fermilab linac overview

f Proton Source Department

Linac Briefing to Directorate August 9, 2002

Fermilab Linac Status and Outlook Briefing to the Directorate

Beams Division / Proton Source Department

August 9,2002



Fermilab Linac Overview

• 200 MeV proton Linac built ~ 1969-71

• Began H- operation in 1977

• 400 MeV upgrade in 1992, original 116 MeV DTL remains

• 15 Hz hardware pulse rate, variable beam pulse rate

• 45mA beam pulse current typical at 400 MeV

• Variable beam pulse length, typically 10-40 microsec

• Typical beam efficiency 10 MeV to 400 MeV ~ >95%

• Typical 400-MeV emittance 6 mm-mr, p/p of 0.25%

• DTL accelerated ~300mA, 5usec beam pulses in 1970’s

• New CCL >90mA (protons) during Jan. 1999 test





Linac in the Big Picture

• All protons for all Fermilab physics programs currently and for the near future depend on this Linac

• Proton demand for HEP is scheduled to increase 10-fold

• All current program planning assumes continued operation at historical reliability, >97% availability

• PreAcc and 200-MHz Linac beamline and power systems are original equipment, >30 years old

• 200-MHz RF power systems in particular are based on outdated technology and at risk of obsolescence (1)

• Original Linac expertise will soon be gone

• Focus here is on PreAcc and 200-MHz Linac





Linac Operational Issues and Risks• Loss of individuals with critical knowledge and skills

– Black Magic of Ion Source maintenance– PreAcc High Voltage DC expertise– Linac vacuum and major mechanical system maintenance– High Power RF Vacuum Tube expertise

• 750-KeV Buncher or DTL Accelerating Cavity failure– Buncher cavity from MURA, still tuned with C-clamp– Drift-tube/quadrupole failure (up to 10 weeks recovery, esp. Tank 1)– Cavity vacuum seals, esp. drift tube stems

• Obsolescence of critical high voltage & RF power tubes– Modulator switch tubes (last manufacturer, Triton, has dropped line)– 7835 type 200-MHz RF power amplifier tubes (single source)

• 30-year old quadrupole power supplies containing a total of ~ 1.5 cubic yards of PCB capacitors





Tank 1• Don Young (Fermilab ID #002) on Tank 1

– “Tank 1 is a kludge, it was built as a prototype”– “It was thrown together with parts from the Village”– “It was rushed to “get a beam at NAL” ”– “There are inherent problems with tuning and drift tube alignment”– “Contributes factor of 3 emittance growth”

• Contains greatest number, smallest, most closely spaced drift tubes of all Tanks (6 cm center-to-center at 750 KeV)

• Drift tube alignment is a serious issue• No post-couplers to stabilize Tank tuning• Concerns are especially important today due to maintenance

vulnerability exacerbated by loss of original expertise

(This background picture is NOT of Tank 1)



7835 Power Amplifier Tubes

• Fewer than 30 sockets in the world -- 20 of these are at FNAL, BNL, and LANL (2)

• No alternative PA tube or 200-MHz power system is available• Burle Industries is the sole 7835 builder/re-builder• Linac staff visited Burle in June and returned with positive

impression of their commitment, but Triton gave little warning • Average tube operating life is apparently becoming shorter

– Can tubes be rebuilt only a limited number of times?– Has vendor lost the magic recipe?– Have we lost the expertise to maximize operating life?

• We must build up spares inventory as hedge against vendor production problems or drop-out; this will not eliminate the vulnerability





Date Received vs. Hours on Tube

0

5000

10000

15000

20000

25000

30000

May-68 Oct-73 Apr-79 Oct-84 Mar-90 Sep-95 Mar-01

5 stations9 stations

Three tubes with>30000 hours excluded

In service now

History of 7835 Tube Operating Lifetimes (2)



200-MHz Modulator Switch Tubes

• Each modulator requires three F1123 switch tubes• We use about 7 tubes/year on average• Final order last year for 50 Triton tubes

– 49 received to date• 38 tested good• 3 tested bad• 6 awaiting test• 2 in test

– 1 yet to be received

• One tube successfully rebuilt by Econco recently• No direct replacement is available





Views of the Future I: Only 6 years

• Present Linac will serve Run II, MiniBooNE, NUMI, and SY120 until LHC turns on in 2008, then limp into oblivion– Just maintain existing equipment

– Plan no major improvement programs

– Rely on present stock of switch tubes

– Build up minimal stock of 7835 PA tubes

– Maintain present operating and maintenance staff levels





Views of the Future II: 10-12 Years

• Present Linac will be expected to run strongly and reliably through delayed LHC turn-on and through B-TeV– Strongly push switch tube rebuild program or, failing

that, begin 200-Mhz modulator redesign program– Build up substantial 7835 PA tube stock, ~5 yr supply– Replace quadrupole power supplies– Execute major improvement programs for aging

conventional systems, e.g. water, vacuum– Begin highly proactive maintenance of existing systems– Augment present operating and maintenance staff to

facilitate improvement programs





Views of the Future III: Beyond 12 Years

• Fermilab expects to run hadron physics programs beyond the foreseeable future– It would seem extremely unwise to plan to rely on the existing

200-Mhz Linac for more than ~12-15 years

– Planning should focus on defining beam requirements ASAP, then get on with design, approval, and construction of new machine

