SLAC Damping Rings in the
April 6-7, 1998 at the Boulevard, Woodside
This summary is intended to recap briefly the presentations
of the last two days and to give us an overview of the workshop theme.
1. In the introduction (after reviewing the present performance)
we began with a list of the future operating requirements for the rings:
- rings have good continuity now in engineering effort
- rings have benefited from reasonable level of expenditure.
b. McKee - reviewed history of failure modes for mechanical
and vacuum systems.
- proposed spending more money to reach our reliability
- replacement spare kicker magnets
- dipole coils (get rid of butt splices)
- sextupole epoxy damage
- LIC kicker chambers ...
- totaling $1.6M
c. Ross - concerns over radiation levels and damage
- different operating schedule than DRs, but same statement
is true: "donÕt switch them off"
- make use of quad shunts to align magnets and BPMS
- orbit correction feedback once per minute
- machine studies scheduled every two weeks.
b. Stanek - SLC operation of Damping Rings
- commissioning of the rings at the start of the last SLC
run undertaken mainly by operators, with physicists called in as necessary.
- extensive usage of web based notes, procedures and checklists
- benefits are that operators more attuned to the state
of the damping rings as they put them in.
- operators can be more "creative" in dealing
with operational problems
- problem sometimes of how to ensure physicists recognize
nonstandard tuning setups.
c. Pennacchi - Area Manager perspective
- review of problems, concerns
- RASK, temperatures, reliability...
- enhanced role of area manager in PEP II era
4. Accelerator Physics
a. Raubenheimer - lowering the operating energy
- emittance proportional to E-3 while damping
time proportional to E3
- lowering energy from 1.19 GeV to 750 MeV and changing
to 30 Hz repetition rate gives 4 times longer store time and 4 times lower
- compatible with 30 Hz PEP II injection, or even higher
injection rates since PEP II can tolerate ~3x SLC emittances. Higher rep
rates are also afforded by a NIT line kicker.
- low emittance beams produced this way are very interesting
for NLC studies
- high phase space density
- longitudinal instability thresholds
- Intra beam scattering limit vs. energy
b. Woodley - implementation of low energy lattice
- although magnets, kickers, RF can all run lower, need
more correctors to compensate saturation in bends
c. Spencer - magnet pole modifications
- partition function altered favorably for transverse damping
by adding focusing to the bends.
d. Zimmerman - frequency shift
- the partition function in this case is changed by moving
the central orbit by shifting fRF mid-store.
e. General discussion session
- opportunity to overcome shortcomings in present
- prototype NLC damping rings cavity
- when mass produced for PEP II, cost $150k ea.
b. Akre - klystron reliability review
- suggested adding interlocks to control mod anode
voltage when either no beam or no RF
- klystrons will eventually become obsolete during
the PEP II era
- replace with IOT station at a cost of $350k each.
c. Hill - relocating the existing klystron
- klystron to be housed upstairs for improved maintenance,
reliability and accessibility.
- compatible with all RF feedback and operation
- cost is $250k for both damping rings
d. Hill - upgrading old interlock system
- mechanical relays to be replaced with Alan Bradley
logic controller, as in PEP II
- improved reliability, standardization and trouble
- cost is $40k for both rings.
e. Corredoura - upgrade to low level RF control
- replace point-to-point wiring and discrete modules
with a PEP II style integrated unit.
- improvements in reliability, low noise, functionality
- operates at base band with digital control of feedbacks
and filtering. Gives flexibility of operation and enhanced diagnostics
- prototype for NLC RF control system
- development and installation cost ~$400k
f. Tighe - pulsed operation of RF control
- compare pulsed 120 Hz operation of damping ring
with steady state operation of storage rings like PEP II.
- in the previously described PEP II style RF controller,
software handles e.g.
- logic controls of cavity tuners for different rate
changes, intensity etc.
- RF gymnastics for pulsed amplitude changes (munch),
pulsed phase shifts, pulsed frequency shifts.
g. Neubauer - RF cavity windows
- thicker ceramic allows air side discharge to occur
before puncturing of ceramic occurs.
- new windows being procured for damping rings.
h. Judkins - S-Band feedback loop
- main issue is minimizing noise while maximizing
- should remeasure performance of present system
- consider digital feedback for future systems.
i. McKee, Schwarz - RF cavity tuners
- upgrade of mechanical design was successful
- improved centering, alignment
- RF design of brushes ongoing
- long conditioning period, outgassing
j. Schwarz - tuning outside the cavity
- adjustable stubs, or equivalent, used in external
waveguide to match load to klystron.
- cavity tuners would not be continually adjusted
- stubs and windows have to be designed with high
level of reactive power in mind - might be possible over a limited range.
a. Kotseroglou - review of beam size monitors
- synchrotron light detection techniques
- light fibers and fast detectors to resolve multi-
bunches and measure multi- turns
- moveable slits to measure diffraction limited spots
b. Turner - energy spread instrumentation in transfer
- a real time energy spread measurement at ring injection
would be helpful
- multiple strip lines appear not to have adequate
horizontal (energy) resolution
- wire scanners read over many machine pulses
- synchrotron light appears ideal
- gated camera captures horizontal spread of single
- very large energy spread of compressed beam in RTL
can be measured on BPM quadrupole mode monitor.
Thank you to all participants for the excellent quality
of the presentations, which will make the proceedings a useful reference
and guide for future evolution of the damping rings in the next millennium!