Notes and Actions:
1. IT Services
PC Support is now called DL IT Support - now in Canal View
No longer particular support hours. Emails now going to Footprints helpdesk support.
New support address: dlitsupport'at'dl.ac.uk
New support website: http://itservices.dl.ac.uk/ - an excellent step forward.
3rd-party access forms - have been updated on the website for now. Some changes will be made, and a web form will be made.
Campus IT may be put out to tender (bad idea). DL would like to do it.
2. Outgoing CI email addresses. Can be done (e.g. Swapan's email address), but will be done on an individual-by-individual basis on request.
3. PPD files - to go onto IT support website http://itservices.dl.ac.uk/printing/printing3.htm. Chris and Hywel to list out printers post-meeting.
4. POPmail instructions. These work, and will be put onto the IT Services website.
5. Backups - We have bought 2 legato licenses. They haven't arrived yet.
6. apsv5 still not working - C.Dean still looking at it. The machine may have to be sent back to Dell.
7. New CI website - Barbara Runcie will be the webmaster.
Design produced in a couple of weeks.
Agree design with Swapan.
Migrate existing content to new design (Barbara/Stuart)
Migrate to Rythmix and updates done by Barbara. Updates by e.g. Liz to be explored.
8. ASTeC/CI website interaction - meeting with Swapan and Mike P. to find out what they want. (Action HLO)
9. C.Dean to upgrade Plone version projects.astec.ac.uk/ (lowish priority).
Friday, April 27, 2007
Thursday, April 26, 2007
Seminar 26th April - Sergiy Khodyachykh, PITZ Diagnostics
Tomography uses MENT algorithm (Maximum ENTropy) to reconstruct the phase space in a 4-screen FODO channel.
David Holland Seminars - Pump Probe Techniques, 24/26th April 2007
Questions:
Multiple pumps per probe/probes per pump?
Relative size of pulse vs. delay? pulse much less than delay
As well as observing a reaction, there is the possibility of active control by using short pulses to affect the outcome of a chemical reaction.
Frequency control - Brumer-Shapiro
The interference between two degenerate pathways. Analogous to affecting the interference in Young's slits experiments.
http://prola.aps.org/abstract/PRL/v79/i21/p4108_1
Time-domain control - Tannor-Rice
Wavepacket control (pump-dump scheme)
Chem. Phys. Lett. 262 362 (1996)
Chem. Rev. 104 1813 (2004)
Shaping the light pulse allows clever control of the optical pulse to give greater control of the chemical reaction. - Question: how does this depend on variations in the input light pulse? e.g. a varying electron bunch will produce a varying photon pulse, which will change the resulting shaped pulse. This must be some sort of limitation.
26th April:
There is a limit to the repetition rate that can be used on the VUV-FEL which arises from the limit rate of time-of-flight detectors. This places a limit of around 10s of kHz for certain types of experiment.
Multiple pumps per probe/probes per pump?
Relative size of pulse vs. delay? pulse much less than delay
As well as observing a reaction, there is the possibility of active control by using short pulses to affect the outcome of a chemical reaction.
Frequency control - Brumer-Shapiro
The interference between two degenerate pathways. Analogous to affecting the interference in Young's slits experiments.
http://prola.aps.org/abstract/PRL/v79/i21/p4108_1
Time-domain control - Tannor-Rice
Wavepacket control (pump-dump scheme)
Chem. Phys. Lett. 262 362 (1996)
Chem. Rev. 104 1813 (2004)
Shaping the light pulse allows clever control of the optical pulse to give greater control of the chemical reaction. - Question: how does this depend on variations in the input light pulse? e.g. a varying electron bunch will produce a varying photon pulse, which will change the resulting shaped pulse. This must be some sort of limitation.
26th April:
There is a limit to the repetition rate that can be used on the VUV-FEL which arises from the limit rate of time-of-flight detectors. This places a limit of around 10s of kHz for certain types of experiment.
Seminar 26th April - John Singleton, BigLight
Tallahassee, NHMFL - National High Magnetic Field Laboratory
3 sites in the USA
3 FELs - NIR, MIR, FIR. NIR could operate simultaneously with MIR, but maybe with less power. NIR is upstream of MIR. Swept-frequency operation would be difficult, but there is not much demand, so will just do spot measurements
Coherent Undulator for Terahertz Spectroscopy (CUFT)
Draft design of light source overseen by George Neil.
