# A Study of Resonant Excitation of Longitudinal HOMs in the Cryomodules of LCLS-II

## Abstract

The Linac Coherent Light Source (LCLS) at SLAC, the world’s first hard X-ray FEL, is being upgraded to the LCLS-II. The major new feature will be the installation of 35 cryomodules (CMs) of TESLA-type, superconducting accelerating structures, to allow for high rep-rate operation. It is envisioned that eventually the LCLS-II will be able to deliver 300 pC, 1 kA pulses of beam at a rate of 1 MHz. At a cavity temperature of 2 K, any heat generated (even on the level of a few watts) is expensive to remove. In the last linac of LCLS-II, L3—where the peak current is highest—the power radiated by the bunches in the CMs is estimated at 13.8 W (charge 300 pC option, rep rate 1 MHz). But this calculation ignores resonances that can be excited between the bunch frequency and higher order mode (HOM) frequencies in the CMs, which in principle can greatly increase this number. In the present work we calculate the multi-bunch wakefields excited in a CM of LCLS-II, in order to estimate the probability of the beam losing a given amount of power. Along theway, we find some interesting properties of the resonant interaction. In detail, we begin this reportmore »

- Authors:

- Publication Date:

- Research Org.:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)

- OSTI Identifier:
- 1221589

- Report Number(s):
- SLAC-PUB-16395

- DOE Contract Number:
- AC02-76SF00515

- Resource Type:
- Conference

- Resource Relation:
- Conference: Presented at17th International Conference on RF Superconductivity (SRF2015), Whistler, B.C., Canada, 9/13/2015-9/18/2015

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 43 PARTICLE ACCELERATORS; ACCPHY

### Citation Formats

```
Bane, Karl.
```*A Study of Resonant Excitation of Longitudinal HOMs in the Cryomodules of LCLS-II*. United States: N. p., 2015.
Web.

```
Bane, Karl.
```*A Study of Resonant Excitation of Longitudinal HOMs in the Cryomodules of LCLS-II*. United States.

```
Bane, Karl. Wed .
"A Study of Resonant Excitation of Longitudinal HOMs in the Cryomodules of LCLS-II". United States. https://www.osti.gov/servlets/purl/1221589.
```

```
@article{osti_1221589,
```

title = {A Study of Resonant Excitation of Longitudinal HOMs in the Cryomodules of LCLS-II},

author = {Bane, Karl},

abstractNote = {The Linac Coherent Light Source (LCLS) at SLAC, the world’s first hard X-ray FEL, is being upgraded to the LCLS-II. The major new feature will be the installation of 35 cryomodules (CMs) of TESLA-type, superconducting accelerating structures, to allow for high rep-rate operation. It is envisioned that eventually the LCLS-II will be able to deliver 300 pC, 1 kA pulses of beam at a rate of 1 MHz. At a cavity temperature of 2 K, any heat generated (even on the level of a few watts) is expensive to remove. In the last linac of LCLS-II, L3—where the peak current is highest—the power radiated by the bunches in the CMs is estimated at 13.8 W (charge 300 pC option, rep rate 1 MHz). But this calculation ignores resonances that can be excited between the bunch frequency and higher order mode (HOM) frequencies in the CMs, which in principle can greatly increase this number. In the present work we calculate the multi-bunch wakefields excited in a CM of LCLS-II, in order to estimate the probability of the beam losing a given amount of power. Along theway, we find some interesting properties of the resonant interaction. In detail, we begin this report by finding the wakes experienced by bunches far back in the bunch train. Then we present a complementary approach that calculates the field amplitude excited in steady-state by a train of bunches, and show that the two approaches agree. Next we obtain the properties of the 450 longitudinal HOMs that cover the range 3–5 GHz in the CMs of LCLS-II, where we include the effects of the inter-CM ceramic dampers. At the end we apply our method using these modes.},

doi = {},

journal = {},

number = ,

volume = ,

place = {United States},

year = {2015},

month = {9}

}