ALICE Commissioning
Part I : General & HV work
Yuri Saveliev
•LogBook Practice
•Shift work practice
•Low or high Q ? (and other notes)
•Strategy
•Gun HV conditioning
•Photocathode HV conditioning
Seminar on 14-15/07/2008
LOGBOOK
&
SHIFT
practice
(sorry about that ….)
LOGBOOK Structure
Start a new Logbook entry with a short title saying what is this entry about.
•This way, instead of, for example, “16:00 Still checking out safety paperwork“
we would see something more meaningful in the right hand side column of the
entries list.
•avoid using “Shift aims”, “Aims” etc
•indicate only a main purpose of work for the shift
•do not use fancy fonts for the first line (bold, italic etc)
Shift Summary should be on top of the shift log entry
Divide the shift log into tasks and subtasks and put a heading line (in
bold) for each of them, e.g.
Steering the beam to FC-02
Measuring bunch charge on FC-02
Energy spectrum at Q=5pC
GOOD
BAD
Data Recording
Every set of data collected (be it a plot, an image, or a single measurement)
must be accompanied by a machine parameters and settings at which this
data was collected
Use tools similar to the previously used “Diagnostic Line Status” tool
It is called now “Machine status” – there is an icon on the Desktop
Please read the Manual before using it !!
Do not report all changes of settings in chronological order unless there
is a comment to make.
Instead, summarise changes when a step is completed or data collected.
The bad practice is to report all the changes made in a time stamped chronological
order scattered over half a page
For table-like data recorded in the shift log,
use [code] and [/code] keys to make sure it stays table-like in a final form
File naming convention
Files are stored in
\\apsv4\Astec\Projects\4gls\ERLP\Work\YEAR\MONTH\DAY\Shift N
Click the Today's work folder shortcut
Each file must start with a time stamp followed by all other descriptive information,
e.g. 1745-yag-01-image.png
Use exact match between the time stamp in the LogBook and the corresponding file
(e.g. do not name the file "1842-?????.png" if the logbook note starts with
a timestamp of "18:40 ...").
If a collection of similar images need to be taken for a measurement
(e.g. emittance), use a single timestamp in all file names related
to this measurement.
Remember, file name timestamping is to facilitate data analysis
and not for chronological reasons.
Better practice is to put all files into a sub-folder but the name of this sub-folder
must start with the four digit timestamp similar to that for files.
Avoid multilevel sub-folder structure in the Work folder.
Ideally, only one sub-folder level in the work folder should be made
Do not record full paths of stored files in the Logbook entry
Shift work practice
Use actual (from DVM) readbacks (not set values) for voltage
Use set values (???) for magnet settings (this still to be decided).
YAG/OTR images:
always ensure that the images recorded and stored are not saturated
(remember- image may not have red pixels but still be saturated !
Always check “one pixel wide” distributions available
in Matlab Image Capture immediately after frame grabbing).
YAG/OTR protection:
there is one in place (TrainLength to 50ns when screen inserted)
but it is not fully “fool-proof” !!!!
BPMs:
use more than ~ 25μs train length
Make sure the scope inputs are set to 1MΩ and there are no
other 50Ω terminations
Laser and QE
keep the laser shutter shut whenever you are not doing measurements
close the laser shutter before you make a significant change in the system
(like, switching linacs on & off, group of magnets on & off etc …)
(remember: in the Procedures, this is not always said explicitly
– please use common sense )
ALICE Manual
• all procedures are in Wiki
• attempt is made to make them as step-by-step instructions
• but it is not a Bible !!! (try not to take everything at face value)
Some
introductory
notes
ERLP diagnostics schematic
ERLP SCHEMATIC DIAGRAM
v.0.2 (15/06/2006)
extracted from AO-180/10078/E
FCUP-01
YAG-??