USD2.5M
1. Design of user facility ('co-location')
2. Research into pulse manipulation using electrostatic accelerator
Parameters:
Injector/dump 10 MeV - thermionic gun
Linac 60 MeV
1m to 1mm wavelengths, plus THz
3 or 4 wigglers - rapid tunability, well-defined polarisation states
Current? 1mA, peak 45A
Bunch repetition rate? Variable bunch trains. 0.5 to 20 ps bunch length, 11.8 MHz repetition rate either pulsed or CW, 0.3% energy spread
1.3 GHZ RF
Emittance 20 mm-mrad
10-20 fs timing jitter - how is it used? (ask George Neil)
NIR lt 60 MeV 1.6 kW
MIR lt 30 MeV 700 W (will actually be 60 MeV because FELs using same electron bunches simultaneously)
FIR 7-10 MeV 300W
Interest is in use of FEL light in combination with high magnetic fields. Fields up to 180 Tesla available at LANL!! (pulsed)
LANL - 65/90 T pulsed fields available to users.
FSU site - 45 T DC field available to users (wow). 2 more magnets 25-30 T and 36 T (so-called series connected design which makes operation and interlocks simpler).
(need to watch out where you site the accelerator, and use passive shielding to reduce the stray fields from the DC magnets).
Experimental need - 1ps, pump-probe, THz to near-IR.
Timeline (hoped)
2008 funding (NSF only) - about 25-30M (not including staff or building)
2012 completion
Detail design - 2008/2009 (15 staff-years).
Make some of it? (injector for 2010)
Collaborate in cryomodule production?
3 sites in the USA
3 FELs - NIR, MIR, FIR. NIR could operate simultaneously with MIR, but maybe with less power. NIR is upstream of MIR. Swept-frequency operation would be difficult, but there is not much demand, so will just do spot measurements
Coherent Undulator for Terahertz Spectroscopy (CUFT)
Draft design of light source overseen by George Neil.
USD2.5M
1. Design of user facility ('co-location')
2. Research into pulse manipulation using electrostatic accelerator
Parameters:
Injector/dump 10 MeV - thermionic gun
Linac 60 MeV
1m to 1mm wavelengths, plus THz
3 or 4 wigglers - rapid tunability, well-defined polarisation states
Current? 1mA, peak 45A
Bunch repetition rate? Variable bunch trains. 0.5 to 20 ps bunch length, 11.8 MHz repetition rate either pulsed or CW, 0.3% energy spread
1.3 GHZ RF
Emittance 20 mm-mrad
10-20 fs timing jitter - how is it used? (ask George Neil)
NIR lt 60 MeV 1.6 kW
MIR lt 30 MeV 700 W (will actually be 60 MeV because FELs using same electron bunches simultaneously)
FIR 7-10 MeV 300W
Interest is in use of FEL light in combination with high magnetic fields. Fields up to 180 Tesla available at LANL!! (pulsed)
LANL - 65/90 T pulsed fields available to users.
FSU site - 45 T DC field available to users (wow). 2 more magnets 25-30 T and 36 T (so-called series connected design which makes operation and interlocks simpler).
(need to watch out where you site the accelerator, and use passive shielding to reduce the stray fields from the DC magnets).
Experimental need - 1ps, pump-probe, THz to near-IR.
Timeline (hoped)
2008 funding (NSF only) - about 25-30M (not including staff or building)
2012 completion
Detail design - 2008/2009 (15 staff-years).
Make some of it? (injector for 2010)
Collaborate in cryomodule production?
Tuesday, April 24, 2007
2D-IR Meeting - 24th April 2007
No AP work has been done since the 2D-IR meeting. FEL work has reviewed differing options for the RF module and bunch repetition rate.
The latest agreed configuration (v1.2) is the original CDR configuration (2 FELs not operating together).
George Neil has made comments that JLab is considering some similar solutions (perhaps with Talahassee).
Perhaps this paper: http://www.bessy.de/fel2006/proceedings/PAPERS/TUPPH009.PDF
Having 2 FELs from one electron beam, the action of one FEL disturbs the electron beam for the next FEL. It is an open question whether these two FELs can output at the same wavelength (to be considered by Neil Thompson) - same-wavelength operation would allow 'on the diagonal' measurements to be made.
It could be possible to use only coherent emission from an undulator rather than an FEL - it is not clear whether an FEL would offer any pulse length advantage (i.e. can it generate shorter pulses than coherent emission alone?), or is this just a limit from the wavelength?
Post-meeting comment - of course, if we have coherent emission at a certain wavelength, then there is no point in having an FEL, as the cavity will not cause any microbunching. Recall that an FEL only works at wavelengths shorter than the bunch length; microbunching of a bunch can't occur at length scales bigger than the bunch (think about it - it doesn't make any sense!).
