
• INFN Ba
• High Energy Section
• INFN Mi
• INFN Ge
• CESI
• Saes Getters
• Zanon

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TRasco Intense Proton Source (LNSHITECSISTEC)

• High intensity (several 10s mA) proton sources
  exist
• Chalk River
• Los Alamos
• CEA-Saclay (Strong collaboration LNS/CEA)
• Critical problem for ADS is the source
  reliability and availability
• Additional efforts with respect to state of the
  art are required for
• Voltage and current stability
• Control of the low beam emittance
• Subprogram is aimed at the construction and
  operation of the source

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TRIPS

• Design completed in 1999
• Source assembled in LNS in May 2000
• First beam of 20 mA _at_ 60 kV in Jan 2001
• Off-resonance microwave discharge source (2.45
  GHz)
• Based on SILHI (CEA/Saclay)
• Modifications focussed on increase of reliability
  and availability
• TRASCO II Optimized source with PM

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Low Energy Linac (LNLCINELBaBoNa)

• The low energy linac is split in two components
• A normal conducting CW Radio Frequency Quadrupole
  (RFQ) from 80 keV to 5 MeV
• A Superconducting linac (ISCL) from 5 MeV to 100
  MeV
• l/4, l/2 cavities at 176 MHz or 352.2 MHz
• Reentrant cavities at 352.2 MHz

TRASCO I Prototype of 1/3 of the full RFQ and
one of the SC cavities TRASCO II full RFQ
structure manifacturing
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The CW RFQ

• LANL LEDA 6.7 MeV RFQ achieved 100 mA CW (point
  of comparison)
• Huge engineering effort, complex design for very
  high current, 3 klystrons
• Different optimization procedure for TRASCO RFQ
• Limit to 1 RF source (1.3 MW CERN-LEP klystron)
• Lower design current of 30 mA (transmission of
  96)
• Peak surface electric field is 33 MV/m, 1.8
  Kilpatrick limit
• Simplified engineering/manufacturing choices
• Heat dissipation in the structure 600 kW total

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ISCL Linac

• The 5-100 MeV linac is made of independently
  phased cavities
• Re-entrant cavity geometry (single cell)
• Each SC cavity is fed by a small 15 kW solid
  state amplifier (Activity in LNL)
• Linac is very tolerant in terms of cavity
  failures (0.5 MeV max cav gain)
• Cavities can be designed multipactor-free
• The He vessel is integrated in the resonator in
  order to provide mechanical stability

Mechanical analysis under 1 bar He bath pressure
Focussing Quadrupoles
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Other resonator types for low energy

• A more cost effective linac can be designed with
  2 gap resonators
• 1-1.5 MeV of energy gain per cavity
• In this case the linac is less tolerant to cavity
  failures
• Half Wave Resonators (dipole-free) and Quarter
  Wave Resonators (like ALPI cavities) are under
  analysis

beam
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The High Energy SC Linac (MIGEZanonSaesCESI)

• Linac Conceptual Design Beam Dynamics (INFN)
• RF Cavity design ? Done
• All e.m., mechanical technological fabrication
  aspects
• Linac design and non-linear beam dynamics ? Done
• Two frequency options analyzed
• 352.2 MHz (CERN LEP)
• Attractive if machine is built NOW, with help of
  CERN infrastructures
• Limited gradients, 4.2 K operation
• Components are ready (RF, ancillaries, ...)
• Long machine and huge infrastructures
• Cheap technology (sputtering)
• 704.4 MHz (CERN2)
• More components engineering but, after TESLA
  achievements, more promising
• Higher gradients, 2 K operation
• Components need to be developed (RF, ...) but can
  be designed after TESLA/SNS
• Shorter machine and small infrastructures
• Bulk niobium cavities
• Prototypes and engineering (with partners)
• High beta single and multi cell cavity at 352.2
  MHz with CERN ? Done

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Extension to the TRASCO program

• TRASCO II extends the program to the end of 2001
• Main goals of TRASCO II
• Source
• TRIPS-PM (permanent magnet version for further
  reliability)
• Beam line to the RFQ (matching section)
• Low Energy
• Manufacturing of the Full RFQ structure
• Engineering of the re-entrant cavity components
  tuners, couplers, etc.
• High Energy
• Multicell cavity at 704.4 MHz (2) Collaboration
  with CEA/IN2P3
• Engineering design of the cryomodule
• Treatment and test infrastructure in LASA
• Class 100 Clean Room
• High Pressure Rinsing station
• RF measurement infrastructure
• BCP is being set up in an external company
  premises

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General Linac Design
From INFN/CEA/IN2P3 Meeting LASA, Feb 23-24,
1999