INJ
EC
TO
R
Q-07
Q-09
Q-08
DIP-3
Q-06
DIP-02
Q-10
DIP-01
Q-05
YAG-03
Q-04
H&V-03
YAG-02
ST4
YAG-04
ARC 2
OTR-01
Q-01 Q-02 Q-03 Q-04 Q-05
BPM-06
DIP-03
Q-03
BPM-03
Q-02
BPM-05
SEXT-02
OTR-02
Q-04
BO
OS
TE
R
Q-01
H&V-06
H&V-01
BPM-02
SOL-02
YAG-01
BUNCHER
BPM-01
GU
N
BPM-01
H&V-01
Q-12
BPM-01
OTR-01 H&V-01
OTR-02 DIP-01
DIP-03
DIP-02
Q-01
BPM-02
H&V-02
Q-02
Q-03
Q-04
LINAC
OTR-02
BPM-02 DIP-01 DIP-02 DIP-03
H&V-02
OTR-04
OTR-03
DUMP-01
DMP
BPM-01
Q-01
Q-02
ARC1
1m
BPM-01
DIP-01
BPM-02
SEXT-01
OTR-01
Q-01
Q-03
V-01
Q-02
OTR-01
BPM-03
Note: scale is for guidance only
DIP-02
DIP-02
BPM-03
BPM-04
Q-02
V-01
Q-03
V-02
OTR-01
SEXT-01
BPM-02
DIP-01
BPM-01
BPM-02
H&V-02
OTR-01
BPM-03
DIP-03 V-03
DIP-02
BPM-01
H&V-01
Q-02 Q-01
Q-07 Q-06 BPM-04
H&V-04 Q-05
ST 3
Q-03
DIP-04
Q-04
DIP-01
BPM-02
H&V-02
OTR-02
BPM-01
H&V-01
OTR-01
OTR-03
WIGGLER
Q-04
ARC 2
SOL-01
ST1
V-02
Q-03
BPM-03
Q-01
H&V-02
ST1
Q-11 BPM-05
H&V-05
BPM-04
H&V-04
BPM-05 TCM-01
PLM-01
H&V-05
ST 3 ST 2
Q-04 Q-03
Q-02 Q-01
ST 2
OTR-02
SEXT-02
BPM-05
DIP-03
BPM-06
ARC1
No Energy Recovery = limitations on either Q or Train Length
RF power available
~15-20kW
Full beam power in main linac
~180kW (80pC; 6.5mA; 27MeV)
Hence: beam loading ~ equal to short circuiting of the cavity
Train Length
~0.5ms
ERLP Train Length = 0-100ms
Q(loaded)~106
tf ~ 0.3ms
Example:
If Train = 25us,
DE/E = 8%
RF pulse
Options:
1) small Q and long TrainLength
2) nominal Q (=80pC) and short TrainLength
Commissioning: Low or High bunch charge ???
Ideally, - set the machine at low Q then just raise the bunch charge up
But the gun beamline is very sensitive to Q
(let alone the effect of the offset of the laser beam on the cathode)
Option I: small Q and long train
If Q=2pC, and TrainLength ~25us
the beam loading in the main linac =4.5kW
Small enough to sustain the beam with available RF source !
GOOD THINGS:
Can use BPMs for steering (minimal TrainLength ~22us required)
?
BAD THINGS:
• the gun beamline settings are very sensitive to Q
(i.e. we cannot set ERLP at low Q and then just boost it up to a nominal value)
• BPM signal/noise ratio may not be enough
?
