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Eric Prebys
Accelerator Technology
Seminar, March 18, 2003 |
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Every long and short section (2x24=48) has |
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A horizontal and vertical BPM |
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Can read out turn by turn for two or 50 time
points for all 96 |
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A beam loss monitor |
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Can snapshot all 96 for each cycle |
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Horizontal and vertical trims |
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Originally DC.
Working on active control for the 24 high-b ones in each plane. |
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Quads and Skew Quads |
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Each has an individual DC setting plus common
ramp. |
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Chromaticity sextupoles controlled by ramps |
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Some individual loss monitors at key locations. |
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Horizontal pinger for tune measurement |
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Couples to V plane |
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Doesn’t work at the moment (had to steal kicker) |
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The proton source is very close the the
specifications in the Run II Handbook. |
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Although it’s the highest priority, support of
collider operations is a relatively minor facet of life in the proton
source. |
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Proton source activities are dominated by the
current and projected needs of the neutrino program (MiniBooNE+NuMI+??) |
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Whatever a WBS chart may say, there’s not a
separate proton source for RunII, MiniBooNE, NuMI, etc. |
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Total protons per batch: 4E12 with decent beam loss, 5E12 max. |
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Average rep rate of the machine: |
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Injection bump magnets (7.5Hz) |
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RF cavities (7.5Hz, maybe 15 w/cooling) |
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Kickers (15 Hz) |
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Extraction septa (was 2.5Hz, now 15Hz) |
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Beam loss |
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Above ground: |
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Shielding |
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Occupancy class of Booster towers |
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Tunnel losses |
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Component damage |
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Activiation of high maintenance items
(particularly RF cavities) |
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Everything measured in 15 Hz “clicks” |
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Minimum Main Injector Ramp = 22 clicks = 1.4 s |
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MiniBoone batches “sneak in” while the MI is
ramping. |
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Cycle times of interest |
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Min. Stack cycle: 1 inj + 22 MI ramp = 23 clicks
= 1.5 s |
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Min. NuMI cycle: 6 inj + 22 MI ramp = 28 clicks
= 1.9 s |
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Full “Slipstack” cycle (total 11 batches): |
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6
inject
+ 2 capture (6 -> 3)
+ 2 inject
+ 2 capture (2 -> 1)
+ 2 inject
+ 2 capture (2 -> 1)
+ 1 inject
+ 22 M.I. Ramp
----------------------
39 clicks = 2.6 s |
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The Time Line Generator (TLG) sequences all
accelerator operations. |
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Traditionally, each sequence (“module”) is
independent, including any necessary Booster prepulses. |
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This wasn’t really compatible with the goal of
getting the maximum possible beam out of the Booster. |
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In the new scheme: |
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Standalone sequences are placed in the time
line, with necessary prepulses |
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MiniBooNE pulses are “trailer-hitched” to the
end of these to achieve a specified average repetition rate, subject to an
overall total rate. |
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If there aren’t enough modules to trailer-hitch
to, new modules will be built (still working the bugs out of this one). |
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Running as we are now, the Booster can deliver a
little over 1E20 protons per year –
this is about a factor of six over typical stacking operations, and gives
MiniBooNE about 20% of their baseline. |
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NuMI will come on line in 2005, initially
wanting about half of MiniBooNE’s rate, but hoping to increase their
capacity – through Main Injector Improvements – until it is equal to
MiniBooNE. |
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Whatever the lab’s official policy, there will
be great pressure (and good physics arguments) for running MiniBooNE and
NuMI at the same time. |
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-> By 2006 or so, the Proton Source might be
called upon to deliver
10 times what it is delivering
now. |
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At the moment, there is no plan for assuring
this, short of a complete replacement! |
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So what are we going to try?… |
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Shielding and new radiation assessment |
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Vastly improved loss monitoring. |
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New (MP02) extraction septum and power supply
(enable high rep. rate running) |
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New tuning strategies. |
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Unshielded copper secondary collimators were
installed in summer 2002, with a plan to shield them later. |
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Due the the unexpected extent of the shielding
and the difficulty of working in the area, the design was ultimately
abandoned as unacceptable. |
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Collimators were removed during the January
shutdown. |
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A new collimator system is being designed with
steel secondary jaws fixed within a movable shielding body. |
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Hope to have then ready before summer shutdown. |
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The existing RF cavities form the primary
aperture restriction (2 ¼” vs. 3 ¼”). |
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They are high maintenance, so their activation
is a worry. |
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There is a plan for a new RF system with 5”
cavities: |
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Powered prototype built |
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Building two vacuum prototypes for the summer
shutdown with substantial machining done at universities. |
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Evaluate these and procede (hopefully?) with
full system. |
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Total cost: $5.5M cavities + $5.5M power
supplies (power supplies would pay for themselves in a few years) |
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Is it worth it? On of the questions for the
study group is how much improvement we might expect. |
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The current injection bump dogleg (ORBUMP)
magnets can ramp at 7.5 Hz, with a substantial temperature rise. |
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Need to go to 10 to support MiniBooNE and NuMI. |
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2 spares for the 4 (identical) magnets. Most
likely failure mode probably repairable. |
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Considering new design which will stretch