– A goal should be to realize and take advantage of benefits of new machine at the earliest possible date (2007 is optimistic)

– Continue proactive maintenance of existing systems

– Maintain current operational/maintenance staffing level and establish separate “project” department to carry out new machine





Minimal Thinking => Domino Thinking

• Replace Cockcroft-Walton PreAcc with RFQ to reduce long-term maintenance problems and vulnerability to loss of key expertise

• It would be foolish to build 750-KeV RFQ to inject into a vulnerable, emittance trashing Tank 1

• It would be foolish to rebuild Tank 1 given the vulnerabilities of the 200-MHz RF power systems

• Ergo: replace the whole front end up to 116 MeV with klystron driven 402-MHz Linac with RFQ Injector





The 402-MHz Upgrade Option• Replace Cockcroft-Walton PreAcc with a 3-MeV, 402-

MHz RFQ• Preserve beam emittance with a 402-MHz, ramped

gradient DTL Tank 1• Accelerate to 70 MeV with three additional 402-MHz DTL

tanks• Match into 805-MHz CCL structure at 70 MeV• Add two modules of present CCL design to reach current

116 MeV transition energy• Requires four 402-MHz klystrons to power the RFQ/DTL

systems and two copies of existing 805-MHz klystron systems to power new CCL modules





(Ambitious) Schedule• Complete definition of goals and requirements and initiate

project approval process - 3/1/03• Begin Linac design activities and communication with

potential commercial partners - 10/1/03• Begin design of control and diagnostics systems - 6/1/04• Obtain construction funds - 10/1/05• Complete fabrication and delivery of commercial

components - 2/1/07• Begin 6 month for construction and installation (in

conjunction with B-TeV construction) - 4/1/07• Begin commissioning - 10/1/07• Return to HEP operation - 11/1/07





Cost and Considerations• Estimated 402-MHz Upgrade cost (3)

– Accelerator systems and components -- $24.6M– Installation and commissioning -- $ 2.5M– Building modifications -- $ 0.5M

• Anticipated operational costs with present Linac– 7835 power tubes (5-6/year) -- $600K/year– Other power tubes -- $30K/year– New quadrupole power supplies -- $1000K– Water system rebuild -- $300-500K

• Manpower and Expertise– Need to obtain expert design assistance not available within Lab– Commercial expertise exists (ACCSYS now Hitachi)– Original Linac required 55 people during construction and

commissioning





Advantages of 402-MHz Upgrade

• Possible ~5x increase in beam brightness• Eliminates RF power vacuum tube vulnerability

– Klystrons are current technology

– Klystron lifetimes are 5 times longer than present tubes

• Replaces all aged Linac equipment and associated maintenance problems

• Leverages on existing tunnel, building and 805-MHz Linac

• Much of design and hardware may be available commercially





Caveats• This Domino Thinking may in fact be “Backward

Thinking”: Is it focused too much upon what we have, rather than what is needed for a sound physics program?

• Does the 402-MHz Linac meet TBD beam requirements?• Is the radiation shielding of the present enclosure adequate

for future operations?• Will the current physics program commitments support the

402-MHz Linac construction/installation schedule?• This is an all or nothing approach with one big shutdown• What is happening with Booster during this time?

– A 400-MeV Linac isn’t much use without a Booster– Booster beamline components are same age as the 200-MHz Linac

and have/will have suffered considerable radiation exposure





Relationship to 8-GeV Linac Option

402-MHz Upgrade

• 15 Hz pulse rate

• ~100 usec beam pulse

• 70 mA beam current

• ~1.2E18 pph potential

• Retains existing 805-MHz Linac

• Uses existing building and infrastructure

• Booster synchrotron required

• Limited future upgrade path

8-GeV Linac

• 10 Hz pulse rate

• 1000 usec beam pulse

• 25 mA beam current

• ~5.4E18 pph potential

• Replaces existing 805-MHz Linac

• Requires all new civil construction

• No Booster synchrotron required

• Avenue to superconducting RF and Linear Collider technology





Conclusions• Linac “problem” ought not be considered in isolation from

Booster “problem”; it is a Proton Source problem relevant to the entire Laboratory community

• Solutions will take considerable lead-time to implement• Six year horizon for “status quo” operation is clear, given

suitable attention to maintenance and acceptance of certain vulnerabilities to failure

• Twelve year horizon requires improvement projects to allow continued reliability and care, planning, and $$$ are necessary to mitigate potential “tube disaster”

• Expectations of a Fermilab hadron physics program beyond 12 years suggest that beam requirements should be defined as soon as possible to avoid lapse in program

• New machines may or may not benefit present day operations





Closing

• The greatest danger of all is failure to chose and actively pursue a well-defined plan for the Proton Source

• At risk is the availability of protons to serve current and future Laboratory objectives and commitments





References

1. “Status of the Low-Energy Linac 200-MHz RF Stations”, Fermilab TM-2166, March 2002

2. “Analysis of Lifetime Data for the Linac 201 MHz Power Amplifiers”, Fermilab TM-2178, July 2002

3. “H- Source and Linac Improvements and Upgrade”, Appendix of Chapter 8 of Proton Driver Study II, Fermilab TM-2169, May 2002

4. Trip Report to Burle Industries, Elliott McCrory, June 2002 (http://mccrory.fnal.gov/memos/BurleVisit2002.htm)

fermilab linac overview

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