• Choices of cavity parameters
• RF Frequency
• b values
• Determined mainly by the machine energy range and
  number of sections
• Number of cells
• Determined by efficient use
• How many cavities per cryomodule?
• Many good use of space (beware of too much
  acceleration in one lattice cell!)
• Few waste of space
• Cavity design provides constraints
• Max B surface field (and Bpeak/Eacc)
• Max E surface field (and Epeak/Eacc)
• Longitudinal beam dynamics constraints
• Longitudinal phase advances
• Longitudinal focussing (synch. phase)
• Beamline space inventory

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The Scaling with Frequency
From INFN/CEA/IN2P3 Meeting LASA, Feb 23-24,
1999

• From the envelope equations, simple scaling laws
  with the design frequency can be derived,
  allowing to reproduce the same dynamics (scaling
  properly emittances, currents, and beamline
  parameters)
• higher frequency means physically smaller
  accelerator components
• ? divide lengths by a factor 2 (700/350)
• ? use a beam physically smaller by a factor 2
• keep the same phase advances per period (the
  basic linac design depends on the choice of the
  phase advance)
• ? the phase advance per meter doubles (the cell
  size halves!)
• ? the quadrupole gradients double, the length and
  bore are halved
• ? the cavity gradients double
• To have the same dynamics we need to divide the
  emittances by a factor 2
• If we also keep the same ratio of the emittance
  term to the space charge term,
• ? use the same peak beam current (twice the
  charge in the bunch)
• In this way the envelope equation is formally the
  same! Of course, the boundary condition at low
  energy is different for the two frequencies
• We did not consider the matching to the focusing
  channel of the previous linac section, which will
  be obviously different in the two cases due to
  the frequency transition

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Linac Beam Dynamics (1 GeV TRASCO linac)
From EPAC 2000, Vienna, June 2000

• The beam dynamics of TRASCO has been analyzed in
  detail
• A multiparticle beam dynamics code with a 3D
  space charge solver has been written
• Time evolution (for space charge consistency)
• Beam propagation in a z-dependent sinusoidal
  cavity field
• 3D Poisson solver based on a Multigrid method
• Presented at the ICAP98
• Compares OK with 2D/3D Parmila versions (N.
  Pichoff/CEA)
• No substantial emittance growth/halo formation
  can be seen from simulations (up to 100.000
  particles)

Beam Emittances
Control of the particle distribution
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Preliminary XADS Beamline

• In response to INFN/ENEA/Ansaldo meetings on the
  ADS interface, we studied the beamline for the
  XADS case
• 600 MeV proton energy
• 6 mA beam current

Study for the windowless solution Full width beam
spot size on target 40 x 80 mm Small beam size is
kept inside the last 90 bending Changes
suggested with respect to base line XADS
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Cavity Design

• Careful analysis of the low beta cavity
  properties
• Short cavity geometry leads to peculiar
  problems, the cavity geometry needs to be
  carefully optimized
• Electromagnetic
• Smaller volumes implies higher surface fields
  than electron cavities
• High surface E field emission! ? Nb quality and
  chemical/surface treatmens
• High surface B thermal quenches ? Nb quality
• Multipacting may be worse than electron cavities
  (no clear indication yet)
• Mechanical
• Different aspect ratio of the cells (long/transv)
• Mechanical stability under vacuum can be critical
  at low beta
• Need for stiffening in case of pulsed operation
  or microphonics
• Criteria/codes developed for cavity optimization
  have been used for
• TRASCO/352 and TRASCO/704
• Collaboration INFN/CEA/IN2P3 _at_ 704 (MOU)
• SNS (MOU INFN/TJNAF for SNS being signed)
• RIA (MOU INFN/MSU under definition)

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Tools for the cavity parametrization
From SNS CCS Workshop TJNAF April 12-13, 2000

• We built a parametric tool for the analysis of
  the cavity shape on the electromagnetic (and
  mechanical)parameters
• All RF computations are handled by SUPERFISH (no
  need for another code)
• Inner cell tuning is performed through the cell
  diameter, all the characteristic cell parameters
  stay constant R, r, ?, d, L, Riris
• End cell tuning is performed through the wall
  angle inclination, ?, or distance, d.
• R, L and Riris are set independently
• End groups for a 4 die cavity can be tuned using
  the end cell diameter (and a,d,R,L, Riris are set
  independently)

• All e.m. cavity results are stored in a database
  for futher parametric investigations.
• A proper file to transfer the cavity geometry to
  ANSYS is then generated

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Final Cavity Output
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Mechanical analysis of
From SNS CCS Workshop TJNAF April 12-13, 2000
Danilo.Barni_at_mi.infn.it
Half cell

• A postprocessor reads the SFO output and builds a
  FEM model
• Radiation pressure calculation (Lorentz forces)
• Evaluation of the Slater coefficients
• An automated ANSYS procedure performs all the
  following calculations for 3 boundary conditions
  