Christine Ramsdale has considered some of the controls/DAQ aspects.
Mark's notes:
-----------------------------
The full suite of FELs to provide complete coverage of the wavelength region requested by David Klug would not be available on day 1 but a phased introduction of facilities is envisaged.
Neil Thompson agreed to look at feasibility of Dual undulator / 2 FELs in one cavity before 25 May. Then to investigate if coherent undulator radiation could also be used, but significant longer pulse lengths expected to be a problem due to slippage. FMQ noted that George Neil may already have proposed a solution for 2 FEL outputs with one injector system- HO will speak to him.
UV-vis detection pulse would be provided by down converting the UV-FEL radiation. This has the advantage of maintaining high rep rate compared to table top laser system.
MB confirms that can transport FEL light with good efficiency and to provide spot size required.
It was agreed that this experiment would be an ideal system to develop data acquisition for. GRM agreed to initiate a flow diagram for this.
The latest agreed configuration (v1.2) is the original CDR configuration (2 FELs not operating together).
George Neil has made comments that JLab is considering some similar solutions (perhaps with Talahassee).
Perhaps this paper: http://www.bessy.de/fel2006/proceedings/PAPERS/TUPPH009.PDF
Having 2 FELs from one electron beam, the action of one FEL disturbs the electron beam for the next FEL. It is an open question whether these two FELs can output at the same wavelength (to be considered by Neil Thompson) - same-wavelength operation would allow 'on the diagonal' measurements to be made.
It could be possible to use only coherent emission from an undulator rather than an FEL - it is not clear whether an FEL would offer any pulse length advantage (i.e. can it generate shorter pulses than coherent emission alone?), or is this just a limit from the wavelength?
Post-meeting comment - of course, if we have coherent emission at a certain wavelength, then there is no point in having an FEL, as the cavity will not cause any microbunching. Recall that an FEL only works at wavelengths shorter than the bunch length; microbunching of a bunch can't occur at length scales bigger than the bunch (think about it - it doesn't make any sense!).
Christine Ramsdale has considered some of the controls/DAQ aspects.
Mark's notes:
-----------------------------
The full suite of FELs to provide complete coverage of the wavelength region requested by David Klug would not be available on day 1 but a phased introduction of facilities is envisaged.
Neil Thompson agreed to look at feasibility of Dual undulator / 2 FELs in one cavity before 25 May. Then to investigate if coherent undulator radiation could also be used, but significant longer pulse lengths expected to be a problem due to slippage. FMQ noted that George Neil may already have proposed a solution for 2 FEL outputs with one injector system- HO will speak to him.
UV-vis detection pulse would be provided by down converting the UV-FEL radiation. This has the advantage of maintaining high rep rate compared to table top laser system.
MB confirms that can transport FEL light with good efficiency and to provide spot size required.
It was agreed that this experiment would be an ideal system to develop data acquisition for. GRM agreed to initiate a flow diagram for this.
Wednesday, April 18, 2007
Seminar - A.Terekhov, 18th April 2007
4GLS photoinjector problems:
10ps response decreases QE
Low (30 meV) energy spread decreases QE
100 mA on cathode needs 50 W laser, needs cooling
100 mA gives short lifetime due to ion back-bombardment
Solve the first 3 using new cathode heterostructure design - the response time depends on the number of random walks through the thickness of the cathode. A cathode with a thin active later is therefore better. But QE drops because of incomplete light absorption, and mean transverse energy can increase.
In reflection mode (RM), can use Distributed Bragg Reflector
In transmission mode (TM), can use Graded Band Gap Layer - can increase QE by maybe 10x.
Band bending near surface can increase transverse energy spread via momentum scattering (and 'acceleration'), up to value of negative electron affinity. This is not the longitudinal energy spread, however, the longitudinal and transverse energy spreads are similar (difference between conduction band minimum and vacuum energy level, around 150 meV at 300 K and 250 meV at 100 K.
If active layer thickness is smaller than the characteristic thermalisation length (of the order of 100 nm) then you get bigger energy spread.
10ps response decreases QE
Low (30 meV) energy spread decreases QE
100 mA on cathode needs 50 W laser, needs cooling
100 mA gives short lifetime due to ion back-bombardment
Solve the first 3 using new cathode heterostructure design - the response time depends on the number of random walks through the thickness of the cathode. A cathode with a thin active later is therefore better. But QE drops because of incomplete light absorption, and mean transverse energy can increase.
In reflection mode (RM), can use Distributed Bragg Reflector
In transmission mode (TM), can use Graded Band Gap Layer - can increase QE by maybe 10x.