existing magnets further apart, which will lower their current, but will
require a pulsed injection septum between the first two. |
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Can new design incorporate injection
improvements?? |
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Some power supply issues as well: |
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One full set of replacement SCR’s for the switch
network. |
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New switchbox being designed, but needs
attention (or order more spare SCR’s). |
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No spare for charge recovery choke. |
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In order to Reduce radiation, a “notch” is made
in the beam early in the booster cycle. |
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Currently, the extraction time is based on the
counted number of revolutions (RF buckets) of the Booster. This ensures
that the notch is in the right place. |
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The actual time can vary by > 5 usec! |
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This is not a problem if booster sets the timing,
but it’s incompatible with multi-batch running (e.g. Slipstacking or NuMI) |
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We must be able to fix this total time so we can
synchronize to the M.I. orbit. |
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This is called “beam cogging”. |
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Detect slippage of notch relative to nominal and
adjust radius of beam to compensate. |
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Historically, the booster has lacked a
fundamental understanding of beam loss mechanisms. |
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If (!!!) it is possible at all to go the the
required beam flux, it will require some mitigation of beam loss. |
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Recently, there has been an great increase in
the involvement of the Beam Physics department in the Booster: |
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Space charge group (W. Chou, et al) has begun to
focus on the Booster again. |
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Chuck Ankenbrandt has moved into Booster group
as “Beam Physics Liaison” to help coordinate studies. |
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Starting to make quantitative comparisons
between predictions and measurement. |
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An almost immediate result of this increased
effort was the discovery of the “dogleg problem”…. |
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Took advantage of recent TeV Magnet failure to
raise the Long 13 (dump) septum and turn off the associated dogleg. |
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Doglegs almost exactly add, so this should
reduce the effect by almost half. |
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The mode of operation prevents short batching,
booster study cycles and RDF operation. |
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Had about 36 hours of study in this mode. |
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Bottom Line: major improvement. |
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Tune to minimize current? |
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helped so far, but near limit. |
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Maybe raise L13 septum a bit? |
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Motorize L13 septum to switch modes quickly? |
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Operational nightmare |
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Eliminate L13? |
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Find another way to short-batch |
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Make a dump in MI-8 for Booster study cycles? |
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Correctors?: |
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These don’t look like quads, so can’t find a fix
– yet. |
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Spread out doglegs (effect goes down with square
of separation): |
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Not a lot of room. Maybe separate downstream
magnets? |
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Three-legged dog? |
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Turn of the third of the four magnets. |
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Need to increase first two reduces net
improvement. |
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Large Aperture Lattice Magnets? |
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Obviously the “right” idea. |
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Must match lattice AND (preferrably work with
existing resonant circuit). |
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Potential for big screw-up. |
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Pulsed extraction bump? |
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Straightforward magnet design. |
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Only part of the lattice for a short period at
the end of the cycle. |
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New ideas welcome. |
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GMPS (upgraded, OK) |
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Transformers (serviced, OK) |
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Vacuum system (being updated, finished 2003) |
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Kicker PS charging cables |
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Run three times over spec |
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Evaluating improved design (better cable,
LCW-filled heliac, etc) |
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Low voltage power supplies, in particular Power
10 Series: |
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Unreliable, some no longer serviced. |
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Starting search for new supplier and evaluate
system to minimize number of different types. |
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Probably a few $100K to upgrade system. |
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RF Hardware |
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(original) Copper tuner cooling lines are
beginning to spring leaks.
Difficult to repair because they’re hot. |
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High Level RF |
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More or less original. |
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Our highest maintenance item. |
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Will probably last, BUT expensive to maintain. |
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John Reid and Ralph Pasquinelli feel a new solid
state system would pay for itself ($5.5M) in about four years. |
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Low Level RF |
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Many old modules, some without spares, some
without drawings. |
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An upgrade plan in place. |
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Not expensive, but NEED people. |
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Personnel!!!! |
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Cables:
frequent replacement of HV cables and connectors for ion pumps. |
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Hoses:
valve actuator hoses have failed and are now being replaced with
stainless steel. |
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Kicker magnets:
A kicker which recently failed showed signs of radiation damage to
the potting rubber. |
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Main magnet insulation: No main magnets have failed in 30 years,
but… |
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Installed radiation “dose tabs” around the ring
in January shutdown to get a real estimate of dosage. |
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The Fermilab Booster has maintained a remarkable
level of reliability over the last 30 years. |
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It has now reached unprecedented performance
levels while maintaining reasonably strict beam loss standards. |
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We still have a lot to do to meet the demands of
the future. |
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