1. Powering scheme for Hollow Electron Lens
D. Mirarchi, S. Redaelli
On behalf of the LHC Collimation team
CWG #232, D. Mirarchi

2. Introduction
Present collimation system designed to handle up to 360 MJ, HL-LHC design ~700 MJ
How much of this energy is in the tails?
Halo population probed by means of collimator scans
BLM signal calibrated using BCT signal
Scaling to HL-LHC parameters: ~33.6 MJ in the tails!
~5% of the beams in the tails (>3.5 s)
while 0.22% if Gaussian
G. Valentino
Orbit jitter
Crab cavity phase slip
Fast failure scenarios:
Magnet quench
Permanent damage to TCPs
Possible consequences:
CWG #232, D. Mirarchi

3. Hollow e-lens assisted collimation
Working principle: hollow electron beam surrounds the p beam as additional hierarchy layer
Primary halo
Secondary halo
Tertiary halo
+ hadronic shower
TCP
TCSG
TCLA
Circulating
beam
Hollow
e-lens
Primary
halo
e- beam
TCP
Increased diffusion speed
and depleted halo population
em-field acting only
on halo particles
CWG #232, D. Mirarchi

4. Possible working mode continuous (DC) Stochastic: Stochastic-ONOFF:
Stochastic-amplitude:
Resonant:
Resonant-turn:
Resonant-tune:
Stochastic-amplitude + Resonant-turn
J. Wagner
CWG #232, D. Mirarchi

5. HL-LHC filling pattern
Baseline HL-LHC filling pattern:
72 bunches train
25 ns spacing
Gap between injection into the SPS
200 ns
Gap between injection into the LHC
800 ns
Abort gap
3 ms ms
CWG #232, D. Mirarchi

6. HEL requirements
At least one train of 72 bunches not affected by HEL due to machine protection reasons
e-beam ON/OFF 3 times in one turn: 35 kHz repetition rate
Modular selection from 1 train of bunches to full beam (excluding abort gap)
e-beam pulse length in the range from 1.2 ms to 86 ms
Possibility to switch e-beam ON/OFF within LHC trains
pulse rise-time (10%-90%) of 200 ns due to internal structure coming from SPS
Ideally full range of current 0 – 5 A always available
studies on-going to define margins
Specs available at: new HL-LHC TDR being published (see next slide)
CWG #232, D. Mirarchi

7. HEL specs
CWG #232, D. Mirarchi