lcls-ii dark current tracks from cathode edge and possible collimation
DESCRIPTION
LCLS-II dark current tracks from cathode edge and possible collimation. Charge assignment from FN parameters. Used the parameters from measurement to assign charges to the dark current particles based on their initial longitudinal E-field. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/1.jpg)
Christopher Mayes – July 23, 2014
LCLS-II dark current tracks from cathode edge and possible collimation
![Page 2: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/2.jpg)
Christopher Mayes – July 23, 2014
Charge assignment from FN parameters
http://www-physics.lbl.gov/seminars/old/Sannibale.pdf
• Used the parameters from measurement to assign charges to the dark current particles based on their initial longitudinal E-field.
• Particles are uniformly distributed in time and at radius 5mm (the edge of the cathode puck)
• The sum of all charges is normalized to 1(Coulomb)
![Page 3: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/3.jpg)
Christopher Mayes – July 23, 2014
Particles from r = 5 mm on cathode colored by charge
(red is higher charge)
![Page 4: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/4.jpg)
Christopher Mayes – July 23, 2014
Particles lost colored by charge (red is higher)
![Page 5: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/5.jpg)
Christopher Mayes – July 23, 2014
Particles escaping colored by charge (red is higher)
![Page 6: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/6.jpg)
Christopher Mayes – July 23, 2014
Particles lost backwards
0.25% of the current turns around and hits the cathode
![Page 7: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/7.jpg)
Christopher Mayes – July 23, 2014
Current lost per meter
![Page 8: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/8.jpg)
Christopher Mayes – July 23, 2014
Forward moving particles in frontend
![Page 9: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/9.jpg)
Christopher Mayes – July 23, 2014
Collimator at z = 2 m
These are the particles passing z=2m in the forward direction.
The fraction captured current for a given collimator radius. Note that some current was already lost prior to this location
![Page 10: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/10.jpg)
Christopher Mayes – July 23, 2014
Collimator placement after buncher summary
This extends the previous plot to all possible z locations for collimation.
For example:
A collimator with radius 5 mm placed at z=1.5 m would capture 80% of the dark current
A collimator with radius 10 mm placed at z = 2.0 m would capture 70% of the dark current
![Page 11: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/11.jpg)
Christopher Mayes – July 23, 2014
Tracks including HTR, Col0 sections
![Page 12: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/12.jpg)
Christopher Mayes – July 23, 2014
Tracks including HTR, Col0 sections
.02% survive
![Page 13: LCLS-II dark current tracks from cathode edge and possible collimation](https://reader030.vdocuments.site/reader030/viewer/2022032607/56813025550346895d95aa87/html5/thumbnails/13.jpg)
Christopher Mayes – July 23, 2014
Tracks including HTR, Col0 sections