• Lorentz forces effects as a function of the
  stiffening ring radial positions
• 2 bar vacuum load on the cavity
• Tuning sensitivity (N/Hz, N/mm, Hz/mm)

Full cavity

• Computation of the vibration eigenmodes of the
  completely free cavity
• Computation of their dependence from suitable
  external knobs
• Helium vessel fixtures for the transverse modes
• Stiffening ring radius for longitudinal modes
• What is the connection Lorentz force excitation ?
  vibrations?
• Contribution of the modes to the Lorentz forces Dn

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TRASCO Cavity Prototyping

• 350 MHz cavities with CERN
• Single cell sputtered b 0.86
• 5 cell sputtered b 0.86
• Cavity integration in a LEP type cryostat Under
  way at CERN
• 700 MHz Cavities with ZANON ( Saclay JLab) b
  0.5
• One single cell - Built (Zanon) and Tested
  (Saclay) RRRgt30
• Three single cells under construction (RRRgt30
  RRRgt250)
• One 2-3 cell under design for fabrication
  optimization and stiffening prototyping
• One or two 5-cell cavities
• Arranging for chemical treatments with a local
  company (Delmet) possible?
• Cryogenic RF Test Bench under Commissioning at
  LASA

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350 MHz Cavities

• MOU with CERN for the fabrication and test of
• Single cell at high beta ? Done!
• 5 cell cavity at high beta ? Done!
• Extension of the contract for the insertion of
  the 5 cell cavity in a LEP cryostat on the way

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The b0.85 Cavity Produced with CERN

• Left, the cavity before the insertion of the Nb
  cathode in the clean room before sputtering
• Below, the cavity after chemical etching

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Five Cell Cavity Results (Q vs. Eacc)
b0.85
Results of the measurements on the TRASCO 5 cell
module _at_ 4.5 K

• The results obtained reached the original TRASCO
  goal!
• The limitation on the operating point of the
  cavity was due to the increase of the RF losses
  with the increasing field due to the growth of
  electron loading
• This limitation is exactly the same limitation
  experienced in the LEP cavities, indeed the
  cavity performed as the best LEP cavities

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Measurements Results and Future Work

• The next step of the joint INFN-CERN development
  will be the test of the 5 cell cavity fully
  equipped with tuners and couplers in an
  accelerator-ready cryostat (a modified LEP spare
  cryostat)
• Here the cavity is shown in its He tank, complete
  with the tuner bars, before insertion in the
  cryomodule

• This activity was delayed till November 2000 due
  to the LEP-Higgs Blues
• cryomodule availability
• Current planning
• Module completed by the end of March 2001
• Module tests (due Cryogenic Facility backlog)
  May-June 2001

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700 MHz Cavities

• The 700 MHz activities are carried out in
  parallel with CEA/Saclay and IN2P3/Orsay, to
  optimise development efforts
• Milano works on prototypes of the lowest beta
  (0.5)
• Saclay/Orsay works on prototypes of the
  intermediate beta (0.65)
• The design work is common between the labs
• So far
• 4 b0.5 single cell cavity have been built and 2
  tested
• 3 b0.65 single cell cavity have been built and
  tested

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Summary of Main Cavity Parameters
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The b0.5 single cell cavity (Z101)

• Used low RRR Nb sheets RRRgt 30
• Built by Zanon (Partner)
• Treated at Saclay
• Standard BCP 1.1.2 (HF HNO3 H3PO4) 100 mm
  removal on surface
• HPWR with ultrapure water (18 MW) _at_ 100 bar
• Class 100 Clean Room Assembling
• Tested at CEA-Saclay gave very good results
  (given the bad Nb used!)
• The vertical insert was not arrived in Milano
• The cavity will be re-tested in Milano soon
• One other single cell with low RRR and two single
  cells with the good high RRR Nb are being built
  by Zanon

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Life cycle of the Z101 treated at Saclay
BCP
Assembling in the insert
HPWR
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TRASCO 700 MHz b0.5 Z101 Prototype

• Fabricated with Reactor Grade (RRRgt30) Niobium
  at ZANON
• Chemical Treatment and HPR at Saclay (no heat
  treatment)
• Tested at Saclay at 1.5 K

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SC RF Cavity Test Facility at INFN-LASA
Class 100 Clean Room
A Class 100 Clean Room has been commissioned A 18
MW clean water plant for high pressure rinsing
has been installed High pressure rinsing (HPR)
system is being installed
The RF bunker
Clean Water Plant
RF Measurement Bunker
The new insert with a 5 cell cavity
The old ARES (500 MHZ) Cryostat from LNF has been
adapted with a new insert (ZANON) to minimize He
consumption and allow fast cooldown times
Assembling of the clean room