BUT:
We can, in principle, set the gun beamline at 80pC and then insert the slit
in INJ-DIA-YAG-01 thus reducing the effective bunch charge to ~2pC
• Awkward “beam shape”
• Not easy to deduce beam size or Twiss parameters
• Eliminates space charge effects in Injector beamline
Option II: nominal 80pC bunch charge and short TrainLength
If we set maximal DE/E ~ 0.3%, maximal TrainLength is ~1us at 80pC
(Max dispersion is ~1m  ~3mm beam motion)
GOOD THINGS:
• Raw BPMs signals still could be used (with good signal/noise ratio)
• The gun beamline is set once and for all
• Normal beam parameters measurements
BAD THINGS:
• Cannot use BPMs for beam position measurements
• OTR sensitivity may not be enough (remains to be seen)
In the following, we
OPT FOR SETTING THE ERLP AT NOMINAL BUNCH CHARGE
AND SHORT TRAIN LENGTH ~1ms
(the worst case scenario)
Earth & stray magnetic fields
Earth field
Assume 0.3G field perpendicular to beamline axis (worst case)
Energy
1m
3m
------------------------------------------------------------8MeV
0.5mm
4.5mm
35MeV
0.1mm
0.9mm
Note: trajectory deviation is proportional to path length squared
Stray field
Assume 1G over 10cm
Energy
1m
3m
------------------------------------------------------------8MeV
0.3mm
0.9mm
35MeV
0.1mm
0.3mm
Note: trajectory deviation is proportional to path length
Beam based ballistic alignment is not straightforward
Energy spread after booster
At present design, two booster cavities operate at +15o and -30o off crest
(which is large !)
The resulting energy spread (4 x sigma): 4 E
after 1st cavity : ~160 keV (at ~4MeV)
at booster exit: ~ 200keV (at ~8MeV)
But YAG-05 – 30mm diameter only (beam pipe limited anyway)
FCUP-01
YAG-05
DIP-02
DIP-01
Q-05
YAG-03
Q-04
H&V-03
YAG-02
Q-03
BPM-03
Q-02
Q-01
Dx ~1.1m at YAG-05
Q-06
BPM-04
H&V-04
Hence: Dx ~28mm  full screen already !
New ALICE injector model:
DE (after booster) ~ 40keV
Dx ~ 5mm  quite acceptable
Strategy
1. First goal: achieving energy recovery
- the undulator is not installed
- correct longitudinal phase space and bunch length are not
of importance
- energy spread is kept to minimal (near on crest at main linac)
2. Machine setting is performed at nominal Q (80pC or less if necessary)
- use YAGs and OTRs only (no BPMs)
- low (~1us) TrainLengths
3. Injector is set carefully but the rest of the machine – coarse setting only (until
energy recovery is established)
4. Fine tuning and measurements after establishment of energy recovery.
5. Procedures (and strategy !) may (and probably will !) be adjusted after
gaining first experience in ALICE commissioning.
All procedures are now in a Wiki format
http://projects.astec.ac.uk/ERLPManual/index.php/Main_Page
6. Commissioning is divided into steps that correlated to ALICE sections, i.e.
Injector, ST1, ARC1, ST2 & 3, ARC2, ST4, Energy Recovery.
Variations (temporal) to a strategy
0. Bakeout at 200oC.
1. HV conditioning not to a “magic number” of 450kV but as far as there is no
appreciable outgassing and FE at ~370kV
- reduce the risk of the ceramic failure
- may (or may not) help the cathode lifetime
2. Machine setting and energy recovery at, e.g. Q ~ 40pC, instead of nominal 80pC
- alleviate a reduced cathode lifetime
- continue to work even at reduced QE below 1%
- a bit easier to get the machine set
3. Operation at reduced gun voltage if FE is found on bare wafer
GUN and CATHODE
conditioning
Gun HV conditioning
A fully refurbished gun ceramic has been installed.
Expect a lot of outgassing.
HV electrodes (stem, ball) have been polished and cleaned.
Expect a bit more of field emission at lower <300kV voltages than usual
-------------------------Time stamp the events on the chart recorder !
Conditioning resistor (200MΩ) inserted !!!