Band bending near surface can increase transverse energy spread via momentum scattering (and 'acceleration'), up to value of negative electron affinity. This is not the longitudinal energy spread, however, the longitudinal and transverse energy spreads are similar (difference between conduction band minimum and vacuum energy level, around 150 meV at 300 K and 250 meV at 100 K.
If active layer thickness is smaller than the characteristic thermalisation length (of the order of 100 nm) then you get bigger energy spread.
Wednesday, April 11, 2007
Notes from 4GLS Physics Meeting 11th April 2007
Forthcoming milestones:
Wakes
Diagnostics
Main linac quads position fixed
Magnet spreader specification fixed - apertures
Magnet spreader design
BC1 optimisation - report due
BC2 optimisation - Sara
Collimators in HACL arcs - Hugh
Beam loss brainstorming - David 27th April
Longitudinal cavity wakefields of 7-cell cavity design and HOM dampers - Emma/Carl? late June
Wakes
Diagnostics
Main linac quads position fixed
Magnet spreader specification fixed - apertures
Magnet spreader design
BC1 optimisation - report due
BC2 optimisation - Sara
Collimators in HACL arcs - Hugh
Beam loss brainstorming - David 27th April
Longitudinal cavity wakefields of 7-cell cavity design and HOM dampers - Emma/Carl? late June
Thursday, April 05, 2007
Notes from ERLP Planning Meeting 5th April 2007
Late Saturday Shift 2/3 go to 350 kV. If there is something wrong,
Heat cleaning on Monday.
Activation on Tuesday.
No problems at 250 kV
Halo - overheating of the cathode? Diffusion of arsenic to the surface of the cathode causing scattering of the incoming laser light rather than reflection through the anode.
Tasks:
Highest Q available
Emittance measurement? No sensible results possible with the halo. For example, a pepperpot measurement revealed a lot of strange images.
Heat cleaning on Monday.
Activation on Tuesday.
No problems at 250 kV
Halo - overheating of the cathode? Diffusion of arsenic to the surface of the cathode causing scattering of the incoming laser light rather than reflection through the anode.
Tasks:
Highest Q available
Emittance measurement? No sensible results possible with the halo. For example, a pepperpot measurement revealed a lot of strange images.
Wednesday, April 04, 2007
Notes from ERLP Planning Meeting 4th April 2007
The halo is around 50% of the beam. This number is not confirmed, so we should try to repeat the measurement using a scanning slit.
Make sure that no cryo equipment is left on the floor at the end of cryo commissioning.
Yuri/Philippe on Shift 1
Make sure that no cryo equipment is left on the floor at the end of cryo commissioning.
Yuri/Philippe on Shift 1
Tuesday, April 03, 2007
Notes from ERLP Planning Meeting 3rd April 2007
Next 2 shifts should look at fringing field in the first correct after SOL-01 (HCOR/VCOR-06). There appears to be a lot of (cruciform) distortion at large apertures (i.e. large corrector angles).
The present halo could be because of laser scattering inside the gun chamber (has the foil been removed? yes it has). The halo is more-or-less round (as seen on screen A) - it could be an image of the whole cathode (with the laser spot in the middle). The edge of the halo is the edge of the wafer?
Anode has a 20mm radius. Since the laser beam comes in at ~6 deg, the image at the cathode should be a clipped 'ellipse' shape. Maybe about half the charge is in the halo? Needs to be measured (by Steve Jamison).
Shield wall has not been replaced since removal for installation of another transfer line girder module.
Any time we get a good average current (e.g. 20 pC), then call Martin Holbourn to do some radiation measurements.
2 options - work at 250 kV to look at source of halo. Or go to 350 kV hoping that the halo will diminish, but could kill cathode. For the next 2 shifts we will therefore work at 250 kV.
The present halo could be because of laser scattering inside the gun chamber (has the foil been removed? yes it has). The halo is more-or-less round (as seen on screen A) - it could be an image of the whole cathode (with the laser spot in the middle). The edge of the halo is the edge of the wafer?
Anode has a 20mm radius. Since the laser beam comes in at ~6 deg, the image at the cathode should be a clipped 'ellipse' shape. Maybe about half the charge is in the halo? Needs to be measured (by Steve Jamison).
Shield wall has not been replaced since removal for installation of another transfer line girder module.
Any time we get a good average current (e.g. 20 pC), then call Martin Holbourn to do some radiation measurements.
2 options - work at 250 kV to look at source of halo. Or go to 350 kV hoping that the halo will diminish, but could kill cathode. For the next 2 shifts we will therefore work at 250 kV.
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