Avoid increase of the base pressure level above 10E-8 mbar unless proven
that the progress is too slow
PMT readings:
if the range is set to, e.g. 1E5, use 0-10 scale;
if you read, e.g. 5 - this means 5E4
if the range is set to, e.g. 3E5, use 0-3 scale;
if you read, e.g. 2 - this means 2E5
Gun HV conditioning
HV PSU
initially, set HV PSU in current trip mode MANUALLY
(in the rack room upstairs) with a setting of 10 on the knob (~100μA)
above ~300kV,
the "current trip" setting may require to be increased to "30-40" on the knob
to avoid too frequent trips
above ~400kV,
HV PSU may require to be set to "current limit" mode with the setting
of "20-30" on the knob
Always set current limits MANUALLY (not from console) to avoid mistakes
Set voltage increment corresponding to one right/left click on the mouse equal to 1kV
Keep gun gate valve CLOSED (unless looking for FE)
never open/close the gate valve with HV ON
Gun HV conditioning
Up to 350kV
raise voltage carefully: below ~150kV, - increments of 5-10kV should be OK
expect some current / vacuum activity after as low as ~100kV;
after first signs of current/vacuum activity, reduce the voltage increments
avoid "aggressive" conditioning;
if a significant vacuum activity begins or baseline pressure increases significantly,
- do not force it, allow vacuum to settle for 5-15 min.
if the baseline pressure increases by x5,
reduce voltage by 5-10kV and wait until vacuum recovers
above ~300kV, the outgassing may become quite intensive;
this may require a reduction of voltage increments to 1-3kV at a time.
take PMT readings from time to time and after major events
at baseline levels of 250 and/or 300 and/or 350kV
Gun HV conditioning
Above 350kV
in the beginning of the shift, make baseline measurements at 350kV
•
HV PSU current
•
both PMT readings
•
vacuum levels (all monitors available)
•
chart record at 350kV for ~10 min
from time to time, reduce voltage to 350kV and
take baseline measurements as above
if in the "current limit" mode,
do not allow the HV PSU being in current limit regime for too long
~1/2 min is enough
avoid increase of average pressure above ~1E-8mbar;
if this happens - reduce voltage to ~350kV and wait until vacuum recovers
take baseline PMT readings at 350kV 3-4 times
during the shift and after major events
Gun HV conditioning
Above 400kV
All of the notes in "Above 350kV" section apply
take baseline PMT readings at 350kV and 400kV
3-4 times during the shift and after major events
!
HV conditioning not to a “magic number” of 450kV but
as far as there is no appreciable FE and outgassing at
~370kV
- reduce the risk of the ceramic failure
- will help the cathode lifetime
Hence:
check the gun conditioning status at ~370kV frequently
Photocathode conditioning
Initial settings
set HV PSU in current trip mode MANUALLY (in the rack room upstairs)
set 10 on the knob (this corresponds to ~100μA)
HV PSU control - from the ERLP control room
set voltage increment corresponding to one right/left click on the mouse equal to 1kV
Aims
condition cathode to 365kV
Before ramping up:
open the gate valve,
insert YAG “A”,
ensure the conditioning resistor is in (200MΩ)
Raise voltage slowly.
If there is even minimal vacuum activity/pressure rise,
wait until it diminishes to approximately baseline.
Look for field emission on YAG-01 by varying SOL-01, and HVCOR-01.
Gun & cathode work : Summary
• Bakeout at reduced temperature of 200o C (as opposed to 220o C)
•HV Gun conditioning
just to make gun good at 370kV (do not go all the way to 450kV unless
absolutely necessary)
• Wafer heat clean & HV tests
to make sure there is no FE on bare (not activated) wafer
if FE is present, decide what to do next:
(i) change wafer – not a viable option at present
(ii) commission at reduced voltage
• Cathode activation
• Cathode HV conditioning (usual 365kV)
• If the FE is present, decide what gun voltage to use (below 350kV)
• Decide on what Q to use for ALICE commissioning
probably ~40pC ? (we will need to readjust the machine later for
the nominal 80pC)